A series of NiMo/Al 2O 3 catalysts containing boron and phosphorus : Part I. Synthesis and characterization

Abstract

In this work, a series of nickel–molybdenum, nickel–molybdenum–boron and one nickel–molybdenum–phosphorus catalysts were prepared by incipient wetness impregnation method. Calcination temperature, nickel, molybdenum and boron concentrations in γ-Al 2O 3 were varied from 450 to 600 °C, 1.8 to 3.1 wt.%, 10.6 to 13.2 wt.% and 0.5 to 1.7 wt.%, respectively. Nickel–molybdenum–phosphorus catalyst was prepared using 2.7 wt.% phosphorus. All catalysts were thoroughly characterized. The catalyst containing 10.6 wt.% Mo and 2.4 wt.% Ni in γ-Al 2O 3 gave maximum BET area of 211 m 2/g. In these catalysts, the molybdenum oxides were present predominantly as polymolybdate and tetrahedral form. Addition of boron to NiMo/Al 2O 3 caused an increase in weak acid centers, whereas phosphorus caused the formation of acid centers with intermediate strength. Also, addition of boron caused the formation of crystalline B 2O 3 and MoO 3 on the catalyst surface, evident from both XRD and SEM analyses. Whereas addition of phosphorus caused the formation of irregular particle size and agglomeration on the catalyst surface, evident from SEM-EDS analysis. New Lewis and Brönsted acid sites on the catalyst surface were observed from FTIR analysis because of the addition of boron and phosphorus to NiMo/Al 2O 3.