Effect of the metal−support interaction in Ag/CeO<Subscript>2</Subscript> catalysts on their activity in ethanol oxidation

The interaction of silver with the surface of CeO₂ in the Ag/CeO₂ catalysts prepared by coprecipitation and impregnation techniques was studied by temperature-programmed reduction, X-ray diffraction, and high-resolution transmission electron microscopy. It was shown that coprecipitation technique led to formation of strong silver–support interaction and the epitaxy of silver particles (d ₁₁₁ = 2.35 Å) on the surface of CeO₂ (d ₁₁₁ = 3.1 Å). This provided incresed catalytic activity in the oxidative dehydrogenation of ethanol at relatively low temperatures (a 15% conversion of ethanol with 100% selectivity for the formation of acetaldehyde was reached at 85°C). Above 130°C, the deep oxidation of ethanol to CO₂ becomes the predominant direction of a catalytic reaction, and the Ag/CеО₂ catalyst obtained by impregnation technique was most active in this region as a consequence of the weaker metal–support interaction.     

Microwave-assisted Ni–La/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst for benzene hydrogenation

A series of Ni–La/γ-Al₂O₃ catalysts were prepared by adopting the methods of isometric impregnation and microwave impregnation. The catalysts were characterized with XRD, BET, and SEM, respectively. Inspecting the effects of adding La and the methods of impregnation on the hydrogenation activity of catalysts. The results show that adding a moderate amount of La promotes the dispersing of Ni on the carrier, the methods of microwave impregnation weaks the interaction between Ni and the carrier further, inhibits the formation of NiAl₂O₄, and the activity of catalyst prepared by the methods of microwave impregnation was significantly higher than that prepared by the methods of isometric impregnation. The hydrogenation activity of the Ni–La/γ-Al₂O₃ (WB) dipped with n(Ni): n(La) = 4: 1, microwave irradiation time 30 min with power 600W as well as calcined at 400°C exhibited the best performance. The conversion rate is 91.21% with reaction conditions: T = 160°C, p = 0.8 MPa, air speed 5 h^–1, n(H₂): n(benzene) = 2: 1.     

State of palladium in palladium-aluminosilicate catalysts as studied by XPS and the catalytic activity of the catalysts in the deep oxidation of methane

Palladium catalysts based on Siralox and AS aluminosilicate supports for the deep oxidation of methane were studied. With the use of XRD analysis, it was found that they were heterophase systems consisting of an amorphous aluminosilicate and γ-Al₂O₃ stabilized against agglomeration. It was found that the catalytic activity of palladium-aluminosilicate catalysts in the deep oxidation of methane at 500°C depended on the support precalcination temperature. X-ray photoelectron spectroscopy (XPS) was used to study the states of the AS-30 aluminosilicate support calcined at 600, 800, or 1000°C and palladium supported on it. It was found that the action of an acid impregnation solution of palladium nitrate on the aluminosilicate calcined at 800°C resulted in a structural rearrangement of the aluminosilicate surface. This rearrangement resulted in the stabilization of both palladium oxide and palladium metal particles at surface defects and the incorporation of these particles into the aluminosilicate after catalyst calcination. As a result, an anomalous decrease in catalytic activity was observed in aluminosilicate samples calcined at 800°C. According to XPS data, palladium in the catalyst was stabilized in the following three phases: metal (E _b(Pd 3d _5/2) = 334.8 eV), oxide (E _b(Pd 3d _5/2) = 336.8 eV), and “interaction” (E _b(Pd 3d _5/2) = 335.8 eV) phases. The ratio between these phases depended on support and catalyst calcination temperatures. The interaction phase, which consisted of PdO_x clusters stabilized in the aluminosilicate structure, was responsible for the retention of activity after calcination at high temperatures (800°C). Based on an analysis of XPS data, it was hypothesized that palladium in the interaction phase occurred in a charged state with the formal charge on the Pd atom close to 1 + (δ+ phase).     

AlZn based Co and Ni catalysts for the partial oxidation of bioethanol — influence of different synthesis procedures

The catalytic performance of Co and Ni catalysts on AlZn mixed oxide supports depends on the synthesis procedure used for their preparation. For this study CoAlZn and NiAlZn catalysts were prepared by conventional sol-gel synthesis of the mixed oxide and subsequent impregnation of the support with the transition metal (SG = sol gel method) as well as by a single-step method were a gel is formed based on salts of all components using citric acid as chelating agent (CM = citrate method). The structure and morphology of the catalysts were characterized by nitrogen sorption, XRD and TPR measurements. They showed high activity in the partial oxidation of ethanol at 600–750 °C, but their properties depend on the preparation method. The higher performance of the catalysts prepared by the citrate method, where the transition metal is incorporated into the crystal structure of the support during preparation, is based on a change in morphology and structure, resulting in more active sites exposed on the surface. Compared to the Co catalysts, Ni catalysts showed a higher performance. This might be due to the higher reducibility and the smaller Ni particles size, which allows a better interaction with the support in NiAlZn catalysts.      

Fischer–Tropsch synthesis over CNT-supported cobalt catalyst: effect of magnetic field

In the present work, the cobalt catalysts supported on carbon nanotubes (CNTs) were prepared by impregnation method in the presence and absence of magnetic field. The prepared catalysts were employed to yield higher hydrocarbons via Fischer–Tropsch synthesis. It is explored that using magnetized water can effectively change the catalyst geometry in impregnation catalyst preparation method. For the preparation of different sizes of cobalt particles on the CNTs support, the physical properties of solvent (water) in impregnation process were changed using the magnetizing process. The results showed that the average particle sizes of impregnated cobalt nanoparticles were decreased by using magnetized water in impregnation step. In addition, in the magnetized treated cobalt catalyst, the cobalt particles mostly dispersed outside the tubes because the capillary forces decreased by reducing water surface tension. Furthermore, the experimental results showed that the probability of chain growth (α) and selectivity to heavier hydrocarbons increased in magnetized water treatment catalysts.     

Formation of the active surface of Ag/SiO2 catalysts in the presence of FeO x additives

Supported FeO _x -modified silver catalysts based on commercial silica gel and prepared via impregnation with a solution of Fe- and Ag-containing salts while varying the amount of modifier from 1 to 10 wt % are studied. It is found that the introduction of Fe-containing compounds leads to the distribution of silver in the form of clusters/ions on the surface of SiO₂, improving the reducibility of the systems in the H₂ TPR mode. After reduction at 800°C, the catalysts containing 10 wt % iron and 5 wt % silver comprise a Fe₂SiO₄ iron silicate phase.     

Electron distribution of small Ni particles and Ce ions in X and Y zeolites related to their catalytic properties

Catalytic behaviour of nickel particles smaller than 1.3 nm, encaged in X and Y zeolites, in the presence of Ce³⁺, is related to their electronic properties. In general the rates of reaction are lower than those of a standard catalyst made of 2.5 nm nickel particles on SiO₂; this is attributed to the strong localization of the Ni 3d states due to the size effect. However a high rate, more than twice the standard, is found for Ni in X zeolite, in relation with a Ni 3d ¹⁰ configuration. On the other hand the fragmentation of butane is deeper with Ni in Y support than in X support and this corresponds to a high density of Nid states at the Fermi level.     

Influence of the Sol-Gel Method on a NiO/Al2O3 Catalyst for CH4/O2 to Syngas Reaction

NiO/-Al₂O₃ catalysts were prepared by the impregnation and the sol-gel method. The sintering and loss of nickel, carbon deposition and 80 h life-test for POM reaction over the catalyst were investigated by a flow-reactor and by XPS, TG, EXAFS and AAS analysis. The results indicated that the sol-gel method could enhance the ability to suppress carbon deposition and to resist nickel sintering and loss over nickel-based catalysts.     

Catalytic epoxidation of alkenes over supported manganese oxide with hydrogen peroxide: effect of supports and manganese loading

Manganese oxides supported on γ-Al₂O₃, amorphous SiO₂, MCM-41, and TiO₂ prepared by an impregnation method were used as heterogeneous catalysts for epoxidation of alkenes with 30 % H₂O₂ in the presence of NaHCO₃ aqueous solution. The effect of support and manganese loading on their activity was studied. The 1.3-MnO _x /γ-Al₂O₃ exhibited superior epoxidazing activity of styrene, compared with other supported MnO _x . Hydrogen temperature-programmed reduction, UV–vis and ESR analyses suggested that Mn²⁺ (catalytic activity species) dominated in 1.3 % MnO _x /γ-Al₂O₃ due to a strong interaction between MnO _x and γ-Al₂O₃. Recycling studies showed the catalyst was a heterogeneous one and retained its activity after recycling four times.     

A cathode for solid polymer electrolyte fuel cells: Designing the optimal structure of the active layer

The complete computer simulation of the cathodic active layer with solid polymer electrolyte (Nafion) is carried out. The active layer structure can be described by 8 parameters. In designing the optimal structure, it is shown that to provide the high overall characteristics of the cathode and save the catalyst, 0.5 of the active layer volume should be set aside for the support grains (agglomerates of carbon particles covered with platinum and containing Nafion incorporations and microvoids). Protons and oxygen molecules must be supplied to the active layer by means of peculiar combined percolation clusters. The latter consist of a combination of support grains with either Nafion grains (to produce “protonic” clusters) or grains-voids (to afford “gas” clusters). The volume fractions of Nafion grains and grain-voids are assumed to be 0.25 and 0.25. The computer simulation of the support grain structure is also carried out. Their composition, i.e., the volume fractions of the carbon component (g _e), Nafion (g _ii), and microvoids (g _gg), is varied. The support grains play the key role in the active layer functioning. It is impossible to organize three full-value percolation clusters (electronic, protonic, and gas); hence, one has to have one or two combined clusters in the active layer. Thus the double load fells on the support grains. Their optimal structure should not only sustain the transport of protons and electrons in the active layer but also create the best conditions for the electrochemical process in each grain. The maximum current I _max (realized upon reaching the optimal active layer thicknesses Δ*) is calculated. The dependences of I _max and Δ* on the main parameters characterizing the support grains (g _e and g _ii) are analyzed. Here, two goals are sought: (1) to obtain the high currents, (2) to provide the low consumption of platinum per power unit. To solve the first problem, one has to work with high values of g _e. The second problem requires the opposite: the values of g _e must be minimal possible.     

Lactic acid based sol–gel process of Ag nanoparticles and crystalline phase control of Ni particles in aqueous sol–gel process

Nickel and silver particles were prepared by using sol–gel auto-combustion method under N₂ atmosphere where lactic acid was applied as chelating agent. The synthesis of nickel particles was carried out at various pH conditions (2–7), resulting in the face-centered-cubic or hexagonal-close-packed crystalline nickel phase. The morphology and structure of synthesized nickel particles and silver nanoparticles were characterized by X-ray diffraction, transmission electron microscope, energy dispersive X-Ray spectroscopy and differential scanning calorimetry-thermogravimetric analysis. The results show that the spherical Ag nanoparticles with diameters in the range of 18–27 nm and narrow size distribution can be obtained by this sol–gel process.     

固相浸渍法制备NiO/CeO2催化剂及其在CO氧化反应中的应用

采用固相浸渍法制备了一系列NiO/CeO2催化剂,并通过与常规湿浸渍法比较,考察了制备方法对催化剂和CO氧化反应性能的影响.同时结合X射线衍射(XRD),N2吸附-脱附(BET),透射电镜(TEM),氢气-程序升温还原(H2-TPR),拉曼(Raman)光谱,X射线光电子能谱(XPS)等手段对催化剂的结构和表面物种分散状态进行了表征.CO氧化活性测试结果表明,当镍负载量相同时,固相浸渍法制备的催化剂相比于湿浸渍法表现出更好的催化性能.TEM、XPS、H2-TPR结果表明,固相浸渍法更有利于加强镍铈间的相互作用和得到高分散的镍物种,从而促进镍物种的还原.Raman结果表明固相浸渍法相比于湿浸渍法能产生更多氧空位,这有利于氧气在催化剂表面的活化,使得CO氧化反应更容易进行.     

Hydrogenating Activity and Adsorption Capacity of Supported Nickel Catalysts Modified by Heteropoly Compounds

The catalytic activity, adsorption capacity, and pore structure of low-percentage nickel catalysts supported on -Al₂O₃or activated carbon and modified by tungsten heteropoly compounds are studied. The activity, selectivity, and thermal stability of the catalysts in the vapor-phase hydrogenation of olefins and aromatic hydrocarbons are higher than those for conventional nickel catalysts. The concentration of nickel in the catalysts is 10–15 times lower than that in commercial catalysts. However, the modified catalysts have higher specific surface areas of metal, higher dispersion, a uniform distribution of metal particles, and a pore-radius distribution other than in the support. The study of water adsorption and desorption showed that the heteropoly compound modifying the -Al₂O₃support covers the support surface completely, and supported nickel interacts with the active surface of the modifying agent rather than with Al₂O₃. A hydrogenation mechanism is proposed, which involves H₂dissociation on Ni particles and the subsequent diffusion of hydrogen atoms via a spillover mechanism to the adsorbed organic compound with the participation of the OH groups of the modifying agent.     

Prereforming of <Emphasis Type="Italic">n</Emphasis>-tetradecane over Ce-promoted 50 wt% Ni/MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst with high coke resistance

The effect of Ce-promotion on 50 wt% Ni-based catalysts during the prereforming of n-tetradecane and its optimum content were investigated. The Ni catalyst was synthesized by deposition–precipitation method. Next, various amounts of Ce (0–13 wt%) were loaded on the Ni catalyst by impregnation. The characteristics of the prepared catalysts were analyzed by XRD, H₂-TPR, BET, BJH, and H₂-chemisorption analyses. The prepared catalysts were tested under the prereforming conditions (temperature = 400 °C, GHSV = 3000 h^?1, and S/C = 3 and 4). The Ni catalyst was easily deactivated under the following conditions: temperature = 400 °C, GHSV = 3000 h^?1, and S/C = 4. The stability of all Ce-promoted Ni catalysts was improved as compared to that of the Ni catalyst. Among the Ce-promoted catalysts, 5 wt% Ce/50 wt% Ni/MgO–Al₂O₃ catalyst showed excellent stability even under the severe condition of S/C = 3. SEM, TEM, and TG analyses were performed in order to identify the main factor responsible for the rapid deactivation of the Ni catalyst. In the case of 0Ce/50Ni, Ni particles were encapsulated by many folds of coke and it was related to the rapid catalyst deactivation. However, after Ce promoted on the Ni catalyst, the thickness of the coke layers and the number of encapsulated Ni particles decreased and the deposited amount of coke on the catalyst also decreased.     

Comparison of two preparation methods of supported Li?Ni catalyst on alumina for selective oxidation of methane

Lithium-added nickel catalysts on alumina were prepared for CO₂ reforming of methane by two methods, precipitation and impregnation. Performances of the catalysts were investigated by TG, CO-adsorption and SEM analysis. The catalyst with ratio of Li/Ni=1.0 prepared by precipitation method has high nickel dispersion, catalytic activity and stability for CO₂ reforming of methane.     

载体表面氧化程度对Ni/SiC甲烷化催化剂性能的影响

采用等体积浸渍法制备了Ni/SiC甲烷化催化剂, 研究了SiC载体表面氧化程度对催化剂低温活性和高温稳定性的影响, 并采用热重-差示扫描量热、N₂物理吸附、傅立叶变换红外光谱、氨程序升温脱附、X射线衍射、氢程序升温还原和氢化学吸附技术对样品进行了表征. 结果表明, 随着载体氧化温度的提高, 催化剂的比表面积和镍分散度降低, 但还原性和反应稳定性提高. 未氧化载体所负载催化剂的高温稳定性最差, 其原因在于载体对镍粒子的固定作用最弱. 负载于500和700℃处理的SiC载体上的催化剂具有较好的低温活性和高温稳定性, 这是因为适度氧化后的载体能较好地分散并固定镍粒子. 900℃处理的载体因过度氧化形成了低活性的氧化层, 使负载的镍粒子变大, 因而催化剂的低温活性最差.     

Ethylenediamine-Derived Chromatographic Ligand to Separate BSA,Lysozyme, and RNase A

Chromatography has become an essential tool for the purification of proteins, since most purification schemes involve some forms of this methodology. Recently, using chromatographic matrices prepared from symmetrical aminosquarylium cyanine dyes immobilized on Sepharose via a central alkylamino residue, we were able to isolate lysozyme, α-chymotrypsin and trypsin from a mixture. Following this, we envisioned that the immobilization of an asymmetric squarylium dye bearing an N-carboxyethyl group in one of its ending nuclei, on ethylenediamine-activated Sepharose, through EDC/NHS amidation coupling, could enhance the ligand’s mobility and improve the interactions with the target proteins. The prepared support was found to separate an artificial mixture of BSA, lysozyme, and RNase A. Unexpectedly, the support prepared in the absence of the dye exhibited a separation performance similar to that of the dyed support, contrary to that observed in all previous studies using cyanine dyes as ligands for affinity chromatography, which prompted us to try to determine the structural molecular constitution of the matrix surface. A synthetic route to the final chromatographic support could be devised, which is believed to consist in the cyclization of two nearby ethylenediamine units, involving the inclusion of a succinimide-derived residue between them and the EDC-mediated Lossen rearrangement of an intermediary hydroxamic acid.     

PMMA films refractive index modulation via TiO2 nanoparticle inclusions and corona poling

The present study is focused on the characterization of optical properties of poly (methyl methacrylate) (PMMA) films and the possibilities of modulation and fine tuning of their refractive index by the inclusion of different concentrations of nano-sized titanium dioxide (TiO₂) particles (less than 33 nm) and corona poling. The samples are prepared by the “spin coating” method and they are charged in a conventional point-to-plain corona system. The transparent PMMA/TiO₂ films exhibit good optical properties in the visible range. An investigation of the film’s surface refractive index by two wavelengths laser refractometry utilizing the disappearing diffraction pattern method is carried out. The refractive index increases with increasing the TiO₂ content in the nanocomposite films. The corona poling increases the refractive index values for all samples regardless of the polarity and concentration of TiO₂ nanoparticles. The results show that the prepared nanocomposite films have a potential application for optical devices.