The Preparation Of Nickel Phosphide Catalyst Using Ni-based Layered Double Hydroxide Precursors And Its Hydrodesulfurization Performance Of Dibenzothiophene

We now report a novel method for the synthesis of supported nickel phosphide catalysts using Ni-Al-CO32- layered double hydroxide(Ni-Al-CO32-LDH) as a nickel material and ammonium dihydrogen phosphate(NH4H2PO4) as a phosphorous material under microwave-hydrothermal(MWH) treatment by temperature-programmed reduction. Then, the addition of Co, Zn and Mg modified catalysts. The catalysts were characterized by XRD, BET,TPR, XPS, TEM, CO uptake. The hydrodesulfurization(HDS) performance of catalysts was tested using the dibenzothiophene(DBT) as a model compound.The Ni-P/ML catalysts were prepared using the precursors which were the mixture of Ni-Al-CO32-LDH and NH4H2PO4 under MWH. The results indicated that the precursors with the initial P/Ni molar ratio more than 0.8, the Ni2 P phase was observed. Furthermore, the mixture of Ni2 P phase and Ni(PO3)2 phase were observed with an initial P/Ni molar ratio above 2. The catalysts exhibited higher surface area and highly dispersed Ni metal for the main products of coprecipitation were Ni-Al-CO32-LDH with an initial Ni/Al molar ratio of 3.On the contrary, the surface area and the dispersion of Ni metal of the catalysts were decreased for the impure products of coprecipitation were Ni(OH)2 with a higher and lower initial Ni/Al molar ratio. When compared with the catalysts via a conventional impregnation method, the catalysts under MWH treatment exhibited smaller particles and highly dispersed Ni2 P particles and a higher surface area and suppressed the enrichment of P on the surface leading to more nickel sites being exposed on the surface. At the conditions of 380 °C, 3.0MPa, a weight hourly space velocity(WHSV) of 2 h-1, and H2/oil ratio of 500(volume ratio),the catalyst with an initial P/Ni molar ratio of 2 and a Ni/Al molar ratio of 3 showed the highest DBT conversion of 99.3%, 10.8% higher than that of the Ni-P/IM catalyst(88.5%)obtained via a conventional impregnation method and the corresponding HDS reaction through the direct desulfurization(DDS) route. Meanwhile, the DBT conversion of the catalysts close to 98.3% and kept for 48 h without activity loss.The results of modified catalysts indicated that Ni-based Co-Ni-Al-CO32-LDH precursors exhibited a lower degree of crystallinity for it incorporated cobalt. The results of HDS reaction indicated that Co modified supported nickel phosphide(CozNi1-z-P/ML) catalysts exhibited comparatively low DBT conversion,but the selectivity of DBT increased with thecontent of cobalt, which might be ascribed to cobalt promoted Ni atoms in pyramidal Ni(II) sites. The hydrogenation(HYD) route was enhanced by the more pyramidal Ni(II) sites.At the conditions of 380 °C, 3.0 MPa, a weight hourly space velocity(WHSV) of 2 h-1, and H2/oil ratio of 500(volume ratio), the Zn and Mg modified supported nickel phosphide(Znw Mg1-wNi-P/ML, Ni loading of 20 wt.%) catalysts showed the highest DBT conversion of81.8% with the initial Zn/Mg molar ratio of 3, 12.0% higher than that of the Ni-P/IM(Ni loading of 20 wt.%) catalysts(69.8%) obtained via a conventional impregnation method.