Quantification of the in situ DRIFT spectra of Pt/K/γ-A12O3 NOx adsorber catalysts

Abstract

A method to quantify DRIFT spectral features associated with the in situ adsorption of gases on a NOx adsorber catalyst, Pt/K/Al2O3, is described. To implement this method, the multicomponent catalyst is analysed with DRIFT and chemisorption to determine that under operating conditions the surface comprised a Pt phase, a pure γ-Al2O3 phase with associated hydroxyl groups at the surface, and an alkalized-Al2O3 phase where the surface –OH groups are replaced by –OK groups. Both DRIFTS and chemisorption experiments show that 93–97% of the potassium exists in this form. The phases have a fractional surface area of 1.1% for the 1.7nm-sized Pt, 34% for pure Al2O3 and 65% for the alkalized-Al2O3. NO2 and CO2 chemisorption at 250°C is implemented to determine the saturation uptake value, which is observed with DRIFTS at 250°C. Pt/Al2O3 adsorbs 0.087μmol CO2/m2and 2.0μmol NO2/m2, and Pt/K/Al2O3 adsorbs 2.0μmol CO2/m2and 6.4μmol NO2/m2. This method can be implemented to quantitatively monitor the formation of carboxylates and nitrates on Pt/K/Al2O3 during both lean and rich periods of the NOx adsorber catalyst cycle.