Low temperature water-gas shift:: The effect of alkali doping on the C-H bond of formate over Pt/ZrO2 catalysts

Using combinatorial methods, doping Pt/ZrO2 With alkali cations such as Li, especially Na, and K, was found to have a positive impact on the low temperature water-gas shift rate. In this investigation, DRIFTS results indicate that the alkali cation significantly shifts the formate C-H band positions toward lower wavenumbers in the order K (2774 cm(-1)) < Na (2842-2804 cm(-1)) < Li (2858 cm(-1)) < none (2880 cm(-1)). Not only were the bands shifted, but the overall intensities were found to be higher with the addition of alkali promoter. Three separate tests were conducted to probe the stability of formates, including (1) steady state experiments at 225 degrees C; (2) transient formate decomposition studies at 130 degrees C in steam; and (3) dry hydrogen-deuterium exchange tests at 225 degrees C. In each case, the alkali significantly impacted the formate decomposition rate, due to the weakening of the forniate C-H bond. The results suggest a new direction in water gas shift catalyst design. (c) 2007 Elsevier B.V. All rights reserved.