Regulation of synergy between metal and acid sites over the Ni-SAPO-11 catalyst for n-hexane hydroisomerization

Abstract Catalytic performance of the hydroisomerization catalysts is strongly influenced by the synergy between metal and acid sites which includes synergy in quantity and intimacy. Here, the metal-acid synergy in quantity over the Ni-SAPO-11 catalyst with excessive metal sites was improved via adding a small amount of β zeolite, and the metal-acid synergy in intimacy was also discussed. The β zeolite was introduced into the Ni-SAPO-11 (obtaining Ni-SAPO-11-β catalyst) using an in-situ solid synthesis method by grinding nickel source with crystallized β and precursors of SAPO-11 before crystallization. The β zeolite is well dispersed in the Ni-SAPO-11-β catalyst with strong interaction with SAPO-11. Compared with Ni-SAPO-11, acidity of of the Ni-SAPO-11-β catalyst is enhanced and a better metal-acid synergy in quantity is obtained. The catalytic performance was assessed for n-hexane hydroisomerization and kinetic measurements were carried out. The Ni-SAPO-11-β catalyst with relatively lower activation energy outperforms the Ni-SAPO-11 in terms of activity and isomers yield due to the improved metal-acid synergy. Its isomers yield is comparable to the optimal value over a commercial hydroisomerization catalyst (Pt based). To further study effect of the metal-acid intimacy, mechanical mixtures of Ni-SAPO-11 and β were prepared and compared with the Ni-SAPO-11-β catalyst in catalytic behavior. Nanometer or micrometer scale intimacy between nickel and acid sites perform better than millimeter or larger scale intimacy. Thus the nickel based hydroisomerization catalyst with high catalytic performance is obtained here and a preferred metal-acid intimacy is proposed.