火焰燃烧法制备氧化铈基催化剂及其CO氧化性能研究

CO对大气环境和人体健康造成了严重的危害。近年来，随着人民生活水平的不断提高，居民对室内空气的品质要求越来越高，室内及封闭/半封闭空间的CO污染引起了广泛的重视。室内及封闭/半封闭空间的CO污染场所湿度大、污染气成分复杂且污染突发性强。活性组份与氧化铈载体之间的相互作用是决定CO催化活性和抗水性能的关键因素，然而对相互作用机制的了解还不够深入，并且当前的研究工作主要集中在相互作用对催化剂活性组份和载体的影响，而较少关注其对反应中间产物的影响。本文通过火焰燃烧法和掺杂调控了氧化铈基催化剂的氧缺陷浓度以及活性组份和载体之间的相互作用，制备了一系列具有高效CO催化活性和抗水性的氧化铈基催化剂以及快速去除CO的催化组件，并运用原位漫反射红外光谱捕捉了催化剂在CO氧化过程中的表面信息，探索了活性组份与氧化铈载体之间相互作用机制及其对反应中间产物的影响，从而深入理解了催化剂物理化学性能、反应中间产物以及催化活性三者之间的关系。主要内容及结果如下：(1)针对室内及封闭/半封闭空间湿度大的工况环境，制备了具有高效CO氧化活性和抗水性的CuO-CeO2催化剂。用乙酸铜和乙酸铈作为前驱物，丙酸为溶剂，采用火焰燃烧法制备了不同CuO含量的CuO-CeO2催化剂。考察了CuO组份对催化剂物理化学、表面结构和化学性能的影响。重点研究了CuO和CeO2之间的相互作用机制及其在有无水蒸气的条件下对CO催化氧化中间产物的影响。结果表明，14%CuCe样品（CuO相对CeO2的重量比为14wt.%）在空速60000 ml g-1 h-1下表现出最佳的CO催化氧化活性、优异的稳定性和抗水性，T90=98 °C。这是由于催化剂CuO和CeO2之间强烈的电子相互作用促进了更多缺陷（晶格扭曲、Ce3+和氧空位）的产生，同时增强了催化剂的还原性。原位漫反射红外分析表明，强烈的相互作用能使催化剂在低温下脱除羟基和吸附CO。值得注意的是，在通入水汽的情况下，虽然水汽带来的羟基覆盖在催化剂表面对活性吸附中心Cu+吸附CO产生了负面影响，但是同时羟基的存在也给催化活性带来了正面效应，使催化剂形成更少的碳中间产物，并且提高了脱附速率更快的碳酸氢盐的比例，使催化剂具有良好的抗水性。(2)在CuO-CeO2催化体系中掺杂Mn以进一步提高CO的催化氧化活性。选用乙酸锰、乙酸铜和乙酸铈作为前驱物，丙酸为溶剂，采用火焰燃烧法制备了MnOx-CuO-CeO2催化剂。研究了Mn掺杂后氧化物之间的相互作用对催化剂表面结构，化学性能和电子性能的影响。重点研究了氧化物之间的相互作用机制及其对CO催化氧化中间产物的影响。结果表明，1Mn-Cu-Ce催化剂（Mn/Cu摩尔比为1:5）的活性最强，这是由于氧化物之间的相互作用最强从而使催化剂具有优异的织构性能，丰富的化学吸附氧和高速的氧迁移率。原位漫反射红外分析表明，以上因素在CO催化氧化过程中会进一步诱导了更多的Cu+吸附CO，且产生了较少的碳中间产物，从而成功地增强了催化剂的活性。此外，1Mn-Cu-Ce催化剂由于氧化物之间的强烈相互作用还表现出优异的稳定性和耐水性。(3)以治理室内及封闭/半封闭空间内高温燃烧器排放的CO混合气（CO为主，少量的NOx和烃类）为目标，制备了具有高活性耐高温的Zr掺杂Pd/CeO2催化剂。考察了Zr 掺杂Pd/CeO2催化剂高温老化前后（1000 °C下热处理5小时）催化剂的表面结构、化学和电子性能对CO混合气去除效率的影响。结果表明，PdCe0.50Zr0.50样品老化前后没有发生相分离和明显的晶粒长大，且Pd到载体的电子转移可以增强两者之间的相互作用从而促进载体表面氧空位的形成，并激发出大量的表面活性氧。因此，PdCe0.50Zr0.50样品在老化前后表现出最佳的催化活性，可以有效地去除混合气中的CO和NO。(4)面对室内及封闭/半封闭空间内的CO突发性污染，制备了快速升温去除CO的催化组件。采用火焰燃烧法在FeCrAl电热丝上沉积催化剂涂层，涂层具有良好的机械结合力，这是由于金属基体中的Al元素在火焰燃烧的高温富氧环境中向外扩散，形成了反应型的中间粘接层。因此，金属整体式催化剂在320 °C下通断电3500次循环后仍然可以保持稳定的高活性；其次，耦合通电加热的方式可以实现使金属整体式催化剂快速升温。从室温升温到320 °C仅需要8秒钟，升温到680 °C仅需要15秒。此外，CuO-CeO2金属整体式催化剂对CO的反应速率要高于其颗粒催化剂，且在320 °C有良好的稳定性。 ;CO poses a serious hazard to the atmospheric environment and human health. In recent years, with the continuous improvement of people's living standards, residents' requirements for indoor air quality are getting higher and higher, and CO pollution in indoor and closed/semi-enclosed spaces has attracted extensive attention. CO-contaminated places including in indoor and closed/semi-enclosed spaces exhibit the characteristics of high humidity, complex pollutants and sudden pollution. The synergistic interaction between the active species and the CeO2 support affects the structure and dispersion state of the active species, as well as the redox performance of the support, which is a key factor determining the CO catalytic activity and water resistance during catalytic oxidation. However, the synergistic interaction mechanism is not in-depth understood currently, and less attention were paid on its influences on the intermediates of the CO catalytic oxidation process.The oxygen defect concentration and the interaction between the active species and the CeO2-based support were regulated by flame spray pyrolysis (FSP) method with doping a second active component. In this research, a series of CeO2-based catalysts with of high-efficiency CO catalytic activities and water resistance, as well as a catalytic module for rapid removal of CO were prepared by FSP method. Furthermore, in situ di?use re?ectance infrared Fourier transform spectroscopy (in situ DRIFTs) was used to capture the surface information of the catalysts during CO oxidation. The synergistic interaction mechanism between the active species and the CeO2 support as well as its influences on the reaction intermediates were investigated. Therefore, the relationships among the physicochemical properties, the reaction intermediates and the catalytic activity were deeply understood. The main contents and results are as follows:(1) For indoor and closed/semi-enclosed spaces with high humidity, the CuO-CeO2 catalyst with efficient CO oxidation activity and water resistance was prepared. CuO-CeO2 catalysts with different CuO contents were prepared by one-step FSP, and using cupric acetate anhydrous and cerium acetate as precursors, as well as propionic acid as solvent. The effects of CuO composition on the physicochemical, surface structure and chemical properties of the catalysts were investigated. The synergistic interaction mechanism between CuO and CeO2 and its effect on CO catalytic oxidation with or without water vapor were studied respectively. The results showed that the 14 wt.% CuO-CeO2 catalyst exhibited the superior CO oxidation activity, with the temperature required to achieve a CO conversion of 90% at 98 °C at a high space velocity (SV=60000 mL g?1 h?1), which was attributed to abundant surface defects (lattice distortion, Ce3+, and oxygen vacancies) and high reducibility supported by strong synergistic interaction. In addition, the sample also displayed excellent stability and resistance to water vapor. Significantly, in situ di?use re?ectance infrared Fourier transform spectroscopy (in situ DRIFTs) showed that the strong synergistic interaction led readily to dehydroxylation and CO adsorption on Cu+ at low temperature in the CO catalytic oxidation process. Furthermore, with the presence of water vapor, there was also a positive effect on the formation of fewer carbon intermediates even with the adverse effect on the access of CO adsorption, and consequently, the catalyst exhibited good water resistance.(2) Doping Mn into the CuO-CeO2 catalyst to further increase CO catalytic oxidation activity. MnOx-CuO-CeO2 catalysts with different amounts of Mn dopping were prepared by FSP, and which using manganese acetate, cupric acetate anhydrous and cerium acetate as precursors, and propionic acid used as solvent. The influences of the synergistic interaction among the oxides after Mn doping on the surface structure, chemical properties and electronic properties of the catalysts were investigated. In particular, the mechanism of the synergistic interaction, and its influences on the intermediates of the CO catalytic oxidation were studied. The results showed that the 1Mn-Cu-Ce sample (Mn/Cu molar ratio of 1:5) exhibited superior catalytic activity for CO oxidation.In situ DRIFTs analysis revealed that the enhanced activity was correlated with fine textual properties, abundant chemically adsorbed oxygen and high lattice oxygen mobility supported by strong synergetic interaction, which further induced more Cu+ species and formation of fewer carbon intermediates during CO oxidation process. In addition, the 1Mn-Cu-Ce sample displayed the excellent stability with prolonged time on CO stream and the highly resistance to water vapor as the strong interaction among the oxides.(3) Targeting CO mixed gas (CO-based, mixed with small amounts of NOx and hydrocarbons) emitted from high-temperature burners in indoor and closed/semi-enclosed spaces, Zr-doped Pd/CeO2 catalysts with high activity and high temperature resistance were prepared. The influences of the Zr-doped Pd/CeO2 catalysts before and after high temperature aging treatment (heat treatment at 1000 °C for 5 hours) on the surface structure, chemical and electronic properties, as well as the catalytic activity were investigated systemically. The results showed that the PdCe0.50Zr0.50 sample exhibited no phase separation and obvious grain growth before and after aging treatment, and the electron transfer from Pd to the support enhanced the synergistic interaction and promoted the formation of oxygen vacancies on the surface of the support, as well as excited a large amount of surface active oxygen. Therefore, the PdCe0.50Zr0.50 sample showed the best catalytic activity, and could remove CO and NO from the mixture effectively.(4) In the face of sudden CO pollution in indoor and closed/semi-enclosed spaces, a catalytic module for rapid removal of CO was prepared. The catalyst coating layer was deposited on the FeCrAl heating wire by FSP, and the coating exhibited good mechanical bonding force because of the Al element in the metal substrate diffused outward in the high temperature oxygen-rich environment of flame combustion, and formed the reactive intermediate bonding layer. Therefore, the metal monolith catalyst could maintain stable high activity after 3500 cycles of power-on and off at 320 °C. Furthermore, the coupling of the electric heating could achieve a rapid temperature rise for the metal monolith catalyst. It took only 8 seconds to raise the temperature from room temperature to 320 °C, and it took only 15 seconds to heat up to 680 °C. In addition, the CuO-CeO2 metal monolith catalyst displayed a higher CO reaction rate than its particulate catalyst, and displayed enhanced stability at 320 °C.