Theoretical Investigation of the Decomposition of Glycerol over Pt(111)

Glycerol is a significant byproduct in biodiesel production and identifying efficient technologies for its conversion into higher value products is highly desirable. Due to its high degree of functionality, glycerol has the potential to be catalytically converted into a number of value-added chemicals such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, and lactic acid, as well as syngas. Gaining a firm understanding of the underlying mechanism involved with glycerol’s conversion over metal surfaces is complicated because of the large number of possible reaction paths. It is for this reason that (computational) research tends to favor the investigation of smaller molecules with lower functionality. Nevertheless, availability of computational resources has increased sufficiently such that trends in the hydrogenolysis of glycerol can be studied from first principles over selected metal surfaces. Pt(111) has been shown to favor C-C bond cleavage over C-O cleavage after high levels of dehydrogenation with the assistance of an empirical scaling scheme to evaluate the binding energies of intermediates. Here, I present Bronsted-Evans-Polanyi (BEP) relations for glycerol over a Pt(111) surface evaluated for a larger number of empirical results in order to gain a deeper understanding of the favorability of dehydrogenation, deoxygenation and decarbonylation relative to each other. All elementary rate constants in the model have been determined from density functional theory (PBE+D3) and harmonic transition state theory.