【作者】 陈清波；

【导师】 罗来涛；

【作者基本信息】 南昌大学 ， 物理化学， 2007， 硕士

【摘要】 高度分散的Au催化剂对CO低温氧化具有良好的催化活性,有利于降低甲醇催化制氢反应中CO的含量,从而实现氢燃料电池中甲醇对氢气的有效替代。本文以甲醇部分氧化制氢为探针反应,考察了第二组分M（M=Pd、Pt、Ag、Ru）和不同预处理条件对Au催化活性的影响。选择以Au-Pd双金属催化剂为主要考察对象,研究了Pd的含量、不同还原剂、不同保护剂、不同制备方法和复合载体对Au-Pd催化性能的影响。采用XRD、ICP、比表面积测定、H2-TPR、CH₃OH（H₂、CO₂）-TPD等技术对催化剂中Au-Pd及其负载量、粒子大小和形态、比表面积、还原性能、吸附性能和表面碱性进行了表征。1.研究了第二组分M（Pd、Pt、Ru和Ag）对Au/CeO₂催化剂进行改性作用,考察了不同预处理条件对Au催化甲醇部分氧化性能的的影响。Pd或Pt的加入能使Au/CeO₂催化剂的活性提高,而Ru或Ag的加入反而使催化活性降低,催化剂的活性顺序Au₇₀Pd₃₀/CeO₂＞Au₇₀Pt₃₀/CeO₂＞Au/CeO₂＞Au₇₀Ru₃₀/CeO₂＞Au₇₀Ag₃₀/CeO₂。还原后的Au₇₀Pd₃₀/CeO₂催化剂有较高的氢气选择性,表明甲醇部分氧化中Au⁰含量高有利于催化剂活性和氢气选择性的提高。2.采用PVP保护乙醇还原法制备了一系列不同Pd含量的Au-Pd/CeO₂催化剂。研究结果表明,Au₆₀Pd₄₀/CeO₂催化剂中形成了较多的富Au型Au_xPd_y合金,降低了对甲醇的吸附温度,有利于吸附态的甲醇在催化剂表面的迁移,同时减少了对反应产物H₂的吸附,这些均对甲醇部分氧化反应有利。3.研究了乙醇（ER）、乙二醇（GR）和水合肼（HR）等不同还原剂对Au-Pd/CeO₂催化甲醇部分氧化活性和氢选择性的影响。与Au-Pd/CeO₂（GR）和Au-Pd/CeO₂（HR）催化剂相比,Au-Pd/CeO₂（ER）催化剂形成的Au_xPd_y合金较多、比表面较大、粒子较小、分散度较高、金属与载体的相互作用较强、金属表面形成的Lewis碱中心较多,同时对甲醇和CO₂的吸附量较大。4.考察了聚乙烯吡咯烷酮（PVP）、聚乙烯醇（PVA）、和聚乙二醇（PEG）等不同保护剂对Au-Pd/CeO₂催化甲醇部分氧化性能的影响。Au-Pd/CeO₂（PVP）催化甲醇部分氧化活性和氢选择性较好,Au沉积率较高。PVP保护剂的使用增加了Au与Pd间的协同作用,形成较多的Au_xPd_y合金,同时也提高了金属与载体的相互作用,载体表面形成的Ce³⁺较多,CeO₂晶格氧较易向表面迁移,对甲醇吸附量较小及对O₂吸附量较大。5.用柠檬酸钠热还原法（CA）,CTAB保护沉淀法（CTAB）,沉积沉淀法（DP）和PVP保护乙醇还原法（ER）等不同还原法制备了Au-Pd/CeO₂催化剂。Au-Pd/CeO₂（DP）催化甲醇部分氧化活性和氢选择性较好,形成的Au和Au_xPd_y合金粒子较小,活性组分的分散度较高,Lewis碱中心较多,对甲醇和CO₂的吸附量较大,同时使甲醇的吸附温度降低,有利于吸附态的甲醇在催化剂表面的迁移。6.以不同金属复合氧化物为载体（CeO₂、CeO₂-TiO₂、CeO₂-ZrO₂）,采用沉积沉淀法（DP）制备了Au-Pd催化剂。Au-Pd/CeO₂催化甲醇部分氧化活性较好,形成的Au_xPd_y合金和氧空穴较多,甲醇部分氧化活性最好。Au-Pd/CeO₂-TiO₂催化剂中载体的比表面积较大、金属分散度较高、金属粒子较小有利于H₂选择性的提高,而Au-Pd/CeO₂-ZrO₂催化剂H₂选择性较高是金属粒子较小和CeO₂-ZrO₂固溶体的形成共同作用的结果。CeO₂-ZrO₂和CeO₂-TiO₂复合载体均能提高Au-Pd催化剂的H₂产率,H₂选择性高是H₂产率提高的主要原因。更多还原

【Abstract】 The hydrogen may be produced directly from methanol in fuel cells.If the level of CO exceeds a few ppm,the precious metal-based anode electrocatalyst of the fuel cell will be deactivated.Au catalysts,exhibiting high activity for CO oxidation at low temperature,are used for partial oxidation of methanol（POM）and can reduce the content of CO.The effects of second constituent M（Ag,Ru,Pd and Pt）,content of Pd,reduce methods,preparing methods and mixed oxide supports on activities of Au-Pd/CeO₂ catalysts for POM were studied.The prepared samples were characterized by XRD,ICP,nitrogen adsorption-desorption,H₂-TPR and CHaOH（H₂, CO₂）-TPD experiments.1.The performance of Au/CeO₂ is influenced by the addition of second constituent M（Ag,Ru,Pd and Pt）.The results indicate that the activity of Au-Pd/CeO₂ bimetallic catalysts for POM was the best.2.A series of the PVP-stabilized Au-Pd/CeO₂ bimetallic catalysts with different Pd content were prepared and the activities of Au-Pd/CeO₂ catalysts for POM were studied.Comparing the Au-Pd/CeO₂ catalysts with other Pd content,catalytic active of Au₆₀Pd₄₀/CeO₂ catalyst is higher, because of it has more AuxPdy and H₂ chemisorption amount,lower reduced temperature.3.Different reduced methods may change the particles size and synergistic effect between Au and Pd.The influence of difference reduced methods on the performance of Au-Pd/CeO₂ catalysts was studied.The results show that Au-Pd/CeO₂（ER）catalyst reduced by ethanol has higher methanol conversion,hydrogen selectivity and lower contentof CO for POM.For Au-Pd/CeO₂（ER）catalyst, it had larger BET surface area,dispersion and CH₃OH adsorption amount,stronger interaction between metal and support,formed more number of Au_xPd_y alloy and smaller particles size.4.The different polyelectrolyte-stabilized Au-Pd/CeO₂ catalysts were prepared by CH₃CH₂OH reductant and the performance of Au-Pd/CeO₂ catalysts is studied.A number of Au_xPd_y alloys are found in Au-Pd/CeO₂（PVP）catalyst.Comparing with the Au-Pd/CeO₂（PEG）and Au-Pd/CeO₂ （PVA）catalysts,Au-Pd/CeO₂（PVP）catalyst has stronger interaction between Au-Pd and support, lower CH3OH adsorption amount,and forms more number of Ce³⁺on the surface of CeO₂ support, all these are advantageous to the catalytic activity enhancement.5.Different approaches to preparing highly dispersed Au-Pd/CeO₂ catalysts may even have excellent resistance to sintering and show high activity.The influence of difference preparation methods on the performance of Au-Pd/CeO₂ catalysts was studied.The results indicated that Au-Pd/CeO₂（DP）catalyst prepared by deposition-precipitation method show higher methanol conversion and hydrogen selectivity,the methanol conversion was 100% and hydrogen selectivity更多还原