Green Diesel Production Catalyzed by MoNi Catalysts Supported on Rice Husk Biochar

Nickel-based catalysts promoted by Mo-oxo species have been proven to be quite promising for transformation of triglycerides into green diesel. The selection of the support for such catalysts is crucial. In the present study, pyrolyzed rice husk subjected to acid and/or alkaline post-treatment was studied as support for the aforementioned catalysts. Biochar produced by slow pyrolysis of raw material at 850 °C for 5 h under limited-oxygen conditions exhibited the most promising textural characteristics. These were substantially improved by alkaline post-treatment. Thus, the corresponding MoNi catalysts proved the most efficient for upgrading used cooking oil (UCO) to green diesel via a solvent-free hydrotreatment process, performed in a semi-batch reactor (at 310 °C, 40 bar, 100 mL/min H2, 100 mL UCO and 1 g of catalyst). The enhanced catalytic performance (complete conversion of UCO and 32 wt.% green diesel yield) of MoNi catalysts supported on biochar subjected at least to an alkaline post-treatment step has been attributed to their high SSA, suitable pore size distribution (enhanced mesoporosity), and acidity (enhanced population of acid sites with moderate strength), as well as to the high dispersion of the active phase.