Study On Ni₂P-based Bifunctional Catalysts For Hydroconversion Of Methyl Laurate

The bifunctional Ni₂P/SAPO-11 and Ni/SAPO-11 were prepared by the temperature-programmed reduction method. The properties were characterized by XRD, CO chemisorption and NH₃-TPD. The influences of reaction conditions on the hydroconversion of methyl laurate and catalyst stability were investigated. To explore the catalyst deactivation, the fresh and the used catalysts were characterized by XRD, TEM, SEM, N₂ adsorption-desorption, TGA, and Raman spectroscopy. The result showed that the increase of temperature and the deceases of weight hourly space velocity?WHSV? and H2 pressure favored the activity for deoxygenation and promoted the decarbonylation of methyl laurate and hydroisomerization of alkanes as well as cracking reactions. Both the Ni sites and the acid sites were dominating for deoxygenation pathway. Due to more medium strength acid sites, Ni/SAPO-11 gave higher selectivity to isoalkanes and more preferentially catalyzed the hydrodeoxygenation pathway to produce the C12 hydrocarbons than Ni₂P/SAPO-11. During the test for 101 h, Ni₂P/SAPO-11 exhibited greatly superior stability to Ni/SAPO-11 for the deoxygenation of methyl laurate, while both Ni₂P/SAPO-11 and Ni/SAPO-11 were deactivated for the hydroisomerization. The sintering of Ni particles and carbonaceous deposit contribute to inferior stability of Ni/SAPO-11 for both deoxygenation and hydroisomerization, while no obvious sintering of Ni2 P particles took place and the carbonaceous deposit mainly led to the loss of the activity for hydroisomerization on Ni₂P/SAPO-11.AlMCM-41-x?x was Si/Al molar ratio? mesoporous sieves with different Si/Al ratios were synthesized by the post-synthesis grafting method using polyaluminium chloride as Al source, and their Si/Al ratios and the Al states were characterized by means of XRF and 27Al-MAS NMR. The Ni/AlMCM-41-x precursors were in situ phosphorized to form Ni₂P/AlMCM-41-x using a triphenylphosphine?TPP? solution on a fixed-bed reactor. For comparison, the NiP/AlMCM-41-5-TPR catalyst was prepared from the precursor with P/Ni ratio of 1.0 via TPR method. The catalysts were characterized by XRD, NH₃-TPD, TEM and N₂ adsorption-desorption, and their performances for the hydroconversion of methyl laurate were evaluated on a fixed-bed reactor. In contrast to the MCM-41 support, the Ni₂P/AlMCM-41-x, Ni/AlMCM-41-5 and NiP/AlMCM-41-5-TPR catalysts possessed smaller surface areas, pore volumes and average pore sizes, while they still maintained the mesoporous structure of MCM-41. As the Si/Al ratio decreased, the amounts of framework Al, non-framework Al and acid amount of AlMCM-41-x increased. And the acid amount of the catalysts increased. At 360 oC, WHSV of 2 h-1, 3.0 MPa and H2/methyl laurate molar ratio of 25, all the catalysts gave the conversion of near 100%. As the Si/Al ratio decreased, the selectivity to iso-C11 and iso-C12 hydrocarbons first increased and then decreased. Ni₂P/Al CMM-41-5 gave the best performance in the hydroconversion of methyl laurate, on which the yield of the iso-C11 and iso-C12 hydrocarbons reached 43.2%. Compared with Ni₂P/AlMCM-41-5, NiP/AlMCM-41-5-TPR and Ni/AlMCM-41-5 showed higher activities for cracking and methanation due to the existence of metallic Ni.