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

• YSZ supports (cubic) are more reducible than zirconia (tetragonal).
• Pt promotion further facilitates reduction.
• Y-doping of zirconia increases the number of surface defects (e.g., bridging OH groups).
• Highest formate decomposition rate (surface O mobility) observed for 0.5%Pt/YSZ.
• The activity of Pt/YSZ catalysts displays a synergy between zirconia and yttrium.

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 Zr0.5Y0.5O1.75 support displayed the cubic phase. A comparison with undoped zirconia suggests that the Zr0.9Y0.1O1.95 support was tetragonal in structure. A slight increase in d-spacing observed in HR-TEM for the Zr0.9Y0.1O1.95 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 LIII edge. A higher concentration of surface defects for the 0.5%Pt/Zr0.9Y0.1O1.95 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/Zr0.9Y0.1O1.95.

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