Exposing the synergistic effect between copper and vanadium in AlPO-5 during the selective oxidation of propene

Abstract

Vanadium and copper were co-deposited into the microporous AlPO-5 to obtain VCu:AlPO-5. The catalytic activity towards selective oxidation of propene with feed gas components C3H6:4 O2 show maximum yield of 3.9% at 400°C with 5.5% acrolein selectivity. The activity towards acrolein is clearly enhanced in VCu:AlPO-5, when compared to monometallic analogues V:APO-5 and Cu:APO-5. The synergism between vanadium and copper was investigated with in situ XAS at the V and Cu K-edge during cycling in reaction components (C3H6/O2). Vanadium is initially present as pentavalent square pyramidal V(5+) indirectly bonded to copper at 2.9Å as confirmed by EXAFS. Vanadium was gradually reduced by propene to obtain 30% V(4+) fraction in VCu:AlPO-5, coinciding with rapid reduction of Cu(II) to Cu(I) (60%). Reduction in propene is accompanied by a decrease in the average VO and CuO first shell multiplicities. Interestingly, acrolein is formed over VCu:AlPO-5 in propene only, but the activity decreases with time on stream. After switching to oxygen the activity is diminished and the local vanadium and copper surroundings are restored. Reduction of vanadium was not observed in V:AlPO-5, hence copper promotes the reducibility of vanadium and propene oxidation is activated by the dynamic nanoparticulate CuVOx/Cu(I)V(4+)Ox−1 species formed in AlPO-5.