【作者】 邹旭华；

【导师】 段雪；

【作者基本信息】 北京化工大学 ， 应用化学， 2006， 博士

【摘要】 负载型金催化剂是一类新型的工业和环保催化材料，其CO低温氧化催化性能在封闭式CO₂激光器、航天器及潜水艇等密闭系统、CO气体传感器、CO气体防护面具以及氢燃料电池等许多领域具有广泛的应用前景。近年来，关于如何制备低负载量、高活性的金催化剂，尤其是如何提高金催化剂的稳定性，是非常活跃的研究领域。本研究采用多种方法制备了Au／Al₂O₃和Au／MO_x／Al₂O₃两类金催化剂，考察了其在CO低温氧化反应中的催化活性，较为详尽地研究了金的负载量、溶液的pH值、还原和焙烧预处理条件等制备因素对催化剂性能的影响，优化了制备条件。比较了催化剂在干燥的原料气和水汽饱和的原料气中的稳定性，考察了经过水汽饱和的空气或者加热的空气处理后催化剂活性的变化，探讨了催化剂失活的原因。运用XRD、BET、XPS、AAS、TEM、TPD、FTIR等多种手段对催化剂的结构进行了表征，并与催化性能进行了关联。主要结果如下：1．采用沉积-沉淀法制备Au／Al₂O₃催化剂时，金的负载量、反应溶液的pH值、反应温度、预处理条件等制备因素对催化活性有显著的影响。还原和焙烧预处理均可以得到金颗粒大小在10nm范围内的Au／Al₂O₃催化剂；还原比焙烧预处理所制得的催化剂活性更高，其原因是还原预处理得到的催化剂中金颗粒的尺寸更小，分散度更高。2．采用阴离子浸渍法制备Au／Al₂O₃催化剂时，浸渍溶液的pH值、浸泡洗涤方式、浸渍时间、预处理条件等制备因素对催化活性有显著的影响。阴离子浸渍法具有制备方法简单、不需加热、金的负载率高和重复性好等优点，而且可以通过氨水浸泡洗涤有效地去除催化剂表面的Cl^-离子而提高其催化活性，适用的pH值广泛，甚至在强酸性条件下都能够制得催化活性很高的Au／Al₂O₃催化剂。3．Au／Al₂O₃催化剂的失活及稳定性研究表明：（1）催化剂在干燥的原料气中反应，其CO氧化催化活性逐渐下降；而在水汽饱和的原料气中比在干燥的原料气中反应具有更长的使用寿命和更高的稳定性。经水汽饱和的空气或者加热的空气处理后催化剂的活性均会下降。（2）Au／Al₂O₃的失活方式主要有：CO氧化失活、热处理失活以及水汽处理失活，前二者主要是由于类似碳酸盐物种的生成、催化剂活性位中-OH的脱除，属可逆失活；水汽处理失活不可逆，主要归因于金颗粒的长大。4．采用改进的两步法制备Au／FeO_x／Al₂O₃催化剂时，FeO_x的负载量、FeO_x的存在状态、浸渍溶液的pH值等制备因素对催化活性存在不同程度的影响。焙烧预处理所制得Au／Fe₂O₃／Al₂O₃催化剂的活性较高，Fe₂O₃的负载量对催化剂的活性几乎没有影响：而还原预处理所制得Au／Fe₃O₄／Al₂O₃催化剂的活性较差，Fe₃O₄的负载量越高，催化活性越差。采用该法在较宽的pH范围内均可以制得活性很高的Au／Fe₂O₃／Al₂O₃催化剂。5．采用一步法制备Au／MO_x／Al₂O₃催化剂时，金的负载量、反应溶液的pH值、焙烧预处理温度、金属氧化物MO_x的种类等制备因素对催化活性有显著的影响。该方法简便有效，重复性好，金的负载率高、分散均匀，能够制得活性比Au／Al₂O₃催化剂更高的系列Au／MO_x／Al₂O₃（M=Fe，Fe+Cu，Co，Zn）催化剂。6．Au／FeO_x／Al₂O₃催化剂的稳定性研究表明：（1）Au／Fe₂O₃／Al₂O₃比Au／Al₂O₃催化剂在CO氧化反应中表现出更高的稳定性和更长的使用寿命。（2）焙烧预处理所制得的Au／Fe₂O₃／Al₂O₃催化剂，比还原预处理所制得Au／Fe₃O₄／Al₂O₃催化剂具有更高的反应稳定性和更长的使用寿命。（3）Au／Fe₂O₃／Al₂O₃催化剂具有更高催化活性的原因可能是Fe₂O₃的加入为CO氧化反应提供了更多的活性氧。更多还原

【Abstract】 Supported gold catalysts are a new kind of catalytic materials. The low-temperature CO oxidation performance over the gold catalysts foreshows a wide application prospect in a large number of industrial and environmental protection fields, such as closed-cycle CO₂ lasers, sealed-spaceships and submarines, CO gas sensors, CO safety masks and hydrogen fuel cells etc. In recent years, more attentions have been paid to the new methods for the preparation of the gold catalysts with low gold loadings and high activity, especially the high stability.In this paper, Au/Al₂O₃ and Au/MO_x/Al₂O₃ catalysts were prepared bymany methods. The catalytic activities for low-temperature CO oxidation ofthese catalysts were investigated. The effects of preparation factors such asgold loadings, pH value of solution and pretreatment conditions etc on thecatalytic activities were studied in detail. The preparation conditions wereoptimized. In addition, the long-time stability of the catalysts reacting in dry reactant gas and reactant gas saturated with H₂O vapor was compared, the activity changes of the catalysts treated by air saturated with H₂O vapor or by air heated above 100℃were examined, and the reasons for the deactivation of the catalysts were discussed. The characterization of the catalysts were carried out by XRD、BET、XPS、AAS、TEM、TPD、FTIR measurements, and the results were related to the catalytic performance.The main results obtained are as follows:1．Study of the preparation of Au/Al₂O₃ by DP methodThe preparation conditions such as gold loadings, the pH value of reaction solution, reaction temperature and pretreatment conditions have great influence on the catalytic activities. The size of gold particles in the catalysts pretreated by reduction or calcination can be controlled below 10 nm. The catalysts pretreated by reduction show higher activity than those obtained by calcination, which may be resulted from that reduction pretreatment gives smaller gold particles with higher dispersion, while calcination pretreatment tends to decrease the catalytic activity by giving bigger gold particles.2．Study of the preparation of Au/Al₂O₃ by anionic IMP methodThe preparation conditions such as the pH value of impregnation solution, the steeping way, impregnation time and pretreatment conditions have great influence on the catalytic activities. Compared with the DP method, the anionic impregnation method has the following merits: simplicity, no need to be heated, higher gold loading ratio and good reproduction. The effect of steeping the samples in NH₃ ? H₂O is to eliminate the Clˉions completely and improve the catalytic activity. The appropriate range of pH value is wider, even under the condition of strong acidity, the high activity of Au/Al₂O₃ catalyst can be obtained.3．Study of the deactivation and stability of Au/Al₂O₃（1） The high initial activity of the Au/Al₂O₃ catalyst is followed by a gradual decrease during CO oxidation; while the catalyst exhibits longer life-time and better stability reacting in reactant gas saturated with H₂O vapor than in dry reactant gas. Treatment either by air saturated with H₂O vapor or by air heated above 100℃may deactivate the catalysts. （2） There are three main deactivations of Au/Al₂O₃ catalysts for CO oxidation: i) CO oxidation deactivation, ii) thermal treatment deactivation, and iii) H₂O vapor treatment deactivation. The first two deactivations are reversible, which may be caused by the accumulation of carbonate-like species during CO oxidation or the removal of-OH ligands in active site. The growing of gold particles may be responsible for the last deactivation, which is irreversible.4．Study of the preparation of Au/FeO_x/Al₂O₃ by two-step methodThe preparation conditions such as the amount and the nature of FeO_x, pH value of impregnation solution have influence on the catalytic activities to the different degree. Au/Fe₂O₃/Al₂O₃ catalyst pretreated by calcination shows higher activity, the Fe₂O₃ loadings have little influence on the activity; while Au/Fe₃O₄/Al₂O₃ catalyst pretreated by reduction exhibits lower activity, the higher the FeO loadings, the lower the catalytic activity. Au/Fe₂O₃/Al₂O₃ catalyst with high activity can be obtained in a wider pH range.5．Study of the preparation of Au/MO_x/Al₂O₃ by one-step methodThe preparation conditions such as the gold loadings, pH value of solution, calcination temperature, the kind of MO_x have great influence on the catalytic activities. This one-step method has the following merits: simplicity, efficiency, higher gold loading ratio, high gold dispersion and good reproduction. Compared with Au/Al₂O₃, all of Au/MO_x/Al₂O₃ （ M = Fe, Fe+Cu, Co, Zn ） catalysts prepared by this method show the improved activity.6．Study of stability of Au/FeO_x/Al₂O₃（1） By comparison with Au/Al₂O₃, Au/Fe₂O₃/Al₂O₃ catalyst shows the improved stability for the CO oxidation and the longer life-time. （2） Au/Fe₂O₃/Al₂O₃ catalyst pretreated by calcination exhibits higher stability and the longer life-time than Au/Fe₃O₄/Al₂O₃ catalyst pretreated by reduction. （3） The reason why the Au/Fe₂O₃/Al₂O₃ is more active than Au/Al₂O₃ may be that the addition of Fe₂O₃ can supply more active O species needed for CO oxidation.更多还原