Guerbet Reactions for Biofuel Production from ABE Fermentation Using Bifunctional Ni-MgO-Al2O3 Catalysts

To upgrade biomass-derived alcohol mixtures to biofuels under solvent-free conditions, MgO–Al2O3 mixed metal oxides (MMO) decorated with Ni nanoparticles (Ni–MgO–Al2O3) are synthesized and characterized. Based on the result, Ni nanoparticles are highly dispersed on the surface of MgAl MMO. As the Ni loading content varies from 2 to 10 wt.%, there is a slight increase in the mean Ni particle size from 6.7 to 8.5 nm. The effects of Ni loading amount, reducing temperature, and Mg/Al ratio on the conversion and product distribution are investigated. With the increase in both the Ni loading amount and reducing temperature, dehydrogenation (the first step of the entire reaction network) is accelerated. This results in an increase in the conversion process and a higher selectivity for the dialkylated compounds. Due to the higher strength and density of basic sites under high Mg/Al ratios, double alkylation is preferred and more long-chain hydrocarbons are obtained. A conversion of 89.2% coupled with a total yield of 79.9% for C5–C15 compounds is acquired by the as-prepared catalyst (prepared with Ni loading of 6 wt.%, reducing temperature of 700 °C, and Mg/Al molar ratio of 3. After four runs, the conversion drops by 17.1%, and this loss in the catalytic activity can be attributed to the decrease in the surface area of the catalyst and the increase in the Ni mean particle size.