Structure and reactivity of Pt–Ru/SiO2 catalysts for the preferential oxidation of CO under excess H2

SiO2-supported Pt–Ru bimetallic catalysts subjected to two different types of pretreatment protocols (i.e., subsequent oxidation–reduction treatments at 300 °C and direct reduction in H2 at 300 °C) were characterized by extended X-ray absorption fine structure spectroscopy (EXAFS), scanning transmission electron microscopy (STEM), Fourier transform infrared spectroscopy (FTIR) of adsorbed CO, and catalytic activity measurements for the preferential oxidation of CO in the presence of excess H2 (PROX). The EXAFS data show that both treatments led to the formation of dispersed bimetallic structures, with an average PtRu bond distance of 2.68 Å. The close proximity between Pt and Ru helped stabilize Ru in a highly dispersed form and prevented its sintering after oxidation treatments. The FTIR results indicate that the adsorption of CO was substantially weaker on bimetallic samples than on the corresponding monometallic ones. Interparticle segregation (i.e., segregation of the two metals into individual particles) was observed with the Pt–Ru/SiO2 sample exposed to direct H2 treatment; in contrast, intraparticle segregation (i.e., segregation of the two metals within the same particle), with Pt preferentially occupying more surface sites, was observed when consequent O2/H2 treatments were used. As a result, the direct H2 treatment yielded samples with PROX activity almost identical to that of monometallic Ru catalysts, whereas the O2/H2 treatment yielded samples with PROX activity intermediate to those of monometallic Pt and Ru catalysts.