Effect of oxygen on produced hydrocarbons and hydrogen from CO₂ reduction photocatalytic process

A possible approach to addressing the challenges of energy scarcity and the effects of global warming through the decrease of greenhouse gases is the manufacture of hydrocarbons, particularly fuel from the photoreduction of CO₂. Here, the determination of activity/selectivity of produced hydrocarbons, hydrogen, and oxygen in the gas phase was demonstrated in the absence and presence of O₂ in an aqueous slurry on TiO₂. The conversion increases with reaction time up to the first hour but then begins to become unchanged in the presence of oxygen, suggesting catalyst deactivation. In contrast, the reaction rate and CO₂ conversion increased over 4 h when there was no oxygen, demonstrating that oxygen can be the cause of TiO₂ deactivation. Intriguingly, light-induced O₂ uptake rather than evolution was seen during optical oxygen detection investigations in photoreactions with a peak region of O₂/CO₂. H₂ production is suppressed by the presence of oxygen. Additionally, the sudden increase in hydrogen generation when oxygen is absent demonstrated that oxygen consumption and hydrogen production are taking place at the reduction site. The availability of oxygen reduced hydrocarbon productivity and H₂ production.