Abstract
The inertness of the C-H bond in CH(4) poses significant challenges to selective CH(4) oxidation, which often proceeds all the way to CO(2) once activated. Selective oxidation of CH(4) to high-value industrial chemicals such as CO or CH(3)OH remains a challenge. Presently, the main methods to activate CH(4) oxidation include thermochemical, electrochemical, and photocatalytic reactions. Of them, photocatalytic reactions hold great promise for practical applications but have been poorly studied. Existing demonstrations of photocatalytic CH(4) oxidation exhibit limited control over the product selectivity, with CO(2) as the most common product. The yield of CO or other hydrocarbons is too low to be of any practical value. In this work, we show that highly selective production of CO by CH(4) oxidation can be achieved by a photoelectrochemical (PEC) approach. Under our experimental conditions, the highest yield for CO production was 81.9%. The substrate we used was TiO(2) grown by atomic layer deposition (ALD), which features high concentrations of Ti(3+) species. The selectivity toward CO was found to be highly sensitive to the substrate types, with significantly lower yield on P25 or commercial anatase TiO(2) substrates. Moreover, our results revealed that the selectivity toward CO also depends on the applied potentials. Based on the experimental results, we proposed a reaction mechanism that involves synergistic effects by adjacent Ti sites on TiO(2). Spectroscopic characterization and computational studies provide critical evidence to support the mechanism. Furthermore, the synergistic effect was found to parallel heterogeneous CO(2) reduction mechanisms. Our results not only present a new route to selective CH(4) oxidation, but also highlight the importance of mechanistic understandings in advancing heterogeneous catalysis.