Low temperature water–gas shift: The effect of alkali doping on the CH 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 CH 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 °C; (2) transient formate decomposition studies at 130 °C in steam; and (3) dry hydrogen–deuterium exchange tests at 225 °C. In each case, the alkali significantly impacted the formate decomposition rate, due to the weakening of the formate CH bond. The results suggest a new direction in water gas shift catalyst design.

Addition of alkali dopants (e.g., Li, Na, and K) to Pt/ZrO2 low temperature water–gas shift catalysts led to an important weakening of the formate CH bond, as indicated by a shift to lower wavenumbers in infrared spectroscopy. Formate CH bond breaking is suggested to be the rate-limiting step of the mechanism, and enhanced WGS rates and formate decomposition rates are can be explained by formate CH bond weakening. Figure optionsDownload as PowerPoint slide