Formation of Pt–Ag alloy on different silicas – surface properties and catalytic activity in oxidation of methanol

Abstract

The idea of this work was to specify the conditions of alloying silver and platinum loaded on different silicas, i.e. commercial amorphous silica, MCF and NbMCF mesoporous cellular foams and to estimate the influence of the metal species on the activity and selectivity of the catalysts in the oxidation of methanol. For this purpose different amounts of both metals were used for achieving Ag/Pt molar ratios between 1.6 and 5.1. The obtained materials were characterized by nitrogen adsorption isotherms, XRD, TEM, XPS and UV-Vis. The measurements were performed after drying the materials at 333 K, followed by their calcination in air at 773 K and activation in argon or hydrogen flow at 673 K. Pt–Ag alloy was formed after calcination independently of the structure and composition of the support, if the Ag/Pt molar ratio achieved at least 2.5. On the majority of samples the alloy disappeared after activation in argon or hydrogen flow, with the exception of 0.5Pt2Ag/MCF material activated in argon. Structural properties of the support influenced the particle size of the alloy and in this way determined the stability of Pt–Ag alloy in this material. The role of the bimetallic alloy on the activity and selectivity of the catalysts in methanol oxidation is discussed in this paper. The metal species on the supports, sensitive to thermal activation in argon or hydrogen media, did not change during the catalytic oxidation of methanol.