Coupled theoretical and experimental analysis of surface coverage effects in Pt-catalyzed NO and O 2 reaction to NO 2 on Pt(1 1 1)

• Published in: Catalysis today Vol. 136; no. 1; pp. 84 - 92
• Main Authors: Smeltz, A.D., Getman, R.B., Schneider, W.F., Ribeiro, F.H.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 2008
• Subjects: AES; DFT; Kinetics; NO oxidation; Peroxynitrite; Pt catalyst; XPS; Peroxynitrite; DFT; NO oxidation; XPS; Kinetics; Pt catalyst; AES
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2007.12.139

Batch reactor results and analysis are reported for the reaction of NO with O 2 to form NO 2 over a Pt(1 1 1) single crystal at atmospheric pressure. The apparent activation energy and NO, O 2, and NO 2 reaction orders are found to be 80 kJ mol −1, 1.3, 1, and −2 and are comparable to previous studies on supported Pt catalysts which take inhibition by the product NO 2 into account. The absolute rates on a per Pt atom basis are the highest yet reported 0.34 ± 0.02 s −1, at 300 °C, 73 ppm NO, 27 ppm NO 2 and 5% O 2. Auger electron spectroscopy and X-ray photoelectron spectroscopy are used to show that the surface chemisorbed oxygen coverage under reaction conditions is 0.76 ± 0.06 ML, consistent with a coverage controlled by NO 2 dissociation. DFT calculations are used to compare the stability of possible surface intermediates on a clean Pt(1 1 1) surface with those on a p(√3 × √3)-2O (2/3 ML) ordering surface. In contrast to the clean surface, O 2 adsorption and dissociation are endothermic at 2/3 ML oxygen, but a peroxynitrite intermediate OONO* is slightly stable and may provide an alternative, associative pathway to NO 2 formation that is consistent with the observed first order reaction kinetics in O 2.