Photoinduced hydrogenation of ethylene and acetylene in aqueous media: The functions of palladium and platinum colloids as catalytic charge relays

Ethylene and acetylene are photohydrogenated in aqueous media that include Ru(bipy)₃²⁺ as sensitizer, NN′-dimethyl-4,4′-bipyridinium, methyl viologen, MV²⁺ as electron carrier, disodium ethylenediamine tetra-acetic acid as electron donor, and metal colloids, i.e. Pt, Pd as hydrogenation catalysts. Ethylene is photohydrogenated to ethane (φ 9.9 × 10^-2). The quantum yield for photohydrogenation of acetylene to ethylene and ethane depends on the composition of the metal catalyst. The highest quantum yield is obtained with a Pt colloid coated by Pd (φ 3.2 × 10^-2). The bimetallic catalyst is active in reduction of protons to metal-bound hydrogen-atom as well as in C₂H₂ activation.