Acetylene Semi-Hydrogenation by Photocatalysis.

Acetylene to ethylene semi-hydrogenation is a cornerstone process in the production of polymer-grade feedstocks, yet it remains dominated by energy-intensive noble metal-based thermocatalysis. Photocatalysis is now emerging as a compelling alternative, using light to generate reactive intermediates under mild conditions and replacing hydrogen gas with safer proton sources such as water or alcohols. Although still in its infancy, this field is rapidly evolving, with a growing number of studies already achieving remarkable performances in both selectivity and efficiency. This Minireview provides an overview of photocatalytic acetylene semi-hydrogenation, framing recent advances within a broader industrial context. Emphasis is placed on mechanistic understanding, comparing π-complex, hydrogen atom transfer (HAT), and concerted proton-coupled electron transfer (CPET) pathways alongside the experimental tools used to distinguish them. Recent developments in both homogeneous and heterogeneous catalytic systems are discussed and key challenges related to efficiency, scalability, and techno-economic viability are presented, outlining design principles for next-generation, earth-abundant photocatalysts, and identifying opportunities for the transition from impurity removal to direct acetylene valorization.