Pt/HAP catalyzed direct decarboxylation of lipid to alkanes via stabilization and synergism effect

Abstract

A highly effective and stable Pt/HAP catalyst was developed for the hydrogen-free deoxygenation of lipids to alkanes via specific stabilization and synergistic effect, which achieved ca. 90% yield at 320 °C at a high rate of 300 g∙gPt−1∙h−1 with 50 wt% reactant concentration in dodecane. Such catalytic system was adapted to various triglyceride feedstock and even unprocessed waste oil, showing superior activities than other reported Pt catalysts. The Pt precursor was ion-exchanged with the OH surface groups of HAP, as confirmed by characterizations of CO2-TPD, NH3-TPD and IR, forming uniform and small Pt nanoparticles with an average size of 0.7 nm after reduction. Even after eight recycling runs, the particle sizes were slightly turned into 1.6 nm with high reactivity and stability. In situ IR spectra showed that carboxylic acid was physically adsorbed on Pt/SiO2 and adsorbed as a bidentate on Pt/Al2O3, while adsorbed as a chelation on Pt/HAP-IE in comparison. Upon adsorption, protons of the carboxyl group were dissociated by phosphate, and the generated carboxylate anions were adsorbed on Ca2+ to form a chelated structure. Such adsorption mode activated carboxylates, which trended to be fast cleaved by the adjacent Pt nanoparticles anchored by OH groups to catalyze the target decarboxylation reaction, achieving the multi-functional synergistic catalysis. This Pt/HAP-IE catalyst can be applied to the hydrogen-free decarboxylation reactions, especially for the deoxygenation of compounds containing unsaturated CC, CO, CO, and OH bonds that are sensitive to hydrogen.