Activity-determining factors for catalytic CO and CH4 oxidation on Pt/CeO2–ZrO2–Al2O3 cryogels

Abstract

Homogeneous 1 wt% Pt/CeO2–ZrO2–Al2O3 cryogels with Ce/Zr = 1 and Ce/Al = 0–1/2 were synthesized by one-pot sol–gel processing and subsequent freeze drying. Catalysis for CO and CH4 oxidation was investigated after heating in air at 800 °C for 5 h. It was shown that Ce/Al = 1/3 was the most desirable to obtain the highest activity. When the ratio was below 1/3, sufficient catalytic activity was not obtained, owing to the lack of ceria which played an important role in improving Pt dispersion and oxygen storage capacity (OSC). On the other hand, when the ratio was above 1/3, the activity decreased, owing to the lack of alumina as a diffusion barrier for ceria–zirconia solid solution, resulting principally in encapsulation of platinum inside the solid solution. It was revealed that catalytic activity correlated positively with Pt dispersion and OSC of the cryogel, implying that the dispersion and OSC were the essential factors for controlling the activity. However, it was also revealed that the dispersion and OSC did not correlate positively with BET surface area and pore volume of the cryogel, which suggested that maintenance of as large surface area and pore volume as possible was not always important to obtain high dispersion and OSC. Since Pt dispersion and OSC increased basically with increasing the Ce/Al ratio until Ce/Al = 1/3 and BET surface area and pore volume decreased, it was suggested that chemical interaction between platinum and cerium oxide was important for improving the dispersion and OSC.