The present work is a study of each step of the process of preparation of catalysts with silica and silica-alumina matrices. The influence of operating variables on catalyst texture at each step of the process is analysed. Firstly, it has been necessary to study the textural determinations: a calorimetric method, thermoporometry, has been used. To our knowledge, it is the only technic available for wet materials (hydrogels) and dry materials (xerogels). The first step of the process is silica gelation. This unit operation has a crucial influence on the texture. The strategy of experimental design theory has been employed to underscore the important effect of the following parameters: temperature, pH, silica content in silica hydrogel, silica-alumina ratio. The results are described by a polynomial model, which predicts final product texture. As demonstrated in this work, the other unit operations (filtration, washing, spray-drying) can modify the texture of the solid. 147 refs., 73 figs., 29 tabs., 9 appendices.