Study On Hydroconversion Of Methyl Laurate On Molybdenum Phosphide Based And Nickel Based Bimetallic Catalysts

We first investigated on the effect of Ni and noble metals?Ru,Pd and Pt?on performance of bifunctional MoP/SiO₂ for hydroconversion of methyl laurate.SiO₂supported bifunctional MoP catalysts modified with different metal promoters?Ni,Ru,Pd,Pt?,where Mo/Ni and Mo/M?M=Ru,Pd and Pt?atomic ratios were respectively10 and 40,were prepared by TPR method from the phosphate precursors.It was found that the introduction of metal promoters facilitated the reduction of phosphate precursor.Apart from MoP,metal promoters were also found to be phosphorized and intimately contacted with MoP,consequently preventing Mo P particles from sintering and enhancing the dispersion of MoP.Additionally,MoP catalyst acidity was scarcely influenced by a small amount of metal promoters.In the hydroconversion of methyl laurate as a model compound to diesel-like hydrocarbons,the promoters enhanced the activity of MoP catalyst for conversion of methyl laurate and hydrogenation of alkenes?intermediate?,but reduced isomerization ability to different extent.Among the promoters concerned,Ru was an optimum to decrease selectivity to alkenes while maintain high selectivity to iso-alkanes.Additionally,the introduction of metal promoters did not obviously affect the deoxygenation pathway on MoP,i.e.,hydrodeoxygenation pathway much prevailed over decarbonylation one.In the stability test at 380 ^oC and 3.0 MPa for 102 hours,Mo₄₀RuP catalyst showed better stability than MoP catalyst.Although the selectivity to alkenes increased,the conversion of methyl laurate,the total selectivity to C11 and C12 hydrocarbons and the selectivity to iso-alkanes maintained at 100%,⁹4%and³0%,respectively.The good stability of Mo₄₀RuP is ascribed to that the presence of Ru prevented the sintering of MoP particles and suppressed carbon deposition.Secondly,the performance of Ni based bimetallic catalysts on hydrodeoxygenation of methyl laurate was investigated.The catalysts were prepared from the layered double hydroxide precursors via calcination and reduction.The introduction of the metal promoter?M=Fe,Co,Cu,Zn,Ga nd In?facilitates the reduction of catalyst precursors and led to the formation of Ni-M alloy in the prepared catalysts.The Ni-M alloy crystallite sizes in the bimetallic catalysts were similar to the metallic Ni crystallite size.However,the H₂ uptakes of bimetallic catalysts were much lower than that of metallic Ni catalyst,which is related to the formation of Ni-M alloy and the enrichment of some M?such as Cu,Zn,Ga and In?with lower surface energy on the alloy surface.In the hydrodeoxygenation of methyl laurate,the deoxygenation activity of catalyst decreased in the following order:Ni₈Al₃?Ni₈FeAl₃?Ni₈CoAl₃>Ni₈CuAl₃>Ni₈ZnAl₃>Ni₈GaAl₃>Ni₈In Al₃.The C-C hydrogenolysis ability decreased in the sequence:Ni₈Al₃?Ni₈CoAl₃>Ni₈FeAl₃>Ni₈ZnAl₃>Ni₈CuAl₃>Ni₈GaAl₃>Ni₈InAl₃.Fe and Co showed a small affect on the catalyst activity for the deoxygenation and C-C bond hydrogenolysis.The introduction of Zn reduced both deoxygenation and C-C bond hydrogenolysis abilities.Compared with Ni₈ZnAl₃,although Ni₈CuAl₃ was less active for deoxygenation,it was also less activie for C-C bond hydrogenolysis.Compared with other metal promoters,Ga and In?especially In?remarkably reduced metallic Ni catalyst activity for deoxygenation,but they promoted the hydrodeoxygenation pathway,and depressed C-C bond hydrogenolysis and methanation significantly.The supression effect of metal promoter on catalyst activity for C-C bond hydrogenolysis and methanation is related to the formation of Ni-M alloys and the enrichment of metal promoters?especially the ones with low surface energy?on the alloy surface.