One-pot synthesis of highly efficient bifunctional Ni/SAPO-11 hydroisomerization catalysts via two-step solid phase crystallization strategy

Abstract

The hydroisomerization process significantly influenced the production of premium-grade environmentally friendly gasoline products. The developing cost-effective and highly efficient hydroisomerization catalysts are the pivotal factor. In this work, to deal with the issue of increased particle size in Ni/SAPO-11 catalyst, traditional hydroisomerization catalysts, with complexity of the preparation process, the one-pot two-step solid phase crystallization approach was employed to fabricate fine-grained Ni/SAPO-11 catalysts. The catalyst was subjected to characterization for the crystal phase structure, pore structure, morphology, acidity and metal coordination environment. The specific surface area and mesoporous pore volume were increased, while the crystal size was smaller. Furthermore, the weaker acid sites and medium-strong acid site were possessed, which was suitable for hydroisomerization reactions. Moreover, compared with the one-step solid phase synthesis method, the lower content of nickel aluminate inert component was contained on the catalyst prepared by two-step solid phase synthesis. In hydroisomerization of n-hexane, it was indicated the increase of conversion of n-hexane and the selectivity for i-hexane to 78.8 % and 93.5 % on Ni/SAPO-11 catalysts prepared by two-step solid phase synthesis process, respectively. This was due to that the reduction in crystal size could decrease the residence time of olefin intermediates and carbon cations within the catalyst pores, thereby preventing cracking reactions.