Regulation of the inter-relationship between the dispersion of Ni and suitable SAPO-11 acidity via solid-state synthesis in n-hexane hydroisomerization

Abstract

The isomerization of n-alkanes through hydrogenation is a crucial process for producing high-quality, clean oil products. The development of high-performance and cost-effective hydroisomerization catalysts is pivotal to this process. In this work, by leveraging the spatial steric effect of SAPO-11, a highly efficient Ni/SAPO-11 catalyst was prepared through a one-step solid-phase synthesis method to enhance isomerization activity. As well as its physicochemical properties, the effects of the aluminum source, template agent, silicon–aluminum ratio, crystallization temperature, crystallization time and nickel–aluminum ratio on the preparation of Ni/SAPO-11 catalyst were investigated. Utilizing pseudo-boehmite, phosphoric acid, silica sol, dipropylamine and nickel nitrate at the molar ratio of 1.0 Al₂O₃ : 1.0 P₂O₅ : 0.4 SiO₂ : 2.0 DPA : 0.2 NiO under crystallization at 200 °C for 24 h obtained a Ni/SAPO-11 catalyst with suitable acid properties for the isomerization process. Three forms of Ni species were obtained by using a Ni/SAPO-11 catalyst: NiO with hydrogenation ability after reduction, framework nickel with acidic sites, and nickel–aluminum spinels. More importantly, achieving a balance between the dispersion of hydrogenation active sites and suitable acid properties with isomerization active sites was essential for highly effective hydroisomerization. In the hydroisomerization of n-hexane, optimizing the relationship between the catalyst metal sites and acidic sites resulted in a 70.9% conversion of n-hexane with a selectivity for isohexane of 93.0% over the Ni/SAPO-11 catalyst.