Mössbauer emission spectroscopy of an unsupported cobalt-molybdenum hydrodesulfurization catalyst

Abstract

A⁵⁷Co doped unsupported CoMo sulfide catalyst with atomic composition ratio r=Co/(Co+Mo)=0.3 was prepared by the homogeneous sulfide precipitation method and exposed to a series of reduction-sulfidation treatments. The treated samples were analyzed by Mössbauer emission spectroscopy using very long accumulation times. Computer decomposition of the spectra revealed the presence of five different cobalt species which were identified as Co₉S₈, CoS_1+x, and three species related to the Co−Mo−S structure. Reduction of the sample under atmospheric pressure of H₂ at (and above) 573 K causes an increase of the amount of Co₉S₈ at the expense of all other species. These results afford a new insight into the stability of the Co−Mo−S structure and of the sulfur rich CoS_1+x phase under hydrotreating conditions.