Water-gas shift: Characterization and testing of nanoscale YSZ supported Pt catalysts

Nano-scale Y-doped zirconium oxide materials were prepared with high surface areas (150-200 m²/g) and small nano-crystallites (<8 nm). A combination of XANES and EXAFS was used to show that ZrO₂ exhibited the tetragonal phase, while the Zr_0.5Y_0.5O_1.75 support displayed the cubic phase. A comparison with undoped zirconia suggests that the Zr_0.9Y_0.1O_1.95 support was tetragonal in structure. A slight increase in d-spacing observed in HR-TEM for the Zr_0.9Y_0.1O_1.95 support relative to undoped ZrO₂, along with a shift to lower 2θ in XRD, provide evidence that Y-doping caused macrostrain. STEM imaging confirmed that the Pt clusters ranged from 0.5 to 2 nm over all three supports. Catalyst reducibility was explored by H₂-TPR, XANES at the Zr K-edge, and TPR-XANES at the Pt L_III edge. A higher concentration of surface defects for the 0.5%Pt/Zr_0.9Y_0.1O_1.95 catalyst relative to 0.5%Pt/ZrO₂ was confirmed by DRIFTS of adsorbed CO, while a greater surface mobility of surface formate was suggested based on forward formate decomposition experiments in steam. The Y-doped Pt promoted catalysts displayed higher water-gas-shift activity relative to the 0.5%Pt/ZrO₂ catalyst when the Y content was at or below 50%, with the best catalyst being 0.5%Pt/Zr_0.9Y_0.1O_1.95.