Study On The Performance Of Hydrodeoxygenation Of Methyl Laurate Over SiO₂-supported Transition Metal Phosphide Catalysts

Silica supported transition metal phosphide catalysts were prepared by thetemperature-programmed reduction method.Their structural properties werecharacterized,by means of N₂adsorption-desorption, XRD, NH₃-TPD and COchemisorption. Their performance in the hydrodeoxygenation of methyl laurate wastested on a fixed-bed reactor.Hydrodeoxygenation of methyl laurate on Ni₂P/SiO₂and Ni/SiO₂was firstcompared. While Ni₂P/SiO₂had lower hydrodeoxygenation activity than Ni/SiO₂, itgave higher total selectivity to n-undecane and n-dodecane and lower selectivities tocracking and decarboxylation/decarbonylation products. Also, it had lowermethanation activity.They are mainly ascribed to the electronic and geometricalproperties of Ni₂P/SiO₂. For Ni₂P/SiO₂, with increasing Ni content from5to20%, thehydrodeoxygenation activity and the selectivity to n-alkanes increased, while then-undecane/n-dodecane ratio decreased.The first case is due to the increases ofsurface Ni site and Ni₂P crystallite size.The activities of different transition metal phosphide catalysts decreased in thefollowing order:Ni₂P/SiO₂>MoP/SiO₂>WP/SiO₂>CoP/SiO₂>FeP-Fe₂P/SiO₂. Thedominating deoxygenation route on Ni₂P/SiO₂, CoP/SiO₂and FeP-Fe₂P/SiO₂wasdecarboxylation/decarbonylation, while it was the direct hydrodeoxygenation onMoP/SiO₂and WP/SiO₂. In addition, undecene and dodecehe were formed onFeP-Fe₂P/SiO₂, MoP/SiO₂and WP/SiO₂.The activities of different nickel phosphide catalysts decreased in the sequence ofNi₂P（1:2）/SiO₂, Ni₂P（1:1）/SiO₂, Ni₂P（1:3）/SiO₂, Ni₁₂P₅/SiO₂and Ni₃P/SiO₂. Thedominating deoxygenation route on the nickel phosphide catalysts wasdecarboxylation/decarbonylation, and the products were n-undecane and n-dodecane.With the decrease of Ni/P molar ratio in the catalysts, the ratio between n-undecaneand n-dodecane tended to decrease.As the temperature increased, the activity of Ni₂P/SiO₂and MoP/SiO₂increased,the selectivity to C11and C12hydrocarbons first increased and then decreased, andthe C11/C12molar ratio increased. The increased temperature did not promote theformation of the cracking products on Ni₂P/SiO₂, while it led to the increased selectivity to the cracking products on MoP/SiO₂. In addition, with the increase oftemperature, the content of isoalkanes on MoP/SiO₂increased, while the content ofalkene first increased and then decreased. As WHSV decreased, the activities ofNi₂P/SiO₂and MoP/SiO₂increased. The total selectivity to n-undecane andn-dodecane and the C11/C12ratio on Ni₂P/SiO₂did not change obviously, while theyincreased on MoP/SiO₂.