Vanadium loaded carbon-based catalysts for the reduction of nitric oxide

Abstract

Carbon-based SCR catalysts for the reduction of NO with NH3 at low temperatures have been prepared using activated carbons obtained from a local Spanish coal, doped with several vanadium compounds. Among them, the ashes of a petroleum coke (PCA) were also employed. Both the catalysts and the carbon supports have been characterized by means of N2 and CO2 physisorption, NH3 and O2 chemisorption and temperature programmed desorption (TPD). The activity of the catalysts has been tested in a laboratory-scale unit, measuring significant conversions of NO (above 50%) with almost 100% selectivity toward N2 at 150°C. The feasibility of using the petroleum coke ashes as the active phase was confirmed comparing the activity of the catalysts doped with these residues, with the one measured for the catalysts prepared using model vanadium compounds. The physical–chemical features of the carbon support resulted of key importance for achieving a considerable catalytic activity. The values of apparent energy of activation calculated for the catalysts presented in this paper were very similar to other carbon-based catalysts and smaller than the ones corresponding to TiO2-supported systems. The gas residence time on the catalytic bed influences the catalytic activity to a great extent, thus being a determinant parameter for designing the SCR de-NOx unit. To avoid ammonia slip, inlet concentrations of NH3 has to be little under the stoichometric NH3/NO ratio (∼0.7). The catalysts stability was tested in terms of carbon support gasification followed by termogravimetric analysis and gas chromatography. The activity of the catalysts was maintained at least over 24h of reaction.