CATALYTIC CERAMIC FILTERS FOR FLUE-GAS CLEANING .2. CATALYTIC PERFORMANCE AND MODELING THEREOF

In paper 1 catalytically active filters for contemporary removal of dust and gaseous pollutants (e.g., NO(x), VOCs), were prepared and characterized. A gamma-Al2O3 layer was deposited on the pore walls of a tubular alpha-Al2O3 filter. By use of isopropyl alcohol dehydration, a reaction which is catalytically promoted by the gamma-Al2O3 itself, the capability of these activated filters of abating chemical compounds present in flue gases flowing through them is assessed. Experimental data show that nearly complete isopropyl alcohol conversion (inlet concentration 1600 ppmv) can be achieved by purely catalytic means (i.e., negligible contribution of the homogeneous reaction), and for superficial velocities of industrial interest (more than 1 m3(NTP).m-2.s-1). Two models are proposed to predict the performance of such filters, based on either a monodisperse or a bidisperse pore structure (this last one possibly taking into account the effect of catalyst nonuniform distribution in the filter pores). The first model properly fits the experimental data for high catalyst loads (obtained through repeated deposition cycles), whereas the second outperforms the first when dealing with a filter prepared with a single deposition cycle. As a consequence, it might be argued that a nonhomogeneous catalyst distribution is obtained after a single deposition, and that already after a second catalyst deposition this problem is overcome. On the basis of the above results, modification of the active filters is in progress with catalysts suitable for reactions of environmental interest (e.g., V2O5 for NO(x) reduction with NH3).