Structural analysis of potential active sites in metallo-zeolites for selective catalytic reduction of NOx.: An attempt for the structure versus activity relationship

The paper reviews the state of the art of the activity of metallo-zeolites and Ag/alumina in catalytic abatement of nitric oxides from exhaust gases from lean-burn combustion processes. The review is centered on the selective catalytic reduction of NO, by hydrocarbons to molecular nitrogen (HC-SCR-NOx) over Co-, Fe- and Ag-zeolites, and Ag/alumina, i.e. those providing high and stable deNO(x) activity in streams containing a high excess of water vapor existing under lean-burn combustion conditions. Analysis of the structure of these catalysts is described by employing a combination of spectral, diffraction, adsorption and redox techniques. An attempt is made to correlate the analyzed structure with the HC-SCR-NOx activity.