(722a) Water-Gas Shift Catalysis Over Supported Platinum Nanoparticles
The water-gas shift (WGS) reaction (CO + H2O → CO2 + H2) is an important industrial chemical process for hydrogen production. Supported Pt catalysts have turnover rates (TOR’s) comparable to the industrial Cu/ZnO/Al2O3 catalysts but are more robust.
The WGS TOR’s, normalized by surface Pt atoms, for Pt/Al2O3, Pt/SiO2, Pt/ZrO2, and Pt/TiO2 catalysts are independent of average Pt particle size. The apparent reaction orders for Ptcatalysts do not vary with particle size. Thus, all surface Pt atoms exhibit the same rate.
The WGS TOR and H2O order (in parenthesis) vary as Pt/Al2O3 (0.93) ~ Pt/SiO2 (0.84) < Pt/TiO2 ~ Pt/ZrO2 ~ Pt/CeO2 (0.66-0.72) at 300 °C. The CO, CO2 and H2 orders do not vary with the support. Further, the TORs for Pt/ZrO2 and Pt/TiO2 catalysts decrease by 125 and 10 times their original TOR, respectively, upon addition of 70 atomic layer deposition (ALD) cycles, ~ 75 wt.% Pt. This is due to excess Pt coverage that limits the number of support sites, shown from their transmission electron microscopy (TEM) images, available for H2O activation. We interpret these data to show that the support plays a direct role in activating H2O.
Lastly, the WGS TOR for 70 ALD cycles 76.4wt.%Pt/np.ZrO2 catalyst is 0.004 s-1 at 300 °C, 10 times less than that for 1.6wt.%Pt/Al2O3 catalysts. Thus, the WGS TOR for the unsupported Pt surface is at least 10 times less than Pt/Al2O3, implying that the assumption that Pt/Al2O3 can be modeled as just unsupported Pt surface may not be true.