Structure and activity of tellurium-molybdenum oxide acrylonitrile catalysts

Abstract

Ammoxidation of propylene to acrylonitrile (ACN) was investigated using various (Te, Mo)O catalysts at temperatures from 360 to 460 °C. Binary oxides are significantly more active than the component oxides and show a completely different product distribution. The reaction leads mainly to ACN and acrolein (80–90%, in varying ratios) and to CH 3CN (3%); the balance accounts for total oxidation products. The active phase is Te 2MoO 7, which acts through activation of the hydrocarbon at Te sites and insertion of oxygen at Mo sites. Site isolation in the active phase accounts for the high selectivity to ACN. The allotriomorphic texture of Te 2MoO 7 rationalizes variations in catalytic activity of the TeO 2MoO 3 system as a function of the composition. Decay of the catalysts by depletion of lattice oxygen was studied. Reactivation of a deactivated catalyst can be effected, but in nonequilibrium conditions transport phenomena lead to a migration of the degradation products, TeMo 5O 16, Te, and reduced molybdenum oxides. The primary function of cerium in an industrial (Ce, Mo, Te)O ammoxidation catalyst is its capacity to reoxidize its partners more readily as compared to a (Te, Mo)O solid.