Al2O3−TiO2 materials were prepared by the sol−gel method using different additives (HNO3, NH4OH, and CH3COOH) and their physical properties were evaluated by various techniques. The materials at two compositions (Al/Ti atomic ratios = 2 and 25) were synthesized at 278 K and calcined at temperatures from 573 to 1173 K. The solids were characterized by TGA, DTA, XRD, BET, and SEM. The complexing (CH3COOH) and the basic (NH4OH) additives led to solids with high pore volumes and broad pore size distributions. On one hand, very high surface areas (525 m2/g for solids calcined at 773 K) were found for samples prepared with CH3COOH. On the other hand, high-temperature stability was obtained with NH4OH addition (200 m2/g, for Al2O3-rich samples at 1173 K). HNO3-catalyzed samples showed lower surface areas and pore volumes. Surface areas and sintering behavior were a function of TiO2 content. TiO2-rich samples showed higher surface areas (773 K) than Al2O3-rich oxides, but at more severe conditions they suffered a severe specific area loss. The alumina-rich formulations showed good stability in the whole range of temperatures studied.

No abstract

No abstract

No abstract

No abstract

No abstract

No abstract

The effect of the synthesis method over the catalytic behavior was investigated in Pt and PtSn catalysts. Catalysts synthesized using the one-step sol−gel method (OSSGM) were compared with those synthesized by conventional impregnation in the n-heptane reforming reaction at 500 °C and 1 atm, showing that the one-step sol−gel synthesis enhances both the activity and the resistance to deactivation by coking. The formation of coordinatively unsaturated aluminum (AlV) in the materials is promoted by the OSSGM, and it can be related to the increment in both their acidity and their platinum dispersion. Therefore, the bifunctionality of the catalysts, measured as the metal/acid site ratio (Ψ parameter), was also correlated to the AlV species. Higher values of Ψ implied a higher resistance to deactivation, higher rates of toluene production, and an inhibition of benzene induced by the OSSGM.