In view of the great importance of finding ways to reduce CO2 by using solar energy, we have examined the advantage of employing heterostructures containing bimetallic alloys for the purpose. This choice is based on the knowledge that metals such as Pt reduce CO2, although the activity may not be considerable. Our studies on the reduction of CO2 by ZnO/M/CdS (M = Ag, Au, Ag1-xAux, Ag1-xCux) heterostructures in liquid phase have shown good results specially in the case of ZnO/Ag1-xCux/CdS, reaching a CO production activity of 327.4 mu mol h(1) g(1). The heterostructures also reduce CO2 in the gas-phase although the production activity is not high. Some of the heterostructures exhibit reduction of CO2 even in the absence of a sacrificial reagent. (C) 2017 Elsevier B.V. All rights reserved.