Acid-Promoted Selective Oxidation of Methane to Formic Acid over Dispersed Rhodium Catalysts under Mild Conditions
Fubo Gu, Xuetao Qin, Liu Pang, Ri Zhang, Mi Peng, Yao Xu, Song Hong, Jinglin Xie, Meng Wang, Dongmei Han, Dequan Xiao, Guangsheng Guo, Xiayan Wang, Zhihua Wang, Ding Ma
Abstract
Direct oxidation of methane into value-added liquid chemicals is a promising route for wide applications. However, the efficient conversion of methane with high selectivity under mild conditions is still challenging. Herein, the catalysts of rhodium dispersed on ZSM-5 were synthesized for the methane conversion utilizing molecular O 2 as the oxidant together with CO and H 2 O under a total pressure of 40 bar at <100 °C. Moreover, the conversion of methane and the selectivity of formic acid could be improved by increasing acidity over the Rh/ZSM-5 catalysts. Promoted by H +, the activities of methane oxidation can reach 3.56 mol HCOOH /mol Rh /h and 23.96 mol HCOOH /mol Rh /h at 50 and 90 °C over the 5.0Rh/H-ZSM-5 catalyst, and the selectivity of HCOOH of 98.48% to all organic oxygenates can be acquired at 90 °C. Dramatically, the activation of the C–H bond can even happen at room temperature. Electron paramagnetic resonance results showed that acidity can promote the generation of ·OH with CO, H 2 O, and O 2 as the reactants, resulting in high catalytic activity under mild conditions.