The role of Sb and Nb in rutile-type Sn/V/Nb/Sb mixed oxides, catalysts for propane ammoxidation to acrylonitrile

This paper describes the role of Sb and Nb, components of Sn/V/Nb/Sb mixed oxides catalysts for the gas-phase ammoxidation of propane to acrylonitrile. In samples without Nb and with atomic ratios Sn/V/Sb 1/0.2/x (x = 0 to 3), Sb in the form of amorphous oxide is necessary in order to obtain an active and selective catalyst. However, during reaction the dispersed Sb oxide segregates to α-Sb2O4, and the yield to acrylonitrile decreases considerably. The addition of Nb gives rise to the formation of Nb-containing SbOx and non-stoichiometric rutile-type V/Nb/Sb mixed oxides. The presence of these compounds enhances the catalytic activity and the selectivity to acrylonitrile. Moreover, the catalyst shows a stable catalytic performance, with no segregation of α-Sb2O4.