Trimboli Joseph, Mottern Matthew, Verweij Henk, Dutta Prabir K
Department of Chemistry, The Ohio State University, Columbus, Ohio 43210-1185, USA.
J Phys Chem B. 2006 Mar 23;110(11):5647-54. doi: 10.1021/jp0551519.
High-temperature gas sensors based on semiconducting metal oxides show potential for optimization of combustion processes, resulting in efficient energy use and minimization of emissions. Such metal oxides can function as gas sensors because of the reaction of the sensing gas (e.g., CO) with ionosorbed oxygen species on the oxide surface with the resulting increase in conductivity. A limitation of metal oxide sensors is their difficulty of distinguishing between different gases. Designing selectivity into sensors necessitates a better understanding of the chemistry of gas-solid interactions at high temperatures. In this paper, we have used in situ infrared spectroscopy to monitor the dehydration of a hydrated anatase surface up to 600 degrees C and also to examine the hydration/dehydration of anatase held at 400 degrees C. When the O-H stretching region (3000-3800 cm(-1)) was primarily focused on, it was found that water loss from the titania surface proceeded at lower temperatures (<200 degrees C) through desorption, whereas at higher temperatures, water dissociation to terminal (approximately 3710 cm(-1)) and bridged (approximately 3660 cm(-1)) hydroxyl groups was noted. With a further increase in temperature to 600 degrees C, the bridged hydroxyl groups disappeared faster than the terminal ones. The electrical resistance of anatase at 600 degrees C was measured in the presence of moist gas streams and resulted in an increase in conductivity in the presence of water. In situ vibrational spectroscopy indicated a temporal correlation between the appearance of the bridging hydroxyl group and the change in electrical resistance. Several possible mechanisms are discussed. The chemical reaction of water with anatase at high temperatures necessitates that water be removed from the gas stream to avoid interference. A strategy involving the use of a hydrophobic microporous filter that can reject water and let gases such as CO pass unimpeded is examined. Successful use of such a concept has been demonstrated with a silicalite filter using moist CO gas streams.
基于半导体金属氧化物的高温气体传感器在优化燃烧过程方面显示出潜力，可实现高效能源利用并将排放降至最低。这类金属氧化物能够作为气体传感器发挥作用，是因为传感气体（如一氧化碳）与氧化物表面离子吸附的氧物种发生反应，从而导致导电性增加。金属氧化物传感器的一个局限性在于它们难以区分不同的气体。要在传感器中设计选择性，就需要更好地理解高温下气固相互作用的化学原理。在本文中，我们利用原位红外光谱法监测了水合锐钛矿表面在高达600摄氏度时的脱水情况，还研究了在400摄氏度下保持的锐钛矿的水合/脱水情况。当主要关注O - H伸缩区域（3000 - 3800 cm⁻¹）时，发现二氧化钛表面的水分流失在较低温度（<200摄氏度）下通过解吸进行，而在较高温度下，会观察到水分解为末端（约3710 cm⁻¹）和桥连（约3660 cm⁻¹）羟基。随着温度进一步升高至600摄氏度，桥连羟基比末端羟基消失得更快。在潮湿气流存在的情况下测量了600摄氏度时锐钛矿的电阻，结果表明在有水存在时导电性增加。原位振动光谱表明桥连羟基的出现与电阻变化之间存在时间相关性。讨论了几种可能的机制。水在高温下与锐钛矿的化学反应要求从气流中除去水以避免干扰。研究了一种涉及使用疏水性微孔过滤器的策略，该过滤器可以排斥水并让诸如一氧化碳等气体畅通无阻地通过。使用含湿一氧化碳气流的硅沸石过滤器已证明成功应用了这一概念。
