Chelating-agent-protected nickel incorporation into TS-1 framework for enhanced phenol hydroxylation catalysis with improved stability and efficiency

Abstract

The phenol hydroxylation reaction represents a promising green strategy for the sustainable production of dihydroxybenzene. However, the high cost and mass transfer limitations associated with traditional titanium silicalite-1 (TS-1) catalysts significantly hinder their industrial scalability. In this study, a novel chelating-agent-protected technique, combined with a tetrapropylammonium hydroxide (TPAOH) hydrothermal treatment strategy, was developed to achieve the uniform incorporation of nickel ions into the TS-1 framework. This dual approach effectively redistributed the charge density, modulated the surface acidity, and introduced hierarchical structures, thereby addressing the intrinsic diffusion and catalytic limitations of conventional microporous TS-1. Unlike conventional nickel modification methods, the chelating-agent-protected strategy successfully prevented nickel ion reduction or the formation of nickel oxide particles, ensuring highly dispersed and framework-integrated nickel species. The incorporation of nickel further enhanced the synergistic interaction with titanium, significantly reducing the binding energy of tetrahedral framework titanium (Ti⁴⁺) and enhancing the electrophilicity of active catalytic sites. These structural and electronic improvements translated into superior catalytic performance, with the framework-engineered nickel-modified catalyst (CSD(1.68)@HTS-1) achieving a phenol conversion rate of 31.0 %, compared to 25.3 % for unmodified HTS-1. Furthermore, the selectivity for hydroquinone increased from 57.8 % to 59.3 %. The CSD(1.68)@HTS-1 catalyst also demonstrated excellent structural stability and recyclability, maintaining consistent activity and selectivity over multiple reaction cycles. This innovative framework-engineering strategy provides a cost-effective and scalable approach for the design of high-performance nickel-modified zeolite catalysts, offering new insights into the development of sustainable and efficient catalytic systems for industrial applications.