Production of bio-paraffin from solvent-free deoxygenation of palm biodiesel over ZrO2-supported nickel phosphide catalysts

This study investigated the effects of Ni/P molar ratio on nickel phosphide species and on the catalytic activity on solvent-free deoxygenation of palm biodiesel to produce n-paraffins. ZrO2-supported nickel phosphide catalysts with different Ni/P molar ratio were synthesized and characterized through HRTEM, XPS, XRD, BET, NH3-TPD, and H-2-TPR analysis techniques, to give an insight into the correlation of the catalyst structure and its performance. The formation of different types of nickel phosphide phases when preparing the catalyst with different Ni/P molar ratio was observed. Only Ni2P was formed with Ni/P molar ratio of 1, while Ni2P and Ni12P5 were detected when Ni/P molar ratio was 2. With further increasing Ni/P molar ratios to 3 and 4, new phases of Ni-0 and Ni3P were formed in addition to those of Ni2P and Ni12P5. NixP/ZrO2 exhibited excellent catalytic performance for deoxygenation of palm biodiesel mainly via decarbonylation/decarboxylation pathways, achieving the high FAME conversion of 50.2-88.0% and n-alkane selectivity of 65.0-95.4%. Conversion and alkane selectivity of the catalysts followed the sequence: Ni3P/ZrO2 approximate to Ni4P/ZrO2 >Ni2P/ZrO2 >Ni1P/ZrO2 >Ni/ZrO2, respectively. These results suggested that Ni/P molar ratio had significantly affected on catalytic performance, which was associated with the type of nickel phosphide phase, metal dispersion, metal particle size, as well as electron density on Ni site.