Dibenzothiophene hydrodesulfurization over cobalt phosphide catalysts prepared through a new synthetic approach: Effect of the support

Abstract

Several cobalt phosphide catalysts, with a cobalt loading of 10wt%, were prepared by means of temperature-programmed reduction (TPR) of cobalt(II) hydrogenphosphite (Co(HPO3H)2) supported on different carriers: two mesoporous supports, MCM-41 and zirconium doped MCM-41 (MCM-Zr), as well as two commercial supports, SiO2 (Cab-osil) and γ-Al2O3. The purpose of this work is to study the role of the support on the formation of CoP or Co2P and the analysis of the catalytic activity in the hydrodesulfurization (HDS) of dibenzothiophene (DBT). It is the CoP phase which is favoured on these catalysts under the given experimental conditions, except for that supported on γ-Al2O3 (CoP-10 (Al)), which only displays the diffraction lines of the Co2P phase after the reduction process. The interaction support–precursor salt seems to determine which of the phases is formed. The catalytic results showed that this family of catalysts obtained high DBT conversion values at high temperatures, mainly via the direct desulfurization (DDS) route, i.e., yielding biphenyl (BP) as majority product and attaining turnover frequency (TOF) values of 0.87×10−3s−1. The stability with time on stream showed that the silica (Cab-osil) supported catalyst, CoP-10 (Cab), was highly stable with time on stream (48h) with conversion values close to 100% and with a performance similar to that of Ni2P catalysts and better than other cobalt phosphide catalysts reported in the literature. In contrast, the CoP-10 (Zr) and CoP-10 (Si) samples decrease in activity after 16h on stream, although their conversions are between 65% and 70% after 48h on stream. Finally, the CoP-10 (Al) catalyst provided lower conversion values and underwent deactivation with time on stream due to the low activity of the Co2P compound formed on this sample. Furthermore, the analysis of the spent catalyst showed the presence of sulfur on the surface, assigned to the formation of phosphosulfide species.