Catalysts and methods for the selective conversion of carbon dioxide and hydrogen into methanol using heat and high pressure in a hydrogenation reactor are disclosed. Key to this process are catalysts, which are comprised of multimetallic, aluminum oxide-supported nanoparticles. In some embodiments of the invention, the catalytic nanoparticles are made from mixtures of zinc and copper, or mixtures of palladium and copper, in different stoichiometric equivalents. In others, stoichiometric additives or dopants are added in order to improve the rate of product formation, improve selectivity, or allow for flow configurations. Methods for the use of these catalysts for the synthesis of methanol, and for the purification of CO2, H2, or CO gas streams by transforming contaminants into liquid methanol are also described.