Citric acid-assisted hydrothermal method for preparing NiW/USY–Al2O3 ultradeep hydrodesulfurization catalysts

This article presents a novel method for preparing NiW/USY–Al2O3 ultradeep hydrodesulfurization (HDS) catalysts via combined citric acid-assisted hydrothermal dispersion of active metals and hydrothermal modification of HY zeolite. The results showed that the citric acid-assisted hydrothermal method yielded monomeric W species as W precursors that were well dispersed by the interaction between citric acid and WO3 particles and were suitably stacked by the preferential interaction between citric acid and the support, guaranteeing a compromised dispersion and stacking of the supported Ni–W–S phases. The citric acid-assisted hydrothermal modification combined the framework dealumination of the HY zeolite and the removal of nonframework Al species, exposing more Brønsted acid sites on the catalyst. The finely tuned morphology of the Ni–W–S phases and the suitably adjusted Brønsted acidity of the zeolite endowed the resulting NiW/USY–Al2O3 catalyst with outstanding hydrogenation and hydrogenolysis activities for 4,6-dimethyldibenzothiophene and coking diesel HDS.