Effect of Cu deposition method on silico aluminophosphate catalysts in NH3-SCR and NH3-SCO reactions

Abstract

In this study, a commercial silicoaluminophosphate of chabazite (CHA) structure with low addition of copper phase (ca. 2–3wt.%) deposited from Cu-acetate, Cu-nitrate, and Cu-chloride precursors (Cu/CHA) with ionic-exchange and impregnation procedures was taken into consideration thanks to its known good de-NOx activity. The Cu/CHA samples were tested in the NH3-SCR (catalytic reduction of NOx by NH3) and NH3-SCO (catalytic oxidation of NH3) reactions, in the 200–500°C interval. Important differences of Cu aggregation on CHA surface were evidenced between the samples prepared by ionic-exchange and impregnation, as observed from Uv-DRS, EPR, and H2-TPR analyses. Well-dispersed Cu-phase on the CHA surface and more aggregated CuOx clusters were formed by depositing the Cu-phase with ionic-exchange and impregnation method, respectively. All the Cu/CHA samples were active and selective in the NH3-SCR reaction in the explored temperature interval, with enhanced performances of the sample prepared by impregnation. NH3-SCO selectivity to N2 was higher (80–95%) on the samples with lower Cu aggregation while sample with surface CuOx species was less selective (65%) but more active at lower temperatures. Temperature to obtain 50% of ammonia conversion (T50°C) was around 250°C, for the sample prepared by impregnation, and in the range 355–390°C for the samples prepared by ionic-exchange. The study permitted to disclose the possibility to use Cu/CHA samples in a cascade NH3-SCR and NH3-SCO reactions in a future process for zero emissions of both NOx and NH3.