H2-free hydrodeoxygenation of microalgae biomass using Pd-Ni/γ-Al2O3 bimetallic nanocatalyst in the supercritical environment

Abstract

Hydrodeoxygenation (HDO) of Chlorella vulgaris bio-oil as a renewable energy source was evaluated in a supercritical fluid mixture as both a hydrogen donor and solvent, with and without the Pd-Ni/γ-Al₂O₃ nanocatalyst. Firstly, RSM was carried out to improve long-chain hydrocarbons (LCHs) production process in a hydrogen-less supercritical n-hexane medium using dry biomass of Chlorella vulgaris. Then, the reaction was run under optimal conditions, which included isopropanol, temperature, feedstock, and reaction time of 10%V/V, 250 °C, 0.1 g, and 20 min, with the Pd-Ni catalyst with different Pd: Ni ratios. FTIR, XRD, BET, and TEM were the methods used to characterize the catalysts. More than 47% of the final product, in the absence of the catalysts, was made up of LCHs (C8–C18). However, an interesting change in the product types occurred when the catalyst was present. The catalyst, specifically the Pd metal, directed the reaction towards the production of C6 and C7 products. Alkyl benzenes and alkyl phenols were among the several products that the catalyst caused to develop, which themselves are introduced as precursors for LCHs production. The catalyst Pd-Ni/γ-Al2O3 with a Pd: Ni ratio of 3:1 had the best production with a yield of 42.3%.