Theoretical study of propylene epoxidation heterogeneous‐homogeneous mechanism over MoOx/SiO2 catalyst

Abstract The green direct propylene (C 3 H 6 ) epoxidation on MoO x is well studied by experimental methods, but detailed molecular reaction mechanism studies using in‐silico experiments method are few. Here, the different oxidation heterogeneous‐homogeneous pathways for MoO x /SiO 2 catalyst are calculated, mainly involving Mo=O on di‐oxo tetracoordinate MoO x , allyl peroxy (C 3 H 5 OO•), and allyloxy (C 3 H 5 O•) radicals. The results show that, for surface reaction mechanism with Mo=O, the barriers of propylene oxide (PO) and acetone generation are too high; in comparison, the byproduct acrolein is more beneficial product with a lower barrier. In heterogeneous‐homogeneous pathways, the desorbed allyl (C 3 H 5 •) from the surface can easily combine with O 2 to synthesize C 3 H 5 OO• radical, and in the partial oxidation of propylene with C 3 H 5 OO• as an oxidant, PO is more beneficial with a low barrier compared to byproducts such as propanal, acetone, acetaldehyde, etc. These indicate that (a) gas‐phase free radical reactions have important effects on PO generation, in which C 3 H 5 OO• is the main active species; (b) on MoO x surface, Mo=O is difficult to be used as the active O species for PO production. Further research is needed on other active sites such as Mo‐O‐Mo or defective sites.