Alloy Formation in Li-Promoted Pd/SiO2 Catalysts for the Synthesis of Methanol

Li-promoted Pd catalysts are active for the synthesis of methanol from synthesis gas and exhibit properties that can be explained by alloy formation. The relative partial Gibbs energy of Li in a solid solution of Li and Pd is very exergonic at a low molar fraction of Li, but much less exergonic at higher concentrations. Therefore, when Li-promoted Pd/SiO2 catalysts are reduced in hydrogen, a reduction of Li+ to Li0 to yield a Li–Pd alloy only proceeds to a low degree, dependent on the temperature and the purity of the hydrogen. This explains a constant hydrogen chemisorption capacity of Li/Pd/SiO2 catalysts at a high Li loading. The properties of Ca-promoted Pd catalysts can be explained by alloy formation as well.