金催化剂在环氧丙烷尾气回收中的应用研究

采用沉积-沉淀法制备了Au负载催化剂。通过对CO在催化剂上的低温催化氧化反应的研究,考察了载体选择,Au的质量分数,金属助剂修饰和反应温度等对反应的影响。结果表明,载体的选择和Au的含量对催化活性都有较大影响,γ-Al2O3是除氧实验中性能优良的催化剂载体材料。使用金属氧化物修饰载体可起到提高催化剂活性,增强催化剂稳定性的作用。     

富氢气体中CO优先氧化催化剂研究进展

以高纯氢为燃料的质子交换膜燃料电池广泛应用于电动汽车,但其阳极容易被富氢气体中含有的少量CO毒化,造成电池性能严重降低。富氢气体在进入燃料电池前,必须进行CO净化处理。优先氧化法是除去富氢气体中少量CO最简单经济有效的方法,常用催化剂主要有Pt系、Au系和Cu系催化剂。着重阐述负载Au催化剂的制备方法、载体调变、助剂改性以及其他因素（如反应气氛中CO与O₂浓度比、水蒸汽和CO₂等）对Au催化剂CO优先氧化反应催化性能的影响。介绍以CuO/CeO₂催化剂为典型的非贵金属氧化物催化剂用于CO优先氧化反应的研究成果以及制备方法、载体和助剂改性等对催化性能的影响和反相结构CeO₂/CuO的催化性能。考虑利用催化剂活性组分,尤其是Au与Cu之间的协同作用,选用合适的载体,进行催化剂组分的设计仍然是今后研究的热点。突破常规无定形金属氧化物作载体,通过设计合成具有特定形貌的载体,研究不同晶面和不同价态等因素对催化剂CO优先氧化催化性能的影响,也是一项很有意义的研究。     

双羟基金属氢氧化物负载的金催化剂的稳定性

以3种层板组成的层状双羟基金属氢氧化物(layered double hydroxides,LDHs)为载体,制备了负载型金催化剂样品(Au/MgAl-LDHs,Au/ZnAl-LDHs和Au/MgFe-LDHs),借助X射线衍射、透射电子显微镜和光电子能谱,表征了金催化剂样品的物性,研究了催化剂样品在CO常温催化氧化反应中的活性及稳定性。结果显示,LDHs载体表面的金以金属态存在,其粒径1~5 nm,在常温下,金催化剂对CO的转化率达100%。另外,金催化剂在使用过程中失活的主要原因是载体晶体结构不稳定:晶体结构的坍塌使载体表面的纳米金颗粒被覆盖,导致表面金含量降低而失活。此外,LDHs的层状结构坍塌也削弱了载体与纳米金颗粒之间的相互作用,使得纳米金颗粒因迁移、聚集、长大而失活。催化剂的稳定性顺序由大到小依次为Au/MgAl-LDHs,Au/ZnAl-LDHs和Au/MgFe-LDHs,稳定性的差异与LDHs层板的电荷密度有关,电荷密度最大的MgAl-LDHs负载的金催化剂稳定性最高,连续使用69 h后,CO的常温转化率仍能保持100%。     

ZnO晶面对纳米Au催化CO氧化性能的影响

采用水热合成法制备了无择优暴露晶面的盘状ZnO（ZnO-D）和优先暴露（100）非极性面的片花状ZnO（ZnO-F）;通过沉积-沉淀法将Au纳米颗粒负载于所制备的ZnO载体表面;采用ICP、XRD、SEM、TEM、XPS和BET对合成的催化剂进行表征;最后,以CO氧化为探针反应研究载体晶面对金纳米颗粒催化性能的影响。结果表明,ZnO形貌对Au颗粒粒径影响甚微,但Au物种的电子价态表现出显著的载体形貌依赖性。以盘状和片花状ZnO为载体所获得的金催化剂的Au^δ+物种的原子分数分别为34.8%和67.4%,说明Au颗粒与片花状ZnO间具有更强的金属-载体相互作用。Au/ZnO-F催化剂的CO氧化活性明显优于Au/ZnO-D,归因于Au/ZnO-F具有较高的O₂吸附活化能力。本文通过调控载体形貌/晶面进而调变金属-载体间相互作用及Au物种的化学态的方法提高了Au催化性能。     

胶体负载法制备Au/C催化剂用于乳酸合成的研究

将预先制备好的十二烷基硫醇保护的纳米金胶体负载到用硝酸处理过的活性炭上,制备得到纳米Au/C催化剂,并用1,2-丙二醇直接氧化合成乳酸的反应考评催化剂。重点讨论载体的预处理方法和负载温度对金胶体负载的影响以及载体上金的含量、粒径、热处理方式等对纳米金催化剂活性的影响。结果表明:胶体负载法制备的纳米Au/C催化剂在1,2-丙二醇直接氧化合成乳酸反应的转化率达到50%以上,选择性达到80%以上。     

Au/Sn-deAl-β的制备及其催化甘油氧化酯化的性能研究

以SnCl₄接枝的脱铝β分子筛(Sn-deAl-β)为载体,采用沉积-沉淀(DP)法制备了不同Au质量分数的Au/Sn-deAl-β催化剂;利用XRD、XRF、N₂物理吸附和NH₃-TPD对Au/Sn-deAl-β进行表征,并考察了催化剂制备方法、组成、结构和反应条件对甘油氧化酯化制备乳酸甲酯性能的影响。结果表明,Si/Al摩尔比为510、Au理论质量分数为1%且DP过程中pH为9.00的条件下制备的Au/Sn-deAl-β催化剂具有最高的乳酸甲酯选择性;Au/Sn-deAl-β催化剂兼具氧化脱氢位点和Lewis酸中心,能够高选择性地实现甘油氧化酯化制备乳酸甲酯。此外,甘油氧化酯化的产物与Au颗粒尺寸和催化剂酸性密切相关,小尺寸的Au颗粒相对有利于甘油酸甲酯和乙醇酸甲酯的生成。     

Au/ZnO催化5-羟甲基糠醛的氧化反应研究

生物质作为一种重要的可再生能源,且可以被转化为多种高附加值化学品和液体燃料,受到众多科研人员的关注。其中,5-羟甲基糠醛(HMF)作为生物质原料与高附加值化学品之间的重要桥梁,被美国能源部认定为十二大高值生物质基平台化合物之一,其催化转化研究已成为当前的研究热点。本研究通过合成不同尺寸的ZnO催化剂载体,并在其表面负载金属Au,得到了不同尺寸的Au/ZnO催化剂。利用XRD和TEM等表征方法,对制备的Au/ZnO系列催化剂进行了物性分析,并评价其对HMF催化氧化反应中的性能。研究结果表明,ZnO载体尺寸大小、Na₂CO₃浓度和HMF的浓度等因素均能够影响HMF的氧化反应效率。     

Au/TiO_2-B催化剂的CO低温氧化性能

探索Au纳米粒子对新型材料的催化性能可以显著拓宽金催化剂的应用范围。使用TiO2-B作为载体,担载Au纳米粒子并应用于低温CO氧化反应体系。TiO2-B为长度5~20?m的微米级纤维,Au纳米粒子粒径在3 nm以下,均匀地分散在TiO2-B表面。CO氧化测试表明,Au纳米粒子的性能受TiO2-B焙烧温度的影响,不同焙烧温度会引起Au分散性以及Au纳米粒子与载体相互作用的改变。分散于纯TiO2-B载体上的金的催化活性可与其分散在锐钛矿纳米粉体上的相媲美。此外,300℃下活化的Au纳米粒子表现出了最佳的CO氧化性能,在氧化性气氛中活化的催化剂的催化性能优于在惰性和还原性气氛中活化的催化剂。     

Au/TiO2-B催化剂的CO低温氧化性能

探索Au纳米粒子对新型材料的催化性能可以显著拓宽金催化剂的应用范围。使用TiO₂-B作为载体,担载Au纳米粒子并应用于低温CO氧化反应体系。TiO₂-B为长度5～20 mm的微米级纤维,Au纳米粒子粒径在3 nm以下,均匀地分散在TiO₂-B表面。CO 氧化测试表明,Au纳米粒子的性能受TiO₂-B焙烧温度的影响,不同焙烧温度会引起Au分散性以及Au纳米粒子与载体相互作用的改变。分散于纯TiO₂-B载体上的金的催化活性可与其分散在锐钛矿纳米粉体上的相媲美。此外,300℃下活化的Au纳米粒子表现出了最佳的CO氧化性能,在氧化性气氛中活化的催化剂的催化性能优于在惰性和还原性气氛中活化的催化剂。     

Au/CeO_2-cube催化1,3-丙二醇氧化酯化反应性能

采用沉积-沉淀法制备了高活性的Au/Ce O2-cube催化剂,并对催化剂进行了电感耦合等离子发射光谱、透射电镜、X射线衍射和X射线光电子能谱表征。将制得的催化剂用于1,3-丙二醇选择性氧化酯化反应,考察了沉淀剂尿素的用量、Ce O2-cube载体焙烧温度、催化剂焙烧温度、Au负载量和沉积温度对反应性能的影响,结果表明:尿素和Ce O2-cube的质量比为6、沉积温度80℃、Ce O2-cube焙烧温度400℃、催化剂焙烧温度200℃制备的1.5%Au/Ce O2-cube,具有最优的催化活性。在100℃、O2分压2 MPa、1,3-丙二醇和Au的物质的量比为75.5的条件下反应4 h,1,3-丙二醇的转化率达到97.5%,3-羟基丙酸甲酯和丙二酸二甲酯的选择性分别达到90.1%和6.1%。将用过的催化剂在200℃焙烧2 h烧掉表面的中毒物质后循环使用4次,催化性能略有降低,性能下降主要是由催化反应过程中Au颗粒粒径的长大造成的;催化剂上2.0~4.0 nm左右的具有少量Auδ+的负载纳米Au单质颗粒有助于醇的氧化酯化反应。     

Solvent free liquid phase oxidation of benzyl alcohol using Au supported catalysts prepared using a sol immobilization technique

Solvent free oxidation of benzyl alcohol was investigated in the absence of a base using Au catalysts prepared by sol immobilization on titania and carbon supports. Comparison between the Au supported catalysts revealed that activity and distribution of products was dependent on the nature of support and heat treatment. Specifically, heat pre-treatment of the Au catalysts has a beneficial effect in terms of activity, but is detrimental in terms of selectivity to the benzaldehyde. We conclude that sol immobilization is a suitable technique for preparing gold catalysts with small particle size and narrow particle size distributions and very high activity and selectivity for benzyl alcohol oxidation.     

Au–TiO2 catalysts stabilised by carbon nanofibres

The catalytic activity and stability in the water–gas shift reaction have been tested for Au-based catalysts prepared by deposition of Au from colloid solutions. The supports that have been used are TiO₂, TiO₂ supported on carbon nanofibres (CNF) and CNF. Thermal treatments of the samples show that the Au particle size depends on the support material and hence the interaction between the Au particles and the support. In situ X-ray absorption spectroscopic (XAS) measurements during the water–gas shift reaction show no changes in the first Au–Au coordination number for the catalysts containing CNF. Furthermore, improved short-time stability is obtained compared to the AuTiO₂ catalysts. The improved stability is achieved by the CNF stabilising small TiO₂ particles and hence prevent subsequent sintering of the Au particles.     

Nanoengineering catalyst supports via layer-by-layer surface functionalization

Recent progress in the layer-by-layer surface modification of oxides for the preparation of highly active and stable gold nanocatalysts is briefly reviewed. Through a layer-by-layer surface modification approach, the surfaces of various catalyst supports including both porous and nonporous silica materials and TiO₂ nanoparticles were modified with monolayers or multilayers of distinct metal oxide ultra-thin films. The surface-modified materials were used as supports for Au nanoparticles, resulting in highly active nanocatalysts for low-temperature CO oxidation. Good stability against sintering under high-temperature treatment was achieved for a number of the Au catalysts through surface modification of the support material. The surface modification of supports can be a viable route to control both the composition and structure of support and nanoparticle interfaces, thereby tailoring the stability and activity of the supported catalyst systems.     

Preservation of the Activity of Supported Gold Catalysts for CO Oxidation

Procedures leading to the preservation of activity of supported gold catalysts for CO oxidation are reviewed. The inclusion of iron as Fe(OH)₃ in preparing catalysts using tin oxide, ceria and zirconia as supports gives better activity and much improved stability with time-on-stream. In the case of Au/Fe-SnO₂ (0.5–0.9% Au), the effect is maximal with ~4% Fe. The stability of catalysts based on ceria as support is also much better when small amounts of either iron or lanthanum during preparation of the support by thermal decomposition of nitrates. Au/SnO₂ catalysts often suffer initial deactivation followed by an increase in activity with time-on-stream; a period of refrigeration (7d) induces an excellent stability at high conversion.     

A comparative study on the selective hydrogenation of α,β unsaturated aldehyde and ketone to unsaturated alcohols on Au supported catalysts

The hydrogenation of trans,4-phenyl,3-buten,2-one (benzalacetone) and trans,3-phenyl, propenal (cinnamaldehyde) was carried out on Au supported on iron oxides catalysts. Commercial goethite (FeOOH), maghemite (γFe₂O₃) and hematite (αFe₂O₃) were used as supports. The catalytic activity of Au/Fe₂O₃ reference catalyst, supplied by the World Gold Council, was also investigated. Gold catalysts and the parent supports were characterized by BET, X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption of ammonia (NH₃-TPD) and high resolution transmission electron microscopy (HRTEM).Among the catalysts investigated Au supported on FeOOH shows the highest activity and selectivity to UA in the hydrogenation of unsaturated carbonyl compounds whereas Au supported on αFe₂O₃ are the less active and selective catalysts.The catalytic activity and selectivity to unsaturated alcohols (UA) in the hydrogenation of benzalacetone and cinnamaldehyde are less influenced by the morphology of gold particles and are mainly influenced by the nature of the support.A correlation between the reducibility of the catalysts and the activity and selectivity to UA has been found. Increasing the reducibility of the catalysts both the activity and selectivity to UA increase. These results let us to argue that active and selective sites are formed by negative gold particles formed through the electron transfer from the reduced support to the metal.     

Characterization by Mössbauer spectroscopy of trimetallic Pd–Sn–Au/Al2O3 and Pd–Sn–Au/SiO2 catalysts for denitration of drinking water

The reduction of nitrate using a catalytic process is one of the most interesting ways to solve the problem of drinking water pollution by this compound. The key parameter of this technique is the selectivity toward nitrogen formation. Palladium/tin-based bimetallic catalysts are well suited for this purpose, but the selectivity of these catalysts is not high enough for a direct application of this process. In the present study, alumina- and silica-supported catalysts were prepared by successive deposition of tin and gold onto palladium particles by using controlled surface reaction. The characterization of trimetallic Pd–Sn–Au catalyst evidenced that trimetallic catalysts supported on silica present a palladium/tin/gold phase. The catalytic test showed that this type of catalyst is very active and selective in nitrate and nitrite reduction. Moreover, the addition of gold improves the stability and the selectivity toward nitrogen formation of the catalyst compared to the parent Pd–Sn catalyst.     

用于丙烯环氧化反应的金催化剂

以氢气和氧气混合气为氧源的丙烯环氧化反应是金催化剂应用研究的主要反应。综述了金催化剂在丙烯环氧化反应中的载体材料影响、金纳米粒子作用以及金纳米粒子与载体之间的协同作用对催化性能的影响,提出气相直接氧化丙烯生产环氧丙烷尚待解决的技术问题和相应的研究新亮点。     

Dendrimer templates for heterogeneous catalysts: Bimetallic Pt–Au nanoparticles on oxide supports

Polyamidoamine (PAMAM) dendrimers were used to template Pt, Au, and bimetallic Pt–Au dendrimer encapsulated nanoparticles (DENs) in solution. Adjusting the solution pH allowed for slow, spontaneous adsorption of the nanoparticles onto silica, alumina, and titania. After dendrimer removal, the catalysts were characterized with infrared spectroscopy of adsorbed CO and tested with CO oxidation catalysis. Infrared spectroscopy of the monometallic Pt catalysts showed a slight shift in the CO stretching frequency for the different supports. For the bimetallic catalysts, infrared spectra showed CO adsorbed on both Pt and on Au sites. Spectra collected during CO desorption showed substantial interactions between the two bands, confirming the presence of bimetallic particles on all the supports. The bimetallic catalysts were found to be more active than the monometallic catalysts and had lower apparent activation energies. The titania supported Pt–Au catalyst was resistant to deactivation during an extended treatment at 300 °C. Correlations between IR spectra and catalytic activity showed differences between the mono- and bimetallic materials and implicated a bimetallic Pt–Au ensemble at the catalytic active site. This is the first study to show that DENs are appropriate precursors for studying support effects on catalysis by metal nanoparticles, although the magnitude of the effects were small.     

CO oxidation activity of gold catalysts supported on various oxides and their improvement by inclusion of an iron component

A number of oxide-supported gold catalysts have been prepared by deposition–precipitation, with variation of the pH over a wide range, the optimum pH for high activity being 9 for TiO₂, 7.5 for Fe₂O₃, and 7 for SnO₂ and CeO₂. Whereas the activity shown by Au/TiO₂ and Au/Fe₂O₃ decreased linearly with time, Au/CeO₂ and Au/SnO₂ underwent an initial major deactivation. Addition of iron in the preparation lowered the rate of deactivation when TiO₂, SnO₂ and CeO₂ were used as supports, and imparted activity when as with Bi₂O₃ it was previously lacking. XPS revealed the existence of a broad multi-state iron-containing region, and TEM and STEM/EDX indicated that small gold particles (1.5–4 nm) were partly in contact with it. Improved stability is therefore due to gold particles being in contact with an iron phase such as FeO(OH); calcination removed the stabilisation.