Metal-acid balance in the in-situ solid synthesized Ni/SAPO-11 catalyst for n-hexane hydroisomerization

Abstract

The catalytic performance of metal-acid bifunctional catalysts is strongly affected by metal-acid balance. However, the key parameter has not been systematically investigated for non-noble metal based hydroisomerization catalysts. Such a study was provided here for Ni/SAPO-11 catalyst prepared by in-situ solid synthesis method via varying nickel loading. Instead of channel properties, activity and selectivity of the catalyst were predominately governed by the metal-acid balance expressed by metal to acid sites ratio (CNi/CA). The activity per acid site (TOF) was shown to increase with CNi/CA until a plateau was reached, an observation that is in agreement with the classical bifunctional mechanism. Reaction scheme over catalysts with higher CNi/CA ratio was more approaching to the “ideal” consecutive one, and a higher selectivity to isomers was obtained. Result indicated that a single nickel site in the Ni/SAPO-11 catalyst was capable of feeding ca. 5 acid sites in n-hexane hydroisomerization. This work contributes to a deep insight into the metal-acid balance in nickel based hydroisomerization catalysts and can be extended to many other non-noble metal based bifunctional catalysts.