DETAILED DESCRIPTION This invention provides a heteropolyacid catalyst for the oxidation of n-butane to maleic anhydride comprising a crystalline oxide of formula I or formula II: H.
sub.
n PM.
sub.
12-x-y V.
sub.
x A.
sup.
z.
sub.
y O.
sub.
40 (I) H.
sub.
n P.
sub.
2 M.
sub.
18-x-y V.
sub.
x A.
sup.
z.
sub.
y O.
sub.
62(II) wherein: P is a heteroatom; M is at least one metal in the +6 oxidation state selected from Mo and W, said metal occupying an octahedral site surrounding the phosphorus atom; x is an integer selected from 1, 2 and 3; y is an integer selected from 1, 2 and 3; A is at least one cation selected from the group consisting of Li, Mg, Sc, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Ru, Rh, Pd, Ta, Re, Os, Ir, Pt, Al, Ga, Ge, Sn, Pb, As, Sb, Bi, Po, Tb, and Pa, said cation occupying an octahedral site surrounding the phosphorus atom; z is a number from 1-6 representing a weighted average of the oxidation states of all of the A cations; and n is a number calculated as follows: in formula I: n=3-yz+x+6y, and in formula II: n=6+x+6y-yz.
This invention further provides an improved process for the oxidation of n-butane to maleic anhydride comprising contacting n-butane with a source of oxygen in the presence of a heteropolyacid catalyst of formula I or formula II as defined above.
The catalyst can be the only source of oxygen .
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Liquid Purification 
