Pt/Ce0.75Zr0.25O2– x Catalysts for Water Gas Shift Reaction: Morphology and Catalytic Properties

Highly dispersed 1.9 wt % Pt/Ce0.75Zr0.25O2 – x and 5 wt % Pt/Ce0.75Zr0.25O2 – x catalysts with an average particle size of 0.9 nm were prepared by sorption-hydrolytic precipitation. It was shown that the catalysts are active in the water gas shift reaction in a mixture simulating synthesis gas produced by steam reforming of natural gas. At an initial CO concentration of 10 vol % and a flow rate of 30000 ncm3 $${\text{g}}_{{{\text{cat}}}}^{{ - 1}}$$ h–1, outlet CO and CH4 concentrations reach 2.5 and 0.01 vol %, respectively, over 1.9 wt % Pt/Ce0.75Zr0.25O2 – x at 325°C and 1.5 and 0.075 vol %, respectively, over 5 wt % Pt/Ce0.75Zr0.25O2 – x at 300°С. The observed reaction orders for CO and H2O over 5 wt % Pt/Ce0.75Zr0.25O2 – x were found to be close to zero, and the apparent activation energy for both catalysts was 86 kJ/mol. Transmission electron microscopy of the catalysts showed that the narrow size distribution and high dispersion of the supported particles are retained during the reaction. However, some coarsening of Pt particles occurs, the average size increases to 1.4 and 1.6 nm for 1.9 wt % Pt/Ce0.75Zr0.25O2 – x and 5 wt % Pt/Ce0.75Zr0.25O2 – x, respectively. For the catalysts after the reaction, the metallic Pt surface area values, measured by CO chemisorption and transmission electron microscopy, differ significantly. Most likely, it is caused by the presence of some of the surface Pt atoms in the oxidized state. It was shown that the temperature dependences of the turnover frequency in the water gas shift reaction per the length unit of the metal-support interface, coincide for catalysts 1.9 wt % Pt/Ce0.75Zr0.25O2 – x and 5 wt % Pt/Ce0.75Zr0.25O2 – x. Based on this, an assumption was made about the leading role of the Pt–Ce0.75Zr0.25O2 – x boundary in the catalysis of the water gas shift reaction.