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含氯挥发性有机物（Chlorinated Volatile Organic Compounds, CVOCs）在工业领域具有广泛的应用，但对环境和人类健康存在巨大的危害。催化氧化技术可以高效地将CVOCs降解为洁净的产物。二氧化钛具有价格便宜、制备简便、表面羟基丰富等优点，因此作为一种常用的催化剂载体，广泛应用于工业催化剂设计制备。本论文系统地研究了TiO2在催化氧化CVOCs反应中的性能和失活机制，并设计制备高活性的TiO2催化剂，研究了负载不同活性组分对催化剂性能的影响。以高活性TiO2催化剂制备工艺为基础，探索了泡沫金属整体式催化剂的制备工艺。本论文的研究内容和主要结果如下：(1) CrOx与TiO2载体协同作用机制探究以硝酸铬、氯铂酸等贵金属盐、钛酸四丁酯（Tetrabutyl Titanate, TBOT）和TiCl4为原料，采用模板辅助的非水解溶胶-凝胶方法（Nonhydrolytic Template-Mediated Sol-Gel Route, NTMSG）制备了负载氧化铬和氧化铬-贵金属的TiO2催化剂。结果表明，单独负载氧化铬和负载双金属的催化剂均具有微-介孔双模孔道结构，比表面积可达250m2/g-350m2/g。催化剂在350℃时可以完全降解二氯甲烷（Dichloromethane, DCM），产物主要为CO和CO2。负载双金属对于催化活性没有明显改变，稳定性测试结果表明催化剂均存在不可逆失活。通过对催化剂进行的原位红外表征分析，确定Cr=O氧空位和TiO2表面羟基为活性位点。初步判断催化剂失活机制是水分子在活性位点的吸附，Cr=O氧空位易与水结合而失活。(2) 贵金属种类、TiO2晶型和制备方法对催化剂性能的影响以氯铂酸、硝酸钯、氯金酸和硝酸银为前驱体，选择水热法制备的锐钛矿TiO2和金红石TiO2以及购买自德固赛公司的气相TiO2（P25），采用浸渍法（Impregnation, IM）和沉积沉淀法（Deposition-Precipitation, DP）制备了负载不同的贵金属的TiO2催化剂。对催化性能对比研究发现，以锐钛矿相TiO2作为载体采用DP法制备的催化剂催化活性优于P25和金红石TiO2。负载Pt的催化剂催化性能优于Pd、Au和Ag，反应产物基本为CO2。通过对反应前后样品的透射电镜形貌和X射线光电子能谱分析，确定了催化剂的失活机制主要是贵金属的烧结与脱离，因此载体在催化反应中对催化剂的稳定性有很大的影响。(3) 活性TiO2载体的制备与催化氧化DCM反应机制探究以TBOT和TiCl4为原料，采用NTMSG方法制备了具有高比表面积的锐钛矿相TiO2。研究表明，在含水1 vol.%条件下，TiO2能够在350℃完全降解DCM，反应产物为CO和一氯甲烷（Chloromethane, CM），催化剂在高湿条件下具有良好的稳定性。通过对催化剂原位红外表征的分析可知该反应主要为歧化反应，同时有氧化反应协同作用，催化剂表面的活性羟基参与反应，反应活性位点为锐钛矿相TiO2的（001）面上的羟基位点，初步判断水分子的解理吸附是活性位点再生的关键步骤。(4) 低负载量Pt/TiO2催化氧化多种CVOCs性能与Pt强化机制探究以氯铂酸为前驱体，采用DP法制备了不同负载量的Pt/TiO2催化剂。结果表明，1%Pt/TiO2催化氧化DCM，氯苯（Chlorobenzene, CB）和三氯乙烯（Trichloroethylene, TCE）的T90均达到300℃。当Pt负载量降至0.1wt.%时催化剂在350℃对DCM和CB的转化率可达90%。在1 vol.%的湿度下对催化剂进行24h稳定性测试，分别考察了在400℃催化氧化CB和TCE以及在350℃催化氧化DCM的稳定性，结果表明催化剂活性没有下降。通过对催化剂原位红外表征的分析，表明Pt增强了催化剂对CO的深度氧化能力，证明贵金属与TiO2能够有较好的协同氧化作用。(5) 泡沫金属整体式催化剂的制备探索 以TBOT和TiCl4为原料，制备了TiO2溶胶前驱液，采用浸渍和原位水解的方法探索了泡沫金属涂覆TiO2催化剂的方法。将涂覆TiO2活性涂层的泡沫钛催化剂通过DP方法负载Pt，制备了负载Pt/TiO2的泡沫钛整体式催化剂。结果表明，该方法制备的TiO2涂层具有合适的厚度、孔隙结构和一定的比表面积。在1 vol.%湿度，1580/h的空速条件下，催化剂在400℃完全催化氧化DCM，在450℃对CB转化率可达88%。350℃保温24h后，催化剂的活性没有下降。;Chlorinated volatile organic compounds (CVOCs) are harmful to environment and human health. However, they are widely used in various industry fields. Catalytic oxidation method can efficiently decompose CVOCs into clean products. Catalysts are key to the applications of catalytic oxidation. TiO2 are common catalyst supports for preparation of variety of catalysts due to its low price, facile preparation process and abundant surface hydroxyl groups. In this thesis, the performance and deactivation mechanism of TiO2 catalysts for CVOCs catalytic oxidation were comprehensively studied. The highly active supported TiO2 catalysts were designed and the influence of different active components to the catalytic activity were discussed. Based on the powder catalyst synthesis process, the preparation of monolith metal foam catalysts was explored. The research contents and main results are as following:(1) Mechanism of synergism between CrOx and TiO2Cr/TiO2 and M-Cr/TiO2 (M= Au, Ag, Pt, Pd) catalysts were prepared by a nonhydrolytic template-mediated sol-gel route, using chromium nitrate, noble metal salts (chloroplatinic acid, palladium nitrate, gold chloride or silver nitrate), TBOT and TiCl4 as the precursors. The results showed that Cr/TiO2 and M-Cr/TiO2 both possessed bimodal micro-mesoporous structures. The surface areas of the catalysts were between 250 m2/g to 350 m2/g. DCM could be totally decomposed at 350℃ and the products were mainly CO and CO2. Noble metals had little promotion to the catalytic activity. The stability test proved irreversible inactivation occurred on the catalysts. Cr=O oxygen vacancy and surface hydroxyl groups were proved to be the active sites by in-situ infrared spectra. It was concluded that the inactivation should be attributed to the adsorption of water on the active sites where Cr=O vacancy could be occupied.(2) Influence of noble metals, TiO2 crystalline structures and preparation methods on catalytic performanceAu, Ag, Pt, Pd were supported on the TiO2 and three different types of TiO2 (anatase, rutile and P25) were used as the support. The influence of preparation methods (impregnation and deposition-precipitation) to the catalytic activity of dichloromethane oxidation was also discussed. Catalyst prepared by DP method using anatase TiO2 as the support was more active than P25 and rutile TiO2. Pt supported catalyst performed better than Pd, Au and Ag supported catalysts. The products were mainly CO2. The inactivation of the catalysts was attributed to the sintering and abscission of noble metals, which was determined by the comparison of TEM micrographs and XPS analysis between samples before and after reaction. The results showed great importance of support to the stability of the catalysts.(3) Preparation of highly active TiO2 supports and its the reaction mechanismA mesoporous anatase TiO2 was prepared via NTMSG method using TBOT and TiCl4 as the precursors. The results showed that DCM was totally decomposed into CO and CM at 350℃ under 1 vol.% humidity. The catalyst remained stable under high humidity. A competing mechanism between disproportionation and oxidation was proved by in-situ IR analysis. Water molecules would dissociatively adsorb at the (001) sites on anatase TiO2 and generated surface hydroxyl groups took part in the reaction. It was concluded that dissociative adsorption of water was the key to the active site regeneration.(4) Promotion mechanism of Pt and catalytic performance of Pt/TiO2 with low loading amountX wt.% Pt/TiO2 catalysts (X=1, 0.1 and 0) were synthesized by DP method using chloroplatinic acid as the Pt precursor. The results showed that 1%Pt/TiO2 was able to decompose 90% of DCM, CB and TCE at 300℃under 1 vol.% humidity. And T90 of 0.1% Pt/TiO2 was 350℃ under 1 vol.% humidity. The 24h stability test of 1%Pt/TiO2 was carried out under 1 vol.% humidity, 400℃ for CB and TCE and 350℃ for DCM. The catalyst remained stable after stability test. It proved that the deep oxidation capacity of the catalyst was promoted by Pt indicating that noble metal would have good synergism with TiO2.(5) Preparation and characterizations of monolith metal foamA novel monolith metal foam catalyst was prepared via impregnation and in-situ hydrolysis of TiO2 sol using TBOT and TiCl4 as the precursors. The TiO2 coated Ti foam was loaded with Pt by DP method. The results showed that TiO2 coatings possessed controllable thickness, high surface area and pore structures. The monolith catalyst could totally decompose DCM and 88% CB at 400℃ under 1 vol.% humidity with GHSV of 1580/h. In addition, the catalyst remained stable after 24h aging at 350℃.
|邓昱洲. TiO2负载型催化剂催化氧化CVOCs的性能研究[D]. 中国科学院大学,2019.|
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