The effect of modifying alumina with sulfate and phosphate on the catalytic properties of Mo/Al2O3 in HDS reaction

The properties of alumina modified with sulfate (AlS) and phosphate (AIP) and Mo catalysts supported on modified alumina (Mo/AIP and Mo/AIS) were characterized by IR, XRD, DRS, ESR, temperature-programmed sulfidation (TPS), and the oxygen chemisorption. Catalytic activities of Mo/AIP and Mo/AlS were evaluated in the thiophene HDS reaction. The point of zero charge (PZC) of the modified alumina and the amount of Mo adsorbed on modified alumina decreased with increasing modifier content. The bonding mode of sulfate on alumina changed with increasing sulfate content. The decrease in the PZC of AlP and in the number of the adsorption sites for Mo anions on AlP facilitated the formation of polymolybdate on Mo/AlP. The sulfidation of Mo catalyst was also promoted in Mo/AlP. The catalytic activity in the thiophene HDS reaction of phosphate-modified catalysts was higher than that of Mo/Al2O3 when the phosphate content was less than 5 wt%. Bulk MoO3 was formed more easily in Mo/AlS than in Mo/AIP. The suppression of the sulfidation of Mo/AlS may be explained by the formation of bulk MoO3 and the presence of the S=0 group. The HDS activity of sulfate-modified catalysts was lower than that of Mo/Al2O3, regardless of the sulfate content.