CHARACTERIZATION OF ALUMINA-TITANIA MIXED-OXIDE SUPPORTS - PART II - AL2O3-BASED SUPPORTS

Bulk and surface characterization of alumina-rich Al2O3-TiO2 mixed oxi des with TiO2/(Al2O3 + TiO2) molar ratios equal to 0, 0.05 and 0.1, pr epared by sol-gel and impregnation procedures have been performed by X RD, 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-g er procedure, an increase in surface area with titania loadings is obt ained, in contrast to their impregnation counterparts, where a decreas e is observed. The results from XRD, Raman and UV-Vis indicate that be tter titania dispersions are obtained by the sol-gel procedure and tha t at the titania loadings used here, no separate titania particles are detected. Additionally, the UV results show that Ti cations are essen tially isolated, possibly into an octahedral form and with a lower coo rdination. In the samples prepared by the sol-gel procedure there is n o evidence of titanium oxide species on the surface, suggesting that t itania is probably dissolved into the alumina bulk. These results woul d explain the activity trends observed in alumina-rich Mo/Al2O3-TiO2 H DS catalysts. (C) 1998 Elsevier Science B.V. All rights reserved.