Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Reexamination Certificate
1999-05-10
2001-01-09
Bell, Mark L. (Department: 1755)
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
C423S508000, C423S606000, C423S641000, C502S215000, C502S311000, C502S312000, C502S317000, C502S353000, C558S321000, C558S322000, C558S323000, C558S325000
Reexamination Certificate
active
06171571
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a new family of crystalline metal oxide compositions. These compositions contain niobium, an alkali metal, at least one M metal where M is tungsten or molybdenum, optionally a M′ metal such as vanadium and a M″ metal such as antimony. This invention also relates to a hydrothermal process for preparing the crystalline compositions and to an ammoxidation process using the compositions.
BACKGROUND OF THE INVENTION
Olefins, e.g., propylene or isobutene are used to prepare a number of higher value products such as aldehydes, acids and nitrites. Since the price of the corresponding alkanes, i.e., propane or isobutane is lower than that of the olefins, it would be advantageous to be able to produce the higher value product directly from the alkanes.
Attempts have been made to synthesize novel materials to catalyze the selective oxidation of paraffins. One such catalyst is described in U.S. Pat. No. 5,750,760 where it is disclosed that a multinary composition having the empirical formula:
Mo
a
V
b
Sb
c
X
x
O
n
where X is an element such as Nb, Ta, W etc. can catalyze the oxidation of an alkane with ammonia in the presence of oxygen. Other compositions which have been disclosed in the art include a Mo
4
VO
14
phase by H. Werner et al. in
Catalysis Letters,
44 (1997) 153-63. In
J. Catalysis
52, 116-132 (1978), E. M. Thorsteinson et al., describe a mixed oxide catalyst containing molybdenum and vanadium along with another transition metal such as Ti, Nb, Ta, etc. The authors present activity data and physically characterize the compositions. MoVNb systems have also been described in
Applied Catalysis,
70 129-148 (1991) and
Topics in Catalysis
3, 355-364 (1996). U.S. Pat. No. 4,524,236 discloses a composition containing molybdenum, vanadium, niobium, antimony plus at least one metal such as lithium, barium, titanium etc. U.S. Pat. No. 4,339,355 discloses a composition comprising Mo
a
V
b
Nb
c
X
d
, where X is Co, Cr, Cu, Fe, In, Mn and/or Y. It is further disclosed that the compositions have spinel or perovskite structures. In U.S. Pat. No. 4,596,787 a catalyst comprising Mo
a
V
b
Nb
c
Sb
d
X
e
is disclosed, where X includes Li, Sc, Na, Fr, Ta, etc. U.S. Pat. No. 4,250,346 discloses a catalyst with an empirical formula of Mo
a
X
b
Y
c
, where X is Cr, Mn, Nb, Ta, Ti, V and/or W and Y=Bi, Ce, Co, Cu, Fe, K, Mg, Ni, P, Pb, Sb, Si, Sn, Ti and/or U. U.S. Pat. No. 4,892,856 discloses a catalyst having the composition Mo
a
V
b
A
c
B
d
C
e
D
f
O
x
where A is tungsten or niobium, B is Fe, Cu, Bi, Cr, Sb or Tl, C is an alkali or alkaline earth metal and D is Si, Al or Ti. U.S. Pat. No. 5,807,531 discloses a multimetaloxide having an empirical formula of Mo
12-a-b-c
V
a
M
1
b
M
2
c
O
x
. However, these materials have a low surface area of 17 m
2
/g or lower. Finally, Ueda et al., in
Chem. Commun.,
1999, 517-518, disclose a Mo—V—M—O(M=Al, Fe, Cr and Ti) composition which is hydrothermally synthesized. Although these compositions have a diffraction peak at about 3.9 Å, they do not have applicant's empirical formula (see below).
In contrast to these reports, applicants have synthesized a new family of crystalline oxide compositions based on niobium, at least one of tungsten and molybdenum, and optionally another metal such as vanadium, tantalum, antimony or tellurium. These novel compositions are prepared hydrothermally and are characterized in that they have an x-ray diffraction pattern with at least one peak at a d spacing of about 3.9 Å and a high surface area. These materials show good activity for converting propane to acrylonitrile.
SUMMARY OF THE INVENTION
As stated, this invention relates to a new family of crystalline compositions, a process for preparing these compositions and a process which uses the compositions. Accordingly, one embodiment of the invention is a crystalline metal oxide composition having an empirical formula of:
A
n
NbM
x
M′
y
M″
m
O
p
where A is an alkali metal ion, ammonium ion or mixtures thereof, M is selected from the group consisting of molybdenum, tungsten or mixtures thereof, M′ is tantalum and M″ is selected from the group consisting of antimony, tellurium and mixtures thereof, “n” varies from about 0.1 to about 2, “x” varies from about 0.01 to about 4, “y” varies from zero to about 4, “m” varies from about zero to about 0.9 and “p” has a value such that it balances the valence of the combined elements A, Nb, M, M′, M″, the composition characterized in that it has at least one x-ray diffraction peak at a d spacing of about 3.9±0.15 Å. M′ can also be vanadium and mixtures of vanadium and tantalum. When M is molybdenum or a mixture of tungsten and molybdenum, M′ is vanadium and y>0, then the composition has a surface area of at least 25 m
2
/g.
Another embodiment of the invention is a process for preparing the crystalline compositions described above. The process comprises forming a reaction mixture containing reactive sources of A, niobium, M, optionally M′ and optionally M″ at a temperature and a time sufficient to form the crystalline composition, the mixture having a composition expressed in terms of mole ratios of oxides of:
aA
2
O:NbO
5/2
:bMO
3
:cM′O
5/2
:dM″O
q/2
:eH
2
O
where “a” has a value from about 0.75 to about 4, “b” has a value of about 0.02 to about 5, “c” has a value from 0 to about 5, “d” has a value from 0 to about 1, “q” is the valence of M″ and “e” has a value of about 10 to about 500.
Yet another embodiment of the invention is a process for the ammoxidation of alkanes comprising reacting an alkane with ammonia in the presence of oxygen over an ammoxidation catalyst at ammoxidation conditions to produce a nitrile. The ammoxidation catalyst comprises one of the compositions described above, while the alkane is propane, isobutane or mixtures thereof.
These and other embodiments will become clearer after a detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
A new family of crystalline metal oxide compositions has been synthesized and characterized. These compositions contain niobium, at least one of tungsten and molybdenum, a third metal selected from vanadium or tantalum and a fourth metal selected from antimony and tellurium. A cation such as lithium is also present. These crystalline metal oxides are described by the empirical formula:
A
n
NbM
x
M′
y
M″
m
O
p
where “n” varies from about 0.1 to about 2. The value of “x” varies from about 0.01 to about 4, while the value of “y” varies from zero to about 4 and the value of “m” varies from zero to about 0.9. M is molybdenum, tungsten, or mixtures thereof, M′ is selected from the group consisting of vanadium, tantalum and mixtures thereof, while M″ is antimony, tellurium or mixtures thereof. Finally, A is an alkali metal cation, an ammonium cation or mixtures thereof. Examples of the alkali metals which can be used include: lithium, sodium, potassium, rubidium, cesium and mixtures thereof.
These novel crystalline metal oxide compositions are hydrothermally prepared. That is, a reaction mixture is prepared from reactive sources of the desired components along with water and heated at a temperature and for a time sufficient to form the desired product. Reactive sources of the alkali metals include the hydroxide, carbonate, halide, acetate, and sulfate compounds. Niobium reactive sources include niobium pentoxide (Nb
2
O
5
), hydrous niobium oxide, niobium ethoxide, and ammonium niobium oxalate. Molybdenum sources include molybdic acid ((NH
4
)
6
Mo
7
O
24
.4H
2
O), molybdenum trioxide (MoO
3
), sodium molybdate and molybdenum (VI) oxychloride. Tungsten sources include ammonium tungstate, tungsten (VI) oxide, tungsten (VI) chloride, sodium tungstate, and tungstic acid. Vanadium sources include vanadium (V) oxide, vanadium (V) oxychloride, vanadium oxide sulfate, and ammonium vanadate. Tantalum sources include tantalum oxide, tantalum butoxide, tantalum bromi
Bedard Robert L.
Bogdan Paula L.
King Lisa M.
Koster Susan C.
Bell Mark L.
Molinaro Frank S.
Sample David
Tolomei John G.
UOP LLC
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