用于合成4-(反-4′-正丙基环己基)环己酮催化剂的研究

环己酮衍生物作为一种重要的液晶中间体,其制备方法尤其是催化加氢合成法的研究受到关注。以质量分数55%HNO₃处理的工业椰壳活性炭为载体,采用等体积浸渍与沉积-沉淀结合的方法制备0.9%Au-5%Pd/C-IM-DP催化剂,并应用于选择性加氢制备4-(反-4′-正丙基环己基)环己酮的反应。以环己烷作为溶剂,在反应温度150 ℃和反应压力0.8 MPa条件下反应2 h,原料转化率为98.7%,目标产物选择性达91.2%。相比于单金属5%Pd/C催化剂,0.9%Au-5%Pd/C-IM-DP催化剂具有较高的活性和选择性。通过XRD和TEM等对催化剂组成和形貌进行表征分析,结果表明,Au和Pd均以单金属颗粒形式存在,而Pd和Au之间的氢溢流作用可能是催化剂具有优异性能的原因。     

新型等离子体光催化剂Au/Cd2Nb2O7的制备和性能研究

通过沉积-沉淀法将纳米Au颗粒负载于宽带隙的Cd2Nb2O7光催化剂上,利用纳米金的表面等离子体效应,使其具有可见光响应。样品通过X射线粉末衍射(XRD)、透射电镜(TEM)、紫外-可见漫反射(UV-Vis DRS)、X射线光电子能谱(XPS)和液体荧光(PL)等表征了其晶相结构、形貌、光吸收性能、表面化学态和活性物种。结果表明,催化剂中的金是以金属态的形式存在,其粒径大约为5nm,并且在载体表面的分散性良好;催化剂在可见光区540nm处有明显的Au纳米粒子的表面等离子体共振吸收峰。光催化降解罗丹明B结果表明所合成的Au-Cd2Nb2O7具有良好的可见光光催化活性,同时对其可能的光催化降解机理也进行了探讨。     

Non-hydrothermal synthesis of copper-, zinc- and copper-zinc hydrosilicates

Cu/SiO₂, Zn/SiO₂ and Cu-Zn/SiO₂ samples have been prepared by the homogeneous deposition-precipitation method. The samples were analyzed by thermal analysis, X-ray diffraction and infrared spectroscopy after various heat treatments and compared with data obtained for several minerals. It has been shown that interaction between the components occurs through formation of hydrosilicates. Copper-silica system at a Cu:Si ratio ≤ 1, gives rise to a hydrosilicate stable up to a calcination temperature of 930 K resembling the mineral Chrisocolla; at higher ratios a hydroxonitrate (gerhardite type) is also formed. Zinc-silica interaction produces two hydrosilicates such as a well crystallized Hemimorphite at Zn:Si = 2 and highly dispersed Zincsilite at Zn:Si ≤ 0.75, both stable up to 1073 K. The Zincsilite structure consists of three layered sheets (an octahedral layer sandwiched by two tetrahedral ones) like the Stevensite mineral group. For the copper-zinc-silica system no copper hydrosilicate is formed. Copper merely enters the Zincsilite structure independenly of the applied (Cu + Zn):Si ratio. Resulting layered copper-zinc hydrosilicate may be described by formula Zn_x-yCu_y(Zn_3-x–zCu_z–y▪_x)[Si₄O₁₀](OH)₂.nH₂O, where Zn_3-x-zCu_z-y– ions are located in octahedral sites, Zn_x-yCu_y–ions in the interlayer; ▪_x are vacancies in the layers. Copper and zinc in excess of the Zincsilite ratio of Me:Si = 0.75, gives rise to copper and copper-zinc hydroxonitrates. Received: 7 November 2000 / Reviewed: 23 January 20001 / Accepted: 23 January 2001     

New redox deposition-precipitation method for preparation of supported manganese oxide catalysts

A new preparation method has been developed to produce homogeneous coatings of manganese compounds on alumina-coated monoliths by redox deposition-precipitation using acetone as solvent. The deposition is produced by reduction of manganese permanganate with ethanol. The Lewis acid sites on the alumina catalyze this reaction. Thus, the precipitation is produced preferentially on the surface of the monolith and not in the bulk of the solution. Monoliths prepared by this method are very active for the complete oxidation of oxygenated volatile organic compounds (VOCs). These monoliths consist of a mixture of complex phases including aluminum, sulfated alumina, potassium sulfate and manganese oxide.     

载体对Au-Pd催化剂甲醇部分氧化性能的影响

采用沉积沉淀法制备了一系列Au-Pd双金属催化剂,研究了不同载体对Au-Pd双金属催化剂甲醇部分氧化性能的影响,并运用XRD、TPD和TPR等手段对催化剂进行了表征。结果表明,Au-Pd/CeO₂催化剂中形成的Au_xPd_y合金和氧空穴较多,致使Au-Pd/CeO₂催化剂的活性较高;CeO₂-TiO₂和CeO₂-ZrO₂复合载体较大的比表面积和固溶体的形成有利于H₂选择性的提高;Au-Pd/CeO₂-ZrO₂和Au-Pd/CeO₂-TiO₂催化剂有较高H₂产率的主要原因是H₂选择性的提高。     

二氧化钛的沉积-沉淀水热制备及其光催化性能

以硫酸钛为原料,采用沉积-沉淀水热法制得了TiO2粉体光催化剂。以光催化降解活性艳红X-3B作为模型反应,考察了所制得的TiO2粉体的光催化性能。发现140℃沉积-沉淀水热反应20 h、600℃焙烧制得的TiO2粉体光催化活性明显高于Degussa P25 TiO2,并且该TiO2粉体光催化剂沉降性好,易分离。     

草酸二甲酯加氢制乙二醇Cu/SiO2催化剂的制备与改性

采用均匀沉淀沉积法制备Cu/SiO₂催化剂。考察了Cu²⁺浓度、洗涤条件及铜与硅物质的量比等的影响,并通过BET和XRD等表征手段研究分析,结果表明,前驱体制备过程及条件对催化剂结构和活性有较大影响。低Cu²⁺浓度、醇洗干燥均有利于形成大孔径高活性的催化剂。铜与硅物质的量比对反应活性的影响较大,存在一个最佳值,在0.4时活性最高。最优条件下制得的催化剂用于草酸二甲酯加氢制乙二醇,在反应温度205 ℃、压力2 MPa、n(H₂) ∶n(DMO)=80和空速1.0 h^-1条件下,草酸二甲酯的转化率为100%,乙二醇选择性为99.1%,乙醇酸甲酯选择性为0.9%,无其他副产物生成。     

SnO2 decorated SiO2 chemical sensors: Enhanced sensing performance toward ethanol and acetone

SnO₂ decorated SiO₂ chemical sensors with different Sn/Si ratios were synthesized by micro-emulsion followed by ultrasonic-assisted deposition-precipitation method and used for highly sensitive and selective detection of ethanol and acetone. XRD, EDS, SEM, and TEM were used to characterize the samples. The results confirm deposition of small crystalline tin oxide particles on the surface of silica particles. Using these formed materials for detection of ethanol and acetone resulted in significant enhancement of the sensitivity and reducing temperature of maximum response in comparison to the pure SnO₂. The selectivity of the sample with the highest sensitivity to ethanol and acetone, i.e. 80 wt% SnO₂/SiO₂, was examined by measuring its sensitivity to some interfering gases including carbon monoxide, methane, toluene, Trichloroethylene (TCE) and propane; the results showed very high selectivity of the sensor to ethanol and acetone, especially at low temperatures. The sensor responses to traces of acetone in the air with the concentration ranging from 0.5 to 5 ppm at different temperatures of 70, 170 and 270, and 370 °C were measured to evaluate the capability of the sensor for detection of acetone in the breath of human, which is helpful in the diabetes diagnosis. The sensor could effectively show high enough sensitivity even to these very low concentrations of acetone which reveals its high potential for being used in acetone detection devices. Finally, the effect of humidity on the sensitivity of sensor to acetone was investigated. Increasing the humidity of background air, caused the sensor response to decrease and the operating temperature of maximum response of the sensor to increase.     

The preparation of Au/CeO2 catalysts and their activities for low-temperature CO oxidation

Au/CeO₂ catalysts prepared by co-precipitation (CP) and deposition-precipitation (DP) methods were tested for low temperature CO oxidation reaction. The structural characters and redox features of the catalysts were investigated by XRD, XPS and H₂-TPR. Their catalytic performances for low temperature CO oxidation were studied by means of a microreactor -GC system. It showed that the catalytic activities of Au/CeO₂ catalysts greatly depended on the preparation method. The catalysts prepared by DP method exhibited a surprisingly higher activity towards CO oxidation than that prepared by CP method. This may arise from the differences in the particle sizes of Au and redox properties of the catalysts. The low Au loading and the resistance to high temperature of DP-prepared catalyst made it more applicable.     

介孔MnO_x-CeO_2/γ-Al_2O_3催化CO低温氧化反应

采用沉积沉淀法制备一系列介孔MnO_x-CeO_2/γ-Al_2O_3催化剂,并进行X射线衍射、H_2程序升温还原表征。考察锰铈摩尔比、锰铈复合氧化物负载量、煅烧温度对CO转化率的影响。实验结果表明,当锰铈元素摩尔比为7∶3,锰铈复合氧化物负载量为9%,催化剂煅烧温度450℃时,催化氧化CO效果最好;在160℃时CO的转化率达到94%,在180℃时CO可完全氧化。