Comparison of MoVTaTeO and MoVNbTeO M1 crystal chemistry

摘要

The structure of a new catalytically active MoVTaTeO variant of the M1-phase propane(amm)oxidation catalyst has been refined.This Ta-containing variant is isostructural with the well-known MoVNbTeO form of the M1 phase,in this case with a = 21.1484(9)A,b = 26.6472(11)A,c = 4.00332(1)A with Z = 4.The formula unit of can be written as(TeO)_(0.43)Mo_(4.08)V_(0.70)Ta_(0.22)O_(14)to be compared to the previously determined composition for the Nb-containing phase:(TeO)_(0.47)Mo_(3.98)V_(0.59)Nb_(0.43)O_(14).The Ta-containing variant is somewhat vanadium-rich compared to its Nb counterpart,but the Ta solubility is only about half of the corresponding Nb solubility.Debate over the true location and role of Nb in the MoVNbTeO M1 phase may be better understood by comparison with the refined structure of this chemically similar Ta analog.In this case Ta is clearly distinguishable from each of the other metals from scattering experiments,unlike Nb.