Urea–organic matrix method: an alternative approach to prepare CoMoS2/γ-Al2O3 HDS catalyst

Abstract

An alternative method using urea as organic matrix to prepare CoMoS2/γ-Al2O3 HDS catalysts based on drying (urea-matrix drying, UMxD) or combustion (urea-matrix combustion, UMxC) processes have been developed and compared with the traditional wet methods (sequential, WSI, and co-impregnation, WCI) and chelating method (ChM) in order to determine their influence on the HDS catalytic process. The catalytic performance of the alumina-supported CoMo catalysts was evaluated in a continuous flow reactor using the hydrodesulfurization of thiophene as a model reaction. The oxidic precursors and the sulfurized catalysts were characterized using elemental analysis, X-ray diffraction (XRD), laser Raman spectroscopy (LRS), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), high resolution transmission electron microscopy (HRTEM), temperature-programmed reduction (TPR-H2) and BET surface area measurements. It has been found that the urea–organic matrix method facilitates well-dispersed Co- and Mo-oxo species (mono and polymolybdate) formation, whereas the conventional impregnation techniques lead to mixed-metal oxides formation. This was reflected in the sulfurized phase morphology and structural disorder degree of carbon material deposited on the catalyst surface upon the sulfurizing process using thiophene as sulfurizing agent. The preparation method notably affects the thiophene-HDS specific rates, showing the following activity order: UMxD>UMxC>WCI>WSI>ChM, while an opposite trend for relative rate of HYD to HDS reactions was observed. A carbon structural effect together with high stacking degree of the sulfurized phases seem to be mainly responsible for the high HDS activity of alumina-supported CoMo catalysts prepared by the urea–organic matrix method, which appears very promising for HDS catalysts development.