The reaction mechanism of highly dispersed Cu atoms and ultrafine MnOx nanoclusters co-modified ZSM-5 based on in-situ heteronuclear substitution for catalytic oxidation C6H14

Abstract

A series of Mn/Cu cosubstituted ZSM-5 (Zeolite Socony Mobil–5) with different Mn/Cu molar ratios were synthesized by a one-step heteronuclear substitution hydrothermal method. Singly substituted Mn- and Cu-ZSM-5 compounds were also prepared. The catalytic oxidation performance of hexane and the catalyst surface physicochemical properties over each catalyst were investigated to determine the reaction activity, the main influencing factors and the mechanism for hexane oxidation. Part of the framework Mn of ZSM-5 was substituted by Cu2+ during Mn/Cu cosubstitution, facilitating the generation of isolated and/or framework Cu2+ and extraframework ultrafine hollow spherical MnOx nanoclusters, and increasing the low-temperature reducibility and the amount and transfer capacity of superficial lattice oxygen. Mn-Cu-HZ(1:1) with an appropriate Mn/Cu cosubstitution ratio exhibited the best catalytic oxidation performance, mainly because it has the most superficial lattice oxygens, a relatively high transfer capacity, the highest low-temperature reducibility and suitable acidity. Synergetic catalysis could occur between isolated and/or framework Cu2+ and ultrafine MnOx nanoclusters via a Mars-Van Krevelen (MvK) mechanism. A reaction route for hexane oxidation over Mn-Cu-HZ(1:1) was proposed based on the in situ DRIFTS and GC–MS results. This work provides new insights into the design of VOC degradation catalysts.