Wells-Dawson type heteropolyacids, their preparation and use...

Details Wells-Dawson type heteropolyacids, their preparation and use... Wells-Dawson type heteropolyacids, their preparation and use...

2000-03-14

2001-01-02

Bell, Mark L. (Department: 1755)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acids and salts thereof

C562S512200

Utility Patent

active

06169202

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to compositions comprising Wells-Dawson type heteropolyacids on supports, such as wide pore polyoxometallate salts, methods for the preparation of such compositions, and the use of supported Wells-Dawson type heteropolyacids for the direct catalytic oxidation of alkanes to unsaturated carboxylic acids.
BACKGROUND OF THE INVENTION
Polyoxometallates and heteropolyacids, both in general and those which can be used to prepare some of the catalysts used in our invention, and their preparation are described in Pope et al.,
Heteropoly and Isopoly Oxometalates
, Springer-Verlag, N.Y. (1983).
Polyoxometallates and heteropolyacids consist of a polyhedral cage structure or framework bearing a negative charge (e.g., [PMo
12
O
40
]
−3
; [P
2
Mo
18
O
62
]
−6
) which is balanced by cations that are external to the cage. If the cations are protons, then the compound is a heteropolyacid (UPA) (e.g., H
6
[P
2
Mo
18
O
62
]). If the cations were not all hydrogen, but either metals such as an alkali metal, potassium, sodium, or lithium, as in K
6
P
2
W
18
O
62
, or ammonium, as in (NH
4
)
6
P
2
Mo
18
O
62
, then it is referred to as a polyoxometallate (POM). In earlier patents, we have used the term “polyoxoanion” to describe compounds in which some or all of the cations are not hydrogen (e.g., K
3
PMo
12
O
40
); in the present case, however, these compounds are referred to as polyoxometallates and the term polyoxoanion is reserved for describing the anionic cage-like portion of the compound (e.g., [P
2
Mo
18
O
62
]
−6
)
As described in Pope et al., supra, heteropolyacids and polyoxometallates are cage-like structures with a primary, generally centrally located atom(s) surrounded by a cage framework, which framework contains a plurality of metal atoms, the same or different, bonded to oxygen atoms. The central element of heteropolyacids and polyoxometallates is different from metal atoms of the framework and is sometimes referred to as the “hetero” element or atom, the condensed coordination elements are referred to as the “framework” elements or metals. The framework metal atoms are ordinarily transition metals. As described by Pope et al., sltpra, the majority of heteropolyacids and polyoxometallates have a centrally located heteroatom (“X”) usually bonded in a tetrahedral fashion through four oxygen atoms to the “framework” metals (“M”). The framework metals, in turn, (i) are usually bonded to the central atom in an octahedral fashion through oxygens (“O”), and (ii) are bonded to four other framework metals through oxygen atoms and (iii) have a sixth non-bridging oxygen atom known as the “terminal oxygen” atom. This can be illustrated as shown below:
The principal framework metal, M, is effectively limited to only a handful of metals including molybdenum, tungsten, vanadium niobium and tantalum. According to Pope et al., supra, this is due to the necessary condition that suitable metals have appropriate cation radius and be good oxygen p&pgr;-electron acceptors. Among the successful candidates, molybdenum and tungsten share a common feature; namely, the expansion of valences of their metal cations from four to six. The coincidence of these characteristics allow these metals to form stable heteropolyacids and polyoxometallates.
Conventional heteropolyacids (and polyoxoanions thereof) can be described by the general formula H
e
(X
k
M
n
O
y
)
−e
. In this formula, X, the central atom, is frequently phosphorus. However, other suitable central atoms include Group IIIB-VIB elements, such as antimony, silicon and boron. Further, the subscript k is preferably 2, but can be from 1 to 5. M is molybdenum, tungsten, or vanadium and n will vary from 5-20. The subscript y may be as low as 18 or as high as 62. The notation e is the negative charge on the (X
k
M
n
O
y
) polyoxoanion and will vary from case to case, but e is always the number of protons needed to balance the formula. In a typical such heteropolyacid, k=2, n=18 and y=62, as in H
6
P
2
Mo
18
O
62
and the polyoxometallate H
2
(VO)
2
[P
2
Mo
18
O
62
].
As described in Pope et al., supra, heteropolyacids are known to exist in a variety of structures including the Keggin, Wells-Dawson and Anderson structures. The different structures correspond to the specific geometry of particular heteropolyacid compositions and vary according to the coordination chemistry and atomic radii of the metals present. These compounds may be substituted at various framework sites as disclosed, inter alia, in our prior patents. The present invention focuses on compounds of the Wells-Dawson type structure.
In our U.S. Pat. No. 4,803,187, issued Feb. 7, 1989, we taught how to prepare heteropolyacids and polyoxometallates with random substitution of framework metals, such as H
7
(PMo
8
V
4
O
40
); K
6
(SiMo
11
MnO
39
) and K
5
(PW
11
VO
40
). The preparation of framework-substituted heteropolyacids or polyoxometallates as described in our U.S. Pat. No. 4,803,187, supra, is adequate for random substitution, but will not provide the regiospecific, trilacunary substitution as described in our U.S. Pat. No. 4,898,989, supra; i.e., replacement of three M in a single, triangular face with three M′. The teaching of U.S. Pat. No. 4,803,187 and U.S. Pat. No. 4,898,989 is incorporated for all purposes by reference herein.
As described in Pope et al., supra, heteropolyacids and polyoxometallates have found a variety of applications. In the area of catalysis, Keggin ion catalysts have been used in connection with the oxidation of propylene and isobutylene to acrylic and methacrylic acids, oxidation of aromatic hydrocarbons; olefin polymerization; olefin epoxidation, and hydrodesulfurization processes. See, for example, M. Ai, “Partial Oxidation of n-Butane with Heteropoly Compound-based Catalysts”,
Proceedings of the
18
th International Congress on Catalysis
, Berlin, 1984, Verlag Chemie, Vol. 5, page 475; Lyons et al., U.S. Pat. No. 4,803,187, issued Feb. 7, 1989; Lyons et al., U.S. Pat. No. 4,859,798, issued Aug. 22, 1989; Ellis et al., U.S. Pat. No. 4,898,989, issued Feb. 6, 1990; Lyons et al., U.S. Pat. No. 4,916,101, issued Apr. 10, 1990; Ellis et al., U.S. Pat. No. 5,091,354, issued Feb. 25, 1992; and Shaikh et al., U.S. Pat. No. 5,334,780, issued Aug. 2, 1994; each of which is incorporated herein by reference.
Framework-substituted Keggin heteropolyacids have been disclosed as catalysts for oxidation of aldehydes, cyclohexene and cyclohexane, and for hydrogen peroxide decomposition. N. Mizuno et al., “Synthesis of [PW
9
O
37
{Fe
3−x
Ni
x
(OAc
3
}]
(9+x)−
(x=predominantly 1) and Oxidation Catalysis by the Catalyst Precursors”,
J.Mol.Cat
., 88, L125-31 (1994); and Wu et al., “Catalytic Behavior of Metal Ions Located at Different Sites of Heteropoly Compounds”,
Catalysis Letters
, 23, 195-205 (1994).
Non-framework substituted Keggin polyoxometallates and heteropolyacids are known in the art as catalysts for oxidation of isobutane to methacrylic acid and methacrolein. W. Ueda et al., “Catalytic Oxidation of Isobutane to Methacrylic Acid with Molecular Oxygen over Activated Pyridinium 12-Molybdophosphate”,
Cat.Lett
., 261-265 (1997); N. Mizuno et al., “Catalytic Performance of Cs
2.5
Fe
0.08
H
1.26
PVMo
12
O
40
for Direct Oxidation of Lower Alkanes”,
J.Mol.Catal
., A, 114, 309-317 (1996); F. Trifiro, “Reactivity of Keggin-type Heteropolycompounds in the Oxidation of Isobutane to Methacrolein and Methacrylic Acid: Reaction Mechanism”,
J.Mol.Catal
., A, 114, 343-359 (1996); N. Mizuno et al., “Direct Oxidation of Isobutane into Methacrylic Acid and Methacrolein over Cs
2.5
Ni
0.08
-substituted H
3
PMo
12
O
40
”, J.Chem.Soc.,Chem.Commun
., 1411-1412 (1994); S. Yamamatsu et al., “Process for Producing Methacrylic Acid and Methacrolein”, European Patent Specification Publication No. 0 425 666 B1, Application No. 89905775.6 filed May 22, 1989, Date of publication of patent specification Apr.

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