Post-combustion emission controls

Quantification of the in situ DRIFT spectra of Pt/K/γ-Al₂O₃ NO_x adsorber catalysts

Authors
T.J. Toops, D.B. Smith, W.P. Partridge

Publication
Applied Catalysis B: Environmental 58 (2005) 245-254.

Abstract
A method to quantify DRIFT spectral features associated with the in situ adsorption of gases on a NO_x 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 1.7 nm-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 0.087 µmol CO₂/m² and 2.0 µmol NO₂/m², and Pt/K/Al₂O₃ adsorbs 2.0 µmol CO₂/m² and 6.4 µmol 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 NO_x adsorber catalyst cycle.