Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
Chemistry. 2011 Oct 24;17(44):12310-25. doi: 10.1002/chem.201001121. Epub 2011 Sep 16.
Nanoparticles of Ti(0.95)V(0.05)O(2) were found to be impregnated in the hexagonal channels of the MCM-41 host, with a distribution of some particles on the surface, thus leading to an effective variation in the particle size as a function of loading host MCM-41 matrix. These catalysts were subjected to the photocatalytic degradation of alkenes under the ambient conditions in which the photocatalytic activity varied as a function of the loading percentage of Ti(0.95)V(0.05)O(2) in the host MCM-41.This is explained in light of the structure-activity correlation, and the better catalytic activity can be attributed to an electronic interaction between the host and guest molecules, as established from X-ray photoelectron spectroscopy. To understand the mechanistic aspect of the photooxidation of ethylene on the vanadium-doped titania dispersed in the MCM-41 matrix, extensive in situ FTIR experiments were undertaken. The intermediate species produced on bare Ti(0.95)V(0.05)O(2) are different from that produced on the Ti(0.95)V(0.05)O(2)/MCM-41 surface. Moreover, different intermediates were produced during ethylene oxidation under UV and visible irradiation, thus leading to different rates. The ethylene decomposition over bare Ti(0.95)V(0.05)O(2) occurs by means of formation of ethoxy groups, transformed to acetaldehyde or enolates, subsequently to acetates, and then to CO(2) under both UV and visible irradiation. However, in the case of Ti(0.95)V(0.05)O(2)/MCM-41 catalyst with UV irradiation, the adsorbed acetaldehyde thus formed undergoes aldol condensation over the Lewis acid sites to lead to the formation of crotonaldehyde, which is subsequently oxidized to acetate and consequently to CO(2). It was observed that during visible irradiation labile ethyl acetate is produced either by the Tischenko reaction or by the reaction between the labile acetic acid and the unreacted ethoxy groups. The ethyl acetate produces acetic acid monomer, which is oxidized to CO(2). Furthermore, in this work the effects of particle size on the intermediate species were also studied.
纳米 TiO(0.95)V(0.05)O(2) 颗粒被发现浸渍在 MCM-41 主体的六方通道中，一些颗粒分布在表面上，从而导致颗粒尺寸作为负载主 MCM-41 基质的函数的有效变化。这些催化剂在环境条件下进行烯烃的光催化降解，其中光催化活性作为负载百分比的函数而变化在 MCM-41 主体中的 Ti(0.95)V(0.05)O(2)。这可以根据结构-活性相关性来解释，更好的催化活性可以归因于主体和客体分子之间的电子相互作用，正如 X 射线光电子能谱所建立的那样。为了了解在 MCM-41 基质中分散的掺杂二氧化钛上乙烯光氧化的机理方面，进行了广泛的原位 FTIR 实验。在裸露的 Ti(0.95)V(0.05)O(2)上产生的中间物种与在 Ti(0.95)V(0.05)O(2)/MCM-41 表面上产生的中间物种不同。此外，在 UV 和可见光照射下，乙烯氧化过程中产生了不同的中间产物，从而导致了不同的速率。在裸露的 Ti(0.95)V(0.05)O(2)上，乙烯分解通过形成乙氧基基团发生，转化为乙醛或烯醇盐，随后转化为乙酸盐，然后在 UV 和可见光照射下转化为 CO(2)。然而，在 Ti(0.95)V(0.05)O(2)/MCM-41 催化剂的情况下用 UV 照射，由此形成的吸附乙醛在路易斯酸位上经历羟醛缩合，导致巴豆醛的形成，随后被氧化为乙酸盐，然后进一步氧化为 CO(2)。观察到在可见光照射下，不稳定的乙酸乙酯要么通过 Tischenko 反应产生，要么通过不稳定的乙酸与未反应的乙氧基之间的反应产生。乙酸乙酯产生乙酸单体，然后将其氧化为 CO(2)。此外，在这项工作中还研究了粒径对中间产物的影响。
