Ba Deposition and Oxidation on θ-Al₂O₃/NiAl(100) Ultrathin Films. Part II:  O₂(g) Assisted Ba Oxidation

Abstract

Ba deposition on a theta-Al(2)O(3)/NiAl(100) substrate and its oxidation with gas-phase O(2) at various surface temperatures are investigated using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and temperature programmed desorption (TPD) techniques. Oxidation of metallic Ba by gas-phase O(2) at 800 K results in the growth of 2D and 3D BaO surface domains. Saturation of a metallic Ba layer deposited on theta-Al(2)O(3)/NiAl(100) with O(2)(g) at 300 K reveals the formation of BaO(2)-like surface states. These metastable peroxide (O(2)(2-)) states are converted to regular oxide (O(2-)) states at higher temperatures (800 K). In terms of thermal stability, BaO surface layers (theta(Ba) < 5 ML) that are formed by O(2)(g) assisted oxidation on the theta-Al(2)O(3)/NiAl(100) substrate are significantly more stable (with a desorption/decomposition temperature of c.a. 1050 K) than the thick (2 < theta(Ba) < 10 ML) metallic/partially oxidized Ba layers prepared in the absence of gas-phase O(2), whose multilayer desorption features appear as low as 700 K.

Model NOx Storage Materials at Realistic NO2 Pressures

“…[13][14][15] Ozensoy et al studied the reaction of NO 2 on BaO/Al 2 O 3 / NiAlA C H T U N G T R E N N U N G (100), using the ultrathin Al 2 O 3 film on NiAlA C H T U N G T R E N N U N G (100). [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.…”

Role of the Exposed Pt Active Sites and BaO2 Formation in NOx Storage Reduction Systems: A Model Catalyst Study on BaOx/Pt(111)

“…Annealing this surface at 473 K in vacuum results in the attenuation of the nitrate signal in XPS (Figure 4a) and the formation of a new N1s signal at 403.5 eV, which can be ascribed to nitrite species. 24,25 Observation of nitrite species during the thermal decomposition of nitrates suggests that the nitrate release mechanism from the BaO x (10 MLE)/Pt(111) model catalyst surface involves nitrite species. This can be mechanistically envisaged by considering the reaction pathway given below…”

SO uptake and release properties of TiO2/Al2O3 and BaO/TiO2/Al2O3 mixed oxide systems as NO storage materials

“…It was shown that sulfate decomposition is facilitated on the smaller sulfate domains. There also exist a number of surface science studies on planar model NSR catalysts [49][50][51][52][53] focusing on the structure and the operational principles of NSR systems at the molecular level. Despite the established sulfur resisting effect of TiO 2 as an additive in the composition of the Pt/Ba/␥-Al 2 O 3 catalysts, a number of crucial aspects regarding the influence of TiO 2 on the interaction between the NO x storage component and the support material have not yet been elucidated.…”