Hydroisomerization of n-dodecane on a new kind of bifunctional catalyst: Nickel phosphide supported on SAPO-11 molecular sieve

• SAPO-11 supported nickel phosphide catalysts were used for hydroisomerization.
• Nickel phosphide/SAPO-11 showed higher isomerization selectivity than Ni/SAPO-11.
• The roles of P in nickel phosphide contribute to high isomerization selectivity.
• A balance between the acid and Ni sites was required.
• Isododecane yield reached 65% on Ni2P/SAPO-11 containing 3 wt.% Ni.

A new type of nickel phosphide catalysts supported on SAPO-11 was used for the hydroisomerization of n-dodecane. Their properties were characterized by means of N2-sorption, H2-TPR, XRD, XPS, DRIFTS of adsorbed pyridine, CO chemisorption, and NH3-TPD and H2-TPD. The effects of the Ni/P ratio and the nickel content on catalyst performance were investigated. For comparison, the property and performance of Ni/SAPO-11 were also considered. Compared to Ni/SAPO-11, SAPO-11 supported nickel phosphides had higher isomerization selectivity due to their lower hydrogenolysis activity. As the Ni/P ratio deceased, the n-dodecane conversion decreased, while the isododecane selectivity reached its maximum at the Ni/P ratio of 1. As the nickel content increased, the n-dodecane conversion and isododecane selectivity reached their maximum. In short, a balance between medium strength acid sites and Ni sites was required for obtaining high n-dodecane conversion and isododecane selectivity. Moreover, there was a synergism between the Ni sites and the medium strength acid site. Under suitable conditions, the isododecane yield reached about 65% on Ni2P/SAPO-11 containing 3 wt% Ni.