There is a considerable interest in the development of photocatalytic CO2 conversion by sunlight, since this process has similarities with natural photosynthesis on which life on Earth is based. At the moment, most of the efforts in this field have been aimed at increasing the productivity, rather than at the control of the product distribution. Particularly, compounds with two or more carbons (C2+) have higher added value than methane, carbon monoxide, or formate, which are typically the major products of CO2 reduction. This review focuses on those reports that have described the formation of compounds of two or more carbon atoms (C2+) in the photocatalytic CO2 reduction either by H2O or as H2 as a source of electrons and protons. The existing literature has been organized according to the main factor considered to be responsible for the selectivity to C2+ products, including photocatalyst structuration, nature of the co-catalyst, influence of defects, and effects of surface plasmon band. Emphasis has been made on remarking the current empirical knowledge based on experimental results and the lack of predictive capability that could lead to the development of efficient photocatalytic systems for C2+ production.

Financial support by the Spanish Ministry of Science and Innovation (Severo Ochoa and No. CTQ2018-89237-CO2-R1) and Generalitat Valenciana (Prometeo 2017/83) is gratefully acknowledged.