Metal and acid sites instantaneously prepared over Ni/SAPO-11 bifunctional catalyst

Abstract

The Ni/SAPO-11 bifunctional catalyst for hydroisomerization of n-hexane was prepared via a novel synthesis method. It involved grinding of nickel source with amorphous precursors used for SAPO-11 followed by crystallization at 473 K for 24 h, thus avoiding the use of extra solvents in the synthesis. The highly dispersed nickel species and acid sites in the Ni/SAPO-11 bifunctional catalyst were instantaneously formed. The Ni/SAPO-11 catalyst contains framework nickel, nickel monoxide (NiO) and nickel aluminate spinel. The nickel monoxide with a size of 2–4 nm provides (de)hydrogenation function after reduction, while the framework nickel supplies more acid sites leading to an enhanced isomerization activity. The Ni/SAPO-11 catalyst shows a great synergetic effect between the metallic nickel and acid sites with a high metal-to-acid sites ratio (CNi/CA) and close proximity. A single metallic nickel site is able to balance ca. 5 acid sites (CNi/CA ≈ 0.19) over the Ni/SAPO-11 catalyst in n-hexane hydroisomerization. The high dispersion of nickel over the catalyst provides relatively excessive metal sites (CNi/CA > 0.19), leaving the rate limiting reaction to occur on the acid sites. The Ni/SAPO-11 catalyst exhibits comparable n-hexane conversion (71.2%) and iso-hexane yield (66.7%) to the classical Pt/SAPO-11 catalyst. With enhancing acidity, the Ni/SAPO-11 catalyst exhibits one of the highest iso-hexane yields reported in the n-hexane hydroisomerization, which render the new material as a promising candidate for the hydroisomerization catalysts.