Characterization of alumina-titania mixed oxide supports - Part II: Al2O3-based supports

Bulk and surface characterization of alumina-rich Al2O3-TiO2 mixed oxides with TiO2/(Al2O3 + TiO2) molar ratios equal to 0, 0.05 and 0.1, prepared by sol-gel and impregnation procedures have been performed by XRD, DTA, surface area, FTIR, UV-Vis, FT-Raman and TPD of ammonia. The results indicate that in the case of the samples prepared by the sol-ger procedure, an increase in surface area with titania loadings is obtained, in contrast to their impregnation counterparts, where a decrease is observed. The results from XRD, Raman and UV-Vis indicate that better titania dispersions are obtained by the sol-gel procedure and that at the titania loadings used here, no separate titania particles are detected. Additionally, the UV results show that Ti cations are essentially isolated, possibly into an octahedral form and with a lower coordination. In the samples prepared by the sol-gel procedure there is no evidence of titanium oxide species on the surface, suggesting that titania is probably dissolved into the alumina bulk. These results would explain the activity trends observed in alumina-rich Mo/Al2O3-TiO2 HDS catalysts. (C) 1998 Elsevier Science B.V. All rights reserved.