Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, P.O. Box 999, MS K8-87, Richland, WA 99352, USA.
Phys Chem Chem Phys. 2010 Jul 28;12(28):8084-91. doi: 10.1039/c003115a. Epub 2010 Jun 4.
The ultraviolet (UV) photon-induced decomposition of hexafluoroacetone ((CF(3))(2)CO; HFA) adsorbed on the rutile TiO(2)(110) surface was investigated using photon stimulated desorption (PSD) and temperature programmed desorption (TPD). HFA adsorbs both molecularly and dissociatively on the reduced TiO(2)(110) surface. The initial approximately 0.2 ML (where 1 ML equates to the cation site density of the ideal surface) coverage of HFA thermally decomposes resulting in the formation of adsorbed trifluoroacetate groups, with further HFA exposure resulting in molecular adsorption. No evidence was found for HFA photochemistry on the reduced surface. HFA adsorbed and desorbed molecularly on a pre-oxidized TiO(2)(110) surface with only a minor amount (approximately 1%) of thermal decomposition in TPD. A new adsorption state at 350 K was assigned to the reversible formation of a photoactive HFA-diolate species [(CF(3))(2)COO]. UV irradiation depleted the 350 K state, resulting in evolution of CF(3), CO, and CO(2) in the gas phase and formation of surface bound trifluoroacetate groups. (18)O isotope scrambling experiments showed that the ejected CO(2) was from photodecomposition of the HFA-diolate species while the CO photoproduct was not. These results are in contrast to the photochemical behavior of acetone, butanone and acetaldehyde on TiO(2)(110), where UV irradiation resulted in the gas phase ejection of one of the carbonyl substituent groups as well as a stoichiometric amount of carboxylate left on the surface. We conclude that fluorination alters the electronic structure of adsorbed carbonyls on TiO(2)(110) in such a way as to promote complete fragmentation of the adsorbed carbonyl complex to form gas phase CO(2) as well as to open up additional photodissociation pathways leading to CO production.
六氟丙酮（(CF(3))(2)CO；HFA）在金红石 TiO(2)(110)表面上吸附后，经紫外（UV）光子诱导分解，利用光子刺激解吸（PSD）和程序升温解吸（TPD）进行了研究。HFA 在还原 TiO(2)(110)表面上既分子吸附又离解吸附。初始大约 0.2 ML（其中 1 ML 等同于理想表面的阳离子位密度）的 HFA 覆盖物经热分解生成吸附的三氟乙酸基团，进一步暴露于 HFA 导致分子吸附。在还原表面上未发现 HFA 光化学的证据。HFA 在预氧化的 TiO(2)(110)表面上分子吸附和解吸，在 TPD 中仅有少量（约 1%）的热分解。在 350 K 处分配了一个新的吸附态，指定为光活性 HFA-二醇化物[(CF(3))(2)COO]的可逆形成。UV 辐照使 350 K 状态耗尽，导致气相中 CF(3)、CO 和 CO(2)的逸出，以及表面结合的三氟乙酸基团的形成。(18)O 同位素混合实验表明，所喷射出的 CO(2)是来自 HFA-二醇化物物种的光分解，而 CO 光产物则不是。这些结果与丙酮、丁酮和乙醛在 TiO(2)(110)上的光化学行为形成对比，在 TiO(2)(110)上，UV 辐照导致气相中羰基取代基之一的喷射，以及留在表面上的化学计量量的羧酸盐。我们的结论是，氟化以促进吸附羰基配合物完全碎裂形成气相 CO(2)的方式改变 TiO(2)(110)上吸附羰基的电子结构，以及开辟导致 CO 生成的其他光离解途径。
