Methanol synthesis from CO2 over industrial catalysts suffers from a lack of selectivity, since large amounts of CO are formed as by-product. The understanding of the Cu-ZnO synergy in the creation of the active sites for methanol and CO formation is therefore a key for the development of catalysts for CO-free methanol synthesis. Cu-ZnO coprecipitate catalysts with variable compositions were employed as a tool for correlating physical to catalytic properties. Hydrogen spillover on two distinct active sites was demonstrated to be the result of Cu-ZnO contacts. The latter were quantified by using a mathematical model for sphere contact quantification in randomly packed binary mixtures. Theoretical calculations were in total agreement with experimental results. This allowed the rational design of catalysts based on core-shell structures for efficient CO-free methanol synthesis. (C) 2015 Elsevier Inc. All rights reserved.