Switch in Formic Acid Decomposition Pathways on Pd and PdAu Catalysts: Insights from Temperature-Programmed Surface Reaction Simulations

Although Pd catalysts modified with Au have been widely used in formic acid (HCOOH) decomposition for hydrogen storage, the active site and reaction mechanism remain under debate. We developed a computational method for simulating temperature-programmed surface reaction (TPSR) experiments that not only captures product desorption features but also tracks the concentration changes of intermediates as a function of temperature. This capability provides mechanistic insights into key intermediates and their associated reaction pathways toward product formation, which are difficult to obtain using conventional surface science techniques. We used this method to simulate TPSR spectra for HCOOH decomposition on Pd(111) and possible PdAu active configurations, including core–shell and surface alloy configurations. The simulated spectra for Pd(111) and Pd2Au/Au(111) surface alloy agree well with the TPSR experiments on Pd(111) and PdAu catalysts, which validates the reliability of our method and suggests that the active sites of the PdAu catalyst resemble PdPdAu sites in the Pd2Au/Au(111) surface alloy. The HCOOH decomposition pathway shifts from the formate pathway on Pd(111) to the carboxyl pathway on Pd2Au/Au(111), which is attributed to the smaller Pd ensemble sites required for the latter. This work enriches the design principles for HCOOH decomposition catalysts and demonstrates the potential of the TPSR simulation method in elucidating catalytic reaction mechanisms.