EISA表面修饰法制备抗烧结催化剂

通过催化剂表面修饰控制催化剂表面活性组分颗粒的表面迁移能力,可以提高催化剂的抗烧结性能。通过蒸发诱导自组装(EISA)法修饰催化剂表面制备抗烧结催化剂,并对其性能进行研究。将经过验证的可形成二维有序介孔薄膜的EISA起始溶液沉积在Pd@Si O_2模型催化剂表面,采用TEM表征m Si O_2@Pd@Si O_2催化剂结构,证明了EISA表面修饰法的可行性。将EISA表面修饰法用于修饰Pd/Al2O3催化剂,通过表面涂覆的次数控制修饰层的厚度。XRD和甲烷燃烧活性结果表明,经过修饰的m Si O_2@Pd/Al2O3催化剂耐高温性能提高,其中,涂覆两次后的催化剂表面Pd O纳米颗粒晶粒尺寸增大程度最小,甲烷燃烧活性最好。EISA表面修饰法制备抗烧结催化剂是一种提高催化剂高温稳定性的有效方法。     

Catalytic activity of PdO/ZrO2 catalyst for methane combustion

Catalytic activity of ZrO₂ supported PdO catalysts for methane combustion has been investigated in comparison with Al₂O₃ supported PdO catalysts. It was found that the drop of catalytic activity owing to decomposition of PdO at a high temperature region (600–900°C) was suppressed by using ZrO₂ support. Temperature-programmed reduction (TPR) measurements of the catalyst with hydrogen revealed that the PdO of PdO/Al₂O₃ catalyst was reduced at the temperature less than 100°C, whereas in PdO/ZrO₂ catalyst the consumption of hydrogen was also observed at 200–300°C. This result indicates that the stable PdO species were present in the PdO/ZrO₂ catalyst. In order to confirm the formation of the solid solution of PdO and ZrO₂, X-ray diffraction (XRD) analyses of the mixtures of ZrO₂ and PdO calcined at 700–900°C in air were carried out. The lattice volume of ZrO₂ in the mixture was larger than that of ZrO₂. Furthermore, the Pd thin film on ZrO₂ substrate was prepared as a model catalyst and the depth profile of the elements in the Pd thin film was measured by Auger electron spectroscopy (AES). It was confirmed that Zr and O as well as Pd were present in the Pd thin film heated at 900°C in air. It was considered that the PdO on ZrO₂ support might be stabilized by the formation of the solid solution of PdO and ZrO₂.     

电镀法制备FeCrAl合金负载的Co_3O_4催化剂及对丙烷的电焦耳催化氧化

金属载体负载型催化剂的电焦耳催化氧化是挥发性有机物控制技术,其核心是向金属载体中通入电流,产生焦耳热来实现负载的催化剂活化。受制于催化剂涂层与金属载体之间较低的黏附力,催化剂在金属表面的负载是技术难点。将Co和Ce电镀到FeCrAl合金表面,焙烧形成氧化物催化剂,并用于丙烷的电焦耳催化氧化。结果表明,对合金载体表面进行阳极氧化预处理,可以有效促进催化剂组分的分散,而且催化剂涂层上有空穴结构,有利于反应过程的传质; CeO_2的存在显著提高Co_3O_4催化剂对丙烷的催化氧化性能。通过进一步优化,电镀法可成为制备金属负载型催化剂的有效方法。     

Preparation of catalyst Pd-Au/1cTiO2/SiO2 and epoxidation of olefins

Two kinds of Pd-Au bimetallic nanocatalysts (0.01% Pd-Au/1cTiO₂/SiO₂ and 0.05% Pd-Au/1cTiO₂/SiO₂) were prepared by using 1cTiO₂/SiO₂ as support, which had a single layer TiO₂ thin film on SiO₂ substrate by atomic layer deposition (ALD) technique. Deposition of Au and Pd on 1cTiO₂/SiO₂ was carried out by means of deposition precipitation and impregnation. Au loading of the two catalysts was both 0.01%(mass), and the Pd loading were 0.01% and 0.05% respectively. The prepared catalysts were characterized by transmission electron microscopy (TEM), energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS), and the morphology of nanoparticles, the chemical valence state and composition of Pd and Au elements were determined. The Pd-Au bimetallic nanocatalysts were used in the selective epoxidation of cyclohexene using oxygen as oxidant, and the conditions such as the reaction solvent, the type of co-reductant and the reaction temperature were screened. The applicability of the catalyst to different structural olefins was investigated under the optimized reaction conditions. For cyclic olefins, the substrate conversion rate is greater than 95%, and the epoxy product selectivity is greater than 91%. After the catalyst is recycled 5 times, the catalytic activity and reaction selectivity remain unchanged.     

Pd-Au/1cTiO2/SiO2催化剂的制备及其烯烃的环氧化性能

使用沉淀沉积法及溶液浸渍法分别将Au和Pd纳米粒子负载在原子层沉积法制备的1cTiO₂/SiO₂载体上,制备出两种不同Pd负载量的Pd-Au双金属活性中心纳米催化剂。采用TEM、EDX、XPS对所制备的催化剂进行了详细的表征,确定了纳米粒子的形貌、Pd-Au元素的化学价态和组成。测试了该类催化剂在以氧气为氧源的环己烯环氧化反应中的活性和选择性,并对反应溶剂、共还原剂种类、反应温度等条件进行了筛选。在优化后的反应条件下考察了该催化剂对不同结构烯烃的适用性。对于环状烯烃,底物转化率均大于95%,环氧产物选择性均大于91%。催化剂在循环回收5次后,催化活性和反应选择性保持不变。     

乙炔氢氯化制氯乙烯Pt/C催化剂的性能

以PtCl₄和PtCl₂为活性组分,活性炭为载体,采用浸渍法制备Pt/C催化剂,考察Pt/C催化剂用于乙炔氢氯化制取氯乙烯的催化性能,并采用热重分析、N₂等温吸附-脱附和H₂-TPR等方法对Pt/C催化剂进行表征。结果表明, 加入少量Pt(Ⅱ)（质量分数20%）有利于提高催化剂的初始活性,但加剧了催化剂失活。而活性组分被还原是催化剂失活的主要原因,反应过程中积炭堵塞微孔结构也是导致催化剂失活的原因。     

助剂Zn对PtSn/Al2O3催化剂丙烷脱氢性能的影响

以羰基铂锡化合物为前体,采用浸渍法将其负载于Zn改性Al₂O₃载体上制备了PtSn/xZn-Al₂O₃催化剂,考察了Zn的添加对催化剂丙烷脱氢性能的影响。采用N₂吸附-脱附、X射线衍射（XRD）、吡啶红外吸附（Py-IR）、氨气程序升温脱附（NH₃-TPD）、透射电子显微镜（TEM）等手段对催化剂的孔结构、表面酸性以及积炭行为进行了分析。结果表明,PtSn/xZn-Al₂O₃催化剂孔道以介孔为主,孔径集中分布于8～10nm;Zn助剂的添加,在催化剂表面会形成ZnO物种,可使PtSn/Al₂O₃催化剂上的金属颗粒粒径减小、分散更加均匀;Zn的加入能有效降低催化剂表面酸量,主要表现为L中强/强酸中心的降低,随着Zn含量的增加,催化剂表面酸量先减少后增加。少量Zn的存在可使PtSn/Al₂O₃丙烯选择性和稳定性显著提高,但过量Zn的加入会降低催化剂的脱氢活性,适宜Zn的质量分数为0.75%～1.0%。反应后催化剂表面积炭主要表现为烯烃性质和芳香烃性质,Zn的添加可有效抑制积炭的形成,提高催化剂稳定性。     

氢气高温还原制备的负载型镍基催化剂用于苯酚加氢的性能

通过等体积浸渍法分别将Ni(NO₃)₂、NiCl₂、NiSO₄ 3种镍前体浸渍于A1₂O₃或SiO₂载体上,然后通过H₂高温还原法制备了负载型镍基催化剂,考察了镍前体、载体种类、镍负载量、反应条件等对镍基催化剂苯酚加氢性能的影响。结果表明,对比3种镍前体,在H₂高温还原体系中Ni(NO₃)₂最容易被还原,制备的镍基催化剂苯酚加氢活性最高。SiO₂负载的镍基催化剂活性远高于γ-Al₂O₃催化剂。适宜的Ni负载量有助于活性组分的分散和催化活性的提高。镍基催化剂的苯酚加氢产物以环己醇为主,相对缓和的反应条件更容易生成环己酮。在非极性溶剂正庚烷或环己烷存在下,苯酚加氢反应速率远远高于极性溶剂水或乙醇存在下的结果,而且环己酮的选择性更高。     

载体改性对Cu/B/Al2O3结构及其催化醋酸仲丁酯加氢性能的影响

以γ-Al₂O₃为载体采用分步浸渍法制备了不同金属氧化物进行载体改性的Cu/B/M/Al₂O₃(M=Mg,Ca,Ni)催化剂,并测试了其催化醋酸仲丁酯加氢反应的性能。结果表明,以NiO进行载体改性的催化剂导致酯加氢反应中大量酸催化产物及烃类出现;以MgO进行载体改性不利于金属Cu的分散且催化剂的结构稳定性较差;以CaO对γ-Al₂O₃载体进行改性不仅能够促进金属Cu的分散,提高催化剂的酯加氢活性和产物选择性,而且可以有效减少反应中非活性碳物种在催化剂表面的沉积。     

Transient kinetic study of the SCR-DeNOx reaction

The unsteady-state kinetics of the selective catalytic reduction (SCR) of NO with NH₃ is studied over V₂O₅–WO₃/TiO₂ model catalysts by means of the transient response method. NH₃ strongly adsorbs onto the catalyst surface whereas NO does not adsorb appreciably. A dynamic mathematical model based on a Temkin-type desorption process for NH₃ and a SCR reaction rate with a complex dependence on the ammonia surface coverage is well suited to represent the data.     

Catalytic wall reactor: Catalytic coatings of stainless steel by VOx/TiO2 and Co/SiO2 catalysts

Catalytic wall (structured) reactors and structured supports are suitable to study the catalytic properties of nanosized materials. The coating of metallic (aluminum and stainless steel) plates by thin layers of active phase is presented in two cases, VO_x/TiO₂ and Co/SiO₂, catalysts used in the oxidative dehydrogenation (ODH) of propane and in Fischer–Tropsch synthesis (FTS) of clean fuels, respectively. The preparation of coated plates and their characterisation by various methods of physicochemical analysis are described. Both chemical and physical methods were used for coating. VO_x/TiO₂ layers were obtained by grafting of Ti (on Al or stainless-steel plates) and V (on TiO₂) alkoxides and use of sol–gel media or suspension. A silica primer was deposited (on stainless-steel plate) by plasma-assisted chemical vapour deposition (PACVD) onto which Co oxide and silica were coprecipitated from sol–gel. The catalytic experiments in the respective reactions were carried out in special plate reactors and compared with those of catalytic powders. The study shows that the coating of a metallic substrate by a catalyst is not straightforward and requires specific studies dealing with both chemistry (chemical affinity between substrate and catalytic layers) and catalytic engineering (catalytic performance in taylor-made reactors).     

Selective oxidation with air on metal catalysts

Oxidation of organic molecules with air on metal catalysts has been known for a long time but there has been a renewed interest in recent years because these catalytic reactions are environmentally safe and could replace stoichiometric oxidations. This paper describes several oxidation reactions conducted either at high temperatures in the gas phase or at moderate temperatures in the liquid phase; in both cases they proceed via a mechanism of oxidative dehydrogenation on the metal surface. Ethylene glycol was converted to glyoxal at 550°C on Ag/SiC catalyst with a 70% yield provided promoters were added to the reaction feed (diethylphosphite or iodine) or deposited on the catalyst (LiPO₄ or H₃PO₄). The promoters improve the conversion and selectivity by modifying the structure and the oxygen concentration on the surface of silver. Oxidation of glyoxal to glyoxylic acid, glucose to gluconic acid and glycerol to various oxygenated derivatives were conducted in water at 60°C in the presence of carbon-supported palladium or platinum catalysts. Bismuth promoter, deposited on the platinum metals by redox reaction, improves the catalyst activity by preventing over-oxidation of the metal surface and favors the oxidation of secondary alcohol functions into keto-derivatives. At higher reaction temperatures, platinum catalysts produce C-C bond rupture with the formation of carboxylic acids with smaller chains. Thus, cyclohexanol was converted into C₆, C₅, and C₄ diacids with a 45% selectivity to adipic acid on Pt/C catalysts at 150°C.     

Propene oxidation over MoO3 film deposited on an Au|YSZ|Ag system

Propene oxidation was carried out with an electrochemical reactor, MoO₃/Au|YSZ|Ag (YSZ: 8 mol.-% yttria-doped ZrO₂), at 475°C under oxygen pumping, and the catalytic activity of the thin MoO₃ film related to its crystal morphologies was discussed. The thin MoO₃ film was deposited on an Au anode by means of vacuum deposition or sputtering method at room temperature or 300°C. Each method showed a characteristic texture as well as crystal morphology of the MoO₃ film, resulting in variations in the catalytic activity. Sputtering at 300°C gave porous films composed of leaf-like crystals with preferential orientation of (010) plane parallel to the pore channel and perpendicular to the Au surface, resulting in the highest activity for acrylaldehyde production. A relatively high step density was observed on the oriented (010) plane of the leaf-like crystal. The high activity of this MoO₃ film is probably due to the high density of active sites for the partial oxidation of propene and also to their highly porous structure, which is favorable to the surface migration of oxygen to the reduced active sites.     

邻二氯苯在钒-钨-钛催化剂上的完全催化氧化

采用等体积浸渍法制备不同系列钒-钨-钛催化剂,以与二噁英TCDD化学结构式相似的邻二氯苯作为替代物,研究催化剂对邻二氯苯的去除效率,考察钒负载质量分数和钨负载质量分数对邻二氯苯催化氧化性能的影响,通过XRD和催化剂比表面积分析对催化剂的微观结构进行表征。结果表明,随着钒负载质量分数的增加,催化剂比表面积降低,催化剂性能降低;随着钨负载质量分数的增加,催化剂比表面积增加,催化剂性能提高。钨的加入有利于促进活性钒的分散,提高催化剂的比表面积,催化剂比表面积是影响催化剂性能的关键因素。     

Raman spectroscopy of KTN thin films

The renewed interest in the KTa_1-x-Nb_xO (KTN) mixed perovskite materials, especially in single crystalline thin film forms, is connected with their remarkable dielectric properties in the dilute compositions. Off-center Nb ions in the highly polarizable KTaO₃ lattice provide a drastic increase in the dielectric peak up to 20 times in comparison with pure KTaO₃ and KNbO_3. KTN thin films with several Nb concentrations were prepared in the range 0 ≤ × ≤ 1 by pulsed laser deposition. The films were deposited onto MgO substrate. The effect of a substrate and symmetry-breaking defects was studied by micro-Raman spectroscopy. An anomalous residual intensity of the forbidden first-order scattering modes in the cubic paraelectric phase of the KTN films was connected with formation of polar microregions even far above the bulk T_c. On the whole, the KTN film behavior shows the existence of specific defects enhancing the unit perovskite cell in the film so that the activity of off-center Nb ions increases in producing larger electric dipoles and extending the precursor phase above T_c.     

助剂二氧化硅对CO2加氢制备甲醇CuO-ZnO-Al2O3-ZrO2催化剂性能的影响

采用共沉淀法制备了一系列CuO-ZnO-Al₂O₃-ZrO₂(CZAZ)催化剂,用于二氧化碳加氢合成甲醇。通过加入少量的助剂二氧化硅得到了一系列CZAZ/SiO₂改性催化剂。采用XRD、BET、H₂-TPR、NH₃-TPD以及CO₂-TPD等技术进行表征,研究了助剂二氧化硅含量对催化剂的物理化学性质以及组织结构的影响。结果表明,助剂二氧化硅的含量对催化剂的组织结构具有较大的影响。同时评价了该组催化剂参与二氧化碳加氢合成甲醇反应的催化性能。测试结果表明,采用助剂二氧化硅质量分数为4%的改性催化剂,表现出较为优良的催化活性。助剂二氧化硅促进了活性组分氧化铜的分散,并且经过二氧化硅改性的CZAZ催化剂具有更大的比表面积,这些因素都对该催化剂在二氧化碳加氢合成甲醇方面的良好表现起到重要作用。     

Gas-phase dehydration of glycerol over commercial Pt/γ-Al2O3 catalysts

Gas-phase dehydration of glycerol to produce acrolein was investigated over commercial catalysts based onγ-Al2O3, viz. A-64, A-56, I-62, AP-10, AP-56, AP-64 and KR-104. To understand the effect of Cl?anions, HCl-impregnated sup-ports have been investigated in the dehydration reaction of glycerol at 375 °C. For comparison, various H-zeolites were also examined. It was found that the glycerol conversion over the solid acid catalysts was strongly dependent on their acidity and surface area. And the relationship between the catalytic activity and the acidity of the catalysts was discussed. The outstanding properties of Pt/γ-Al2O3 catalyst systems for the dehydration of glycerol were revealed. Pt/γ-Al2O3 catalyst (AP-64) showed the highest catalytic activity after 50 h of reaction with an acrolein selectivity of 65%at a conversion of glycerol of 90%. Based on these results, catalysts based onγ-Al2O3 appear to be most promising for gas phase dehydration of glycerol.     

Model catalyst studies with single crystals and epitaxial thin oxide films

The paper describes recent results from our relatively new program to perform detailed studies of the catalytic properties of metal-oxide materials; in particular, to effect a determination of the active catalytic site(s) and the mechanism for reactions over this especially important class of heterogeneous catalysts. Issues of structure-sensitivity, poisoning and promotion, and competing reaction mechanisms are critical questions that need to be addressed in a detailed manner for catalysis by oxides. As just one important example, both surface (Langmui–Hinshelwood) and direct (Eley–Rideal) reaction mechanisms have been proposed for the selective catalytic reduction (SCR) reaction of nitrogen oxides (NO_x) over vanadia/titania catalysts. For this program, we are using a number of unique, state-of-the-art capabilities available in the Environmental Molecular Sciences Laboratory (EMSL) at Pacific Northwest National Laboratory; for example, the first molecular beam epitaxy (MBE) system dedicated to the growth of model metal-oxide films, and a unique moderate-pressure catalytic reactor/surface science apparatus. We describe the growth, characterization, and water adsorption properties of a thin Fe₃O₄(0 0 1) film grown on a lattice-matched MgO(0 0 1) substrate. Because our moderate pressure catalysis studies are preliminary at this point, we instead describe our previous results on the CO oxidation reaction over a Ru(0 0 0 1) model catalyst to demonstrate the utility of the experimental approach. We specifically discuss the possibility that this reaction occurs by an Eley–Rideal mechanism.     

复合氧化物催化剂催化氧化甲苯性能

以γ-Al2O3为催化剂载体,铜、锰为活性组分,稀土元素铈为助催化剂,采用浸渍法制备复合氧化物催化剂5%Cu/γ-Al2O3、5%Mn/γ-Al2O3、5%Cu-5%Mn/γ-Al2O3和5%Cu-5%Mn-1.6%Ce/γ-Al2O3,并考察其催化氧化甲苯性能。研究表明,复合氧化物催化剂催化氧化甲苯具有显著的效果,5%Cu-5%Mn/γ-Al2O3催化剂和5%Cu-5%Mn-1.6%Ce/γ-Al2O3催化剂表现出良好的低温活性和催化性能,对甲苯的完全燃烧温度分别为340℃和285℃。采用SEM和BET对催化剂进行表征,结果表明,催化剂的催化活性与活性组分在催化剂表面的分散度和催化剂的孔结构相关。     

Low-temperature catalytic combustion of methanol and its decomposed derivatives over supported gold catalysts

Gold can be compared favorably with Pd and Pt in the catalytic combustion of CH₃OH, HCHO and HCOOH when it is deposited on some reducible metal oxides (-Fe₂O₃, TiO₂, etc.). While the supported gold catalysts are less active in H₂ oxidation, they exhibit much higher activities in CO oxidation. For Au/TiO₂, the effect of catalyst preparation was further investigated. Since the activity for CO oxidation of the gold catalysts is not depressed but enhanced by moisture, they are practically applicable to CO removal from air at room temperature. Gold supported on manganese oxide is especially effective in the selective CO removal from hydrogen, indicating its potential applicability to polymer electrolyte fuel cells using the reformed gas of methanol.