J.A. Martín

Alumina- and titania-based monolithic catalysts for low temperature selective catalytic reduction of nitrogen oxides

Abstract The selective catalytic reduction of NO+NO2 (NOx) at low temperature (180–230°C) with ammonia has been investigated with copper-nickel and vanadium oxides supported on titania and alumina monoliths. The influence of the operating temperature, as well as NH3/NOx and NO/NO2 inlet ratios has been studied. High NOx conversions were obtained at operating conditions similar to those used in industrial scale units with all the catalysts. Reaction temperature, ammonia and nitrogen dioxide inlet concentration increased the N2O formation with the copper-nickel catalysts, while no increase was observed with the vanadium catalysts. The vanadium-titania catalyst exhibited the highest DeNOx activity, with no detectable ammonia slip and a low N2O formation when NH3/NOx inlet ratio was kept below 0.8. TPR results of this catalyst with NO/NH3/O2, NO2/NH3/O2 and NO/NO2/NH3/O2 feed mixtures indicated that the presence of NO2 as the only nitrogen oxide increases the quantity of adsorbed species, which seem to be responsible for N2O formation. When NO was also present, N2O formation was not observed.

Study of the efficiency of monolithic activated carbon adsorption units

Although the use of activated carbons as a purification step in the treatment of gaseous effluents from industrial plants is a well established technique, when large volumes of gas need to be treated pressure drop limitations may arise from the use of conventional adsorption beds. For these applications the conformation of the adsorption bed as honeycomb monoliths with high activated carbon content take advantage of the almost null pressure drop of these open channel structures and significantly improves the handling characteristics. In this study a commercial activated carbon was conformed as a ceramic monolith using a natural magnesium silicate as the agglomerating agent. The adsorption studies employed ortho-dichlorobenzene (o-DCB) as a probe molecule, since it can be considered as representing approximately half a molecule of tetra-chloro-dibenzene-dioxin (TCDD) the most toxic isomer of the dioxin family. It has been shown that the dynamic adsorption capacity of these units at 30°C was equivalent to the micropore volume. However, in industrial applications the adsorption step should take place at higher temperatures so that the gases exiting from the chimney rise rapidly into the upper atmosphere. Thus, the adsorption capacities of these units were determined over a range of temperatures from 30°C to 150°C at linear gas velocities between O.3m·s −1 to 2m·s −1 . The effects of variation in the monolith geometry: overall length versus gas linear velocity, on the dynamic adsorption capacity were studied in order to predict the optimum monolith dimensions depending on the gas flow to be treated. Key words: Activated Carbon, Gas Purification, Honeycomb monolith, VOCs.