An investigation of NOx storage on Pt–BaO–Al2O3

Abstract

A series of samples containing 5-wt% or 20-wt% BaO on γ-Al 2 O 3 with different loadings of Pt were prepared and examined for their NO 2 adsorption properties using temperature programmed desorption (TPD), temperature programmed reduction (TPR), and x-ray diffraction (XRD). For calcination at 873 K or above, BaO/Al 2 O 3 formed BaAl 2 O 4. While carbonates were found to be unstable on the aluminate phase, NO 2 reacted with the aluminate to form bulk Ba(NO 3) 2 and Al 2 O 3 , even at room temperature. With BaO/Al 2 O 3 , reaction to form the nitrate required slightly higher temperatures because of the need to displace CO 2 ; however, pulsing NO 2 over pure Ba(CO 3) showed rapid reaction to form CO 2 and NO in the gas phase, along with Ba(NO 3) 2 , at 673 K. The decomposition temperature for Ba(NO 3) 2 shifted by more than 100 degrees when TPD was carried out in vacuum rather than in a carrier gas, showing that re-equilibration with the gas phase is important in the decomposition process. The addition of Pt had a minimal effect on the thermal stability of the nitrates but was essential for the reduction of the nitrate in H 2. Since a relatively small amount of Pt was sufficient to cause the complete reduction of the Ba(NO 3) 2 phase at temperatures below 400 K, it appears that the nitrates must be extremely mobile within the Ba-containing phase. Finally, trapping studies of NO 2 at 573 K, with or without 10% CO 2 in the gas phase, showed no measurable difference between BaO/Al 2 O 3 and BaAl 2 O 4 , with or without CO 2 .

Effect of Co addition to Pt/Ba/Al2O3 system for NOx storage and reduction

“…In addition, oxygen desorption peaks were observed over the same temperature range. It has been reported that the nitrate desorption may follow the equation: Ba(NO 3 ) 2 → BaO + 2NO 2 + 1/2O 2 [40]. However, the signal of NO 2 (m/e = 46) in our experiment was very weak and the main desorption feature was NO (m/e = 30) and O 2 (m/e = 32).…”

Formation and removal of Ba-carbonates or carboxylates on Pt/BaO/γ-Al2O3 lean NOx traps

“…Any discussion about the application of these LNTs to realistic cases is not complete without inclusion of CO 2 and H 2 O, which are invariably present in the exhaust of lean burn engines. It is well known that CO 2 and H 2 O result in the presence of carbonate and hydroxide species on Ba which are detrimental to the NO x storage capacity of the traps due to morphological changes in the Ba phase caused by H 2 O and the thermodynamic stability of the surface species resulting in slower NO x adsorption kinetics [1,[10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Many of these studies were performed on samples with various Pt and Ba loadings, at different CO 2 and H 2 O concentrations in the lean feed with various lean-rich cycling protocols, and at a range of operating temperatures.…”

NO x Storage at Low Temperature over MnO x –SnO2 Binary Metal Oxide Prepared Through Different Hydrothermal Process

“…A typical NSR catalyst consisted of three parts: precious metal as an oxidative and reductive, alkali or alkaline-earth oxide as a storage component and support, for example Pt/BaO/Al 2 O 3 [4][5][6]. Under lean-burn condition, NO was oxidized to NO 2 and stored in the catalyst.…”