Effect of hetero atom on dispersion of NiMo phase on M-SBA-15 (M = Zr, Ti, Ti-Zr)
NiMo catalysts were prepared on different hetero atom doped SBA-15 supports for hydrotreatment evaluation. The nature of the hetero atom (Ti, Zr and TiZr) was observed to have a profound impact on the final molybdenum phase formed after calcination of the catalysts. Mo L3 edge XANES analysis of the catalysts along with results from Raman and XRD, show that Zr-SBA-15 support is able to disperse the Molybdenum oxide phase better than the other supports. The formation of bulk phases viz., MoO3 and NiMoO4 is accelerated in pure SBA-15 supports. Evidence of Mo present as tetrahedral MoO4 units was only found in TiZr-SBA-15 support. The presence of tetrahedral Mo species on TiZr-SBA-15 support was attributed to be due to the relative positive charge on the Zr site arising from the electronegative difference between Ti and Zr leading to [MoO4]2− stabilization. Sulfidation studies of the catalysts revealed that formation of active NiMoS phase is maximum in Zr-SBA-15 support and minimum in the SBA-15 supported catalysts. The low sulfidation of Mo in SBA-15 and TiZr-SBA-15 was due to the presence of bulk MoO3 phase. The hydrotreating activities were in confirmation with the characterization studies, with NiMo/Zr-SBA-15 and NiMo/Ti-SBA-15 exhibiting highest HDS and HDN conversions respectively.
Graphical abstract. Stabilization of [MoO4]2− on TiZr-SBA-15 support.Figure optionsDownload full-size imageDownload high-quality image (42 K)Download as PowerPoint slideHighlights► Effect of hetero atom on dispersion of NiMo phase was. ► Zr helped in dispersing molybdenum oxide phase better than others. ► Zr improved the active NiMoS phase formation. ► HDS and HDN followed the dispersion.
Journal: Catalysis Today - Volume 207, 30 May 2013, Pages 133–144