介孔Beta沸石负载钯在甲烷催化燃烧反应中的性能研究

Enhanced Performance for Mesoporous Beta Zeolites Supported Pd in the Methane Catalytic Combustion

甲烷催化燃烧是处理尾气/废气中微量甲烷最有效的方法之一,而设计高效催化剂是提升甲烷催化燃烧技术的核心.使用高分子聚合物聚二甲基二丙烯基氯化铵(PDADMAC)为介孔模板剂制备一系列介孔Beta沸石,并负载Pd用于甲烷催化燃烧反应.样品经过X射线衍射(XRD)、氮气吸附、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线光电子能谱技术(XPS)、程序升温还原(H_(2)-TPR)等一系列表征,证实介孔存在条件下, Pd的纳米颗粒更小且更易于还原,因此介孔Beta沸石负载Pd催化剂在甲烷催化燃烧反应中表现出更好的活性.动力学研究表明,介孔Beta沸石负载Pd催化剂在该反应中具有更低的表观活性能.

The environmental problems caused by the release of unburned methane from stationary and mobile combustion processes is becoming more serious in recent years.The catalytic combustion of methane has been regarded to be superior to the conventional combustion,and consequently efficient catalysts play important roles during the process.In this study,mesoporous Beta zeolites have been prepared in the presence of a kind of polymer polydiallyldimethylammonium chloride(PDADMAC)as the mesoscale template and been used for the catalytic combustion of methane after supporting Pd.The samples have been intensively characterized by a series of techniques including X-ray diffraction(XRD),N_(2) adsorption,scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray photoelectron spectroscopy(XPS),temperature program reduction(H_(2)-TPR)etc.It was found that mesoporous volume of the samples could be controlled by altering the amount of mesoporous template(PDADMAC)and Pd nanoparticles supported on mesoporous Beta zeolites were smaller and more reducible than those supported on the conventional Beta zeolites.Furthermore,Pd(Ⅱ)species were assigned to be the crucial active sites based on the results of XPS together with H_(2)-TPR,and the ratio of the Pd(Ⅱ)determined the catalytic performance.The relatively strong interaction between Pd and the hydroxyl group(caused by the formation of mesopores)of mesoporous Beta zeolites benefit the high ratio of Pd(Ⅱ)species.As a result,mesoporous Beta zeolites supported Pd showed better catalytic performance in the catalytic combustion of methane than the conventional Beta zeolites supported Pd.As a typical example,Pd/meso-Beta-H2 sample gave T90(90%conversion temperature)at only 342℃,which was much lower than that of Pd/Beta without mesopores(384℃)at the same condition.Additionally,catalytic life test exhibited that Pd/meso-Beta-H_(2) sample was stable and the conversion remained even after 50 h at high temperatures.Kinetics analysis revealed that the apparent activation energies for mesoporous Beta zeolites supported Pd(86~118 kJ/mol)were much lower than that of the conventional Beta zeolites supported Pd(140 kJ/mol).The excellent catalytic performance of mesoporous Beta zeolites supported Pd would be potentially important for the catalytic combustion of methane in the future.