Ligand assistance via solid-state coordination for promoting nickel dispersion over the Ni/Beta hydroisomerization catalyst

Abstract

Hydroisomerization of alkanes is a vital process to improve cold flow properties of lubricant oil and increase octane number of gasoline in petrochemical industry. Non-noble metal catalysts used in this process always suffer from low metal dispersion due to weak interaction between metal species and support. Herein, density functional theory (DFT) calculations show that Ni2+ prefers to coordinate with two carboxyl oxygen of glycine in the absence of water. It makes the amino groups well exposed, forming strong interaction between the nickel-complex and aluminum groups over Beta zeolites. In contrast, Ni2+ coordinates with amino nitrogen and one of carboxyl oxygen of glycine in the presence of water. This structure has weaker interaction with support due to the absence of exposed amino groups. Based on the DFT results, a solid-state ligand assistance strategy was developed to increase metal dispersion over the Ni/Beta catalyst. UV-vis, XPS and FTIR characterization results match well with the DFT results and confirm the strong interaction between the nickel-complex and support in the absence of water. The Ni/Beta catalyst has smaller particle size of nickel oxide (0.8 nm) than that of the catalyst prepared by liquid-state ligand assistance method (5.1 nm). With increasing metal dispersion, the Ni/Beta outperforms the counterpart by liquid-state ligand assistance method and exhibits comparable isomers yield to commercial Pt catalysts in n-hexane hydroisomerization. This work provides a promising approach to boost metal dispersion on catalysts.