苯乙烯环氧化反应分子筛催化剂研究进展

综述了苯乙烯环氧化制取环氧苯乙烷的几种分子筛／H2O2催化体系，介绍了微孔分子筛（TS-1）、Ti-ZSM-5和Ti-ZSM-11分子筛介孔分子筛（MCM-41），β-钛硅分子筛、负载金属配合物的中孔分子筛及其在苯乙烯环氧化反应中的性能。     

Styrene Epoxidation over Carbon Nanotube-Supported Gold Catalysts

Carbon nanotube supported gold catalysts prepared by deposition–precipitation with urea (DP urea) were characterized by various techniques. Its catalytic activity was examined for the oxidation of styrene using t-butylhydroperoxide as oxidant. This system showed good epoxide selectivity. The other factors, such as solvent, reaction time, concentrations of oxidant and catalyst, have also been investigated and reaction conditions are optimized. It is a novel highly active/selective and reusable heterogeneous catalyst for styrene epoxidation.     

Vapor-Phase Epoxidation of Propene over Au/Ti-MCM-41 Catalysts: Influence of Ti Content and Au Content

Ti-MCM-41 samples were used for propene epoxidation using H₂ and O₂ after Au deposition by deposition--precipitation. Au nanoparticles supported on Ti-MCM-41 with Ti incorporated hydrothermally followed by post-synthesis grafting gave higher propene oxide yields than Ti-MCM-41 with Ti incorporated hydrothermally or by grafting. Au L₃-edge EXAFS spectra show the presence of metallic Au for the low Au content (0.21 wt%) catalyst which is more selective to epoxidation, while at high Au loadings (0.42 wt%) oxidic Au species are observed and the catalyst shows lower epoxide selectivity.     

The Effects of Water on CO Oxidation over TiO2 Supported Au Catalysts

Polarization modulation infrared reflection absorption spectroscopy (PM-IRAS) was used to investigate the effects of water on CO oxidation catalyzed by TiO₂ supported Au. The introduction of water into the reactant mixture caused two effects: (1) a decrease in the CO coverage; and (2) the appearance of a carbonate species. Since both effects inhibit CO oxidation, the promotional effects of water found by previous researchers can only be rationalized by its effects on molecular oxygen adsorption and activation. Although this argument is not confirmed by the PM-IRAS data alone, this conclusion is consistent with previous studies. It is further inferred from this study that carbonate species first form on TiO₂ sites and then migrate to Au sites. Surface hydroxyl species may play the same promotional role as adsorbed water.     

负载型Au／TiO2催化剂的研制及其性能研究

一氧化碳（CO）是涉及到工业、环保、军事和人类生活等多个方面的空气污染物,用于氧化CO的催化剂的研究是催化领域里的一个重要课题,目前用于氧化CO的催化剂主要是以铂、钯、铑等贵金属为主要活性组分和以氧化铜、氧化锰等一些过渡金属氧化物作为活性组分的催化剂。虽然这些催化剂已经商品化,但其在抗湿、抗硫中毒等诸多性能方面仍存在一些缺陷。因而有必要研制和开发用于CO净化的高效催化剂。目前的研究表明,沉积沉淀法是制备负载型催化剂最好的方法。金（Au）作为活性组分具有较好的催化效果,且其价格相对于铂、钯等贵金属较为低廉．从一定程度上降低了原材料的成本;而以具有多相光催化性能的半导体二氧化钛（TiO2）为载体,将会兼具二者的优势,与活性组分产生协同效应。可是,目前关于Au／TiO2催化剂在抗水／抗硫性能等方面的研究尚有欠缺。 为此,本实验以TiO2为载体,分别采用沉积沉淀法和改良浸渍法制备一系列Au／TiO2催化剂,探索高性能Au／TiO2催化剂的制备技术,同时考察该类催化剂在不同条件下对CO的催化氧化效果及其抗湿、抗硫性能。     

Ni2P/TiO2对甲苯的催化加氢反应性能

以TiO2为载体,磷酸盐为前驱物,用程序升温还原方法制备了系列Ni2P/TiO2催化剂。用X射线衍射（XRD）对催化剂样品的物相进行了分析表征。以甲苯气相加氢反应考察了Ni2P/TiO2催化剂的加氢反应性能。结果表明,TiO2载体上制备的催化剂主要物相为Ni2P。Ni2P/TiO2催化剂对甲苯加氢反应具有较高的转化率、100％产物选择性以及良好的稳定性能。反应温度和反应H2流速对甲苯转化率有影响,随反应温度的增加,甲苯转化率先增加后降低,250℃时,相对较高。随反应H2流速的增加,甲苯转化率降低。Ni负载量及前驱体中P含量对催化剂的性能也有影响,随Ni负载量及P含量的增加,催化剂的活性均先升高后降低,P含量较低的催化剂有部分失活。     

Mesoporous Au/TiO2 Catalysts for Low Temperature CO Oxidation

The activity and stability of structurally well defined mesoporous Au/TiO₂ catalysts with different support morphologies and pore sizes for low temperature CO oxidation was investigated by kinetic measurements and in-situ IR spectroscopy. The resulting catalysts with Au particle sizes of ∼3 nm exhibit a high activity for CO oxidation, similar to or exceeding that of highly active standard Au/TiO₂ catalysts with similar size Au nanoparticles and loading, and a significantly lower tendency for deactivation. Possible reasons for the improved performance of these catalysts are discussed.     

Low temperature CO oxidation over Au/TiO2 and Au/SiO2 catalysts

After a high-temperature reduction (HTR) at 773 K, TiO₂-supported Au became very active for CO oxidation at 313 K and was an order of magnitude more active than SiO₂-supported Au, whereas a low-temperature reduction (LTR) at 473 K produced a Au/TiO₂ catalyst with very low activity. A HTR step followed by calcination at 673 K and a LTR step gave the most active Au/TiO₂ catalyst of all, which was 100-fold more active at 313 K than a typical 2% Pd/Al₂O₃ catalyst and was stable above 400 K whereas a sharp decrease in activity occurred with the other Au/TiO₂ (HTR) sample. With a feed of 5% CO, 5% O₂ in He, almost 40% of the CO was converted at 313 K and essentially all the CO was oxidized at 413 K over the best Au/TiO₂ catalyst at a space velocity of 333 h^–1 based on CO + O₂. Half the chloride in the Au precursor was retained in the Au/TiO₂ (LTR) sample whereas only 16% was retained in the other three catalysts; this may be one reason for the low activity of the Au/TiO₂ (LTR) sample. The reaction order on O₂ was approximately 0.4 between 310 and 360 K, while that on CO varied from 0.2 to 0.6. The chemistry associated with this high activity is not yet known but is presently attributed to a synergistic interaction between gold and titania.     

Catalytic oxidation of hydrogen over Au/TiO2 catalysts

Selective catalytic oxidation of hydrogen in the presence of hydrocarbons was studied in a fixed bed quartz reactor, over 3 wt%Au/TiO₂ and 5 wt%Au/TiO₂ catalysts. This reaction can be utilised in the production of light alkenes via catalytic dehydrogenation, providing in situ heat to the endothermic dehydrogenation reaction and simultaneously removing a fraction of the produced hydrogen. It is important to avoid the non-selective combustion of the hydrocarbons in the mixture. Both 3 wt%Au/TiO₂ and 5 wt%Au/TiO₂ are active for the combustion of hydrogen, but in a gas mixture with propane and oxygen the selectivity is dependent upon the feed ratio of hydrogen and oxygen. At 550 °C, with propane present, no carbon oxides are formed when the H₂:O₂ ratio is four, but at lower ratios some CO₂ and some CO is formed.     

酒石酸钛配合物在MCM-41上的组装和催化苯乙烯环氧化

采用表面模板组装途径合成了MCM-41介孔材料,研究了这类载体上键合钛酸异丙酯+酒石酸二乙酯(Ti(OiPr)4+DET)和TiCl4+DET两类钛配合物的组装方法。XRD和FT-IR分别被使用来表征载体的晶体结构和载体与钛配合物的键合作用,结果表明:MCM-41在焙烧过程中,其介孔长程有序结构会发生退化,这种结构退化将导致1219和580cm-1红外带的消失,并诱发载体产生强的Si-OH畸变振动。在催化苯乙烯环氧化反应中,用焙烧载体组装钛催化剂显示了最好的氧化活性;而用含模板剂载体组装钛催化剂则显示出最高的环氧化选择性。胺基模板剂和DET配体对钛活性中心的调变作用将造成其活性下降,而环氧选择性上升。     

Performance of Au/M x Oy/TiO2 Catalysts in Water-Gas Shift Reaction

Our group recently developed a series of Au/M _x O _y /TiO₂ catalysts for CO oxidation, and demonstrated that some of these catalysts are still active after high-temperature treatment whereas Au/TiO₂ deactivates significantly due to the sintering of gold nanoparticles at elevated temperatures (Ma Z, Overbury SH, Dai S (2007) J Mol Catal A 273:97). In the current work, the performance of Au/M _x O _y /TiO₂ (M = Al, Ca, Fe, Zn, Ga, Y, Zr, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb) catalysts in water-gas shift (WGS) reaction was evaluated. The influences of different metal oxide (M _x O _y ) additives and pretreatment temperatures were investigated, and the catalyst stability as a function of reaction time on stream was tested. Some of these novel gold catalysts, with high activity and stability in water-gas shift, furnish new possibilities for further fundamental research and industrial development.     

Structure sensitivity of CO oxidation over model Au/TiO2 2 catalysts

Model catalysts of Au clusters supported on TiO₂ thin films were prepared under ultra-high vacuum (UHV) conditions with average metal cluster sizes that varied from ~2.5 to ~6.0 nm. The reactivities of these Au/TiO₂ catalysts were measured for CO oxidation at a total pressure of 40 Torr in a reactor contiguous to the surface analysis chamber. Catalyst structure and composition were monitored with Auger electron spectroscopy (AES) and scanning tunneling microscopy and spectroscopy (STM/STS). The apparent activation energy for the reaction between 350 and 450 K varied from 1.7 to 5 kcal/mol as the Au coverage was increased from 0.25 to 5 monolayers, corresponding to average cluster diameters of 2.5–6.0 nm. The specific rates of reaction ((product molecules) × (surface site)^-1 × s^-1 were dependent on the Au cluster size with a maximum occurring at 3.2 nm suggesting that CO oxidation over Au/TiO₂(001)/Mo(100) is structure sensitive. This revised version was published online in July 2006 with corrections to the Cover Date.     

Microwave Synthesized Mesoporous Vanadium-MFI Catalysts for Epoxidation of Styrene Using Molecular Oxygen

Carbon templated mesoporous vanadium MFI catalysts with different Si/V ratios were successfully synthesized using microwave irradiation. X-ray diffraction studies revealed the formation of more crystalline MFI structures. SEM and TEM imaging also showed well ordered zeolite single crystals having mesoporosity. The N₂ sorption isotherm showed the formation of bimodal mesoporous zeolites. FT-IR studies showed absorbance around 970 cm^?1 corresponding to Si–O–V stretching vibration and the UV–Vis studies revealed strong peaks in the range of 230–340 nm which is related to the presence of tetrahedral V⁵⁺ state. The catalytic activity of the microwave synthesized catalysts was evaluated for epoxidation of styrene using molecular oxygen. The catalysts exhibited 20–40% styrene conversion with 60–75% epoxide selectivity. With increasing Vanadium content, the conversion as well as the selectivity was observed to increase. The catalyst could be recycled for three cycles without a loss in activity.     

苯乙烯催化环氧化制备氧化苯乙烯

以苯乙烯为原料 ,双氧水为氧化剂 ,钼酸铵为催化剂 ,氧化三丁锡为相转移剂 ,硫酸钠为引发剂 ,氯仿为溶剂制备氧化苯乙烯。研究了催化剂、相转移剂、反应时间、氧化剂等因素的影响。实验表明 :当加入 2 5ml苯乙烯、2 5ml双氧水、2 5ml三氯甲烷、0 9g钼酸铵、2 5ml氧化三丁锡和0 1g硫酸钠时 ,双氧水转化率为 86 96%,氧化苯乙烯收率为 74 42 %,反应的选择性为 85 5 8%。     

CO oxidation over Au/TiO2 prepared from metal-organic gold complexes

A series of Au/TiO₂ catalysts has been prepared from precursors of various metal-organic gold complexes (Au _n , n = 2–4) and their catalytic activity for CO oxidation studied. The Au/TiO₂ catalyst synthesized from a tetranuclear gold complex shows the best performance for CO oxidation with transmission electron microscopy of this catalyst indicating an average gold particle size of 3.1 nm.     

Effect of Pretreatment on Carbon-Supported Au/TiO2 Catalysts for Preferential Oxidation of CO

The impact of thermal treatment at various preparation stages of carbon supported Au/TiO₂ catalysts prior to oxidation of CO in the presence and absence of hydrogen was studied. An increase in catalytic activity for thermally treated samples due to a more ordered structure of TiO₂ was observed. A reversible deactivation of the catalysts occurred in the absence of hydrogen. However, the activity was restored at preferential CO oxidation conditions in presence of hydrogen.     

Epoxidation of Cyclohexene over Crystalline and Amorphous Titanosilicate Catalysts

A microporous titanosilicate (TS-1) catalyst was synthesised from an amorphous titanosilicate precursor, and both the amorphous precursor and TS-1 were characterised by Ti K-edge X-ray absorption spectroscopy which revealed that Ti (IV) ions are in tetrahedral coordination in the calcined state. Each of these solids is catalytically active for the conversion of cyclohexene to cyclohexene oxide in the presence of H₂O₂. Use of urea–H₂O₂ adduct as oxidant increased the activity and selectivity for the formation of the epoxide with TS-1 as catalyst. However, a significant loss in catalytic activity is seen for the amorphous precursor.     

制备参数对Au/TiO_2催化剂上CO低温氧化性能的影响

以溶胶-凝胶法制备TiO2载体,用沉积-沉淀法制备出一系列负载型Au/TiO2。系统考察了焙烧温度、金的负载量、反应液pH值、沉淀剂种类以及Cl-存在与否等制备参数对催化剂活性的影响。以室温下CO的催化氧化为探针反应,确定催化剂的最适宜制备参数,并对优化的质量分数为1.0%的Au/TiO2催化剂进行了活性稳定性测试。结果表明：Au/TiO2的最适宜焙烧温度是200～350℃;反应液的最适宜pH值为9;最适宜沉淀剂是NaOH;金的负载量（质量分数,下同）在0.5%～5.0%范围内时,金含量越高,催化剂活性和热稳定性越好。大量Cl-的存在能导致催化剂活性的显著下降。对优化的Au/TiO2催化剂在室温下催化氧化不同浓度的CO进行循环测试,经历3次循环,连续反应2 160 min后,CO的转化率仍为100%。