The infrared and Raman spectra of a sulfur-resistant NiO/Cr<sub>2</sub>O<sub>3</sub>/MgSiO<sub>3</sub> methanation catalyst are presented and compared to the spectra of the catalyst after being reduced, sulfided, and tested for methanation activity. The molecular structure of the catalyst is shown to be represented by NiO and MgO dispersed in a quasi-tridimensional Cr-O-Si network. Reduction and sulfiding reorders this network and alters the SiO<sub>n</sub> coordination while reducing Cr<sup>6+</sup> to Cr<sup>3+</sup> or Cr<sup>2+</sup>. The data indicate that the SO<sub>4</sub><sup>−2</sup> which is present after sulfiding and methanation testing may have been formed during the methanation reaction.
J. M. Stencel, E. B. Bradley, and Fred R. Brown, "Infrared and Raman Spectra of a Sulfur-resistant Methanation Catalyst," Appl. Spectrosc. 34, 319-323 (1980)