Monodisperse AgPd Alloy Nanoparticles and Their Superior Catalysis for the Dehydrogenation of Formic Acid

摘要

Formic acid (FA, HCOOH) is a common small organic acid with a melting point of 8.4 °C and boiling point of 100.8 °C. It can undergo a dehydrogenation reaction, HCOOH →H2 + CO2, releasing H2 that will be important for hydrogen-based energy applications. Traditionally, the dehydrogenation of FA is catalyzed by metal complexes dissolved in an organic solvent and the catalysis is enhanced by adding an additive, such as sodium formate or amine adducts. To make more practical catalyst for the dehydrogenation reaction of FA, heterogeneous catalysts based on metal nanoparticles (NPs) have been developed. These catalysts are generally more stable but much less active than the homogeneous ones. Recently, bimetallic NP catalysts were found to be more active than their single component counterparts for the dehydrogenation of FA. For example, AgPd NPs supported on cerium oxide or AuPd NPs immobilized in a metal-organic framework showed an enhanced FA dehydrogenation catalysis with the initial turnover frequency (TOF) reaching 210 h~(-1) or 192 h~(-1) at 90 °C, respectively. However, the high rate of hydrogen generation observed from these heterogeneous catalysts could only be achieved when an additive was present and the reaction was maintained at temperatures close to 100°C. Under these "harsh" conditions, HCOOH was also subject to an undesired dehydration reaction, HCOOH→H2O + CO. Interestingly, Ag/Pd core/shell NPs were found to be promising in catalyzing the dehydrogenation of FA in an aqueous FA solution at lower temperatures (up to 50 °C) without any additive. But their initial TOFs were in the range of 125-252 H~(-1) at temperatures between 25-50 °C.