Zhang, Jian; Miao, Zezhong; Yang, Haiyan; Bu, Xianni; Wang, Hao; Li, Jiong; Ji, Te; Wei, Zhangqian; Li, Shenggang; Gao, Peng

APPLIED CATALYSIS B-ENVIRONMENT AND ENERGY

2025, ,

Zhang, Jian; Miao, Zezhong; Yang, Haiyan; Bu, Xianni; Wang, Hao; Li, Jiong; Ji, Te; Wei, Zhangqian; Li, Shenggang; Gao, Peng

The ZnFe2O4 spinel oxide was reported be effective in the CO2 hydrogenation to methanol reaction due to its superior catalytic activity and high thermal stability. However, the effects of the pretreatment conditions and the presence of the multiple crystalline phases on its catalytic performance remain to be fully elucidated due to the potential dynamic structural changes from pretreatment and side reactions. Here, we investigated the effect of pretreatment atmosphere on the structure and catalytic performance of the spinel ZnFe2O4 oxides. The catalyst pretreated in Ar offers a high methanol selectivity of 96.1 % with no obvious changes in its spinel structure under the reaction conditions of 280 degrees C, 5 MPa, H2/CO2 = 3, and a gaseous hourly space velocity (GHSV) of 20,000 mL & sdot;gcat - 1 & sdot;h- 1. However, for the catalyst activated in H2, the spinel structure was largely destroyed, resulting in CO and hydrocarbons as the main products. Through in situ spectroscopic, kinetic and computational analyses, we conclude that the spinel ZnFe2O4 oxide with the well-defined spinel structure provides optimal oxygen vacancy sites for the adsorption and activation of CO2 and H2, enabling higher methanol selectivity, whereas CO formation is more favorable on the ZnO and Fe3O4 nanoparticle surfaces due to the much lower energy barriers of CO2 dissociation to CO. In addition, the Fe5C2 species present in the ZnFe2O4 catalyst pretreated in H2 is mainly responsible for producing methane and C2+ alkanes. Thus, our combined experimental, spectroscopic and computational studies provide crucial insights for designing more efficient methanol synthesis catalysts for CO2 hydrogenation.