U.S. patent application number 14/171868 was filed with the patent office on 2014-06-05 for catalyst from flame-spray pyrolysis and catalyst for autothermal propane dehydrogenation.
This patent application is currently assigned to BASF SE. The applicant listed for this patent is BASF SE. Invention is credited to Dirk Gro schmidt, Stefan Hannemann, Frank Kleine Jager, Peter Pfab, Goetz-Peter Schindler, Dieter Stutzer.
Application Number | 20140155257 14/171868 |
Document ID | / |
Family ID | 46544607 |
Filed Date | 2014-06-05 |
United States Patent
Application |
20140155257 |
Kind Code |
A1 |
Hannemann; Stefan ; et
al. |
June 5, 2014 |
CATALYST FROM FLAME-SPRAY PYROLYSIS AND CATALYST FOR AUTOTHERMAL
PROPANE DEHYDROGENATION
Abstract
The invention relates to a method of production of catalyst
particles, comprising platinum and tin and also at least one
further element, selected from lanthanum and cesium, on zirconium
dioxide as support, comprising the steps: preparation of one or
more solutions containing precursor compounds of Pt, Sn and at
least one further element of La or Cs and also ZrO.sub.2,
converting the solution(s) to an aerosol, bringing the aerosol into
a directly or indirectly heated pyrolysis zone, carrying out
pyrolysis, and separation of the particles formed from the
pyrolysis gas. Suitable precursor compounds comprise zirconium(IV)
acetylacetonate, lanthanum(II) acetylacetonate and cesium acetate,
hexamethyldisiloxane, tin 2-ethylhexanoate, platinum
acetylacetonate, zirconium(IV) propylate in n-propanol and
lanthanum(II) acetylacetonate. The invention also relates to the
catalyst particles obtainable using the method according to the
invention, and to the use thereof as dehydrogenation catalysts.
Inventors: |
Hannemann; Stefan;
(Mannheim, DE) ; Stutzer; Dieter; (Dudenhofen,
DE) ; Schindler; Goetz-Peter; (Ludwigshafen, DE)
; Pfab; Peter; (Shaker Heights, OH) ; Jager; Frank
Kleine; (Bad Durkheim, DE) ; Gro schmidt; Dirk;
(Mannheim, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BASF SE |
Ludwigshafen |
|
DE |
|
|
Assignee: |
BASF SE
Ludwigshafen
DE
|
Family ID: |
46544607 |
Appl. No.: |
14/171868 |
Filed: |
February 4, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13356787 |
Jan 24, 2012 |
8680005 |
|
|
14171868 |
|
|
|
|
61435797 |
Jan 25, 2011 |
|
|
|
Current U.S.
Class: |
502/242 |
Current CPC
Class: |
B01J 35/006 20130101;
B01J 23/63 20130101; B01J 35/023 20130101; B01J 37/0072 20130101;
B01J 35/1014 20130101; B01J 35/002 20130101; B01J 23/58 20130101;
B01J 37/349 20130101 |
Class at
Publication: |
502/242 |
International
Class: |
B01J 23/63 20060101
B01J023/63 |
Claims
1-17. (canceled)
18. A catalyst particle, comprising platinum and tin and also at
least one further element, selected from lanthanum and cesium, on a
support comprising zirconium dioxide and optionally silicon oxide,
wherein said catalyst particle is obtained by a method comprising
the steps (i) preparing one or more solutions containing precursor
compounds of platinum, tin and the at least one further element,
selected from lanthanum and cesium, and also of zirconium dioxide
and optionally silicon dioxide, (ii) converting the solution(s) to
an aerosol, (iii) bringing the aerosol into a directly or
indirectly heated pyrolysis zone, (iv) carrying out pyrolysis with
a gas, and (v) separating the catalyst particles formed from the
pyrolysis gas.
19. The catalyst particle of claim 18, wherein said catalyst
particle contains 0.05 to 1 wt. % Pt and 0.05 to 2 wt. % Sn.
20. The catalyst particle of claim 18, wherein said catalyst
particle has a specific surface of 36 to 70 m2/g.
21. The catalyst particle of claim 18, wherein said catalyst
particles comprises 30 to 99.5 wt. % ZrO.sub.2 and 0.5 to 25 wt. %
SiO.sub.2 as support, and 0.1 to 1 wt. % Pt, 0.1 to 10 wt. % Sn,
relative to the mass of the support, La and/or Cs, wherein at least
Sn and at least La or Cs are contained.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S.
Non-Provisional Application No. 13/356,787, filed Jan. 24, 2012,
which claims the benefit (under 35 USC 119(e)) of U.S. Provisional
Application 61/435,797, filed Jan. 25, 2011, the contents of each
of which are incorporated herein by reference in their
entireties.
BACKGROUND OF THE INVENTION
[0002] The invention relates to catalyst particles, a method of
production thereof and the use of the catalyst particles as
dehydrogenation catalyst.
[0003] Production of dehydrogenation catalysts by impregnation
processes or spray drying is known. In these methods the
catalytically active metals are applied on an oxide support or a
silicate support by impregnation processes or the catalyst is
produced by spray drying of coprecipitated oxide precursors.
[0004] DE-A 196 54 391 describes the production of a
dehydrogenation catalyst by impregnation of essentially monoclinic
ZrO.sub.2 with a solution of Pt(NO.sub.3).sub.2 and Sn(OAc).sub.2
or by impregnation of ZrO.sub.2 with a first solution of
Pt(NO.sub.3).sub.2 and then a second solution of
La(NO.sub.3).sub.3. The impregnated supports are dried and then
calcined. The catalysts thus obtained are used as dehydrogenation
catalysts for the dehydrogenation of propane to propene.
[0005] A known method of production of metal catalysts by
flame-spray pyrolysis is described in Pisduangnawakij et al.,
Applied Catalysis A: General 370 1-6, 2009. In this, a solution
containing precursor compounds of platinum and tin and of aluminum
oxide as support in xylene is converted to an aerosol, this is
treated in an inert carrier gas in a pyrolysis reactor at a
temperature above the decomposition temperature of the precursor
compounds and then the finely-divided metal that has formed is
separated from the carrier gas.
[0006] The known synthesis of precious metal powder catalysts by
wet-chemical preparation is time-consuming and costly.
[0007] The methods for the production of dehydrogenation catalysts
are therefore still in need of improvement in terms of the time and
costs they involve.
A SUMMARY OF THE INVENTION
[0008] The problem to be solved by the present invention is to
provide an inexpensive and time-saving method of production of
dehydrogenation catalysts, wherein the dehydrogenation catalysts
obtained should be comparable in activity and selectivity to the
catalysts of the prior art, produced by impregnation processes or
spray drying.
[0009] This problem is solved by a method of production of catalyst
particles, comprising platinum and tin and also at least one
further element, selected from lanthanum and cesium, on a support
comprising zirconium dioxide, comprising the steps
(i) preparation of one or more solutions containing precursor
compounds of platinum, tin and the at least one further element,
selected from lanthanum and cesium, and also of zirconium dioxide,
(ii) converting the solution(s) to an aerosol, (iii) bringing the
aerosol into a directly or indirectly heated pyrolysis zone, (iv)
carrying out pyrolysis, and (v) separation of the particles formed
from the pyrolysis gas.
A BRIEF DESCRIPTION OF THE FIGURE
[0010] FIG. 1 illustrates activities and selectivities for the
flame-synthesized catalysts (.tangle-solidup. example 13,
.box-solid. example 17) and for the reference catalyst (-) in the
autothermal dehydrogenation of propane to propene.
A DETAILED DESCRIPTION OF THE INVENTION
[0011] The metal compounds and oxide-forming precursor compounds
are fed as aerosol to the pyrolysis zone. It is preferable if the
aerosol fed to the pyrolysis zone is obtained by nebulization of
just one solution, which contains all the metal compounds and
oxide-forming precursor compounds. In this way it is always ensured
that the composition of the particles produced is homogeneous and
constant. During preparation of the solution that is to be
converted to an aerosol, the individual components are thus
preferably selected so that the oxide-forming precursors and the
precious metal compounds used contained in the solution are
dissolved uniformly alongside one another until nebulization of the
solution. Alternatively it is also possible to use several
different solutions, which, on the one hand, contain the
oxide-forming precursors and, on the other hand, contain the active
or promoter metal compounds. The solution or solutions can contain
both polar and apolar solvents or solvent mixtures.
[0012] In the pyrolysis zone, decomposition of the precious metal
compound to form the precious metal and decomposition and/or
oxidation of the oxide precursors, with formation of the oxide,
take place. It may also happen that some of the precious metal
evaporates and then redeposits in cooler zones on support particles
already formed. Pyrolysis generally results in spherical particles
with varying specific surface.
[0013] The temperature in the pyrolysis zone is above the
decomposition temperature of the precious metal compounds at
sufficient temperature for oxide formation, usually between 500 and
2000.degree. C. Pyrolysis is preferably carried out at a
temperature from 900 to 1500.degree. C.
[0014] The pyrolysis reactor can be heated indirectly from outside,
for example by means of an electric furnace. Owing to the
temperature gradient from outside to inside that is required in
indirect heating, the furnace must be much hotter than corresponds
to the temperature required for pyrolysis. Indirect heating
requires a thermally stable furnace material and an expensive
reactor construction, but the total amount of gas required is less
than in the case of a flame reactor.
[0015] In a preferred embodiment the pyrolysis zone is heated by a
flame (flame-spray pyrolysis). The pyrolysis zone then comprises an
ignition device. For direct heating, usual combustible gases are
used, although preferably hydrogen, methane or ethylene is used.
The temperature in the pyrolysis zone can be adjusted as required
by means of the ratio of the amount of combustible gas to the total
amount of gas. To keep the total amount of gas low but nevertheless
achieve a temperature as high as possible, the pyrolysis zone can
also be supplied with pure oxygen instead of air as the O.sub.2
source for combustion of the combustible gases. The total amount of
gas also comprises the carrier gas for the aerosol and the
evaporated solvent of the aerosol. The aerosol or aerosols supplied
to the pyrolysis zone are preferably fed directly into the flame.
Although air is generally preferred as carrier gas for the aerosol,
it is also possible to use nitrogen, CO.sub.2, O.sub.2 or a
combustible gas, for example hydrogen, methane, ethylene, propane
or butane.
[0016] In another embodiment of the method according to the
invention, the pyrolysis zone is heated by an electric plasma or an
inductive plasma. In this embodiment, the catalytically active
precious metal particles are deposited on the surface of the
support particles and are fixed firmly thereon.
[0017] A flame-spray pyrolysis device generally comprises a storage
container for the liquid to be nebulized, feed pipes for carrier
gas, combustible gas and oxygen-containing gas, a central aerosol
nozzle, and an annular burner arranged around this, a device for
gas-solid separation comprising a filter element and a discharging
device for the solid and an outlet for the exhaust gas. The
particles are cooled by means of a quench gas, e.g. nitrogen or
air.
[0018] The pyrolysis zone preferably comprises a so-called
pre-drier, which subjects the aerosol to preliminary drying before
its entry into the pyrolysis reactor, this preliminary drying
taking place, for example, in a flow tube with a heating assembly
disposed around it. Where preliminary drying is not carried out,
the risk exists of obtaining a product with a relatively broad
particle size spectrum, and more particularly an excessive fine
fraction. The temperature of the pre-drier is dependent on the
nature of the dissolved precursors and on the concentration
thereof. The temperature in the pre-drier is typically above the
boiling point of the solvent, up to 250.degree. C.; in the case of
water as a solvent, the temperature in the pre-drier is preferably
between 120 and 250.degree. C., more particularly between 150 and
200.degree. C. The pre-dried aerosol, supplied to the pyrolysis
reactor via a line, then enters the reactor via an exit nozzle.
[0019] To produce a balanced temperature profile, the combustion
space, which is preferably tube-shaped, is heat-insulated.
[0020] As the pyrolysis result, a pyrolysis gas is obtained, which
contains spherical particles with varying specific surface. The
size distribution of the pigment particles obtained results
essentially directly from the droplet spectrum of the aerosol fed
into the pyrolysis zone and the concentration of the solution or
solutions used.
[0021] Preferably, prior to separation of the particles formed from
the pyrolysis gas, the pyrolysis gas is cooled so that sintering
together of the particles is excluded. For this reason the
pyrolysis zone preferably comprises a cooling zone, which adjoins
the combustion space of the pyrolysis reactor. Cooling of the
pyrolysis gas and of the catalyst particles contained therein to a
temperature of about 100-500.degree. C. is generally required,
depending on the filter element used. Cooling to approx.
100-150.degree. C. preferably takes place. After leaving the
pyrolysis zone, the pyrolysis gas, containing catalyst particles,
and partially cooled, enters a device for separating the particles
from the pyrolysis gas, which comprises a filter element. For
cooling, a quench gas, for example nitrogen, air or water-moistened
air, is fed in.
[0022] Suitable zirconium dioxide--forming precursor compounds are
alcoholates, such as zirconium(IV) ethanolate, zirconium(IV)
n-propanolate, zirconium(IV) isopropanolate, zirconium(IV)
n-butanolate and zirconium(IV) tert-butanolate. In a preferred
embodiment of the method according to the invention, zirconium(IV)
propanolate, preferably as solution in n-propanol, is used as
ZrO.sub.2 precursor compound.
[0023] Other suitable zirconium dioxide--forming precursor
compounds are carboxylates, such as zirconium acetate, zirconium
propionate, zirconium oxalate, zirconium octoate, zirconium
2-ethyl-hexanoate, zirconium acetate, zirconium propionate,
zirconium oxalate, zirconium octanoate, zirconium 2-ethylhexanoate,
zirconium neodecanoate zirconium stearate and zirconium propionate.
In another preferred embodiment of the method according to the
invention, zirconium(IV) acetylacetonate is used as precursor
compound.
[0024] In one embodiment, the precursor compounds additionally
comprise a silicon dioxide precursor compound. Possible precursors
for silicon dioxide are organosilanes and reaction products of
SiCl.sub.4 with lower alcohols or lower carboxylic acids. It is
also possible to use condensates of the aforementioned
organosilanes and/or -silanols with Si--O--Si units. Siloxanes are
preferably used. It is also possible to use SiO.sub.2. In a
preferred embodiment of the method according to the invention, the
precursor compounds comprise hexamethyldisiloxane as silica-forming
precursor compound.
[0025] Besides zirconium dioxide and optionally silicon dioxide as
supports, the catalyst particles according to the invention further
comprise platinum and tin and also at least one further element,
selected from lanthanum and cesium.
[0026] In one preferred embodiment of the invention, the Pt loading
is 0.05 to 1 wt. % and the Sn loading is 0.05 to 2 wt. %.
[0027] Preferred precursor compounds for lanthanum and cesium,
respectively, are carboxylates and nitrates, corresponding for
example to the carboxylates identified above in connection with
zirconium. In one preferred embodiment of the method according to
the invention, the precursor compounds comprise lanthanum(III)
acetylacetonate and/or cesium acetate.
[0028] In a further, preferred embodiment of the method according
to the invention, the precursor compounds comprise lanthanum(III)
2-ethylhexanoate.
[0029] Preferred precursor compounds for tin are carboxylates and
nitrates, corresponding for example to the carboxylates identified
above in connection with zirconium. In a further, preferred
embodiment of the method according to the invention, the precursor
compounds comprise tin 2-ethylhexanoate.
[0030] Preferred precursor compounds for platinum are carboxylates
and nitrates, corresponding for example to the carboxylates
identified above in connection with zirconium, and ammonium
platinates. In a preferred embodiment of the method according to
the invention, the precursor compounds comprise platinum
acetylacetonate.
[0031] Both polar and apolar solvents or solvent mixtures can be
used for production of the solution or solutions required for
aerosol formation.
[0032] Preferred polar solvents are water, methanol, ethanol,
n-propanol, iso-propanol, n-butanol, tert-butanol, n-propanone,
n-butanone, diethyl ether, tert-butyl-methyl ether,
tetrahydrofuran, C.sub.1--C.sub.8 carboxylic acids, ethyl acetate
and mixtures thereof.
[0033] In a preferred embodiment of the method according to the
invention, one or more of the precursor compounds, preferably all
the precursor compounds are dissolved in a mixture of acetic acid,
ethanol and water. Preferably this mixture contains 30 to 75 wt. %
acetic acid, 30 to 75 wt. % ethanol and 0 to 20 wt. % water. In
particular, zirconium(IV) acetylacetonate, hexamethyldisiloxane tin
2-ethylhexanoate, platinum acetylacetonate, lanthanum(II)
acetylacetonate and cesium acetate are dissolved in a mixture of
acetic acid, ethanol and water.
[0034] Preferred apolar solvents are toluene, xylene, n-heptane,
n-pentane, octane, isooctane, cyclohexane, methyl, ethyl or butyl
acetate or mixtures thereof. Hydrocarbons or mixtures of
hydrocarbons with 5 to 15 carbon atoms are also suitable. Xylene is
especially preferable.
[0035] In particular, Zr(IV) propylate, hexamethyldisiloxane tin
2-ethylhexanoate, platinum acetylacetonate and lanthanum(III)
acetylacetonate are dissolved in xylene.
[0036] The present invention also relates to the supports and
catalyst particles obtainable by the method according to the
invention. These preferably have a specific surface of 20 to 70
m.sup.2/g.
[0037] In a preferred embodiment the catalyst particles have the
following percentage composition: 30 to 99.5 wt. % ZrO.sub.2 and,
0.5 to 25 wt. % SiO.sub.2 as support, 0.1 to 1 wt. % Pt, 0.1 to 10
wt. % Sn, La and/or Cs, relative to the mass of the support,
wherein at least Sn and La or Cs are contained.
[0038] The present invention also relates to the use of the
catalyst particles as hydrogenation catalysts or dehydrogenation
catalysts. Alkanes, such as butane and propane, but also
ethylbenzene, are preferably dehydrogenated.
[0039] The use of the catalysts according to the invention for the
dehydrogenation of propane to propene is especially preferred.
[0040] The invention is explained in more detail with the following
examples.
Examples
[0041] Chemicals used
[0042] Zirconium acetylacetonate Zr(acac).sub.2 (98%)
[0043] Zirconium(IV) propoxide Zr(OPr).sub.4 (70% in
1-propanol)
[0044] Hexamethyldisiloxane (HMDSO) (98%)
[0045] Tin(II) 2-ethylhexanoate (approx. 95%)
[0046] Platinum(II) acetylacetate (98%)
[0047] Lanthanum(III) 2-ethylhexanoate (10% w/v)
[0048] Lanthanum(III) acetylacetonate (99.99%)
[0049] Cesium acetate (99.99%)
[0050] Mixture of acetic acid (100%), ethanol (96%) and water
(deionized)
[0051] Xylene (BASF, mixture of isomers)
Preparation of the Solutions of the Precursor Compounds
[0052] The solvent is HoAc: EtOH: H.sub.2O in the proportions by
weight 4.6 to 4.6 to 1. The acetic acid-ethanol mixture is freshly
prepared. The precursor compounds for Sn, Cs, La, Si, Pt and Zr are
dissolved therein.
[0053] The composition of the polar solutions of the precursor
compounds for the examples 1, 2, 3, 9 and 10 is shown in Table
1.
TABLE-US-00001 TABLE 1 Compositions of the solutions of the
precursor compounds for polar mixtures (EtOH:HoAc:H.sub.2O) [g]
Substance Purity [wt. %] 99.52 Zirconium(IV) acetylacetonate 98
1.77 Hexamethyldisiloxane 99 0.93 Tin 2-ethylhexanoate 95 0.27
Platinum acetylacetonate 98 2.45 Lanthanum(III) acetylacetonate
99.9 0.38 Cesium acetate 99.99
[0054] For preparing the solution of the precursor compound for
example 4, the following substances were dissolved in xylene. The
composition is shown in Table 2.
TABLE-US-00002 TABLE 2 Compositions of the solutions of the
precursor compounds for apolar mixtures (xylene) [g] Substance
Purity [wt. %] 374.40 Zr(IV) propylate in n-propanol 70 10.11
Hexamethyldisiloxane 99 5.32 Tin 2-ethylhexanoate 95 1.52 Platinum
acetylacetonate 98 103.47 Lanthanum(III) 2-ethylhexanoate 10
[0055] In the case of the preparation of the solutions of the
precursor compounds for examples 5, 6 and 8, an additional 2.14 g
of cesium acetate are used as well.
Examples 1 to 10
[0056] Production of the catalyst particles by flame-spray
pyrolysis
[0057] The solution containing the precursor compounds was supplied
by means of a piston pump via a two-component nozzle and atomized
with a corresponding amount of air. To reach the corresponding
temperatures, sometimes a support flame from an ethylene-air
mixture was used, which was supplied via an annular burner located
around the nozzle. The pressure drop was kept constant at 1.1
bar.
[0058] The flame synthesis conditions are summarized in Table
3.
TABLE-US-00003 TABLE 3 Test parameters relating to the production
of flame-spray pyrolysis catalysts c.sub.Zr Flow rate Total
Dispersion [mol/kg of precursor gas flow gas flow Ethylene Example
Solvent solution] compound [l/h] [l/h] [l/h] GLMR.sup.1 1 HoAc,
EtOH, 0.5 500 3500 1200 40 3 H.sub.2O 2 HoAc, EtOH, 0.5 510 3500
1200 20-40 3 H.sub.2O 3 HoAc, EtOH, 0.2 515 3500 1200 10-50 3
H.sub.2O 4* Xylene 1 280 3500 1200 0 5 5 Xylene 1 290 3500 1200 0 5
6 Xylene 1 310 3500 1200 0 4 7** Xylene 1 310 3500 1200 0 4 8
Xylene 1 255 3500 1200 20-40 5 9 HoAc, H.sub.2O 0.2 520 3500 1200
130-120 3 10 HoAc, H.sub.2O 0.25 385 4140 1740 190-230 5 Solution
without cesium precursor compound **Only Si and Zr precursors
present .sup.1GLMR = Gas to Liquid Mass Ratio.
[0059] A baghouse filter was used for separating the particles.
These filters could be cleaned by applying 5 bar pressure surges of
nitrogen to the filter bags.
[0060] Particle characterization was carried out by means of X-ray
diffractometry (XRD) and BET measurement, and an element analysis
was carried out as well. The crystallite size of the catalyst
particles formed using the solution of the precursor compounds 3
and 4 is set out in Table 4.
TABLE-US-00004 TABLE 4 X-ray powder diffractometry for the
characterization of the ZrO.sub.2 Crystal- Crystal- Average
Precursor Tetragonal Monoclinic lite size, lite size crystal-
compound ZrO.sub.2 ZrO.sub.2 tetragonal monoclinic lite size used
[%] [%] [nm] [nm] [nm] 3 82 18 19 13 18 4 90 10 28 9 26
[0061] The syntheses of the catalysts from the above solutions
comprising precursor compounds with the settings specified above
produced particles having a specific surface area of 36-70
m.sup.2/g (see Table 5).
[0062] In a further experiment, the BET surface area was
investigated as a function of the temperature of the combustion
chamber. This involved a comparison of the solutions comprising the
precursor compounds, in terms of their solvent (acetic acid versus
xylene). In the case of the acetic acid mixtures, there was no
clear trend apparent.
[0063] The xylene mixtures exhibited an increasing BET surface area
with increasing temperature, and this may be attributed to a
shorter residence time, thereby restricting particle growth.
Examples 11 to 17
Catalytic Measurements
[0064] Propane dehydrogenation was carried out at approx.
600.degree. C. (Flows at 20 ml cat. volume, mass see Table 5): 21
Nl/h total gas (20 Nl/h propane, 1 Nl/h nitrogen as internal
standard), 5 g/h water. Regeneration is carried out at 400.degree.
C. as follows: 2 hours 21 Nl/h N.sub.2+4 Nl/h air; 2 hours 25 Nl/h
air; 1 hour 25 Nl/h hydrogen.
[0065] The support of the reference catalyst from hydrothermal
synthesis (ZrO.sub.2) with subsequent spray drying is composed of
95% ZrO.sub.2 and 5% SiO.sub.2. The active/promoter metals are 0.5%
Pt, 1% Sn, 3% La, 0.5% Cs and 0.2% K, and were applied to the
support wet-chemically by impregnation in accordance with the
instructions of EP 1 074 301, example 4.
[0066] The conversion, the long-term stability and the selectivity
of propene formation were investigated in the catalytic tests. The
results are summarized in Table 5. The activities and selectivities
relate to an optimum operating state.
TABLE-US-00005 TABLE 5 Catalyst results for the flame-synthesized
catalyst particles in autothermal propane dehydrogenation Mass of
Catalyst used BET Activity Selectivity Example catalyst/g from
example [m.sup.2/g] % % 11 15.24 1 66 17 83 12 16.22 2 50 38 94 13
16.41 3 51 47 96 14 22.26 4 36 46 95 15 16.90 5 59 35 94 16 17.75 6
52 31 92 17 16.80 7 23 48 95
[0067] FIG. 1 shows activities and selectivities for the
flame-synthesized catalysts (.tangle-solidup. example 13,
.box-solid. example 17) and for the reference catalyst (-) in the
autothermal dehydrogenation of propane to propene. In the case of
the catalyst (.box-solid.), only the support was produced by
pyrolysis, and the support was subsequently subjected to
wet-chemical impregnation as for the reference catalyst. The time
in hours is plotted on the abscissa, and the conversions (40 to
50%) and selectivities (>80%) are plotted on the ordinate.
[0068] It can be seen that the three catalysts have comparable
performance. The reference catalyst has lower initial
selectivities. However, over the test cycles of a few weeks it
equalizes to the catalysts according to the invention. Thus, the
flame-synthesized catalyst behaves like an aged catalyst, which was
produced by a conventional wet-chemical process.
* * * * *