Adsorption and reaction of NO2 on ordered alumina films and mixed baria–alumina nanoparticles: Cooperative versus non-cooperative reaction mechanisms

Model NOx Storage Materials at Realistic NO2 Pressures

“…[16][17][18][19][20] More recently, the reaction of NO 2 with BaO deposits on Al 2 O 3 / NiAlA C H T U N G T R E N N U N G (110) were studied by Szanyi et al [21][22][23][24] and our group. [25][26][27][28][29][30][31] Some of the key results of these studies may be summarized as follows: A strong interaction with the support gave rise to interdiffusion of Al 3 + and Ba 2 + ions, resulting in the formation of barium aluminate-like nanoparticles. [29] As the exact stoichiometry was not established, we denoted these particles BaAl 2x O 1 + 3x .…”

“…Upon annealing, a well-defined composition was established, which was tentatively attributed to a barium aluminate stoichiometry ("BaAl 2 O 4 "). [26,29,31] Particles with a higher Ba 2 + /Al 3 + ratio could be prepared by avoiding high-temperature treatment during preparation. [26,29] Pure BaO layers were prepared by Szanyi and co-workers by deposition of thick films of BaO on thick Al 2 O 3 supports.…”

“…[26,29,31] Particles with a higher Ba 2 + /Al 3 + ratio could be prepared by avoiding high-temperature treatment during preparation. [26,29] Pure BaO layers were prepared by Szanyi and co-workers by deposition of thick films of BaO on thick Al 2 O 3 supports. [23,24] These different Ba-containing model systems showed pronounced differences with respect to reactivity: On the BaAl 2x O 1 + 3x nanoparticles, reaction…”

“…Szanyi et al detected nitrite-nitrate pair formation upon reaction with NO 2 on pure BaO, [23,24] whereas on BaAl 2 O 4 nanoparticles such pairs were only detected at low temperature. [26] Surface IR spectroscopy allows the detection of numerous surface species and intermediates. [27] To some extent, the assignment of the observed bands has been controversial and we refer to the literature for a more detailed discussion.…”

NO Oxidation Catalysis on Pt Clusters: Elementary Steps, Structural Requirements, and Synergistic Effects of NO2Adsorption Sites

“…[40][41][42] Low exposures of NO 2 (<10 -4 Pa-s) to BaO surfaces formed nitrite and nitrate species at 100 K, but only nitrites at 300 K, consistent with molecular adsorption of two NO 2 species onto a single BaO site at the lower temperatures (step 2a of Scheme 2). 43,44 We have observed that NO and NO 2 were consumed in equimolar amounts upon exposure of BaCO 3 / Al 2 O 3 to NO/NO 2 mixtures (170 Pa NO, 30 Pa NO 2 , 573 K), 45 consistent with the exclusive formation of nitrites via concurrent adsorption of NO and NO 2 (Scheme 2, step 2), instead of the adsorption of two NO 2 molecules, even at the NO/NO 2 ratios (∼6) and high temperatures in these experiments. The additional NO adsorption step (Scheme 2, step 2) occurs at the same rate as the first adsorption step (step 1 of Scheme 2) so that BaO-NO 2 species remain at pseudosteady state and NO 2 /NO consumption ratios at their measured equimolar values.…”