Thiophene hydrodesulfurization over nickel phosphide catalysts: effect of the precursor composition and support

Abstract

Silica- and alumina-supported nickel phosphide (Ni x P y ) catalysts have been prepared, characterized by bulk and surface sensitive techniques, and evaluated for the hydrodesulfurization (HDS) of thiophene. Series of 30 wt% Ni x P y /SiO 2 and 20 wt% Ni x P y /Al 2O 3 catalysts were prepared from oxidic precursors with a range of P/Ni molar ratios by temperature-programmed reduction (TPR) in flowing H 2. Oxidic precursors with molar ratios of P/Ni = 0.8 and 2.0 yielded catalysts containing phase-pure Ni 2P on the silica and alumina supports, respectively. At lower P/Ni ratios, significant Ni 12P 5 impurities were present in the Ni x P y /SiO 2 and Ni x P y /Al 2O 3 catalysts as indicated by X-ray diffraction. The HDS activities of the Ni x P y /SiO 2 and Ni x P y /Al 2O 3 catalysts depended strongly on the P/Ni molar ratio of the oxidic precursors with optimal activities obtained for catalysts containing phase-pure Ni 2P and minimal excess P. After 48 h on stream, a Ni 2P/SiO 2 catalyst was 20 and 3.3 times more active than sulfided Ni/SiO 2 and Ni–Mo/SiO 2 catalysts, respectively. A Ni 2P/Al 2O 3 catalyst was 2.7 times more active than a sulfided Ni/Al 2O 3 catalyst but only about half as active as a sulfided Ni–Mo/Al 2O 3 catalyst.