Theoretical Study of the Propene Combustion Catalysis of Chromite Spinels: Reaction Mechanism and Relation between the Activity and Electronic Structure of Spinels

Abstract

Oxides of base-metal elements play an important role as catalysts in alkene combustion, but correct knowledge of the reaction mechanism and determination factors for activity remains elusive. Herein, we report a systematic study of propene combustion catalyzed by ZnCr2O4(111) as one example using DFT + U calculations. The combustion occurs through three parallel reaction pathways starting from C–H σ-bond cleavage. In each pathway, acetate, carbonate, or formate is formed as a key intermediate, which is consistent with the experimental detection of several different kinds of intermediates in propene combustion. Effects of tetrahedral metal (MTd) and octahedral metal (MOh) atoms on the catalytic activity are discussed by comparing propene combustion by MgCr2O4(111), Cu-doped ZnCr2O4(111) (named Zn1 – x Cu x Cr2O4(111)), and Co-doped ZnCr2O4(111) (named ZnCr2 – x Co x O4(111)) with that by ZnCr2O4(111). Catalytic activity increases in the order MgCr2O4(111) < Zn1 – x Cu x Cr2O4(111) < ZnCr2O4(111) < ZnCr2 – x Co x O4(111). The higher activity of ZnCr2O4(111) than that of MgCr2O4(111) agrees with the experimental findings. ZnCr2 – x Co x O4(111) is computationally predicted here to be more active than ZnCr2O4(111) which has been experimentally used as a good catalyst. Based on computational findings, a discussion is presented on the relation between the activity and electronic structure of spinels.

Recent Advances of VOCs Catalytic Oxidation over Spinel Oxides: Catalyst Design and Reaction Mechanism

“…(E) Reaction mechanism of propylene on ZnCr 2 O 4 -based spinels. Reprinted with permission from ref . Copyright 2021 American Chemical Society.…”

“…152 The oxidation centers were Cr 3+ and Co 3+ , and the surface lattice oxygen with nucleophilic properties was the main active oxygen species. Zhao et al 153 investigated the reaction mechanism of propylene on ZnCr 2 O 4 -based spinels through DFT+U calculations (Figure 9E). Acetate, carbonate, and formate were key intermediates in the whole propylene reaction process.…”