Partial Oxidation of Methane on Anatase and Rutile Defective TiO2 Supported Rh4 Cluster: A Density Functional Theory Study

We have studied the effect of CH4 dissociation and partial oxidation on carbon deposition resistance on oxygen-defective anatase TiO2 supported Rh (Rh4/Ana-Ov) and rutile TiO2 supported Rh (Rh4/Rut-Ov) by the density functional theory. We computed the adsorption structure of CHx species, and the adsorption of CHx species on Rh4/Rut-Ov was stronger than that on Rh4/Ana-Ov. On the Rh4/Ana-Ov surface, the activation energy barrier of C–H bond cleavage involved in methane decomposition was higher than that on Rh4/Rut-Ov, which means the Rh4/Ana-Ov was favored to carbon deposition resistance. Additionally, the dominant process of methane partial oxidation was CH2*+O* → CH2O*, where the energy barrier on Rh4/Ana-Ov is lower relative to Rh4/Rut-Ov. This implies that the oxidation reaction was also favorable to the carbon deposition resistance on Rh4/Ana-Ov. As the strong carbon deposition resistance effect on Rh4/Ana-Ov, a high activity for syngas formation can be expected. The energetic span model analysis showed that the apparent activation energy was beneficial to the partial oxidation of methane on Rh4/Ana-Ov compared to that of Rh4/Rut-Ov. Moreover, the selectivity of CO was high and up to 90% by using the microkinetic model analysis, which was consistent with the experimental results. The present work may help people to design an efficient catalysts for methane partial oxidation in which there is a strong interaction with support in order to reduce the carbon deposition.