Acid Etching-Induced In Situ Growth of λ-MnO<sub>2</sub> over CoMn Spinel for Low-Temperature Volatile Organic Compound Oxidation
Cangpeng Shan, Yan Zhang, Qian Zhao, Kaixuan Fu, Yanfei Zheng, Rui Han, Caixia Liu, Na Ji, Weichao Wang, Qingling Liu
Abstract
Surface lattice oxygen is crucial to the degradation of volatile organic compounds (VOCs) over transition metal oxides according to the Mars–van Krevelen mechanism. Herein, λ-MnO2 in situ grown on the surface of CoMn spinel was prepared by acid etching of corresponding spinel catalysts (CoMn-Hx-Ty) for VOC oxidation. Experimental and relevant theoretical exploration revealed that acid etching on the CoMn spinel surface could decrease the electron cloud density around the O atom and weaken the adjacent Mn–O bond due to the fracture of the surface Co–O bond, facilitating electron transfer and subsequently the activation of surface lattice oxygen. The obtained CoMn-H1-T1 exhibited an excellent catalytic performance with a 90% acetone conversion at 149 °C, which is 42 °C lower than that of CoMn spinel. Furthermore, the partially maintained spinel structure led to better stability than pure λ-MnO2. In situ diffuse reflectance infrared Fourier transform spectroscopy confirmed a possible degradation pathway where adsorptive acetone converted into formate and acetate species and into CO2, in which the consumption of acetate was identified as the rate-limiting step. This strategy can improve the catalytic performance of metal oxides by activating surface lattice oxygen, to broaden their application in VOC oxidation.