Combined Zr and S XANES Analysis on S–ZrO₂/MWCNT Solid Acid Catalyst

Sulfated zirconia (S–ZrO₂) is a versatile solid acid catalyst that has wide application in hydrocarbon conversion reactions. In our previous work, we have developed well-dispersed ZrO₂ nanoparticles supported on multi-walled carbon nanotubes (MWCNT) to form a ZrO₂/MWCNT composite, which, upon sulfation, becomes a S–ZrO₂/MWCNT solid acid catalyst. While X-ray absorption spectroscopy (XAS) of this composite at the C, O, Zr K-edges has been well studied in our previous reports, XAS at the S K-edge is complicated by the Zr L-edges that bracket the S K-edge. In this study, we have used conventional S XANES, together with first-derivative and third-derivative analysis, to probe the sulfur species formed during the catalyst preparation and their interaction with Zr. We have also designed combined Zr and S XANES, which spans 400 eV and covers all three Zr L-edges and the S K-edge, to study the Zr and S interaction. Such use of multiple-edge XANES to study the S–ZrO₂ system at low X-ray energy (2,200–2,600 eV) was first reported in the previous publication of our research group, and in this paper we elaborate on the comprehensive study of our catalyst system using this method.