Edge dispersion of supported MoS2 and WS2 catalysts as evaluated by using Co(CO)3NO as a probe molecule

SiO₂- and Al₂O₃-supported MoS₂ and WS₂ catalysts were prepared to exploit the evaluation technique of the edge dispersion of MoS₂ and WS₂ particles. A chemical vapor deposition (CVD) technique using Co(CO)₃NO as a probe molecule was used for the evaluation. Results were compared with those from conventional techniques such as NO adsorption and TEM. A proportional correlation was obtained between the amount of NO adsorption and the amount of Co atoms accommodated by the CVD technique on WS₂/SiO₂ and WS₂/Al₂O₃ catalysts, demonstrating a selective location of the Co atoms on the edges of WS₂ particles, as previously established for MoS₂ catalysts. A comparison of the amounts of NO adsorption and Co accommodation on MoS₂ and WS₂ catalysts suggested a 70% higher density of sulfur vacancy on MoS₂ particles than on WS₂ particles regardless of the support. The Co atoms on the edges of MoS₂ and WS₂ particles showed the identical NO adsorption property. We propose that Co(CO)₃NO can be used as a probe molecule to evaluate and directly compare the edge dispersions of MoS₂ and WS₂ catalysts. The dispersion of MoS₂ particles was about two times higher than that of WS₂ particles with the SiO₂-supported catalysts. With the Al₂O₃-supported catalysts, MoS₂ and WS₂ particles were dispersed to a similar extent but much more highly dispersed than the counterparts in the SiO₂-supported catalysts. The evaluation of the edge dispersion of MoS₂ and WS₂ particles by means of TEM may pose problems when SiO₂- and Al₂O₃-supported catalysts are compared. The edges of unpromoted MoS₂ particles exhibited a significantly higher intrinsic activity for the HDS of thiophene than those of WS₂ particles.