First in situ temperature quantification of CoMoS species upon gas sulfidation enabled by new insight on cobalt sulfide formation

Abstract

Insights into the cobalt sulfide formation upon sulfidation (10% H2S/H2) of cobalt-based materials with 4 wt % CoO supported on alumina or silica were obtained by Quick-X-ray absorption spectroscopy monitoring analysed by multivariate curve regression analysis. A common pathway is evidenced involving the formation of supported defective CoS2 species transformed around 200-250°C into supported Co9S8 species. Upon cooling down under sulfiding atmosphere, a reverse transition towards CoS2 was observed by XAS multivariate analysis and supported by Raman analysis. This reverse transition is sensitive to the Co9S8 crystallite size: the smaller the Co9S8 nanoparticles the higher the amount of formed CoS2 after cooling. The knowledge gained on the sulfidation of monometallic cobalt-based catalysts has been used in order to isolate the X-ray absorption spectrum of the CoMoS active species formed during the sulfidation of a calcined cobalt-promoted HDS catalyst. The evolution of the concentration of the CoMoS species upon temperature increase is determined for the first time, together with those of the pristine oxidic CoMo catalyst and CoS2 and Co9S8 supported species. Although the conversion of Co9S8 into CoS2 is still observed for the HDS catalyst when temperature is decreased under H2S/H2 atmosphere, no change of the CoMoS percentage is evidenced.

Surface-dependent activity of model CoMoS hydrotreating catalysts

“…Processing of the XAS data was carried out with the Demeter package [32]. The reference Co 9 S 8 XAS spectrum was kindly provided by V. Briois (SOLEIL synchrotron) following a temperature-programmed method reported by Plais et al [33].…”

“…11) by comparison with references in the oxide (cobalt nitrate or Co 2+ ) and sulfide states (Co 9 S 8 ). It has to be noted that XANES alone cannot discriminate Co 9 S 8 from the CoMoS phase although a chemometric analysis method has been recently developed to extract the CoMoS contribution from EXAFS spectra of CoMo catalysts [33]. From the Co 2+ and Co 9 S 8 reference spectra (Fig.…”

Role of Phosphorus and Triethylene Glycol Incorporation on the Activity of Model Alumina‐Supported CoMoS Hydrotreating Catalysts

“…Conversely, the presence of a distinct pre‐edge (7709 eV) as well as the onset of the edge aligned with the shoulder of Co 9 S 8 (7717 eV) on the four experimental spectra suggests the presence of a sulfide phase [10] . Co 9 S 8 is taken as a reference of a sulfide phase as a general term since XANES can hardly discriminate Co atoms in either Co 9 S 8 or a CoMoS phase, although a chemometric analysis method has been recently developed to extract the CoMoS contribution from EXAFS spectra of CoMo catalysts [28] . Linear combination fitting of the XANES spectra of the model catalysts on the C(0001) and R(1 02) planes using Co 9 S 8 and oxidic Co 2+ reference spectra (Figure 3) allowed to calculate approximate percentages of cobalt in the sulfide (Co 9 S 8 and CoMoS) and oxide phases.…”

“…Processing of the XAS data was carried out with the Demeter package [51] . The reference Co 9 S 8 XAS spectrum was kindly provided by V. Briois (SOLEIL synchrotron) following a temperature‐programmed method reported by Plais et al [28] …”

“…[10] Co 9 S 8 is taken as a reference of a sulfide phase as a general term since XANES can hardly discriminate Co atoms in either Co 9 S 8 or a CoMoS phase, although a chemometric analysis method has been recently developed to extract the CoMoS contribution from EXAFS spectra of CoMo catalysts. [28] Linear combination fitting of the XANES spectra of the model catalysts on the C(0001) and R(1 � 102) planes using Co 9 S 8 and oxidic Co 2 + reference spectra (Figure 3) allowed to calculate approximate percentages of cobalt in the sulfide (Co 9 S 8 and CoMoS) and oxide phases. The results were compared to those obtained by XPS (Table 1).…”