CONTROL OF POROSITY AND SURFACE-AREA IN TIO2-AL2O3 MIXED OXIDES CATALYTIC SUPPORTS - A STATISTICAL APPROACH

The synthesis of TiO2-Al2O3 mixed oxides catalytic supports with a TiO2/(TiO2 + Al2O3) molar ratio equal to 0.5 was made, at various experimental conditions, by the co-precipitation of the corresponding metallic isopropoxides using ammonium carbonate as pore regulating agent. The influence of the preparation parameters (amount of ammonium carbonate, water and the procedure for the precipitation of the isopropoxides) on the surface area and pore structure of the final solid were studied using a full 2(3) factorial experimental design. Within the experimental conditions used here, the model response equations for surface area, cumulative pore volume and mean pore diameter showed good agreement with the experimental results. It was found that the amount of ammonium carbonate was the most important parameter, affecting the three responses in a positive way. The amount of water resulted in a positive influence on surface area and a negative influence on cumulative pore volume and mean pore diameter. The manner in which the precipitation was made also had a significant influence on pore diameter and pore volume. The differences in the responses may be mainly due to an interaction between the carbonate ions and the aluminium or titanium hydroxide gels which favours the link between particles leading to high surface areas and different porosities depending on the carbonate concentration.