Coupled theoretical and experimental analysis of surface coverage effects in Pt-catalyzed NO and O2 reaction to NO2 on Pt(1 1 1)

✍ Scribed by A.D. Smeltz; R.B. Getman; W.F. Schneider; F.H. Ribeiro

• Publisher: Elsevier Science
• Year: 2008
• Tongue: English
• Weight: 588 KB
• Volume: 136
• Category: Article
• ISSN: 0920-5861
• DOI: 10.1016/j.cattod.2007.12.139

✦ Synopsis

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 À1 , 1.3, 1, and À2 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 AE 0.02 s À1 , at 300 8C, 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 AE 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(H3 Â H3)-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 .