Theoretical Investigation of Aqueous Phase Reforming of 1,2 Propanediol over a Pt catalyst

Abstract

Aqueous Phase Reforming (APR) process is one of the most efficient solution for producing hydrogen from biomass renewable feedstocks, such as polyalcohols. [1] Generally the reaction is catalyzed by supported platinoid metals and among these platinum has been recognized as the most active and selective toward the production of hydrogen. However, due to its really high complexity, the reaction mechanism is today poorly understood. DFT methods can be useful for understanding the APR catalytic mechanism at atomistic level. A detailed mechanistic study was carried out using a Pt30 cluster for the modelization of the catalyst and 1,2 propanediol (1,2PDO) as a model feedstock for the APR. Even for this simple molecule five chemically different hydrogen atoms can be recognized which lead to five different reaction paths. The activation energy required for the methylic C-H bond cleavage is approximately 40 kJ mol-1 higher than the HOCH-H and HOC-H bond breakings. This effect arises directly from the presence of the OH group that reasonably enhances the possibility of the C-H bond to break. The key step of the reaction seems to be the formation of the unsaturated 1,2 propenediole species that, if coordinated to the catalyst surface, can be reformed through a C-C bond cleavage or can be easily converted to ketonic species, which are experimentally found as byproducts. [2] The C-C bond cleavage is the rate determing step requiring 95.7 kJ mol-1.