U.S. patent application number 15/790235 was filed with the patent office on 2018-03-08 for nanoparticle catalysts for conversion of cyclohexanol to cyclohexanone.
This patent application is currently assigned to University of Southampton. The applicant listed for this patent is AdvanSixResins & Chemicals LLC, University of Southampton. Invention is credited to Arran M. Gill, Scott R. Keenan, Alan B. Levy, Matthew E. Potter, Robert Raja, Sivan A. Van Aswegen.
Application Number | 20180065910 15/790235 |
Document ID | / |
Family ID | 58427914 |
Filed Date | 2018-03-08 |
United States Patent
Application |
20180065910 |
Kind Code |
A1 |
Levy; Alan B. ; et
al. |
March 8, 2018 |
NANOPARTICLE CATALYSTS FOR CONVERSION OF CYCLOHEXANOL TO
CYCLOHEXANONE
Abstract
Methods for converting an alcohol, such as cyclohexanol to a
ketone, such as cyclohexanone, include reacting the alcohol in the
presence of a catalyst and oxygen to produce the ketone. In one
exemplary embodiment, the catalyst comprises a microporous copper
chloropyrophosphate framework including a plurality of noble metal
nanoparticles. In one exemplary embodiment, the noble metal
nanoparticles include at least one metal selected from the group
consisting of platinum, palladium, and gold.
Inventors: |
Levy; Alan B.; (Randolph,
NJ) ; Keenan; Scott R.; (Marlton, NJ) ; Raja;
Robert; (Fair Oak, GB) ; Gill; Arran M.;
(Guiseley, GB) ; Potter; Matthew E.; (Leigh,
GB) ; Van Aswegen; Sivan A.; (Tunbridge Wells,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AdvanSixResins & Chemicals LLC
University of Southampton |
Parsippany
Southampton |
NJ |
US
GB |
|
|
Assignee: |
; University of Southampton
Southampton
NJ
AdvanSix Resins & Chemicals LLC
Parsippany
|
Family ID: |
58427914 |
Appl. No.: |
15/790235 |
Filed: |
October 23, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15279837 |
Sep 29, 2016 |
9822052 |
|
|
15790235 |
|
|
|
|
62235684 |
Oct 1, 2015 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 27/1856 20130101;
B01J 23/44 20130101; B01J 37/18 20130101; B01J 37/04 20130101; B01J
35/0013 20130101; B01J 23/42 20130101; B01J 37/343 20130101; C07C
45/39 20130101; B01J 37/088 20130101; B01J 27/13 20130101; B01J
23/52 20130101; B01J 35/002 20130101; C07C 2601/14 20170501; B01J
23/8926 20130101; B01J 37/08 20130101; C07C 45/39 20130101; C07C
49/403 20130101 |
International
Class: |
C07C 45/39 20060101
C07C045/39; B01J 37/08 20060101 B01J037/08; B01J 37/04 20060101
B01J037/04; B01J 27/13 20060101 B01J027/13; B01J 27/185 20060101
B01J027/185; C07C 49/403 20060101 C07C049/403 |
Claims
1. A catalyst comprising a microporous copper chloropyrophosphate
framework comprising a plurality of noble metal nanoparticles, the
catalyst activated in a reducing atmosphere.
2. The catalyst of claim 1, wherein the microporous copper
chloropyrophosphate framework has the general formula:
[A.sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl].[MX.sub.4]Cl.sub.y where:
A is selected from K, Rb, Cs, and NH.sub.4; M is selected from Cu,
Au, Pt, and Pd; X is selected from Cl and Br; and y is 2 when M is
Pt, Pd, or Cu and y is 3 when M is Au.
3. The catalyst of claim 2, wherein the microporous copper
chloropyrophosphate framework has a general formula selected from
the group consisting of:
Rb.sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl.sub.4(AuCl.sub.4),
Rb.sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl.sub.3(PtCl.sub.4), and
Rb.sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl.sub.3(PdCl.sub.4).
4. The catalyst of claim 1, wherein the catalyst comprises
precursor complexes that result in isolated noble metal
nanoparticle sites upon activation.
5. The catalyst of claim 4, wherein the precursor complexes are
selected from the group consisting of [PtCl.sub.4].sup.2-,
[PdCl.sub.4].sup.2-, and [AuCl.sub.4].sup.-.
6. The catalyst of claim 1, wherein the noble metal nanoparticles
include at least one metal selected from the group consisting of
platinum, palladium, and gold.
7. The catalyst of claim 6, wherein the microporous copper
chloropyrophosphate framework includes a plurality of mono-metallic
platinum nanoparticles.
8. The catalyst of claim 7, wherein the catalyst has been activated
at a temperature of about 200.degree. C.
9. The catalyst of claim 1, wherein the microporous copper
chloropyrophosphate framework includes a plurality of mono-metallic
palladium nanoparticles.
10. The catalyst of claim 1, wherein the reducing atmosphere
includes hydrogen and nitrogen.
11. A catalyst comprising a microporous copper chloropyrophosphate
framework including a plurality of mono-metallic platinum
nanoparticles, the microporous copper chloropyrophosphate framework
having a general formula of
Rb.sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl.sub.3(PtCl.sub.4), the
catalyst activated in a reducing atmosphere.
12. The catalyst of claim 11, wherein the catalyst is activated at
a temperature of about 200.degree. C.
13. The catalyst of claim 11, wherein the reducing atmosphere
includes hydrogen and nitrogen.
14. A catalyst comprising a microporous copper chloropyrophosphate
framework having the general formula:
[(NH.sub.4).sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl].[MX.sub.4]Cl.sub.2
wherein: M is selected from Pt, and Pd; and X is selected from Cl
and Br.
15. The catalyst of claim 14, wherein the microporous copper
chloropyrophosphate framework has a general formula selected from
the group consisting of:
(NH.sub.4).sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl.sub.3(PtCl.sub.4)
and
(NH.sub.4).sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl.sub.3(PdCl.sub.4).
16. The catalyst of claim 14, wherein the catalyst comprises
precursor complexes selected from the group consisting of
[PtCl.sub.4].sup.2- and [PdCl.sub.4].sup.2-, that result in
isolated noble metal nanoparticle sites upon activation.
17. The catalyst of claim 14, wherein the noble metal nanoparticles
include at least one metal selected from the group consisting of
platinum and palladium.
18. The catalyst of claim 17, wherein the microporous copper
chloropyrophosphate framework includes a plurality of mono-metallic
platinum nanoparticles.
19. The catalyst of claim 14, wherein the microporous copper
chloropyrophosphate framework includes a plurality of mono-metallic
palladium nanoparticles.
20. The catalyst of claim 14, wherein the catalyst is activated in
a reducing atmosphere, the reducing atmosphere including hydrogen
and nitrogen.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
patent application Ser. No. 15/279,837, filed Sep. 29, 2016, which
claims priority under 35 U.S.C. .sctn. 119(e) to U.S. Provisional
Patent Application No. 62/235,684, filed Oct. 1, 2015, the
disclosure of which is hereby incorporated herein by reference in
its entirety
FIELD
[0002] The present invention relates to catalysts, and in
particular catalysts including noble metal nanoparticles useful for
the conversion of cyclohexanol to cyclohexanone.
BACKGROUND
[0003] Cyclohexanone is commonly used in the production of
.epsilon.-caprolactam, which is a raw material used in the
production of nylon 6. Nylon 6 has many uses including as a raw
material used in industry and manufacturing.
[0004] Cyclohexanone is typically produced industrially by the
hydrogenation of phenol or the oxidation of cyclohexane. These
typical processes produce the by-product cyclohexanol, leading to
the formation of a mixture of cyclohexanone and cyclohexanol known
as KA-oil.
[0005] Improvements in the foregoing processes are desired.
SUMMARY
[0006] The present disclosure provides catalysts and methods for
the conversion of cyclohexanol to cyclohexanone. In one embodiment,
the catalysts comprise a microporous copper chloropyrophosphate
(CuClP) framework including a plurality of noble metal nanoparticle
sites.
[0007] In one exemplary embodiment, a method of converting an
alcohol to a ketone is provided. The method includes reacting the
alcohol in the presence of a catalyst to produce the ketone,
wherein the catalyst comprises a microporous copper
chloropyrophosphate framework including a plurality of noble metal
nanoparticles. In one more particular embodiment, the reaction is
performed in the presence of oxygen. In one more particular
embodiment, the alcohol is a cyclic alcohol. In an even more
particular embodiment, the alcohol is cyclohexanol and the ketone
is cyclohexanone. In an even more particular embodiment, the
cyclohexanol is provided as a mixture of cyclohexanone and
cyclohexanol, wherein the mixture comprises 5 wt. % to 95 wt. %
cyclohexanol, 40 wt. % to 60 wt. % cyclohexanol, or about 50 wt. %
cyclohexanol, based on the total weight of the cyclohexanol and
cyclohexanone.
[0008] In one exemplary embodiment, a catalyst is provided. The
catalyst comprises a microporous copper chloropyrophosphate
framework including a plurality of noble metal nanoparticles.
[0009] In a more particular embodiment, the microporous copper
chloropyrophosphate framework has the general formula:
[A.sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl].[MX.sub.4]Cl.sub.y
where: A is selected from K, Rb, Cs, and NH.sub.4;
[0010] M is selected from Cu, Au, Pt, and Pd;
[0011] X is selected from Cl and Br; and
[0012] y is 2 when M is Pt, Pd, or Cu and y is 3 when M is Au.
[0013] In more particular embodiment of any of the above
embodiments, the microporous copper chloropyrophosphate framework
has a general formula selected from the group consisting of:
Rb.sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl.sub.4(AuCl.sub.4),
Rb.sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl.sub.3(PtCl.sub.4), and
Rb.sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl.sub.3(PdCl.sub.4).
[0014] In a more particular embodiment of any of the above
embodiments, the catalyst comprises precursor complexes that result
in isolated noble metal nanoparticle sites upon activation. In an
even more particular embodiment, the precursor complexes are
selected from the group consisting of [PtCl.sub.4].sup.2-,
[PdCl.sub.4].sup.2-, and [AuCl.sub.4].sup.-.
[0015] In one more particular embodiment of any of the above
embodiments, the noble metal nanoparticles include at least one
metal selected from the group consisting of platinum, palladium,
and gold. In one more particular embodiment, the metal is platinum.
In another more particular embodiment, the metal is palladium. In
still another more particular embodiment, the metal is gold. In
still another more particular embodiment, the noble metal
nanoparticles include at least two metals selected from the group
consisting of platinum, palladium, and gold, and even more
particularly, the two metals are platinum and gold.
[0016] In one more particular embodiment, the catalyst comprises a
microporous copper chloropyrophosphate framework including a
plurality of mono-metallic platinum nanoparticles. In a more
particular embodiment, the catalyst has been activated at a
temperature of 175.degree. C. or greater. In an even more
particular embodiment, the catalyst has been activated at a
temperature of about 200.degree. C. In another more particular
embodiment, the catalyst has been activated while exposed to a
mixture of hydrogen and nitrogen.
[0017] In one more particular embodiment, the catalyst comprises a
microporous copper chloropyrophosphate framework including a
plurality of platinum and gold nanoparticles. In a more particular
embodiment, the catalyst has been activated at a temperature of
200.degree. C. or greater. In an even more particular embodiment,
the catalyst has been activated at a temperature of about
300.degree. C. In another more particular embodiment, the catalyst
has been activated while exposed to a mixture of hydrogen and
nitrogen.
[0018] In one more particular embodiment of any of the above
embodiments, the metal is in the metallic state. In one more
particular embodiment of any of the above embodiments, the metal
has an oxidation state of zero.
[0019] In one exemplary embodiment, a method of making a catalyst
is provided. The method includes mixing copper (II) fluoride,
orthophosphoric acid, rubidium hydroxide, rubidium chloride, and a
source of metal chloride; heating the mixture in a sealed container
to form a catalyst precursor including precursor complexes; and
activating the catalyst by heating the catalyst precursor at a
temperature of at least 150.degree. C. to convert the precursor
complexes to noble metal nanoparticle sites. In a more particular
embodiment, the catalyst precursor is heated at a temperature of at
least 175.degree. C. or at least 200.degree. C. to activate the
catalyst.
[0020] In one more particular embodiment, the source of metal
chloride is selected from the group consisting of
K.sub.2PtCl.sub.4, K.sub.2PdCl.sub.4, HAuCl.sub.4, and KAuCl.sub.4.
In another more particular embodiment, the precursor complexes are
selected from the group consisting of [PtCl.sub.4].sup.2-,
[PdCl.sub.4].sup.2-, and [AuCl.sub.4].sup.-.
[0021] The above mentioned and other features of the invention, and
the manner of attaining them, will become more apparent and the
invention itself will be better understood by reference to the
following description of embodiments of the invention taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1A illustrates an exemplary copper chloropyrophosphate
framework as viewed down the c-axis.
[0023] FIG. 1B illustrates the exemplary copper chloropyrophosphate
framework of FIG. 1A as viewed down the a-axis.
[0024] FIG. 2A illustrates the hydrogenation of phenol to form
cyclohexanone.
[0025] FIG. 2B illustrates the hydrogenation of phenol to form
cyclohexanol.
[0026] FIG. 3 illustrates the reaction of the mixture of
cyclohexanone and cyclohexanol to cyclohexanone with an exemplary
catalyst.
[0027] FIGS. 4A and 4B are related to Example 2 and illustrate
stacked XPS spectra, with data fits and appropriate reference
samples, of exemplary Pt/CuClP catalyst materials activated at
different temperatures.
[0028] FIG. 5 is related to Example 2 and illustrates stacked XPS
spectra, with data fits and appropriate reference samples, of
exemplary Au/CuClP catalyst materials activated at different
temperatures.
[0029] FIG. 6A is related to Example 2 and illustrates stacked Pt
L.sub.3 edge XANES data for exemplary Pt/CuClP catalyst materials
activated at different temperatures.
[0030] FIG. 6B is related to Example 2 and illustrates the
magnitude and imaginary component of the k.sup.3 weighted Fourier
transform for the EXAFS data, with data fits, of three exemplary
Pt/CuClP catalyst species reduced using different activation
temperatures.
[0031] FIG. 7 is related to Example 2 and illustrates the magnitude
and imaginary component of the k.sup.3 weighted Fourier transform
for the EXAFS data, with data fits, of three exemplary Au/CuClP
catalyst species reduced under increasing activation
temperatures.
[0032] FIG. 8 is related to Example 2 and illustrates the magnitude
and imaginary component of the k.sup.3 weighted Fourier transform
for the EXAFS data, with data fits, of three exemplary Pd/CuClP
catalyst species reduced under increasing activation
temperatures.
[0033] FIG. 9 is related to Example 2 and illustrates indexed
powdered X-ray diffraction of Pt/CuClP materials activated at
different temperatures with the pre-activation, as-synthesized
sample.
[0034] FIG. 10 is related to Example 2 and illustrates powdered
X-ray diffraction of Pt/CuClP materials activated at 200.degree. C.
both before (fresh) and after catalysis (recycle) in the oxidation
of KA-oil for 6 hr.
[0035] FIG. 11 is related to Example 2 and illustrated indexed
powdered X-ray diffraction of Au/CuClP materials activated at
different temperatures with the pre-activation, as-synthesized
sample for comparison demonstrating the structural integrity of the
material at the various activation temperatures.
[0036] FIG. 12 is related to Example 2 and illustrates indexed
powdered X-ray diffraction of Pd/CuClP materials activated at
different temperatures with the pre-activation, as-synthesized
sample for comparison, demonstrating the structural integrity of
the material up to 175.degree. C. and then the introduction of
additional rubidium phosphate phases at temperatures close to
200.degree. C.
[0037] FIGS. 13A-C are related to Example 2 and illustrate ADF
AC-STEM images of the Pt/CuClP material activated at 200.degree.
C.
[0038] FIGS. 14A-C are related to Example 2 and illustrate ADF
AC-STEM images of the Pd/CuClP material activated at 200.degree.
C.
[0039] FIGS. 15A-C are related to Example 2 and illustrate ADF
AC-STEM images of the Au/CuClP material activated at 200.degree.
C.
[0040] FIGS. 16A-F are related to Example 2 and illustrate ADF
AC-STEM images of the respective nanoparticle (NP)-framework
materials activated at 200.degree. C.
[0041] FIG. 17 is related to Example 2 and provides an EDXS spectra
for the Pt/CuClP material activated at 200.degree. C.
[0042] FIG. 18 is related to Example 2 and provides an EDXS spectra
for the Pd/CuClP material activated at 200.degree. C.
[0043] FIG. 19 is related to Example 2 and provides an EDXS spectra
for the Au/CuClP material activated at 200.degree. C.
[0044] FIG. 20A is related to Example 3 and illustrates the aerobic
production of cyclohexanone with supported nanoparticle/CuClP
catalysts activated at different temperatures.
[0045] FIG. 20B is related to Example 3 and illustrates the
catalytic lifetime of the Pt/CuClP catalyst.
[0046] FIG. 21 is related to Example 3 and illustrates the effect
of temperature on the conversion of cyclohexanol to
cyclohexanone.
[0047] FIG. 22 is related to Example 3 and illustrates the effect
of oxygen flow rate on the conversion of cyclohexanol to
cyclohexanone.
[0048] FIG. 23 is related to Example 3 and illustrates the effect
of cyclohexanol flow rate on the conversion of cyclohexanol to
cyclohexanone.
[0049] FIG. 24 is related to Example 4 and is a photograph of the
as-synthesized bimetallic CuClP materials.
[0050] FIG. 25 is related to Example 4 and illustrates the PXRD
spectra of two different as-synthesized AuPt/CuClP samples.
[0051] FIG. 26 is related to Example 4 and illustrates the PXRD
spectra of two different as-synthesized AuPd/CuClP samples
[0052] FIG. 27 is related to Example 4 and illustrates the PXRD
spectra of two different as-synthesized PtPd/CuClP samples.
[0053] FIG. 28 is related to Example 4 and is a photograph of the
bimetallic AuPt/CuClP material reduced at different
temperatures.
[0054] FIG. 29 is related to Example 4 and illustrates the PXRD
spectra of the as-synthesized AuPt/CuClP material and samples
reduced at different temperatures.
[0055] FIG. 30 is related to Example 4 and illustrates the PXRD
spectra of the as-synthesized AuPt/CuClP material and samples
reduced at 250.degree. C.
[0056] FIG. 31 is related to Example 4 and is a photograph of the
bimetallic AuPd/CuClP material reduced at different
temperatures.
[0057] FIG. 32 is related to Example 4 and illustrates the PXRD
spectra of the as-synthesized AuPd/CuClP material and samples
reduced at different temperatures.
[0058] FIG. 33 is related to Example 4 and is a photograph of the
bimetallic PtPd/CuClP material reduced at different
temperatures.
[0059] FIG. 34 is related to Example 4 and illustrates the PXRD
spectra of the as-synthesized PtPd/CuClP material and samples
reduced at different temperatures.
[0060] FIG. 35 is related to Example 2 and illustrates an EDXS
spectra for the Au/CuClP material activated at 250.degree. C.
[0061] FIG. 36 is related to Example 2 and illustrates an EDXS
spectra for the Au/CuClP material activated at 350.degree. C.
[0062] FIGS. 37A-D are related to Example 2 and illustrate ADF-STEM
images of the Au/CuClP material activated at 200.degree. C.
[0063] FIGS. 38A-E are related to Example 2 and illustrate ADF and
bright-field STEM images of the Au/CuClP material activated at
250.degree. C.
[0064] FIGS. 39A-E are related to Example 2 and illustrate ADF-STEM
images of the Au/CuClP material activated at 350.degree. C.
[0065] FIGS. 40A and 40B are related to Example 2 and illustrates
ADF images of the small nanoparticles in the Au/CuClP sample
activated at 250.degree. C.
[0066] FIG. 40C is related to Example 2 and provides an EDXS
spectrum for the small nanoparticles in FIGS. 40A-B.
[0067] FIG. 40D is related to Example 2 and provides elemental maps
obtained from the EDXS spectrum of FIG. 40C.
[0068] FIGS. 41A and 41B are related to Example 2 and illustrates
ADF images of the large faceted nanoparticles in the Au/CuClP
sample activated at 350.degree. C.
[0069] FIG. 41C is related to Example 2 and provides an EDXS
spectrum for the large faceted nanoparticles in FIGS. 41A-B.
[0070] FIG. 41D is related to Example 2 and provides elemental maps
obtained from the EDXS spectrum of FIG. 41C.
[0071] FIGS. 42A and 42B are related to Example 2 and illustrates
ADF images of the large nanoparticles and agglomerations in the
framework support in the Au/CuClP sample activated at 350.degree.
C.
[0072] FIG. 42C is related to Example 2 and provides an EDXS
spectrum for the large nanoparticles and agglomerations in the
framework support in FIGS. 42A-B.
[0073] FIG. 42D is related to Example 2 and provides elemental maps
obtained from the EDXS spectrum of FIG. 42C.
[0074] FIG. 43 is related to Example 4 and illustrates stacked XPS
spectra, with data fits and appropriate reference samples, of
exemplary AuPt/CuClP catalyst materials activated at different
temperatures.
[0075] FIGS. 44A and 44B are related to Example 4 and illustrate
stacked XPS spectra, with data fits and appropriate reference
samples, of exemplary PtPd/CuClP catalyst materials activated at
different temperatures.
[0076] FIGS. 45A and 45B are related to Example 4 and illustrate
stacked XPS spectra, with data fits and appropriate reference
samples, of exemplary AuPd/CuClP catalyst materials activated at
different temperatures.
[0077] FIGS. 46A and 46B are related to Example 4 and illustrate
TEM images of the AuPd/CuClP material activated at 200.degree.
C.
[0078] FIG. 47 is related to Example 4 and illustrates a TEM image
of the Pt/Pd/CuClP material activated at 150.degree. C.
[0079] FIGS. 48A-C are related to Example 4 and illustrate TEM
images of the PtPd/CuClP material activated at 200.degree. C.
[0080] FIGS. 49A and 49B are related to Example 4 and illustrate
TEM images of the AuPt/CuClP material activated at 200.degree.
C.
[0081] FIGS. 50A and 50B are related to Example 4 and illustrate
TEM images of the AuPt/CuClP material activated at 250.degree.
C.
[0082] FIGS. 51A and 51B are related to Example 4 and illustrate
TEM images of the AuPt/CuClP material activated at 300.degree.
C.
DETAILED DESCRIPTION
[0083] The present disclosure is directed to catalysts and methods
for the conversion of cyclohexanol to cyclohexanone.
[0084] In one exemplary embodiment, the catalyst is based on a
microporous copper chloropyrophosphate (CuClP) framework bearing
flexible anion exchange properties. FIG. 1 illustrates an exemplary
catalyst 102 having a copper chloropyrophosphate microporous
framework architecture. The copper chloropyrophosphates (CuClPs)
are a family of microporous framework materials having have the
general formula:
[A.sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl].[MX.sub.4]Cl.sub.y
where: A is selected from K, Rb, Cs, and NH.sub.4;
[0085] M is selected from Cu, Au, Pt, and Pd;
[0086] X is selected from Cl and Br; and
[0087] y is 2 when M is Pt, Pd, or Cu and y is 3 when M is Au.
[0088] In one more particular embodiment, the copper
chloropyrophosphate has a formula selected from the group
consisting of:
Rb.sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl.sub.4(AuCl.sub.4),
Rb.sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl.sub.3(PtCl.sub.4) and
Rb.sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl.sub.3(PdCl.sub.4). In one
more particular embodiment, the formula is
Rb.sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl.sub.4(AuCl.sub.4). In
another more particular embodiment, the formula is
Rb.sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl.sub.3(PtCl.sub.4). In
another more particular embodiment, the formula is
Rb.sub.9Cu.sub.6(P.sub.2O.sub.7).sub.4Cl.sub.3(PdCl.sub.4).
[0089] In one exemplary embodiment, the catalyst comprises a copper
(II) framework including 1-dimensional channels with diameters of
about 13 .ANG.. An exemplary framework is shown in the a-b plane
down the c-axis in FIG. 1A and in the b-c plane down the a-axis in
FIG. 1B. The oxygen atoms have been omitted for clarity in FIGS. 1A
and 1B. As shown in FIG. 1, the framework is composed of a
.mu..sup.4 chloride ion at the apex of 4xCuO.sub.4 square-based
pyramids. These quartets are linked by pyrophosphate,
P.sub.2O.sub.7, groups to form one dimensional chains, with the
cavities between [CuO.sub.4].sub.4Cl[P.sub.2O.sub.7].sub.4 blocks
along the c-direction occupied by A.sup.+ cations. The
[CuO.sub.4].sub.4Cl[P.sub.2O.sub.7].sub.4 units are crosslinked,
via a shared oxygen atom on a P.sub.2O.sub.7 unit, in the ab plane
by square-planar CuO.sub.4 groups. This produces a square grid of
one-dimensional channels with dimensions approx. 12.times.12 .ANG..
The channels are lined with A.sup.+ cations and, bar structure,
chloride ions weakly coordinated to the cross-linking CuO.sub.4
square planar units (Cu--Cl approx. 2.7 .ANG.). The orientation of
the resulting CuO.sub.4Cl square-based pyramids alternates along
the c-axis. The relative orientation of successive P.sub.2O.sub.7
di-tetrahedral units in the
[CuO.sub.4].sub.4Cl[P.sub.2O.sub.7].sub.4 blocks along the c-axis
allows the structure to flex with expansion and contraction of the
channels to incorporate of A.sup.+ cations and [MX.sub.4] anions of
differing sizes.
[0090] The CuClP materials are a series of complex anion-inclusion
compounds that contain weakly coordinated square planar MCl.sub.4
groups (e.g. [AuCl.sub.4].sup.- [PtCl.sub.4].sup.2-,
[PdCl.sub.4].sup.2-) that stack neatly on one another in the
channels. Without wishing to be bound by any particular theory, it
is believed that upon activation, such as by calcination, these
anions were found to be extruded from the channels, and generate
isolated noble metallic nanoparticles with a size distribution of
2-10 nm.
[0091] In one exemplary embodiment, a catalyst is provided. The
catalyst comprises a microporous copper chloropyrophosphate
framework including a plurality of noble metal nanoparticles.
[0092] In one exemplary embodiment, the catalyst comprises a
plurality of noble metal nanoparticle sites. Exemplary noble metals
include platinum, palladium, and gold. In one exemplary
embodiments, the noble metal is in the metallic state or has an
oxidation state of zero.
[0093] In one exemplary embodiment, the catalyst comprises noble
metal nanoparticles of a single metal, referred to herein as
mono-metallic noble metal catalysts. Exemplary mono-metallic noble
metal catalysts include catalysts with exactly one of platinum,
palladium, or gold noble metal nanoparticle sites.
[0094] In one exemplary embodiment, the catalyst comprises noble
metal nanoparticles of two metals, referred to herein as
bi-metallic noble metal catalysts. Exemplary bi-metallic noble
metal catalysts include catalysts with exactly two metal selected
from the group consisting of platinum, palladium, and gold, such as
platinum and palladium, platinum and gold, and palladium and
gold.
[0095] In one exemplary embodiment, the catalyst comprises a
plurality of precursor complexes. Exemplary precursor complexes
include metal chloride ions such as [PtCl.sub.4].sup.2-,
[PdCl.sub.4].sup.2-, and [AuCl.sub.4].sup.-. In one exemplary
embodiment, the precursor complexes are converted to the noble
metal nanoparticle sites by activating the catalyst. Exemplary
methods of activating the catalyst include heating the catalyst in
the presence of hydrogen at a temperature as little as 150.degree.
C., 175.degree. C., 200.degree. C., as great as 250.degree. C.,
300.degree. C., 350.degree. C. or higher, or within any temperature
range defined between any two of the foregoing values, such as at
least 150.degree. C., at least 175.degree. C., at least 200.degree.
C., at least 300.degree. C., 150.degree. C. to 300.degree. C.,
150.degree. C. to 250.degree. C., 175.degree. C. to 200.degree. C.,
or 200.degree. C. to 350.degree. C., for as little as 30 minutes, 1
hour, 1.5 hours, as long as 2 hours, 2.5 hours, 3 hours, or longer,
or within any range defined between any two of the foregoing
values, such as at least 30 minutes, at least 2 hours, 1.5 hours to
3 hours, or 2 hours to 3 hours. In one more particular embodiment,
the catalyst is heated in a hydrogenous environment. In another
more particular embodiment, the catalyst is activated by heating
the catalyst under a flow of 5% hydrogen/nitrogen at a flow rate of
150 mLmin.sup.-1.
[0096] In one exemplary embodiment, the catalyst is an Au/CuClP
mono-metallic material activated by heating the material in the
presence of hydrogen at a temperature of about 350.degree. C. In
one exemplary embodiment, the catalyst is a Pt/CuClP mono-metallic
material activated by heating the material in the presence of
hydrogen at a temperature of about 200.degree. C. In one exemplary
embodiment, the catalyst is a Pd/CuClP mono-metallic activated by
heating the material in the presence of hydrogen at a temperature
of about 150.degree. C. In one exemplary embodiment, the catalyst
is a PtPd/CuClP bi-metallic material activated by heating the
material in the presence of hydrogen at a temperature of
150.degree. C. to 200.degree. C. or about 200.degree. C. In one
exemplary embodiment, the catalyst is an AuPt/CuClP bi-metallic
material activated by heating the material in the presence of
hydrogen at a temperature of 200.degree. C. to 350.degree. C.,
250.degree. C. to 300.degree. C., or about 300.degree. C.
[0097] In one embodiment, an exemplary catalyst is made by mixing
copper (II) fluoride, orthophosphoric acid, rubidium hydroxide,
rubidium chloride, and a source of metal chloride; heating the
mixture in a sealed container to form a catalyst precursor
including precursor complexes. In one exemplary embodiment, a
mono-metallic catalyst is formed by selecting a single source of
metal chloride. In another exemplary embodiment, a bi-metallic
catalyst is formed by selecting two sources of metal chlorides,
each containing a different metal. Exemplary sources of metal
chloride include K.sub.2PtCl.sub.4, K.sub.2PdCl.sub.4, and
HAuCl.sub.4. In some exemplary embodiments, the catalyst comprises
the metal in an amount as little as about 0.1 wt. %, 0.5 wt. %, 1
wt. %, as great as 2 wt. %, 5 wt. %, 10 wt. %, 15 wt. %, or within
any range defined between any two of the foregoing values, such as
0.1 wt. % to 15 wt. %, or 1 wt. % to 10 wt. % for example.
[0098] In one exemplary embodiment, nanoparticles of substantially
uniform size are formed based on the extrusion of metal chloride
precursor complex anions, such as MCl.sub.x where M=Au, Pt or Pd,
from a crystalline microporous copper chloropyrophosphate
framework. The framework is illustratively of CU-2 topology and has
flexible anion-exchange properties. As illustratively shown in
FIGS. 1A and 1B, the parent CU-2 framework consists of a .mu..sup.4
chloride ion at the apex of 4x CuO.sub.4Cl square-based pyramids.
These quartets are linked by pyrophosphate, P.sub.2O.sub.7, groups,
to form one dimensional chains, with the cavities between
[CuO.sub.4].sub.4Cl[P.sub.2O.sub.7].sub.4 blocks along the
c-direction occupied by A.sup.+ cations. The
[CuO.sub.4].sub.4Cl[P.sub.2O.sub.7].sub.4 units are cross-linked,
via a shared oxygen atom on a P.sub.2O.sub.7 unit, in the a-b plane
by square-planar CuO.sub.4 groups, this produces producing a square
grid of 1-dimensional channels extending through the catalyst in
the c-axis direction with dimensions .about.12.times.12 .ANG.. In
some exemplary embodiments, the channels are lined with A.sup.+
cations and/or chloride ions, with weakly coordinated (Cu--Cl
.about.2.7 .ANG.) to the cross-linking CuO.sub.4 square planar
units. The orientation of the resulting CuO.sub.4Cl square-based
pyramids alternates for copper sites along the c-axis. Without
wishing to be held to any particular theory, it is believed that
the relative orientation of successive P.sub.2O.sub.7
di-tetrahedral units in the
[CuO.sub.4].sub.4Cl[P.sub.2O.sub.7].sub.4 blocks along the c-axis
allows the structure to flex with expansion and contraction of the
channels to incorporate of A.sup.+ cations and [MX.sub.4] anions of
differing sizes. For a specific anion a linear relationships exists
between cation radius, lattice parameters and the torsional angle
(O--P . . . P--O) between neighboring pyrophosphate units. The
channels contain site-disordered free (fluoro- or hydrogen-)
phosphate tetrahedra [P(O/OH/F).sub.4] (see. FIG. 1). In some more
particular embodiments, the phosphate anions are replaced with
square planar species (CuCl.sub.4.sup.2- is a flattened
tetrahedron, D.sub.2d) which stack with their faces orientated
perpendicular to the channel direction This elongation and
compression of the channels is believed to produce an interaction
between cross-linking CuO.sub.4 unit copper site and the oxygen of
a free phosphate anion within the channels, with a Cu--O distance
of 2.285 .ANG.; it also is believed to allow for the formation of a
more ideal coordination geometry.
[0099] As illustrated by the reaction 104 in FIG. 2A, phenol can be
hydrogenated in the presence of a catalyst, to form cyclohexanone.
Exemplary catalysts include palladium, platinum, ruthenium, and
other suitable catalysts. However, a portion of the phenol is
hydrogenated to form cyclohexanol according to reaction 106 in FIG.
2B.
[0100] As shown in FIG. 3, a mixture 108 of cyclohexanol 110 and
cyclohexanone 112 is brought in to proximity with the catalyst 102
and oxygen 116. The catalyst 102 illustratively includes a
microporous copper chloropyrophosphate framework 114 and a
plurality of noble metal nanoparticles 118 that serve as activation
sites for the conversion of cyclohexanol 110 to cyclohexanone
112.
[0101] In one exemplary embodiment, the cyclohexanol to be
converted to cyclohexanone is provided as a mixture of
cyclohexanone and cyclohexanol. In some exemplary embodiments, the
weight percent of cyclohexanol is as little as 5 wt. %, 10 wt. %,
20 wt. %, 25 wt. %, 30 wt. %, 40 wt. %, 45 wt. %, 50 wt. %, as
great as 55 wt. %, 60 wt. %, 70 wt. %, 75 wt. %, 80 wt. %, 90 wt.
%, 95 wt. %, based on the total weight of the cyclohexanol and
cyclohexanone in the mixture, or within any range defined between
any two of the foregoing values, such as 5 wt. % to 95 wt. %, 20
wt. % to 80 wt. %, 40 wt. % to 60 wt. %, or 45 wt. % to 55 wt. %.
In one exemplary embodiment, the mixture comprises about 50 wt. %
cyclohexanol, based on the total weight of the cyclohexanol and
cyclohexanone.
[0102] In one exemplary embodiment, the catalytic conversion of
cyclohexanol to cyclohexanone is typically performed at a
temperature beneath 250.degree. C. In one exemplary embodiment, the
catalytic conversion of cyclohexanol to cyclohexanone is typically
performed at a temperature beneath 350.degree. C. In other
embodiments, the reaction may be performed at a temperature as low
as about 150.degree. C., 180.degree. C., 190.degree. C., as high as
200.degree. C., 210.degree. C., 220.degree. C., 250.degree. C., or
within any range defined between any pair of the foregoing values,
such as 150.degree. C. to 250.degree. C., 180.degree. C. to
220.degree. C., or 190.degree. C. to 210.degree. C. In one
exemplary embodiment, the catalytic conversion of cyclohexanol to
cyclohexanone is performed at atmospheric pressure; in other
exemplary embodiments, higher or lower pressures may be used.
[0103] The efficiency of the conversion may be expressed in terms
of conversion of cyclohexanol, selectivity of the desired
cyclohexanone product, or yield. Conversion is a measure of the
amount of cyclohexanol reactant that is consumed by the reaction.
Higher conversions are more desirable. The conversion is calculated
as:
Conversion ( mol % ) = 100 % .times. ( 1 - moles of reactant
remaining moles of reactant supplied ) ##EQU00001##
[0104] Selectivity is a measure of the amount of the desired
cyclohexanone product that is produced relative to all reaction
products. Higher selectivities are more desirable. Lower
selectivities indicate a higher percentage of reactant being used
to form undesired products. The selectivity is calculated as:
Selectivity ( mol % ) = 100 % .times. moles of desired
cyclohexanone product produced moles of reactant supplied - moles
of reactant remaining ##EQU00002##
[0105] Yield is a measurement that combines selectivity and
conversion. Yield indicates how much of the incoming reactant is
reacted to form the desired cyclohexanone. The yield is calculated
as:
Yield (mol %)=Selectivity (mol %).times.Conversion(mol %)/100%
[0106] In some exemplary embodiments, the methods according to the
present disclosure result in high conversion and selectivity for
the desired cyclohexanone.
[0107] In one embodiment, the conversion of cyclohexanol is 50% or
higher. In a more particular embodiment, the conversion is from
about 50% to about 100%. For example, the conversion may be as low
as about 50%, 60%, 70%, 75%, or as high as about 80%, 85%, 90%,
95%, 97.5%, 99%, 99.5%, approaching 100%, or 100%, or may be within
any range defined between any pair of the foregoing values.
[0108] In one embodiment, the selectivity of cyclohexanone is 50%
or higher. In a more particular embodiment, the selectivity is as
low as about 50%, 55%, 60%, 65%, or as high as about 70%, 75%, 80%,
85%, 90%, 95%, 97.5%, 99%, 99.5%, approaching 100%, or may be
within any range defined between any pair of the foregoing
values.
[0109] In one embodiment, the yield is 30% or higher. In a more
particular embodiment, the yield is as low as about 30%, 35%, 40%,
45%, 50%, 55%, 60%, 65%, or as high as about 70%, 75%, 80%, 85%,
90%, 95%, 97.5%, 99%, 99.5%, approaching 100%, or may be within any
range defined between any pair of the foregoing values.
Example 1: Synthesis and Activation of Catalyst
[0110] Synthesis: Chemicals for synthesis were purchased from Sigma
Aldrich or Fisher Scientific and used without further purification,
except RbCl, which was dried under vacuum at 100.degree. C.
[0111] Copper(II) fluoride (0.1168 g, 1.150 mmol), 85 wt. %
orthophosphoric acid (0.2 mL, 2.922 mmol), 50 wt. % RbOH (0.24 mL,
2.037 mmol), RbCl (0.28 g; 2.316 mmol) and a source of MCl.sub.x;
HAuCl.sub.4.xH.sub.2O (0.0489 g, 0.144 mmol, 7 wt. % Au),
K.sub.2PtCl.sub.4 (0.0598 g, 0.144 mmol, 7 wt. % Pt) or
K.sub.2PdCl.sub.4 (0.0470 g, 0.144 mmol, 4 wt. % Pd) were mixed in
the Teflon.RTM. liner of a custom-made 23 mL hydrothermal vessel.
The vessel was sealed and heated to 175.degree. C. for 2 days.
[0112] Copper(II) fluoride (0.1168 g, 1.15 mmol), rubidium chloride
(0.2800 g, 2.32 mmol) and a source of metal chloride salt selected
from 0.0489 g (0.144 mmol) gold(III) chloride hydrate, 0.0515 g
(0.124 mmol) potassium tetrachloroplatinate, or 0.0405 g (0.124
mmol) potassium tetrachloropalladate were accurately weighed out to
4 decimal places and ground in an agate pestle and mortar for 2
minutes to homogenize.
[0113] The mixture was added to the Teflon.RTM. liner of a 23 mL
hydrothermal vessel, and 85% orthophosphoric acid in water (0.20
mL, 2.92 mmol) was added dropwise wetting the entire contents. The
mixture was sonicated for 5 minutes to encourage mixing. 0.24 mL
(2.38 mmol) of 50 wt. % rubidium hydroxide in water was added
dropwise, wetting the entire contents, and the mixture was
sonicated for 10-15 minutes until the mixture was homogenous.
Caution was taken due to production of hydrogen fluoride gas.
[0114] The hydrothermal vessel was sealed and heated to 175.degree.
C. for 48 hours in a convection oven. The vessels were allowed to
cool naturally before collecting the product by filtration, washing
with deionized water (100 mL) and drying overnight at 80.degree.
C.
[0115] Products formed as brilliant green cuboid crystals for both
the Au and Pt material, and as light brown crystals for the Pd
material.
[0116] Activation Procedure: Gases were sourced from BOC Industrial
Gases and used as purchased. Materials were activated by reduction
under a flow of 5% H.sub.2/N.sub.2 at approx. 150 mLmin.sup.-1, for
2 hours at the specified temperature, generating the active
nanoparticle catalysts. After reduction, the Au material appeared
unchanged in color when activated at temperatures below 250.degree.
C., but a dark red color when activated at temperatures above
250.degree. C., while the Pd material appeared black in color and
the Pt catalyst a darker khaki-green.
Example 2: Characterization of Catalysts
X-Ray Photoelectron Spectroscopy (XPS) and X-Ray Absorption
Spectroscopy (XAS)
[0117] X-ray photoelectron spectroscopy (XPS) was employed to probe
the nature of noble metal species adjacent to the surface of the
microporous framework, with respect to different activation
temperatures. XPS analysis was performed using a Thermo Scientific
K-Alpha instrument equipped with monochromated Al K.sub..alpha.
source at the EPSRC XPS User's Service (NEXUS), University of
Newcastle. A flood gun was used for charge compensation. A pass
energy of 200 eV and a step size of 1.0 eV was employed for all
survey spectra while a pass energy of 40 eV and a step size of 0.1
eV was used for high-resolution spectra of the elements of
interest. All XPS spectra were calibrated against the carbon and/or
oxygen 1s peaks, and high resolution spectra were fitted with
Shirley backgrounds before peak analysis using the CasaXPS
software.
[0118] FIG. 4A illustrates stacked XPS data with data fits and
appropriate reference samples for the Pt/CuClP materials activated
at different temperatures, with the appropriate standards for
comparisons showing the progressive decrease in Pt(II) content and
the mirrored increase in Pt(0) species with increased activation
temperature, with the final sample exhibiting complete formation of
Pt(0).
[0119] FIG. 4B depicts the XPS spectra with data fits and
appropriate reference samples of the three Pt/CuClP species reduced
using different activation temperatures. A clear trend was observed
for the Pt/CuClP catalyst, which showed a transition from a mixture
of Pt(II) and Pt(0) with 4f.sub.7/2 peaks at 72.4 eV and 70.8 eV
respectively, to purely Pt(0) species, as the activation
temperature was progressively increased from 150 to 200.degree. C.:
(FIG. 20A). Furthermore, it was established that an activation
temperature of 200.degree. C. was sufficient for the complete
reduction of the Pt precursors to form nanoparticles under these
activation conditions
[0120] FIG. 5 illustrates stacked XPS data with data fits and
appropriate reference samples for the Au/CuClP materials activated
at different temperatures, with the appropriate standards for
comparisons showing the loss of Au(III) content and the complete
formation of Au(0) at temperatures above 200.degree. C.
[0121] XAS for palladium, platinum, and gold were carried out on
the B18 beam line at the Diamond Light Source, Didcot, UK.
Measurements were performed using a QEXAFS set-up with a
fast-scanning Si (111) or Si (311) double crystal monochromator.
The normal time resolution of the spectra reported herein was 1
min/spectrum (k.sub.max=16), on average six scans were acquired to
improve the signal-to-noise level of the data. All samples were
diluted with cellulose and pressed into pellets to optimize the
effective edge-step of the XAFS data and measured in transmission
mode using ion chamber detectors. All transmission XAFS spectra
were acquired concurrently with the appropriate reference foil
placed between I.sub.t and I.sub.f. XAS data processing and EXAFS
(extended X-ray absorption fine structure) analysis were performed
using IFEFFIT with the Horae package (Athena and Artemis). The
amplitude reduction factor, S.sub.0.sup.2, was derived from EXAFS
data analysis of known compounds, and used as a fixed input
parameter.
[0122] FIG. 6A illustrates stacked X-ray absorption near edge
structure (XANES) data for the Pt/CuClP materials activated at
different temperatures, showing the progressive decrease in white
line intensity as the activation temperature is increased,
signifying the decrease in Pt oxidation state.
[0123] FIG. 6B illustrates the magnitude and imaginary component of
the k.sup.3 weighted Fourier transform for the fitted EXAFS data of
the three Pt/CuClP species reduced using different activation
temperatures.
[0124] Both the XPS and XAS techniques demonstrate the progressive
reduction of the [PtCl.sub.4].sup.2- precursor towards the metallic
Pt(0) species with increase in temperature. FIG. 4B is plotted with
reference samples in FIG. 4A. For FIG. 6B the associated scattering
paths are included for the imaginary component and the fitting
parameters are displayed in Table 1.
TABLE-US-00001 TABLE 1 Pt EXAFS fitting parameters for the fits
displayed in FIG. 6B. Sample Abs Sc N R/.ANG.
2.sigma..sup.2/.ANG..sup.2 E.sub.f/eV R.sub.factor Pt/CuClP Pt--Cl
3.7 (2) 2.320 (5) 0.0027 (3) 9.5 (8) 0.012 150.degree. C. Pt--Pt
3.4 (5) 2.768 (7) 0.0056 (5) Pt/CuClP Pt--Cl 0.8 (1) 2.31 (9)
0.0026 (8) 7.9 (7) 0.006 175.degree. C. Pt--Pt 8.9 (3) 2.76 (2)
0.0059 (1) Pt/CuClP Pt--Cl 0.4 (1) 2.32 (2) 0.003 (2) 7.6 (6) 0.006
200.degree. C. Pt--Pt 9.6 (4) 2.760 (3) 0.0059 (2) Pt sample -
S.sub.0.sup.2 = 0.91 as deduced by Pt foil standard; Fit range 3
< k < 14, 1.15 < R < 3; # of independent points =
12.
[0125] FIG. 7 illustrates the magnitude and imaginary component of
the k.sup.3 weighted Fourier transform for the fitted EXAFS data of
the three Au/CuClP species reduced under increasing activation
temperatures, exhibiting the majority [AuCl.sub.4].sup.- precursor,
with minimal signs for the reduction from the Au(III) towards Au(0)
in the bulk. Associated scattering paths are included for the
imaginary component and the fitting parameters are provided in
Table 2.
TABLE-US-00002 TABLE 2 Au EXAFS fitting parameters for the fits
displayed in FIG. 7. Sample Abs Sc N R/.ANG.
2.sigma..sup.2/.ANG..sup.2 E.sub.f/eV R.sub.factor Au/CuClP Au--Cl
3.7 (1) 2.287 (4) 0.0027 (2) 9.9 (6) 0.004 150.degree. C. Au/CuClP
Au--Cl 2.24 (7) 2.269 (4) 0.0028 (3) 7.3 (7) 0.009 200.degree. C.
Au/CuClP Au--Cl 3.1 (1) 2.282 (5) 0.0029 (3) 9.4 (9) 0.010
250.degree. C. Au sample - S.sub.0.sup.2 = 0.75 as deduced by
KAuCl.sub.4 standard; Fit range 3.5 < k < 12.5, 1.1 < R
< 3; # of independent points = 10.
[0126] FIG. 8 illustrates the magnitude and imaginary component of
the k.sup.3 weighted Fourier transform for the fitted EXAFS data of
the three Pd/CuClP species reduced under increasing activation
temperatures, demonstrating a minor reduction in Pd--Cl
contribution with increase in activation temperature. Associated
scattering paths are included for the imaginary component and the
fitting parameters are provided in Table 3.
TABLE-US-00003 TABLE 3 Pd EXAFS fitting parameters for the fits
displayed in FIG. 8. Sample Abs Sc N R/.ANG.
2.sigma..sup.2/.ANG..sup.2 E.sub.f/eV R.sub.factor Pd/CuClP Pd--Cl
4.2 (1) 2.322 (5) 0.0028 (4) 5.2 (7) 0.007 150.degree. C. Pd--Pd
0.3 (2) 2.76 (3) 0.003 (3) Pd/CuClP Pd--Cl 3.2 (3) 2.35 (1) 0.003
(1) 4 (2) 0.041 175.degree. C. Pd--Pd 0.9 (4) 2.77 (3) 0.003 (2)
Pd/CuClP Pd--Cl 3.4 (3) 2.35 (1) 0.0027 (7) 13 (1) 0.025
200.degree. C. Pd--Pd 0.9 (4) 2.77 (2) 0.002 (2) Pd sample -
S.sub.0.sup.2 = 0.82 as deduced by PdCl.sub.2 standard; Fit range 3
< k < 12, 1 < R < 3; # of independent points = 11.
[0127] XAS was used to probe the coordination geometry and local
structural environment of the active sites with a view to gaining a
better understanding on nanoparticle formation and extrusion, with
progressive increase in activation temperatures. Concurrent trends
with the XPS are exhibited in both the EXAFS (FIG. 6B) and XANES
(FIG. 6A) data of the Pt/CuClP material, with evident progressive
reduction of the [PtCl.sub.4].sup.2- precursor species across the
bulk of the sample. FIG. 6B demonstrates the significant decrease
in contribution from Pt--Cl neighboring atoms with a concurrent
increase in Pt--Pt neighbors as a function of activation
temperature. Analogously, due to the direct relationship between
the white-line intensity of the L.sub.3-edge and the number of
unoccupied Pt 5d states, the diminishing white line energies
displayed in FIG. 6A suggest that the Pt species are approaching
the metallic state with progressive increase in activation
temperature.
[0128] In addition, Table 1 shows that Pt--Pt bond lengths remain
consistent with that expected of Pt nanoparticles above 2.4 nm
(2.76 .ANG.) and that the coordination numbers of the first shell
Pt--Pt scattering path are also lower at 9.6(4) than would be
expected of bulk Pt metal at 12. This indicates that an
overwhelming majority of the [PtCl.sub.4].sup.2- precursor are
reduced to their metallic state with increase in activation
temperature, as evidenced by the drastic reduction in the average
number of adjacent CI atoms around the central Pt species. These
observations juxtaposed with those of the Au and Pd systems
highlight the ease of extrusion of [PtCl.sub.4].sup.2- species from
the micropores, while corresponding powder X-ray diffraction (PXRD)
data confirms the retention of the structural integrity of the
surrounding framework architecture (FIG. 9). In the case of Pt, it
is clear that the absence of discrete precursor anions within the
pores is not detrimental to the overall stability of the
microporous framework structure (FIG. 9). This is in contrast to
that of the Pd/CuClP catalyst (FIG. 12) where, at temperatures
above 200.degree. C., the structural integrity becomes susceptible
to additional phase impurities and degradation of the framework.
Without wishing to be held to any particular theory, it is believed
that this could be indicative of stronger interactions between the
discrete [PdCl.sub.4].sup.2- anions and the internal pores of the
framework.
[0129] The Au XAS (FIG. 7) emphasizes that the [AuCl.sub.4].sup.-
precursor requires much higher activation temperatures, despite the
XPS showing surface species, with slightly reduced binding energies
characteristic of nanoparticulate Au, being generated above
200.degree. C. (FIG. 5). This suggests that although metallic Au
species form on the surface of these materials at 200.degree. C.,
higher temperatures and/or alternate activation conditions might be
required to achieve comparable extrusions to the Pt catalyst.
Powder X-Ray Diffraction (PXRD)
[0130] X-Ray diffraction patterns were collected on a Bruker D2
Phaser diffractometer. FIG. 9 provides indexed PXRD spectra of the
Pt/CuClP materials activated at different temperatures with the
pre-activation, as-synthesized sample for comparison demonstrating
both the structural integrity of the material at the various
activation temperatures and a broad signal at 40.degree. assigned
to the metallic Pt (111) reflection. Additionally the broad nature
of the peak is indicative of small particle (nanoparticulate)
size.
[0131] FIG. 10 provides PXRD spectra of the Pt/CuClP materials
activated at 200.degree. C. both before (fresh) and after catalysis
(recycle) in the oxidation of KA-oil for 6 hr, signifying the
robust nature and extended lifetime of these catalytic
materials.
[0132] FIG. 11 provides indexed PXRD spectra of the Au/CuClP
materials activated at different temperatures with the
pre-activation, as-synthesized sample for comparison demonstrating
the structural integrity of the material at the various activation
temperatures.
[0133] FIG. 12 provides indexed PXRD spectra of the Pd/CuClP
materials activated at different temperatures with the
pre-activation, as-synthesized sample for comparison, demonstrating
the structural integrity of the material up to 175.degree. C. and
then the introduction of additional rubidium phosphate phases at
temperatures close to 200.degree. C.
Transmission Electron Microscopy (TEM)
[0134] Aberration-corrected TEM was performed on an FEI Titan.sup.3
80-300 (S)TEM equipped with a CEOS CESCOR aberration corrector in
the probe forming lens. The Titan was operated at 80 or 300 kV,
employing annular dark-field (ADF) aberration-corrected scanning
TEM (AC-STEM) as the primary investigative technique. Samples were
prepared for the STEM analysis by dusting the dry powder onto
standard copper TEM support grids with holey carbon support film.
Between analyses, samples were stored in a vacuum desiccator with
anhydrous calcium sulfate desiccant. Under various combinations of
electron beam current, dwell time and pixel size (magnification),
and at both 80 and 300 kV, all samples were found to be highly
susceptible to beam-induced damage. Considerable care was therefore
taken to obtain representative images before overwhelming
beam-induced modification of the samples occurred.
[0135] FIGS. 13-16 present various ADF AC-STEM images.
[0136] FIG. 13 presents ADF AC-STEM images of the Pt/CuClP material
activated at 200.degree. C. FIG. 13A shows nanoparticle formation
across the framework (nanoparticle size in this area .about.2-3 nm
in diameter). FIGS. 13B and 13C present high-resolution images of
the nanoparticles, in which the measured d-spacing's are consistent
with nanocrystalline Pt. The crystalline integrity of the framework
is also rendered visible, by virtue of the framework lattice planes
containing heavy-metal atoms.
[0137] FIG. 14 presents ADF AC-STEM images of the Pd/CuClP material
activated at 200.degree. C. FIG. 14A shows the crystalline
structure of the framework rendered visible by the framework
lattice planes containing heavy metal atoms. Here no nanoparticle
formation is observed. FIGS. 14B and 14C show limited nanoparticle
formation, with a suggestion of higher propensity to form on the
surface of the support, as highlighted in FIG. 14C.
[0138] FIG. 15 presents ADF AC-STEM images of the Au/CuClP material
activated at 200.degree. C. Nanoparticle formation is abundant
across the framework, whose crystalline structure is rendered
visible in both FIGS. 15A and 15B via heavy metal atom containing
lattice planes of the framework. As shown in FIG. 15C, in addition
to the small nanoparticles, significant larger nanoparticles are
also present.
[0139] FIG. 16 presents ADF AC-STEM images of the respective
nanoparticle-framework materials activated at 200.degree. C. The
crystalline structure of the framework is rendered visible via the
lattice planes containing heavy atoms. FIGS. 16A and 16B show an
abundance of Pt nanoparticles with [PtCl.sub.4].sup.2- precursor.
FIGS. 16C and 16D show a paucity or limited Pd nanoparticle
formation. FIGS. 16E and 16F show a prevalence of Au
nanoparticles.
[0140] High-resolution studies, using AC-STEM, have shown in detail
the abundant formation of nanocrystalline Pt nanoparticles (2-5 nm
in diameter), which are well-dispersed on the copper
chloropyrophosphate framework, whose crystalline integrity could
also be visualized directly (FIGS. 13A-C, 16A, and 16B). In this
regard it is apparent that the atomic number contrast and often
`direct interpretability` of ADF STEM imaging, combined with the
high-spatial resolution enabled by AC optics, can yield significant
insight into the crystallographic structures of both the extruded
nanoparticles and the microporous framework. The much more limited
nanoparticle formation in the Pd/CuClP system is also readily
apparent from AC-STEM, as exemplified in FIGS. 14A-C, 16C, and 16D.
Complementary compositional studies using STEM-EDXS also confirmed
the well-defined nature of the Pt/CuClP and Pd/CuClP systems, with
abundance and paucity of nanoparticles, respectively (FIGS. 15A and
15B).
Energy-Dispersive X-Ray Spectroscopy (EDXS)
[0141] EDXS was performed on an FEI Tecnai Osiris 80-200 (S)TEM
operated at 80 kV, equipped with an FEI Super-X EDXS system.
Spectral processing was performed using the FEI TIA and HyperSpy
(http://hyperspy.org) software packages.
[0142] The results are provided in FIGS. 17-19. For each figure,
the area analyzed is indicated by the box in the inset ADF-STEM
image. FIG. 17 provides an EDXS spectra for the Pt/CuClP material
activated at 200.degree. C. FIG. 18 provides an EDXS spectra for
the Pd/CuClP material activated at 200.degree. C. FIG. 19 provides
an EDXS spectra for the Au/CuClP material activated at 200.degree.
C.
[0143] To verify overall composition, for all samples, EDX spectra
were acquired and integrated from large regions across the
micron-sized as well as smaller fragments of the samples.
Characteristic regions of the samples typically showed presence of
the expected constituent elements (viz. Pt, Pd or Au and Cu, Rb,
Cl, O, P), as seen in the example spectra of FIGS. 17-19. Some
(usually small in size and prevalence) fragments showed presence of
F, Ca, or Si impurities and/or absence of expected constituent
elements, which may be remnants from the synthesis process,
contamination during synthesis, sample storage or TEM sample
preparation, or the result of segregation over time.
[0144] The potentially more complex phenomena in the Au/CuClP
system (as seen from the EXAFS) was also systematically
investigated in AC-STEM and STEM-EDXS studies, including samples
activated at different temperatures. As shown in FIGS. 15, 16E,
16F, and 37, regions of extensive well-defined small nanoparticle
formation could be observed for the Au/CuClP system, even when the
sample was activated at 200.degree. C. (analogous to the Pt/CuClP).
Consistent with the XPS studies, these would appear to predominate
at thin or surface regions of the framework. Further, STEM and
spatially resolved STEM-EDXS elemental mapping also indicates the
potential for Au/Cu alloying or joint extrusion.
[0145] By employing a combination of complimentary structural,
spectroscopic and high-resolution microscopy techniques, we have
contrasted the varying degrees of nanoparticle formation and the
superior properties of the [PtCl.sub.4].sup.2- precursor to yield
well-defined, isolated nanoparticles (predominantly 2-3 nm) within
microporous framework architectures. The local structural
environment, and the precise nature and location of these active
sites, is exigent for their performance (approaching yields of
>90% by adapting a `closed-loop` system) in the aerobic
oxidation of KA-oil, under continuous-flow conditions.
[0146] To investigate the effects of different activation
temperatures on the morphology and composition of the Au/CuClP
materials, further STEM imaging and EDXS investigations were
undertaken using the Tecnai Osiris. To ensure correct
interpretation, note that some of the ADF images in this section
show contrast inversion at thicker regions of the sample and often
at the larger nanoparticles. Elemental maps were obtained by
integrating the area under the relevant X-ray peaks, using the
HyperSpy software package (http://hyperspy.org), with the
particular peaks chosen to minimize effects of peak overlap. As the
samples were supported on Cu TEM grids, the Cu L.sub..alpha. rather
than Cu K.sub..alpha. peak has been used for the Cu maps; the
former being more representative of Cu in the sample itself. FIG.
35 illustrates an EDXS spectra for the Au/CuClP material activated
at 250.degree. C. FIG. 36 illustrates an EDXS spectra for the
Au/CuClP material activated at 350.degree. C. The area analysed for
elemental content is indicated by the box in the inset ADF-STEM
image.
[0147] FIGS. 37-39 illustrate ADF-STEM images of the Au/CuClP
material activated at various temperatures. A combination of EDXS
point spectra, line scans and spectrum images were performed to
probe the chemical identity of the nanoparticles and distribution
of elements within the framework. These confirmed the identity of
smaller (2-5 nm) and larger (>10 nm) nanoparticles as dominantly
Au, although some nanoparticles were found to be dominantly Cu,
often concomitant with substantial agglomeration of elements from
the framework.
[0148] FIGS. 37A-D illustrate ADF-STEM images of the Au/CuClP
material activated at 200.degree. C. Medium/small nanoparticle
formation is visible at the periphery of the fragments of the
sample, as highlighted in FIGS. 37B and 37D. A limited number of
larger nanoparticles are visible, particularly in FIG. 37D, but the
majority of the fragments of the sample show smooth intensity,
indicative of a more pristine framework (compared to the strong
mottled contrast and extensive nanoparticle formation seen in FIGS.
39B and 39D).
[0149] FIGS. 38A-E illustrate ADF and bright-field STEM images of
the Au/CuClP material activated at 250.degree. C. ADF images such
as shown in FIGS. 38A, 38B, and 38D, and bright-field STEM images,
such as shown in FIGS. 38C and 38E illustrate the morphology of the
sample. In addition to abundant small nanoparticle formation,
particularly illustrated in FIG. 38C, there is also considerable
large nanoparticle formation. Variation in image contrast
throughout the bulk of the framework. Without wishing to be held to
any particular theory, this is believed to suggest morphological
and compositional re-distributions as a result of the heat
treatment process.
[0150] FIGS. 39A-E illustrate ADF-STEM images of the Au/CuClP
material activated at 350.degree. C. ADF-STEM images revealing the
morphology of the Au/CuClP sample activated at 350.degree. C.
Extensive large nanoparticle formation and variation in image
contrast throughout the bulk suggests substantial morphological and
compositional re-distributions as a result of the heat treatment
process
[0151] FIG. 40 illustrates images of the small nanoparticles in the
Au/CuClP sample activated at 250.degree. C. FIG. 40A shows an ADF
image of the region analysed prior to EDXS. FIG. 40B shows an ADF
image acquired simultaneous to EDXS mapping. FIG. 40C illustrates
an EDXS sum-spectrum, obtained by summing all spectra from the
spectrum image. FIG. 40D illustrates elemental maps obtained from
the spectrum image by peak integration. As illustrated in FIG. 40D,
the spectrum image, acquired with a relatively short dwell time and
coarse pixel size to minimise beam-induced modification of the
sample, associates the Au signal with the nanoparticles, with the
other elements distributed more evenly across the framework
support.
[0152] FIG. 41 illustrates images of the large faceted
nanoparticles in the Au/CuClP sample activated at 350.degree. C.
FIG. 41A shows an ADF image of the region analysed prior to EDXS.
FIG. 41B shows an ADF image acquired simultaneous to EDXS mapping.
FIG. 41C illustrates an EDXS sum-spectrum, obtained by summing all
spectra from the spectrum image. FIG. 41D illustrates elemental
maps obtained from the spectrum image by peak integration. As shown
in FIG. 41D, even though significant spatial drift has occurred
during the spectrum image acquisition, the spectrum image supports
that the large faceted nanoparticles are Au, while the supporting
framework is Cu rich. (Rb, P and CI maps not shown here due to peak
overlap and dominance of the Au signal in this spectrum image).
[0153] FIG. 42 illustrates images of the large nanoparticles and
agglomerations in the framework support in the Au/CuClP sample
activated at 350.degree. C. FIG. 42A shows an ADF image of the
region analysed prior to EDXS. FIG. 42B shows an ADF image acquired
simultaneous to EDXS mapping. FIG. 42C illustrates an EDXS
sum-spectrum, obtained by summing all spectra from the spectrum
image. FIG. 42D illustrates elemental maps obtained from the
spectrum image by peak integration. FIG. 42 D indicates significant
Cu nanoparticle formation and agglomeration. Without wishing to be
held to any particular theory, the slightly mottled appearance of
the Au map suggests formation of Au nanoparticles may have occurred
across the framework, although the relatively uniform distribution
of Au also suggests that a significant fraction of Au may also
still reside within the original framework material.
Example 3: Catalytic Testing
Comparative Examples
[0154] Chemicals for catalytic tests were purchased from Sigma
Aldrich or Fisher Scientific and used without further purification.
Catalytic reactions were carried out in a fixed-bed flow reactor
using pelletized catalyst (approx. 0.1-1 g). The reactor assembly
was set up and purged under the flow of air at 200.degree. C. for
one hour before the substrate feed was allowed to saturate the
system. The substrate and air flow rates were adjusted to their
experimental level and left to equilibrate for one hour. All
reactions were carried out using an air flow of 25 mLmin.sup.-1, a
cyclohexanol flow of 7.5 .mu.Lmin.sup.-1 or a KA-oil flow of 15
.mu.Lmin.sup.-1 and at 200.degree. C. unless stated otherwise.
KA-oil solutions were made up of 50:50% wt. ratio of cyclohexanol
and cyclohexanone.
[0155] An external standard solution of triethyleneglycol dimethyl
ether (2 M) in acetone was fed into the off-stream of the reactor
at the same rate as the substrate. The solution obtained was
diluted at a ratio of 1:10 with acetone before being subject to GC
analysis.
[0156] Samples were analyzed by GC (PerkinElmer, Clarus 480) using
an Elite-5 column equipped with a flame ionization detector (FID).
Products were identified against authenticated standards and
quantified by calibration to obtain response factors against the
known external standard.
[0157] Results for the un-doped framework in the absence of
catalyst are provided in Table 4, showing minimal levels of
conversion for both the un-doped framework and the reactions in the
absence of catalyst.
TABLE-US-00004 TABLE 4 Catalytic data from the aerobic oxidation of
cyclohexanol and KA-oil in Comparative Examples Cyclohexanol
Cyclohexanone Conversion/ Selectivity/ Catalyst Substrate
Temp/.degree. C. mol. % mol. % Mass Balance/% CuClP Cyclohexanol
200 1 >99 95 CuClP Cyclohexanol 300 2 >99 94 None
Cyclohexanol 200 1 >99 97 None Cyclohexanol 300 2 >99 92 None
KA-oil 200 3 >99 94 None KA-oil 300 3 >99 93
Catalytic Conversion of Cyclohexanol to Cyclohexanone
[0158] The copper chloropyrophosphate framework doped with gold,
platinum or palladium tetrachloride precursors were hydrothermally
synthesized at 175.degree. C. for 48 hr. Materials were
post-synthetically activated under reduction for 2 hr. at specified
temperatures (150.degree. C.-250.degree. C.) under a 150
mLmin.sup.-1 flow of 5% hydrogen in nitrogen. The aerobic oxidation
of KA-oil was studied under continuous-flow conditions under
atmospheric pressure employing a custom-made fixed-bed reactor
(Cambridge Reactor Design, UK).
[0159] FIG. 20A contrasts the aerobic production of cyclohexanone
with supported nanoparticle/CuClP catalysts. Showing the superior
activity of Pt/CuClP for this process and the ability to optimize
this reaction with adroit catalyst design. FIG. 20B highlights the
exceptional catalytic lifetime of the Pt/CuClP catalyst. Displaying
consistent cyclohexanol conversion and cyclohexanone selectivity
profiles over a 10 hr. period. Reaction temperature: 200.degree.
C., air flow: 25 mLmin.sup.-1, substrate flow: 15 .mu.Lmin.sup.-1,
WHSV: 1.8 hr.sup.-1. Full tabulated data is presented in Tables 5
and 6. Table 5 presents catalytic results summarizing the
activities and selectivities of Au, Pt & Pd catalysts activated
under specific conditions in the aerobic oxidation of KA-oil. Table
6 presents the influence of time-on-stream on activity and
selectivity in KA-oil oxidation using Pt/CuClP (activated at
200.degree. C.) catalyst.
TABLE-US-00005 TABLE 5 Catalytic results summarizing the activities
and selectivities of activated Au, Pt & Pd catalysts in the
aerobic oxidation of KA-oil. Activation Cyclohexanol Cyclohexanone
Temperature/ WHSV/ Conversion/ Selectivity/ Catalyst .degree. C.
hr.sup.-1 mol. % mol. % Mass Balance/% Au/CuClP 150 1.84 4 >99
95 Au/CuClP 175 1.65 4 >99 91 Au/CuClP 200 1.76 3 >99 98
Au/CuClP 250 1.71 1 >99 94 Pt/CuClP 150 1.81 7 >99 90
Pt/CuClP 175 1.74 16 >99 92 Pt/CuClP 200 1.76 74 >99 97
Pd/CuClP 150 1.84 1 >99 99 Pd/CuClP 175 1.82 1 >99 97
Pd/CuClP 200 1.77 5 >99 93
TABLE-US-00006 TABLE 6 Influence of time-on-stream on activity and
selectivity in KA-oil oxidation using activated Pt/CuClP catalyst.
Cyclohexanol Time/ Conversion/ Cyclohexanone Mass hr. mol. %
Selectivity/% Balance/% 1 72 >99 99 2 74 >99 97 3 76 >99
87 4 76 >99 84 5 74 >99 87 6 75 >99 85 7 74 >99 86 8 75
>99 84 9 74 >99 86 10 73 >99 88
[0160] FIG. 20A highlights the superior performance of the Pt
catalyst over that of its corresponding Pd and Au analogues, and it
is remarkably noteworthy that the selectivity for the desired
cyclohexanone was in excess of 99+% for the Pt catalyst (HPLC and
GC-MS investigations did not reveal the presence of dibasic acids
and esters). Not only is the Pt/CuClP a highly effective and
selective aerobic oxidation catalyst (the undoped framework is
inert), but the robust nature of this material is evidenced by its
ability to maintain both high levels of activity and selectivity
over extended periods on stream (as displayed in FIG. 20B). More
importantly, the material retains its structural integrity
post-catalysis (FIG. 10), and negligible metal leaching (as
measured by inductively coupled plasma optical emission
spectroscopy (ICP-OES)) was observed. These findings support the
hypothesis that the catalytic activity of these materials can be
intrinsically linked to the degree of nanoparticle formation: the
[PtCl.sub.4].sup.2- precursor has a greater propensity for
nanoparticle formation over a range of activation temperatures and
this, in concert with the surrounding microporous architecture,
bestows superior catalytic performance for the aerobic oxidation of
KA-oil.
Catalytic Conversion of Cyclohexanol to Cyclohexanone--Closed Loop
System
[0161] The parameters described above with respect to the KA-oil
oxidation examples were used. However, in order to mimic a closed
loop system new substrate feed solutions were prepared to the
measured molar ratio of the appropriate out-stream. After the
initial purge the substrate (15 .mu.Lmin.sup.-1) and air (25
mLmin.sup.-1) flow rates were set up and the system left to
equilibrate for one hour. After which a sample was analyzed by GC
(as above) and the cyclohexanol to cyclohexanone molar ratio
determined. At which point a new substrate feed solution was made
to the predetermined molar ratio of the previous sample. This
process was repeated for the number of cycles shown in Table 7.
TABLE-US-00007 TABLE 7 Catalytic data from closed-loop experiments
involving the Pt/CuClP catalyst (activated at 200.degree. C.).
Substrate Cyclohexanol Cyclohexanone Feed Molar Conversion/
Selectivity/ Mass Cycle Ratio (Cyol:Cyone) mol. % mol. % Balance/%
1 1:1 67 >99 88 2 0.5:1 81 >99 85 3 0.1:1 93 >99 84 4
0.04:1 95 >99 90
Catalytic Conversion of Cyclohexanol to Cyclohexanone--Varying
Temperature and Flow Rates
[0162] A 7 wt. % Pt/CuClP catalyst was prepared similar to
described above and reduced at 200.degree. C. for 2 hours under 5%
hydrogen in nitrogen. A 1:1 mass ratio of cyclohexanol to
cyclohexanone was provided as the feed stream. The percentage
cyclohexanol, cyclohexanone and the mass balance for each sample
during the reaction was plotted, and for clarity, the percentage
conversion, selectivity for cyclohexanone and the normalized
selectivity were also plotted. The selectivity was reported as
>99% as only one product, cyclohexanone, was detected by GC.
From this, the normalized selectivity was determined by taking into
account the mass balance for the reaction using the equation
below:
Normalised selectivity (mol %)=selectivity (mol %).times.mass
balance (%)/100%
[0163] The effect of temperature was first investigated, as shown
in FIG. 21. A 0.24 g sample of catalyst was exposed to a 15
.mu.Lmin.sup.-1 flow of the 1:1 mixture of cyclohexanol and
cyclohexanone and 25 mLmin.sup.-1 flow of air. The reaction
temperature was varied from 180.degree. C. to 220.degree. C. Over
the temperature range investigated it can be seen that the
conversion, selectivity and normalized selectivity remains fairly
constant, with the highest conversion being achieved at 200.degree.
C.
[0164] Next, the effect of air flow rate was investigated. The
reaction conditions were the same as for the temperature
investigation, except that a reaction temperature of 200.degree. C.
was utilized, and the air flow rate was varied between 10
mLmin.sup.-1 and 40 mLmin.sup.-1. FIG. 22 provides the results as a
function of the oxygen flow in mmolmin.sup.-1, which increases with
an increase in air flow rate. As shown in FIG. 22, the conversion
starts to level off at an oxygen concentration of approximately
0.22 mmolmin.sup.-1, and the mass balance (as reflected by the
normalized selectivity) also starts to decrease around this point.
Without wishing to be held to any particular theory, it is believed
that the cyclohexanol is being oxidized to products that cannot be
detected by GC, or is being lost in potential vapor loss during
sampling and sample handling. Overall, FIG. 22 shows the trend of
increased conversion with increased oxygen concentration.
[0165] Next, the effect of the incoming cyclohexanol/cyclohexanone
mixture flow rate was investigated. The reaction conditions were
the same as for the temperature investigation, except that a
reaction temperature of 200.degree. C. was utilized, and the flow
rate of the cyclohexanol/cyclohexanone mixture was varied between
5-25 .mu.Lmin.sup.-1. FIG. 23 provides the results as a function of
the weighted hourly space velocity (WHSV), which increases with the
flow rate of the cyclohexanol/cyclohexanone mixture. WHSV was
calculated according to the formula:
WHSV ( hr . - 1 ) = Cyclohexanol flow ( g hr . - 1 ) Mass catalyst
( g ) ##EQU00003##
[0166] As shown in FIG. 23, the conversion decreases with
increasing WHSV. Without wishing to be held to any particular
theory, it is believed that the decrease is due to lower contact
times of the substrate with the catalyst.
Example 4--Bi-Metallic Examples
Synthesis, Activation, and Characterization
[0167] All chemicals were purchased from Sigma Aldrich or Fisher
Scientific and used without further purification. Gases were
sourced from BOC Industrial Gases and used as supplied.
[0168] Copper(II) fluoride (0.1168 g, 1.15 mmol), rubidium chloride
(0.2800 g, 2.32 mmol) and two sources of metal chloride salt
selected from 0.0245 g (0.072 mmol) gold(III) chloride hydrate,
0.0299 g (0.072 mmol) potassium tetrachloroplatinate, or 0.0250 g
(0.077 mmol) potassium tetrachloropalladate were accurately weighed
out to 4 decimal places and ground in an agate pestle and mortar
for 2 minutes to homogenize.
[0169] The mixture was added to the Teflon.RTM. liner of a 23 mL
hydrothermal vessel, and 85% orthophosphoric acid in water (0.20
mL, 2.92 mmol) was added dropwise wetting the entire contents. The
mixture was sonicated for 5 minutes to encourage mixing. 0.24 mL
(2.38 mmol) of 50 wt. % rubidium hydroxide in water was added
dropwise, wetting the entire contents, and the mixture was
sonicated for 10-15 minutes until the mixture was homogenous.
Caution was taken due to production of hydrogen fluoride gas.
[0170] The hydrothermal vessel was sealed and heated to 175.degree.
C. for 48 hours in a convection oven. The vessels were allowed to
cool naturally before collecting the product by filtration, washing
with deionized water (100 mL) and drying overnight at 80.degree.
C.
[0171] A photograph of the as-synthesized bimetallic CuClP
materials is provided in FIG. 24, showing, from left to right,
AuPt/CuClP, AuPd/CuClP and PtPd/CuClP. Products formed as brilliant
green cuboid crystals for AuPt material, and as light brown/green
crystals for the AuPd and PtPd materials.
[0172] The PXRD spectra of the as-synthesized bi-metallic materials
were obtained as discussed above with respect to the mono-metallic
materials. FIG. 25 shows the PXRD spectra of two different
as-synthesized AuPt/CuClP samples. FIG. 26 shows the PXRD spectra
of two different as-synthesized AuPd/CuClP samples. FIG. 27 shows
the PXRD spectra of two different as-synthesized PtPd/CuClP
samples.
[0173] Materials were activated under reducing conditions under a
flow of 5% H.sub.2/N.sub.2 at approximately 150 mLmin.sup.-1 for 2
hours at the specified temperature.
[0174] The AuPt/CuClP bi-metallic material was reduced at
temperatures of 200.degree. C., 250.degree. C., 300.degree. C., and
350.degree. C. for 2 hours under hydrogen. As shown in FIG. 28,
after reduction, the AuPt material appeared progressively darker
with temperature. The color of the sample reduced at 350.degree. C.
is actually a black-green color with a hint of red suggesting that
gold nanoparticles have formed. Without wishing to be held to any
particular theory, it is believed that that gold nanoparticles are
only formed in significant amounts at temperatures of 350.degree.
C. and above.
[0175] FIG. 29 shows the PXRD spectra of the AuPt/CuClP samples
as-synthesized and as reduced at 200.degree. C., 250.degree. C.,
300.degree. C., and 350.degree. C. As indicated in FIG. 29, the
PXRD patterns suggest that the framework is still intact after
reduction at different activation temperatures. Broad peaks
signifying the presence of nanoparticulate platinum usually appear
.about.40.degree.. This can also be seen in FIG. 30, which compares
the PXRD pattern of the as-synthesized AuPt/CuClP material with a
sample reduced at 250.degree. C. The nanoparticle platinum peaks
are highlighted in the circled portion of the reduced spectrum.
[0176] The AuPd/CuClP bi-metallic material was reduced at
temperatures of 150.degree. C., 200.degree. C., 250.degree. C., and
300.degree. C. for 2 hours under hydrogen. As shown in FIG. 31, the
material changed from light brown/green to dark green from
150.degree. C. to 200.degree. C., and then black at temperatures
higher than 250.degree. C. where the framework degrades, as
confirmed by PXRD analysis. Similarly to the AuPt/CuClP sample, the
AuPd/CuClP materials also get darker at higher activation
temperatures.
[0177] The PXRD patterns for the reduced AuPd/CuClP bi-metallic
material are shown in FIG. 32 below alongside the as-synthesized
material. As shown in FIG. 32, the AuPd/CuClP framework begins to
degrade when reduced above 250.degree. C., as illustrated by the
decrease in signal intensity and by the disappearance of key peaks
around 7 and 25.degree.. An additional rubidium phosphate phase is
also present around 25.degree., as highlighted by the box in FIG.
32, further suggesting the breakdown of the framework.
[0178] The PtPd/CuClP bi-metallic material was reduced at
temperatures of 150.degree. C., 200.degree. C., and 250.degree. C.
under hydrogen. As shown in FIG. 33, the material changed from
light brown/green to dark green from 150.degree. C. to 200.degree.
C., and then black at temperatures higher than 250.degree. C. where
the framework degrades, as confirmed by PXRD analysis.
[0179] The PXRD patterns for the reduced PtPd/CuClP bi-metallic
materials are shown in FIG. 34 alongside the as-synthesised
material. Similarly to the AuPd/CuClP material, the sample reduced
at 250.degree. C. has started to degrade. The rubidium phosphate
phase is also present in this sample, as highlighted by the box in
FIG. 34, confirming the change in the sample due to
degradation.
[0180] FIGS. 43-47 illustrate stacked XPS spectra, with data fits
and appropriate reference samples, of various bimetallic materials
activated at different temperatures. The XPS spectra for exemplary
AuPt/CuClP catalyst materials activated at different temperatures
is provided in FIG. 43. The XPS spectra for exemplary PtPd/CuClP
catalyst materials activated at different temperatures are provided
in FIGS. 44A and 44B. The XPS spectra for exemplary AuPd/CuClP
catalyst materials activated at different temperatures are provided
in FIGS. 45A and 45B.
[0181] FIGS. 46-51 illustrate TEM images of various bimetallic
materials activated at different temperatures. FIGS. 46A and 46B
illustrate TEM images of the AuPd/CuClP material activated at
200.degree. C. FIG. 47 illustrates a TEM image of the PtPd/CuClP
material activated at 150.degree. C. FIGS. 48A-48C illustrate TEM
images of the PtPd/CuClP material activated at 200.degree. C. FIGS.
49A and 49B illustrate TEM images of the AuPt/CuClP material
activated at 200.degree. C. FIGS. 50A and 50B illustrate TEM images
of the AuPt/CuClP material activated at 250.degree. C. FIGS. 51A
and 51B illustrate TEM images of the AuPt/CuClP material activated
at 300.degree. C.
Catalytic Conversion of Cyclohexanol to Cyclohexanone
[0182] Catalytic reactions were performed in a fixed-bed flow
reactor (4 mm in diameter) with a glass frit, in which a layer of
pelletized catalyst approximately 0.24 g) was packed between two
layers of glass beads. The system was pre-heated to 200.degree. C.
under a 25 mLmin.sup.-1 flow of air for 1 hour. The substrate flow
rate was set to 15 .mu.Lmin.sup.-1, in order to achieve a WHSV of
1.8 hr.sup.-1, and the system was allowed to equilibrate for 1
hour.
[0183] The KA-oil substrate feedstock solutions were made up as a
1:1 weight ratio of cyclohexanol and cyclohexanone, and an external
standard solution of triethylene glycol dimethyl ether (2 M) in
acetone was fed into the off-stream of the reactor at the same flow
rate as the substrate. The solution obtained from the off-stream
was diluted in a ratio of 1:10 with acetone before being subject to
GC analysis. Samples were analyzed on an hourly basis using a
Clarus 400 gas chromatogram with FID using an Elite 5 column, and
the peak areas were calibrated using known response factors.
[0184] The bi-metallic CuClP materials were tested for the
conversion of cyclohexanol to cyclohexanone, and a summary of the
results for all three systems is tabulated below in Tables 8 and
9.
TABLE-US-00008 TABLE 8 Percentage conversions in the oxidation of
KA-oil for the bimetallic CuClP catalysts reduced at 200.degree. C.
Catalyst Percentage Conversion/mol. % AuPt/CuClP 36 AuPd/CuClP 0
PtPd/CuClP 69
TABLE-US-00009 TABLE 9 Percentage conversions in the oxidation of
KA-oil for the AuPt/CuClP bimetallic catalyst reduced at different
temperatures Activation Temperature/.degree. C. Cyclohexanol
Conversion/mol. % 200 36 250 59 300 93 350 37
[0185] While the present disclosure is primarily directed to the
conversion of cyclohexanol to cyclohexanone, it should be
understood that the features disclosed herein have application to
the production of other ketones and cyclic ketones.
[0186] While this invention has been described as relative to
exemplary designs, the present invention may be further modified
within the spirit and scope of this disclosure. Further, this
application is intended to cover such departures from the present
disclosure as come within known or customary practice in the art to
which this invention pertains.
* * * * *
References