Sdudy On Hydroconversion Of Methyl Laurate On Supported Nickel Phosphide And Molybdenum Phosphide Catalysts

?-Al₂O₃-supported nickel phosphides?mNi-P?were prepared by the TPR method and tested for the deoxygenation of methyl laurate to hydrocarbons.The catalysts were characterized by UV-vis,H2-TPR,XRD,TEM,NH3-TPD,XPS,TEM and N2 adsorption-desorptionand CO chemisorption.The effect of the Ni content?m = 5–15 wt.%?on their structure and performance were investigated.Ni/?-Al2O3 and Ni2P/SiO2 was also studied for comparison.It was found that the formation of Al PO4 in the precursor inhibited the reduction of phosphate and so the formation of nickel phosphides.With increasing the Ni content,the Ni3 P,Ni12P5 and Ni2 P phases orderly formed,accompanying with the increases of their particle size and the amount of weak acid sites?mainly due to P-OH group?,while the CO uptake and the amount of medium strong acid sites?mainly related to Ni sites?first increased and then decreased.In the deoxygenation reaction,the conversion and the selectivity to n-C11 and n-C12 hydrocarbons achieved maximum on 8%Ni-P.We propose that the conversion was influenced by the Ni site and catalyst acidity while the TOF was influenced by the nickel phosphide phases,the catalyst acidity and the particle size as well as the synergetic effect between the Ni site and acid site.Again,the hydrodeoxygenation pathway of methyl laurate was promoted with increasing Ni content,ascribed to the phase change in the order of Ni3 P,Ni12P5 and Ni2 P in the prepared catalysts.Compared with Ni/?-Al2O3,the mNi-P catalysts showed much lower activities for decarbonylation,C-C hydrogenolysis and methanation due to the ligand and ensemble effects of P.Also,8%Ni-P had higher activity than Ni2P/SiO2 with the same Ni content.Supported molybdenum phosphide catalysts were synthesized by the TPR method from the phosphate precursors on different supports?MCM-41,A-SiO2,SiO2-B,Si O2-C,SBA-15?.They were characterized by means of H2-TPR,XRD,TEM,NH3-TPD,TEM and ICP-AES and CO chemisorption,and their performances for the hydroconversion of methyl laurate were evaluated on a fixed-bed reactor.For comparison,the bulk MoP was also prepared and tested.It was found that,apart from metallic Mo formed on SiO2-A,the MoP phase was formed on other supports.20%MoP/MCM-41 and 20%MoP/SiO2-A with smaller pore size had much lower CO uptakes than other catalysts,and 20%MoP/SiO2-A possessed the lowest one due to the large particles and the coverage of metallic sites with more P species.Moreover,20%MoP/SiO2-A had much less acid sites than other catalysts.In the hydroconversion of methyl laurate,20%MoP/SiO2-A and 20%MoP/MCM-41 gave lower conversions and total selectivities to i-C11 and i-C12 hydrocarbons but higher selectivities to alkene than 20%MoP/SiO2-B,20%MoP/SiO2-C and 20%MoP/SBA-15.This is mainly attributed to their lower CO uptakes.Although 20%MoP/MCM-41 had similar acid amount to MoP/SiO2-B,MoP/Si O2-C and MoP/SBA-15,its lower CO uptake led to an unbalance between the acidic and metallic functions,which is unfavorable for the hydroisomerization.Different from bulk MoP on which the main deoxygenation pathway of methyl laurate was decarbomylation to produce to C11 hydrocarbons,the supported MoP catalysts mainly gave C12 hydrocarons via the hydrodeoxygenation pathway.This mainly relates to their high MoP dispersions and the large amounts of acid sites?especially Br?nsted ones?.