Quantification of the in situ DRIFT spectra of Pt/K/γ-A12O3 NOx adsorber catalysts |
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Authors: | Todd J. Toops D. Barton Smith William P. Partridge |
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Affiliation: | Oak Ridge National Laboratory, 2360 Cherahala Blvd., Knoxville, TN 37932-1563, USA |
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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 1.7 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/m2and 2.0 μmol NO2/m2, and Pt/K/Al2O3 adsorbs 2.0 μmol CO2/m2and 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 NOx adsorber catalyst cycle. |
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Keywords: | NOx adsorber catalysts Lean NOx traps Quantified DRIFTS Chemisorption Potassium Pt γ-Al2O3 Pt/K/Al2O3 |
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