Extending Oxygen-Tolerant Photocatalysis: From CO2 Reduction to NO Reduction

Abstract

The photocatalytic reduction of carbon dioxide (CO2) into high-value chemical feedstocks and the conversion of nitric oxide (NO) to N2 represent promising strategies for mitigating greenhouse gas emissions and air pollution. However, the practical implementation of these processes is often hindered by the presence of O2, which suppresses catalytic activity through competitive adsorption and activation. While recent advances in photocatalysis have led to the development of oxygen-tolerant catalysts for selective CO2 reduction, achieving efficient NO reduction under oxygen-rich conditions remains a significant challenge. In this review, the mechanistic insights and material design strategies behind oxygen-tolerant CO2 photoreduction are first analyzed, emphasizing key breakthroughs in the field. Building on these principles, a reaction strategy for the selective photocatalytic conversion of NO to N2 in oxygen-rich environments is explored and proposed. However, directly extrapolating strategies from CO2 reduction is inadequate, given the distinct molecular properties and reaction pathways of NO. Therefore, this review aims to reframe such extrapolation as a hypothesis-driven conceptual advance. It is proposed that while core design principles from oxygen-tolerant CO2 reduction, such as preferential adsorption and site isolation, can inspire novel catalyst design, their implementation must be adapted to address the unique and more stringent challenges inherent to the selective reduction of NO in oxygen-rich streams. It is also crucial to distinguish between detrimental competitive oxygen reduction and beneficial, controlled oxygen activation pathways. In the latter, O2-derived species can modulate active sites and steer reaction selectivity, as demonstrated in several CO2 reduction systems.