Thermal Chemistry of 1,4-Difluoro-2-butenes on Pt(111) Single-Crystal Surfaces

• Published in: Journal of physical chemistry. C 2008-09, Vol.112 (36), p.14117-14123
• Main Authors: Lee, Ilkeun, Nguyen, Michael K, Morton, Thomas H, Zaera, Francisco
• Format: Article
• Language: English
• Subjects: C: Surfaces, Interfaces, Catalysis
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp804360z

The thermal chemistry of cis- and trans-1,4-difluoro-2-butenes on Pt(111) single-crystal surfaces was characterized by temperature programmed desorption (TPD) and reflection−absorption infrared spectroscopy (RAIRS). The study was motivated by the possibility of differentiating the two isomers directly by mass spectrometry, something that is not possible with the nonfluorinated olefins. On the clean surface a preference was identified for the conversion of the cis isomer to its trans counterpart, the opposite to what had been previously reported with regular 2-butenes on hydrogen (or deuterium)-predosed Pt(111). Indeed, the formation of trans-1,4-difluoro-2-butene from the adsorbed cis isomer occurs at around 260 K, as identified directly by RAIRS and in the gas phase by mass spectrometry. Some cis is also formed from the trans, but only in a small yield and at much higher temperatures (∼315 K). The preference for trans-to-cis conversion with the nonfluorinated olefins may therefore be explained by a reversal in adsorption stability induced by coadsorbed hydrogen. It was also determined that significantly more hydrogenation of the fluorinated olefins to their fluorinated alkanes occurs upon coadsorption with hydrogen or deuterium compared with what is seen with the regular olefins. Finally, the inductive effect of the fluorine substitutions leads to some changes in the high-temperature conversion of the adsorbed species.