【作者】 苏孝文；

【导师】 罗孟飞；

【作者基本信息】 浙江师范大学 ， 物理化学， 2009， 硕士

【摘要】 催化燃烧技术是一种能耗低、效率高的有机废气（VOCs）治理手段,由于具有设备简单,不易形成NO_x二次污染等优点,是当前VOCs处理技术中备受关注的领域。VOCs催化燃烧技术的核心是催化燃烧催化剂。近几十年发展起来的新型催化燃烧催化剂主要是整体式催化剂,该类催化剂一般以堇青石蜂窝陶瓷为基体,表面涂覆Al₂O₃涂层作为第二载体,然后负载Pt、Pd等活性组分来制备。由于传统Al₂O₃涂层热稳定性差,高温易与助剂发生固相反应生成尖晶石（AB₂O₄）类化合物,影响催化性能。而用Y₂O₃涂层代替Al₂O₃涂层制备负载Pd整体式催化剂虽然对甲苯表现出优良的催化性能,但对乙酸乙酯的催化活性较差。目前非贵金属Cu、Mn等催化剂对含氧类有机物活性较高,Pd等贵金属催化剂对芳烃类有机物催化性能优良,而实际工业排放的VOCs往往是混合有机物。因此,本课题制备一种Ce_xCu_1-xO_2-δ涂层负载Pd整体式双功能催化剂,使其兼具贵金属和非贵金属特性,从而对芳烃类和含氧类有机物均具较高催化性能,并用XRD、Raman、H₂-TPR、BET、CO Chemisorption等方法对催化剂进行了详细的表征。本课题以Y₂O₃为粘结剂,将Ce_xCu_1-xO_2-δ固溶体涂载于堇青石陶瓷蜂窝载体上,再负载贵金属Pd,制得Pd/Ce_xCu_1-xO_2-δ-Y₂O₃催化剂,并以甲苯、乙酸乙酯氧化为模型反应考察催化剂的催化活性和热稳定性。同时以非固溶体CeO₂-CuO-Y₂O₃涂层负载Pd催化剂进行比较。研究表明,Pd/Ce_xCu_1-xO_2-δ-Y₂O₃陶瓷蜂窝催化剂对甲苯和乙酸乙酯均具有较高的催化活性和高温热稳定性,具有显著的双功能特性;催化剂的活性与Ce_xCu_1-xO_2-δ的组成密切相关,且Ce_0.9Cu_0.1O_1.9-Y₂O₃催化剂催化活性最好。因此认为Ce_0.9Cu_0.1O_1.9为涂层的最佳组成,采用此涂层负载Pd制备Pd/Ce_0.9Cu_0.1O_1.9-Y₂O₃整体式催化剂的催化性能最好。通过对Pd/Ce_0.9Cu_0.1O_1.9-Y₂O₃（Pd/CCY）整体式催化剂进行深入研究,发现涂层中Ce_0.9Cu_0.1O_1.9或CuO对乙酸乙酯的催化起着主导作用,而活性组分Pd-PdO则是甲苯催化氧化的活性中心,且CCY涂层中引入Pd并未影响其对乙酸乙酯的氧化活性;Pd/CCY催化剂具有良好的低温甲苯和乙酸乙酯催化活性,同时具有优良的高温热稳定性。低温焙烧的Pd/CCY催化剂活性组分分散均匀,对甲苯和乙酸乙酯催化活性高;高温焙烧后其对乙酸乙酯活性缓慢下降可能与Ce_0.9Cu_0.1O_1.9固溶体粒子增大有关。而催化剂在900℃以下的焙烧温度范围内对甲苯的氧化也随着焙烧温度的升高,Pd-PdO粒子增大而活性下降,但当焙烧温度升至1000℃时,其对甲苯的氧化活性又有一定幅度的回升,这可能是高温焙烧时生成的Pd物种为甲苯提供了更多的吸附位,因而活性比PdO更高,从而弥补了催化剂的部分失活。总之,涂层涂覆前Ce_0.9Cu_0.1O_1.9固溶体的形成是Pd/CCY催化剂具有较高的催化活性和高温热稳定性的关键;Pd-PdO物种是甲苯催化氧化的活性中心,而Ce_0.9Cu_0.1O_1.9或CuO对乙酸乙酯的氧化发挥主要作用;催化剂在1000℃焙烧后,金属态Pd的形成是催化剂活性提高的主要原因。由于目前工业废气及汽车尾气中往往是多种有机废气的共存体,且通常催化剂消除有机物种类单一,而Pd/CCY催化剂具有明显的双功能特性。因此,此类双功能催化剂具有十分重要的应用意义和广阔的应用前景。更多还原

【Abstract】 Among technologies for elimination of volatile organic compounds（VOCs） emissions, catalytic combustion has been paid much attention because of low energy consumption, high efficiency and simple equipment.Moreover,there is no associated pollution such as nitrogen oxides（NO_x）,as it operates at low temperature.A catalyst with high activity is the key to catalytic combustion.Monolithic catalysts with cordierite honeycomb ceramics developed in last decades are novel catalysts.For the catalysts,the cordierite honeycomb usually used as the substrate and a washcoat of Al₂O₃ is coated on its surface as the second support,and then active species such as Pt,Pd is deposited.As Al₂O₃ has poor thermal stability,and it can easily react with the promoters to form spinel phases（AB₂O₄） at high temperature,which is detrimental to the catalytic performance.Instead of Al₂O₃,the Pd monolithic catalysts prepared with the Y₂O₃ washcoat exhibit excellent activity for catalytic combustion of toluene,but its activity for catalytic combustion of ethyl acetate is poor.At present,non-noble metals such as Cu and Mn show good activities for catalytic combustion of oxygenated compounds and noble metals show good activities for catalytic combustion of aromatics.Since the industrial exhaust gases usually contain various kinds of VOCs,a dual-functional catalyst was developed with the Ce_xCu_1-xO_2-δ solid solution washcoat supported Pd,which are effective for both oxygen-free and oxygenated VOCs. The catalysts were characterized by XRD,Raman spectroscopy,H₂-TPR,BET and CO chemisorption.The detailed contents of this thesis are as follows:Using Y₂O₃ as a binder,the Ce_xCu_1-xO_2-δ solid solution was adhered to the substrate of cordierite honeycomb,and the Pd/Ce_xCu_1-xO_2-δ-Y₂O₃ catalysts were prepared by supporting Pd on the washcoat.Model reactions for the catalytic combustion of toluene and ethyl acetate were carried out to evaluate the activity and thermal stability of the catalysts.The results show that the Pd/Ce_xCu_1-xO_2-δ-Y₂O₃ catalysts possess dual-function properties,and exhibit good activity and thermal performance for catalytic combustion of both toluene and ethyl acetate.The catalytic activities of the Pd/Ce_xCu_1-xO_2-δ-Y₂O₃ catalysts are closely related to the component of Ce_xCu_1-xO_2-δ,and the Ce_0.9Cu_0.1O_1.9-Y₂O₃ catalyst exhibits the best activity.Further study of the Pd/Ce_0.9Cu_0.1O_1.9-Y₂O₃（Pd/CCY） catalyst found that the Ce_0.9Cu_0.1O_1.9 or CuO plays a main role in catalytic combustion of ethyl acetate,while Pd-PdO entities are the active site for oxidation of toluene,and the addition of Pd does not inhibit the activity for ethyl acetate combustion.The active sites of the catalyst calcined at low temperature are well dispersed,leading to a high activity.However,when calcined at high temperature,the Pd/CCY exhibits a degraded activity for ethyl acetate oxidation, which is probably related to the growth in the particle size of Ce_0.9Cu_0.1O_1.9 or CuO.For the catalytic combustion of toluene,the reactivity first declines with increasing calcination temperature up to 900℃,then recovers to some extent when the catalyst was calcined at 1000℃.This probably due to the fact that increased metallic Pd may compensate deactivation of the catalyst to some extent,since metallic Pd is possibly more active than PdO,through providing more adsorption sites for toluene.In summary,the formation of the Ce_0.9Cu_0.1O_1.9 solid solution before coating is the key to high activity and thermal stability.Moreover,Pd-PdO species are the active phase for oxidation of toluene,while Ce_0.9Cu_0.1O_1.9 or CuO is responsible for oxidation of ethyl acetate,and the formation of the Pd probably impels the enhancement of activity for the catalyst calcined at 1000℃.The Pd/CCY catalysts are dual-functional for both oxygen-containing and oxygen-free VOCs compounds,which may have applicable potentials.更多还原