Water-gas shift reaction over supported Pt and Pt-CeOx catalysts

A comparison study was performed of the water-gas shift (WGS) reaction over Pt and ceria-promoted Pt catalysts supported on CeO2, ZrO2, and TiO2 under rather severe reaction conditions: 6.7 mol% CO, 6.7 mol% CO2, and 33.2 mol% H2O in H2. Several techniques—CO chemisorption, temperature-programmed reduction (TPR), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES)—were employed to characterize the catalysts. The WGS reaction rate increased with increasing amount of chemisorbed CO over Pt/ZrO2, Pt/TiO2, and Pt-CeOx/ZrO2, whereas no such correlation was found over Pt/CeO2, Pt-CeOx/CeO2, and Pt-CeOx/TiO2. For these catalysts in the absence of any impurities such as Na+, the WGS activity increased with increasing surface area of the support, showed a maximum value, and then decreased as the surface area of the support was further increased. An adverse effect of Na+ on the amount of chemisorbed CO and the WGS activity was observed over Pt/CeO2. Pt-CeOx/TiO2 (51) showed the highest WGS activity among the tested supported Pt and Pt-CeOx catalysts. The close contact between Pt and the support or between Pt and CeOx, as monitored by H2-TPR, is closely related to the WGS activity. The catalytic stability at 583K improved with increasing surface area of the support over the CeO2- and ZrO2-supported Pt and Pt-CeOx catalysts.