Theoretical study of propylene epoxidation heterogeneous‐homogeneous mechanism over MoOx/SiO2 catalyst. Issue 18 (16th July 2020)

• Record Type: Journal Article
• Authors: Wan, Zhehong; Lin, Zenan; Peng, Jiahui; Chen, Wei; Li, Xiaohan; Chen, Xiaohui
• Is Part Of: International journal of quantum chemistry. Volume 120:Issue 18(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-07-16
• Subjects: Propylene Oxide (PO) -- heterogeneous‐homogeneous reaction mechanism -- MoOx/SiO2 -- propylene epoxidation; Quantum chemistry -- Periodicals; 541.28
• DOI: 10.1002/qua.26328
• Languages: English
• ISSNs: 0020-7608

Abstract

Abstract: The green direct propylene (C3 H6 ) epoxidation on MoOx 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 MoOx /SiO2 catalyst are calculated, mainly involving Mo=O on di‐oxo tetracoordinate MoOx, allyl peroxy (C3 H5 OO), and allyloxy (C3 H5 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 (C3 H5 ) from the surface can easily combine with O2 to synthesize C3 H5 OO radical, and in the partial oxidation of propylene with C3 H5 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 C3 H5 OO is the main active species; (b) on MoOx 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. Abstract : The heterogenerous and surfaced‐induced homogeneous reaction mechanism of propylene epoxidation over MoOx /SiO2 were both investigated thoroughly, providing a deeper understanding for experimental exploration. Compared to Mo(=O)2 species, C3 H5 OO radical from desorbed C3 H5 and gas‐phase O2 has a relatively good effect on generation of PO. While the possibility of higher PO selectivity in gas‐phase radical mechanism has been limited.