Influence of CO2 and H2O co-feeding in the NOx abatement by SCR over an efficient Cu-CHA catalyst.

Abstract

Cu-SAPO-34 materials with 2 wt% of copper synthesized in one pot with all the copper inside the framework are hydrothermally stable. Copper oxide species were not detected by XRD after thermal and hydrothermal aging at 750 C. CO2 and H2O molecules are retained on Cu-SAPO catalyst and are related to CO2 adsorption aided by water involving the Cu-species. Copper species coordination is modified by the reaction atmosphere and the species are directly involved in the SCR-process. A decrease in the ammonia storage capacity in the presence of water has been justified due to the cooperative competition between the ammonia and water adsorption and/or CO2 carbonation over the same sites. Higher coordinated Cu species localized inside of CHA-framework, up to a loading close to 4% with this methodology, are highly efficient in the removal of NOx by reaction with ammonia, in the presence of oxygen, water (1.5%) and CO2 (0.3%) as reaction atmosphere. The SCR mechanism is essentially the same as in dry conditions because the Cu2+/Cu+ ions, in equilibrium with H2O+CO2, are the active species in the SCRreaction. Hydrated-carbonated Cu(II) and hydrated-carbonated Cu(I) species are associated with the redox-chemistry of NOx abatement as responsible for the improvement in the standard SCR; favoring the hindering of ammonia oxidation and nitrate decomposition. In the SCR temperature range, the conversion values registered for this catalyst are higher than 80% with total selectivity to N2.