Insight into the active site and reaction mechanism for selective oxidation of methane to methanol using HO on a Rh/ZrO catalyst

Direct methane conversion into value-added products has become increasingly important. However, it remains a great challenge to effectively activate methane and simultaneously suppress its over-oxidation. In this study, we performed a combined ab initio thermodynamics and DFT+ U study to investigate the selective oxidation of methane to methanol on a ZrO 2 -supported Rh single-atom catalyst. The most preferred local environment of a Rh single atom was proposed according to the ab initio thermodynamics results. The DFT calculation results show that the five-coordinated Rh structure leads to the over-oxidation of CH 3 species and thus prevents the formation of methanol. In contrast, the four-coordinated Rh can effectively stabilize the CH 3 species by suppressing its further dehydrogenation. This is attributed to the fact that the geometric configuration of CH 3 species at the four-coordinated Rh hinders the interaction between H in CH 3 species and neighboring O. Two different methanol formation mechanisms at the four-coordinated Rh, namely the direct pathway and the CH 3 OOH intermediate pathway, were studied. It was found that the four-coordinated Rh facilitates the activation of H 2 O 2 and the formation of CH 3 OOH, and thus the CH 3 OOH intermediate pathway plays a dominant role in methanol formation, in which CH 3 O species reacts with the OH group in H 2 O 2 to form the CH 3 OOH intermediate and subsequently the deoxygenation of CH 3 OOH leads to the formation of methanol. This study provides atomic-scale insights into the active site and reaction mechanism for selective oxidation of methane to methanol on Rh 1 /ZrO 2 catalysts. Five-coordinated Rh leads to the over-oxidation of CH 4 , while four-coordinated Rh stabilizes CH 3 and facilitates methanol formation via the CH 3 OOH intermediate.