White J M, Henderson Michael A
Interfacial Chemistry and Engineering Group, Pacific Northwest National Laboratory, Richland, Washington 99353, USA.
J Phys Chem B. 2005 Jun 30;109(25):12417-30. doi: 10.1021/jp050944g.
The preparation and anaerobic ultraviolet photolysis of trimethyl acetate (TMA) on rutile TiO(2)(110) have been examined with an emphasis on reaction paths. Substrates for photolysis were prepared by dosing trimethyl acetic acid at 100, 300, and 550 K. The chemistry was characterized by mass spectrometry during dosing and by H(2)O adsorption and temperature programmed desorption (TPD) after dosing. Using TPD after photolysis and mass spectrometry during photolysis, the products ejected and retained during photolysis were sought. The photolysis results are interpreted using the following mechanistic model. Photons with energies exceeding 3 eV create electron-hole pairs in the substrate. With probabilities of 10(-5) or lower, the holes initiate TMA chemistry by extracting an electron from the pi orbital of the carboxylate moiety. The accompanying electrons are trapped at the surface and inhibit subsequent events of this chemistry. The electron-deficient intermediate, TMA, decarboxylates to form CO(2) and either chemisorbed tert-butyl (-C(CH(3))(3)) or physisorbed i-butene. For photolysis at 100 or 200 K, the -C(CH(3))(3) accumulates and there is a slow photon-driven secondary reaction that, with a source of H, hydrogenates adsorbed tert-butyl to physisorbed i-butane. For photolysis at 300 K, -C(CH(3))(3) thermally reacts to form and desorb i-butene and i-butane during photolysis.
研究了三甲基乙酸（TMA）在金红石型TiO₂(110)上的制备及其厌氧紫外光解过程，重点关注反应路径。通过在100K、300K和550K下通入三甲基乙酸来制备光解底物。在通入过程中通过质谱对化学过程进行表征，在通入后通过H₂O吸附和程序升温脱附（TPD）进行表征。利用光解后的TPD和光解过程中的质谱，寻找光解过程中喷射出和保留的产物。使用以下机理模型解释光解结果。能量超过3eV的光子在底物中产生电子-空穴对。空穴以10⁻⁵或更低的概率通过从羧酸根部分的π轨道提取一个电子来引发TMA化学过程。伴随产生的电子被困在表面并抑制该化学过程的后续事件。缺电子中间体TMA脱羧形成CO₂和化学吸附的叔丁基（-C(CH₃)₃）或物理吸附的异丁烯。对于在100K或200K下的光解，-C(CH₃)₃积累，并且存在一个缓慢的光子驱动的二级反应，在有氢源的情况下，该反应将吸附的叔丁基氢化为物理吸附的异丁烷。对于在300K下的光解，-C(CH₃)₃在光解过程中发生热反应形成并解吸出异丁烯和异丁烷。
