Influence of some precursors on the physico-chemical characteristics of transition aluminas for the preparation of ceramic catalytic filters

This work deals with the development of a new type of product, a catalytic filter, which could be used for treating flue gases, coupling particulate filtration and catalytic abatement of noxious gases. The first step of this project concerned the coating of the pore walls of a ceramic candle filter (made of α Al2O3) with a high specific surface area phase (i.e. a transition alumina). This layer will act as a catalyst support. The coating was obtained by impregnation of the porous support and subsequent calcination, using three different precursors. An alumina sol (A), an aluminium nitrate solution (B) and an urea + aluminium nitrate solution (C) were compared as regards the thermal stability and surface characteristics of the transition aluminas produced. The transition aluminas were investigated in the operation temperature range which can be of potential interest for the foreseen application (400 °-800 °C). Both physico-chemical and surface characterization results indicated precursors A and C as the most promising. Preliminary coating tests have demonstrated the feasibility of a continuous, homogeneously distributed layer of transition alumina on the pore walls of the support, enabling further development of the manufacture by deposition of specific catalytic principles.