The effects of silica gel (carrier) on the activity (hydrogen yield) of photocatalytic decomposition of water over [pol-Ti(OBu)4 + CH3OH]-complex

A significant effect of pore size has been found on the yield of photolysis of water to hydrogen, ozone (oxidising product) and methane (decomposing product of catalyst or solvent) using [pol-Ti(OBu)₄ + CH₃OH]-complex/SiO₂. The pore structure of silica gel has been found to provide good conditions for forming this type of catalyst.     

Heterogeneous Baeyer-Villiger oxidation of ketones with H2O2/nitrile, using Mg/Al hydrotalcite as catalyst

We synthesized a magnesium-aluminium hydrotalcite and used it as a catalyst in the Baeyer-Villiger (BV) oxidation of cyclohexanone with a mixture of 30% aqueous hydrogen peroxide and benzonitrile as oxidant. The hydrotalcite proved an excellent catalyst for the process. The influence of experimental variables was examined in depth in order to bring the working conditions as close as possible to those usable on an industrial scale. We optimized the cyclohexanone/hydrogen peroxide/benzonitrile proportion and used various nitriles, solvents and amounts of catalyst, benzonitrile and methanol proving the most effective nitrile and solvent, respectively, for the intended purpose. The reaction was found to occur to an acceptable extent with other carbonyl compounds as substrates; by exception, α,β-unsaturated carbonyl compounds provided poor results by effect of their undergoing competitive epoxidation of their double bonds.     

Kinetics of the Hydrogenation of Pinane Hydroperoxide to Pinanol on Pd/C

The liquid-phase hydrogenation of pinane hydroperoxide (PHP) to pinanol on a Pd/C catalyst at 20–80°C and hydrogen pressures of 1–11 atm was studied. It was found that the rate of hydrogenation decreased with PHP concentration. The rate of PHP hydrogenation dramatically increased as the pressure of hydrogen was increased in a range of 2.5–3 atm. A mechanism was proposed for the hydrogenation of PHP. According to this mechanism, the step of hydrogen activation (homolytic or heterolytic addition) depends on the redox properties of the catalyst surface (the ratio between adsorbed PHP species and H₂). It was found that pinanol can be prepared with high selectivity by the hydrogenation of PHP on a Pd/C catalyst under mild conditions.     

Effect of the reduction conditions of the supported palladium precursor on the activity of Pd/C catalysts in hydrogenation of sodium 2,4,6-trinitrobenzoate

The study addresses the effect of the reduction conditions of palladium polynuclear hydroxo complexes (PHC) supported on the Sibunit carbon material on the dispersion of the metal particles and the activity of 0.5%Pd/Sibunit catalysts in the selective hydrogenation of sodium 2,4,6-trinitrobenzoate to 1,3,5-triaminobenzene in an aqueous solution (temperature of 323 or 343 K, pressure of 0.5 MPa). The palladium PHC were reduced using the most common methods pertaining to catalyst preparation: liquid-phase reduction with sodium formate and reduction in a hydrogen flow at elevated temperature. It was found that high-temperature reduction in the gas phase gives rise to Pd particles with a markedly lower dispersion compared with the sample obtained under mild liquid-phase reduction conditions. The catalytic activity of the sample containing large Pd particles proved to be higher than the activity of the catalyst obtained by reduction with sodium formate.     

Thermal degradation of polystyrene in the presence of hydrogen by catalyst in solution

For the first time, low temperature degradation (170-240 °C) of polystyrene in benzene is carried out in the presence of hydrogen using iron(III) oxide catalyst. The effect of temperature, catalyst loading and polymer loading on degradation are studied in hydrogen atmosphere. Degradation is also carried out at different initial hydrogen partial pressure. The time dependent molecular weight is calculated using viscosity average method. It is found that the degradation is enhanced considerably in the presence of hydrogen and followed random degradation chain scission. A random degradation kinetic model of Kelen [Kelen T. Polymer degradation. New York: Van Nostrand Reinhold Company; 1983.] is used to estimate the degradation rate constants. Empirical correlations are proposed to account for the effect of catalyst loading and initial hydrogen partial pressure on degradation. The true thermal degradation rate constants are calculated using these proposed correlations at given catalyst loading and initial hydrogen partial pressure with varying temperature. The frequency factor and activation energy are also determined using Arrhenius equation considering the true thermal degradation rate constants.     

Steam-reforming of ethanol for hydrogen production

Production of hydrogen by steam-reforming of ethanol has been performed using different catalytic systems. The present review focuses on various catalyst systems used for this purpose. The activity of catalysts depends on several factors such as the nature of the active metal catalyst and the catalyst support, the precursor used, the method adopted for catalyst preparation, and the presence of promoters as well as reaction conditions like the water-to-ethanol molar ratio, temperature, and space velocity. Among the active metals used to date for hydrogen production from ethanol, promoted-Ni is found to be a suitable choice in terms of the activity of the resulting catalyst. Cu is the most commonly used promoter with nickel-based catalysts to overcome the inactivity of nickel in the water-gas shift reaction. γ-Al₂O₃ support has been preferred by many researchers because of its ability to withstand reaction conditions. However, γ-Al₂O₃, being acidic, possesses the disadvantage of favouring ethanol dehydration to ethylene which is considered to be a source of carbon deposit found on the catalyst. To overcome this difficulty and to obtain the long-term catalyst stability, basic oxide supports such as CeO₂, MgO, La₂O₃, etc. are mixed with alumina which neutralises the acidic sites. Most of the catalysts which can provide higher ethanol conversion and hydrogen selectivity were prepared by a combination of impregnation method and sol-gel method. High temperature and high water-to-ethanol molar ratio are two important factors in increasing the ethanol conversion and hydrogen selectivity, whereas an increase in pressure can adversely affect hydrogen production.     

A Convenient Synthesis of Pyridophenanthroline Derivatives under Catalyst Free Conditions

A three‐component reaction between an aromatic aldehyde, quinolin‐6‐amine or quinolin‐5‐amine, and tert‐butyl 2,4‐dioxopiperidine‐1‐carboxylate in reflux EtOH gave pyrido phenanthroline derivatives in high yields under catalyst free conditions. The rare C‐H…F hydrogen bond is found in the crystal structure of 6h .     

Ni/γ-Al2O3催化剂上萘加氢生成十氢萘的催化反应研究

采用Ni/Al₂O₃催化剂,在高压固定床反应器中考察了反应温度、压力、空速和氢油体积比比等因素对萘饱和加氢反应行为的影响,尤其是反应条件对反式十氢萘和顺式十氢萘选择性的影响。研究表明,反式十氢萘和顺式十氢萘的选择性与反应操作条件密切相关;反式十氢萘与顺式十氢萘的比例随着氢油比和温度的升高而增加,而随着压力和空速的增加而减小。在反应温度260-290℃、反应压力为5-7 MPa、空速为1-1.5 h^-1及氢油体积比大于250时,十氢萘的选择性最高可达99%以上,萘的转化率接近100%,产物中反式和顺式十氢萘的比例最高,可达4.0左右。对Ni/γ-Al₂O₃催化剂稳定性进行了考察,初步发现催化活性组分的烧结或流失是催化剂失活和影响产物中反式十氢萘和顺式十氢萘比例的主要原因。     

Enantioswitchable catalysts for the asymmetric transfer hydrogenation of aryl alkyl ketones

A subtle change in the ligand structure, replacing the carbonyl oxygen with sulfur in simple alpha-amino acid amides, resulted in a dramatic activity and selectivity improvement in the rhodium- or ruthenium-catalyzed reduction of ketones under hydrogen transfer conditions. In addition, in most cases, a switch of the product's absolute configuration was observed on going from amides to the corresponding thioamides. Under optimized conditions, we obtained the secondary alcohol products in high yield and enantioselectivity (up to 97% ee) using only 0.25 mol % catalyst loading. [structure: see text]     

Microsecond X‐ray Absorption Spectroscopy Identification of CoI Intermediates in Cobaloxime‐Catalyzed Hydrogen Evolution

Rational development of efficient photocatalytic systems for hydrogen production requires understanding the catalytic mechanism and detailed information about the structure of intermediates in the catalytic cycle. We demonstrate how time‐resolved X‐ray absorption spectroscopy in the microsecond time range can be used to identify such intermediates and to determine their local geometric structure. This method was used to obtain the solution structure of the Co^I intermediate of cobaloxime, which is a non‐noble metal catalyst for solar hydrogen production from water. Distances between cobalt and the nearest ligands including two solvent molecules and displacement of the cobalt atom out of plane formed by the planar ligands have been determined. Combining in situ X‐ray absorption and UV/Vis data, we demonstrate how slight modification of the catalyst structure can lead to the formation of a catalytically inactive Co^I state under similar conditions. Possible deactivation mechanisms are discussed.     

Selective hydrogen peroxide oxidation of sulfides to sulfoxides or sulfones with MWW-type titanosilicate zeolite catalyst under organic solvent-free conditions

Selective oxidation of sulfides to sulfoxides and sulfones with hydrogen peroxide under organic solvent-free conditions was demonstrated by the MWW-type titanosilicate zeolite catalyst. Sulfides were oxidized smoothly to give sulfoxides with good selectivities at ambient temperature using 1.0–1.2 equiv of hydrogen peroxide with the MWW-type titanosilicate zeolite catalyst. Especially, the Ti-MWW with an interlayer-expanded structure (Ti-IEZ-MWW) catalyst showed high activity with good chemoselectivity for the oxidation of various sulfides. The catalyst is recyclable for at least five cycles, and the only byproduct is water. Sulfides were directly oxidized to give sulfones in high yields by 2.5 equiv of hydrogen peroxide with the MWW-type titanosilicate zeolite catalyst under organic solvent-free conditions.     

燃料电池中氢电极催化剂的研究

燃料电池是借助于电池内的燃烧反应，将化学能直接转为电能的装置，是一种新型的高效化学电源，是除火力、水力、核能之外的第四种发电方式。对燃料电池，性能良好的催化剂至关重要，它决定着大电流密度放电时的电池性能、运行寿命和成本。燃料电池的催化剂应该满足以下条...     

Effect of surface structure on the catalytic behavior of Ni：Cu/Al and Ni：Cu：K/Al catalysts for methane decomposition

Methane decomposition using nickel, copper, and aluminum （Ni：Cu/Al） and nickel, copper, potassium, and aluminum （Ni：Cu：K/Al） modified nano catalysts has been investigated for carbon fibers, hydrogen and hydrocarbon production. X-ray photoelectron spectroscopy （XPS）, static secondary ion mass spectrometry （SSIMS）, thermal gravimetric analysis （TGA）, Fourier transform infrared （FT-IR）, secondary electron microscopy/X-ray energy dispersive （SEM-EDX）, and temperature programmed desorption （TPD） were used to depict the chemistry of the catalytic results. These techniques revealed the changes in surface morphology and structure of Ni, Cu, Al, and K, and formation of bimetallic and trimetallic surface cationic sites with different cationic species, which resulted in the production of graphitic form of pure carbon on Ni：Cu/Al catalyst. The addition of K has a marked effect on the product selectivity and reactivity of the catalyst system. K addition restricts the formation of carbon on the surface and increases the production of hydrogen and C2, C3 hydrocarbons during the catalytic reaction whereas no hydrocarbons are produced on the sample without K. This study completely maps the modified surface structure and its relationship with the catalytic behavior of both systems. The process provides a flexible route for the production of carbon fibers and hydrogen on Ni：Cu/Al catalyst and hydrogen along with hydrocarbons on Ni：Cu：K/Al catalyst. The produced carbon fibers are imaged using a transmission electron microscope （TEM） for diameter size and wall structure determination. Hydrogen produced is COx free, which can be used directly in the fuel cell system. The effect of the addition of Cu and its transformation and interaction with Ni and K is responsible for the production of CO/CO2 free hydrogen, thus producing an environmental friendly clean energy.     

The Effect of Start-Up Conditions on Deactivation of Hydrotreating Catalyst for Heavy Residue with High Asphaltene Content

This article describes a pilot plant test, which was carried out to examine the effect of start-up operation conditions on catalytic performance in the commercial hydrotreating equipment. From the simulated several pilot tests, it was found that the operation conditions of this commercial equipment were very severe and the hydrogen supply to the catalyst active site was critical. When the heavy residue containing large amount of asphaltene was supplied at the start of run (SOR) in the commercial equipment, the permanent adsorption of carbonaceous deposit on the active site should cause leading the catalyst deactivation.     

Hydrogen-free homogeneous catalytic reduction of olefins in aqueous solutions

Herein we report a study involving the homogeneous catalytic reduction of unsaturated substrates in aqueous solutions or water-organic solvent mixtures. The reduction of olefins has been carried out in the presence of catalytic amounts of [Fe(CN)5NH3](3-) and excess of NH2OH, which under mild reaction conditions can be used to reduce carbon-carbon unsaturations without affecting carbonyl functionalities and aromatic rings. To explore the scope of the catalytic reduction, a wide variety of representative unsaturated substrates have been examined. The steric effects of the substituents on the carbon-carbon multiple bond as well as the regioselectivity and stereoselectivity of the catalyst have been studied. The deuterium kinetic isotope effect on the catalytic reduction of double bonds in olefins has been analyzed, and no significant kinetic isotope effect was found. Among the great advantages of this novel procedure for catalytic reduction are that hydrogen and high pressures are not needed, the catalyst is inexpensive and easily prepared, and water as well as water-organic solvent mixtures can be used as reaction media.     

稳定同位素方法研究正构烷烃与四氢萘二元体系的反应

以正构烷烃作为模型化合物的热反应、临氢反应、临氢催化反应中,添加供氢剂抑制正构烷烃所裂化;气相氢和供氢剂的供氢参与饱和烯烃,两者是性质不同的氢源,前者加速裂化,后者抑制裂化。供氢剂供氢行为依赖于反应体系自由基的多少和温度以及反应过程,反应体系较多的自由基和较高的反应温度有利于供氢行为。稳定同位素方法研究模型化合物的裂化反应表明,供氢剂的作用是通过脱氢湮灭自由基来抑制裂化反应,同时发现H12－四氢萘和D12－四氢萘的供氢（氘）率上存在着动力学同位素效应,在临氢及临氢催化体系中尤其是临氢催化体系中,动力学同位素效应变得不再明显。     

Photodecomposition of water with methane over titanium oxide photocatalysts modified with metal

Metal-loaded titanium oxide photocatalysts produced hydrogen in the photodecomposition of water vapor with methane in the flow reactor. Ag/TiO₂ has the highest activity in comparison with other metal-loaded catalysts. The experiment in the absence of methane indicated that methane could effectively function as a reducing reagent of water. The significant decrease in the hydrogen formation rate with the time on stream was observed under all reaction conditions. The recalcination and the hydrogen rereduction of the used catalyst led to the restoration of the activity of the hydrogen formation. The adsorption of products and/or reactants on the catalyst surface seemed to cause these deactivations of the hydrogen formation.     

New Rh—ZnO／Carbon Nanotubes Catalyst for Methanol Synthesis

A new catalyst for methanol synthesis,ZnO-promoted rhodium supported on carbon nanotubes,was developed.It was found that the Rh-ZnO/CNTs catalyst had high activity of 411.4mg CH3OH/g/cat/h and selectivity of 96.7% for methanol at 1 MPa and 523 K.The activity of this catalyst is much higher than that of NC 207 catalyst at the same reaction conditions.It was suggested that the multi-walled strueture CNTs favored both the couple transfer of the proton and clectron over the surface of the catalyst and the uptake of hydrogen which was favorable to methanol synthesis.     

氢对气相甲醇羰基化催化体系的影响

 主要讨论了氢对甲醇气相羰基化催化体系的影响．采用多孔碳化聚偏二氯乙烯小球负载金属镍催化体系，在不同进气条件下进行甲醇羰基化反应，得到不同氢含量时催化剂的活性和稳定性数据，以及氢对催化体系的微扰数据，并对催化剂的表面形态用SEM进行了表征，以评价氢的影响．从三个方面分析了氢对气相甲醇羰基化催化体系的影响，认为适量存在的氢对长时间保持催化剂活性是有利的．     

Kinetic Study of the Copolymerisation of Ethylene with a Single Site Catalyst in Propane Slurry Polymerisation

Summary: The kinetic behaviour of a supported metallocene catalyst in slurry polymerisation of ethylene with 1-hexene under industrially relevant reaction conditions has been studied. Polymerisation experiments were carried out in a 5-litre stirred tank reactor in a temperature range from 60 to 80 °C and ethylene partial pressures from 5 to 15 bar. Comonomer and hydrogen amounts were varied as well. The catalyst showed pronounced activation and slow deactivation during runtimes of about 1 hour. Strong influences of 1-hexene (“hexene effect”) and hydrogen (“hydrogen effect”) on the activity profiles were observed. Based on the experimental results, a kinetic model has been derived in order to describe and predict important polymerisation data such as activity profile, comonomer content and molecular weight distributions with respect to the reaction conditions. The presented kinetic model is able to describe the observed effects of 1-hexene and hydrogen on the activity profiles, as well as the comonomer incorporation across a broad range of polymerisation conditions. The molecular weight distributions can be simulated with good qualitative agreement to the experimental data.