A comparative investigation on the properties of Cr-SBA-15 and CrO x/SBA-15

Abstract

High-surface area and well-ordered mesoporous Cr-incorporated SBA-15 (Cr-SBA-15) and SBA-15-supported chromia (CrO x /SBA-15) with Cr surface density = 0.05–1.11 Cr-atom/nm 2 have been prepared, respectively, using the one-step synthesis and incipient wetness impregnation method, and characterized by AAS, XRD, BET, ESEM, TEM, XPS, laser Raman, UV-Vis, FT-IR, and H 2-TPR. It is observed that the Cr-SBA-15 and CrO x /SBA-15 samples showed an evolution of surface morphology from long chain-shaped to short rod-like and further to an irregularly spherical architecture at elevated Cr content, which might arise from the interaction of Cr ions or CrO x domains with SBA-15. There were co-presence of tetrahedrally coordinated mono- and poly-chromate (Cr 6+) as well as octahedrally coordinated Cr 3+ species in Cr-SBA-15 and CrO x /SBA-15, with the Cr 6+ species being dominant at Cr surface density ≤0.22 Cr-atom/nm 2 in Cr-SBA-15 and Cr ≤0.54 Cr-atom/nm 2 in CrO x /SBA-15, whereas the amount of the Cr 3+ species increased markedly at Cr surface density ≥0.53 Cr-atom/nm 2 due to the formation of crystal Cr 2O 3 phase. Maximal Cr incorporation into Cr-SBA-15 and one monolayer surface CrO x coverage on CrO x /SBA-15 occurred at Cr surface density ≤0.53 Cr-atom/nm 2 and <1.11 Cr-atom/nm 2, respectively. The CrO x /SBA-15 samples exhibited better reducibility than the Cr-SBA-15 samples, with the best reducibility exhibited at Cr surface densities of 0.54 and 0.12 Cr-atom/nm 2, respectively.