Water-gas shift reaction over supported Pt-CeO_x catalysts

We conducted a comparative study for the water-gas shift (WGS) reaction over ceria-promoted Pt catalysts supported on various supports such as γ-Al₂O₃, SiO₂, TiO₂ (P-25), CeO₂, SiO₂-Al₂O₃, yttria-stabilized zirconia (YSZ) and ZrO₂ in a rather severe reaction condition such as 6.7 vol.% CO, 6.7 vol.% CO₂, and 33.2 vol.% H₂O in H₂. Among them, Pt-Ce/TiO₂ showed the highest WGS activity especially at low temperatures. The effect of preparation sequences on the catalytic activity was also examined for ceria-promoted Pt supported on TiO₂ and Pt-Ce/TiO₂ prepared with a single-step co-impregnation method showed the highest water-gas shift activity. The CO chemisorptions, the temperature-programmed reduction (TPR), an inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and a transmission electron microscopy (TEM) with an energy dispersive X-ray spectroscopy (EDX) were conducted to characterize catalysts. The close correlation between the low-temperature water-gas shift activity and the amounts of chemisorbed CO as well as the degree of interaction between Pt and ceria has been observed. This Pt-Ce/TiO₂ showed the more stable catalytic activity in the cyclic operation and the start-up/shut-down operation compared with the conventional Pt-Ce/CeO₂.