A theoretical study of propionic acid decarboxylation over hydroxyapatite supported platinum catalysts

Abstract

Heterogeneous catalytic conversion of renewable biomass resources into transportation fuels and value-added chemicals is of great significance in recent years. Of various deoxygenation processes used in the upgrading of bio-oils such as fatty acids, decarboxylation of fatty acids is highly desired because of less hydrogen consumption. In the present work, the active center for propionic acid decarboxylation on the hydroxyapatite (HAP) supported Pt catalysts was investigated using density functional theory (DFT) calculations. Five model surfaces, i.e., HAP(001), Pt(111), Pt(211), the HAP(001) supported Pt13 nanocluster, and the interface between the supported Pt13 nanocluster and the HAP(001) were chosen to different reaction sites for decarboxylation. It has been found that the decarboxylation is kinetically inhibited on the pristine HAP(001), Pt(111) and Pt(211) surfaces due to the high activation barriers for the CC bond scission. While the interfacial site is identified as the most active site for propionic acid decarboxylation. Propionic acid first adsorbs at the interfacial sites over the Pt13/HAP(001) surface, then dissociates into propionate via the OH bond scission. The neighboring supported Pt13 nanocluster is responsible for the CC bond scission and the CH bond recombination leading to ethane and carbon dioxide formation. The CC bond scission of the propionate is the kinetically relevant step in the propionic acid decarboxylation over the HAP supported Pt catalysts.