Activity of copper–cerium–zirconium catalysts in oxidation of hydrogen

We have studied the catalytic properties in oxidation of hydrogen for copper–cerium oxide systems deposited on supports obtained by calcination of yttrium-stabilized zirconium dioxide at 300–1000 °C. We have shown that the catalytic activity of the samples obtained depends on the specific surface area of the original supports and the amount of reduced copper within the composition of the catalyst. In samples whose support has high specific surface area, the content of reduced metallic copper is greater and the catalytic activity is higher.     

Surface and interface engineering in transition metal–based catalysts for electrochemical water oxidation

A tremendous effort has been provided in last two decades to develop efficient transition metal–based heterogeneous catalysts for the electrochemical water oxidation. Several approaches such as composition modulation, heteroatom doping, morphological development, particle size tuning, surface area enhancement, and control over electronic structure have been explored for the designing of the materials with improved water oxidation activity. As the electrochemical process is a surface phenomenon, surface structure plays a crucial role in controlling the water oxidation activity. Rational engineering of the catalyst surface by composition modulation, crystal facet tuning, and generating functional overlayer has been reported to enhance the water oxidation activity. Heteroatom doping, cationic and anionic deficiencies, and ultrathin 2D morphology are also found to promote electrochemical performance. In addition, engineering in the interface provides intrinsic improvement of the catalytic activity and stability for the electrochemical water oxidation. Although, surface and interface engineering of the catalyst has come out as the major factors in the electrochemical water oxidation, no dedicated review is available in this field. In this review, we have described the strategies of improving water oxidation activity of the catalysts by surface and interface engineering. The progress in this field discussed in detail; the challenges have been identified and addressed to attain a clear understanding in this field.     

Catalytic oxidation of NO over Mn–Co–Ce–Ox catalysts: effect of reaction conditions

Manganese–cobalt–cerium oxide (Mn–Co–Ce–Ox) catalysts were synthesized by the co-precipitation method and tested for activity in low-temperature catalytic oxidation of NO in the presence of excess O₂. With the best Mn–Co–Ce mixed-oxide catalyst, approximately 80 % NO conversion was achieved at 150 °C and a space velocity of 35,000 h^?1. The effect of reaction conditions (reaction temperature, volume fractions of NO and O₂, gas hourly space velocity (GHSV), and catalyst stability) was investigated. The optimum reaction temperature was 150 °C. Increasing the O₂ content above 3 % results in almost no improvement of NO oxidation. This catalyst enables highly effective removal of NO within a wide range of GHSV. Furthermore, the stability of the Me–Co–Ce–Ox catalyst was excellent; no noticeable decrease of NO conversion was observed in 40 h.     

Transport of C1–C3 hydrocarbons in poly(phenylene oxides) membranes

Transport of CH₄, C₂H₄ and C₂H₆ in poly(phenylene oxides) membranes at low pressures has been studied. The relation between the free volume and permeability of the polymers was analyzed in terms of the `dual-sorption' model. The accessible free volume of the polymers was estimated assuming the density of a sorbed fluid is equal to the density of the corresponding liquid. Transient separation of the three-component mixture CH₄/C₂H₄/C₂H₆ was studied.     

Proton exchange reactions of C2–C4 alkanes sorbed in ZSM-5 zeolite

Photoelectrochemical cells with TiO₂ electrodes to convert sunlight and water into gaseous hydrogen and oxygen are a source of clean and renewable fuel. Despite their great potential, far-from-ideal performance and poor utilization of the solar spectrum have prevented them from becoming a widespread and practical technology. We review recent experimental work that uses dynamics measurements to study limitations of photoelectrochemical cells from a fundamental level and the use of TiO₂ nanotube arrays as a superior alternative to TiO₂ nanoparticles. Through a combination of nanoscale size control, doping, composite materials, and the incorporation of noble-metal nanoparticles, improved performance and light harvesting are demonstrated.     

Catalytic oxidation of 4-tert-butyltoluene over Ti-MCM-41

The surface-grafted titanium MCM-41 materials were prepared by anchoring titanocene onto the inner walls of MCM-41. The materials were characterized by powder X-ray diffraction (XRD), N2 adsorption-desorption isotherm and diffuse reflectance UV-visible (UV-vis) spectroscopies. The catalytic properties of Ti-MCM-41 were tested in oxidation of 4-tert-butyltoluene with tert-butylhydroperoxide (TBHP) in liquid phase. MCM-41 with loading 4.8 mol% Ti gave the maximal conversions of 23.6% of 4-tert-butyltoluene with a complete selectivity to 4-tert-butylbenzaldehyde.     

Hydrogenation–dechlorination of 2-chloro-4,6-dinitroresorcinol over Pd/C catalysts

Research on Chemical Intermediates - Pd catalysts supported on active carbon (Pd/C) prepared by impregnation–deposition were used in catalytic hydrogenation and hydrodechlorination (HDC) of...     

Total oxidation of ethanol and toluene over ceria—zirconia supported platinum catalysts

The effect of platinum loading (0.09–1.00 mass %) on the performance of ceria-zirconia supported catalysts in the total oxidation of ethanol and toluene in air was investigated. The introduction of platinum promoted the reduction of surface cerium and decreased the acidity of the catalysts. In ethanol oxidation, the temperature of 50 % conversion decreased with increasing platinum content. This increase in catalytic performance was more pronounced for the catalysts with 0.59 mass % and 1.00 mass % Pt. On the other hand, higher amount of by-products (mainly acetaldehyde) was observed at increased platinum loadings. For all catalysts, a correlation between their H₂-TPR profiles and catalytic performance was revealed. In toluene oxidation, only the catalysts with 0.59 mass % and 1.00 mass % Pt exhibited a lower temperature of 50 % conversion than pristine ceria-zirconia. The effect of platinum loading was less pronounced than in ethanol oxidation and a correlation between reduction behaviour and catalytic performance was not observed. The superior catalytic performance of the catalysts with 0.59 mass % and 1.00 mass % of Pt in both ethanol and toluene oxidation was ascribed to the presence of large platinum nanoparticles, which were not observed at lower Pt loadings.     

Cu(I) metal organic framework catalyzed C–C and C–N coupling reactions

DABCO (1,4-diazabicyclo[2.2.2]octane) based Cu(I) metal organic framework (here after represented as Cu(I)-MOF) catalyzed Sonogashira cross-coupling reaction of iodobenzene and phenylacetylene was conducted smoothly to afford diphenylacetylene in excellent yield under N₂ atmosphere. For comparative study, piperidine based Cu(I) clusters were also investigated. Among these catalysts, Cu(I)-MOF exhibited higher activity with good selectivity for the C–C cross-coupled product. Cu(I) catalysts investigated in this study exhibited similar activity in the C–C homo-coupling reaction of phenylacetylene in O₂ atmosphere. Application of these catalysts was extended in the C–N coupling reactions between phenylboronic acid and aromatic/aliphatic/heterocyclic amines. Cu(I)-MOF can be readily recovered from the reaction mixture and reused for several cycles without loss in the catalytic activity.     

Immobilized complexes of the salen Schiff’s base with metal as oxidation catalysts

The immobilized metal complexes with the Schiff’s base of salen have shown high catalytic activity in oxidation of alkenes, cycloalkenes, and alcohols as compared with their unsupported analogs. Due to the heterogeneous nature of such catalysts, their separation and recycling is rather simple.     

Scission of C–O and C–C linkages in lignin over RuRe alloy catalyst

The performance of lignin depolymerization is basically determined by the interunit C–O and C–C bonds.Numerous C–O bond cleavage strategies have been developed, while the cleavage of C–C bond between the primary aromatic units remains a challenging task due to the high dissociation energy of C–C bond.Herein, a multifunctional Ru Re alloy catalyst was designed, which exhibited exceptional catalytic activity for the cleavage of both C–O and C–C linkages in a broad range of lignin model compounds(β...     

Redox properties of hydrogenated quinoline derivatives — inhibitors in oxidation processes of hydrocarbons

Half-wave potentials of the one-electron electrochemical oxidation (E _1/2 ^ox) of hydroquinolines with different degrees of heterocycle hydrogenization as well as containing substituents of various natures in the benzene ring and heterocycle have been measured. Linear correlations betweenE _1/2 ^ox and the values of the Hammett polar -constants form- andp-substituents in dihydroquinolines and related sulfur-containing dithiolthiones were established. The character of the variation ofE _1/2 ^ox in the series of hydroquinolines was found to correlate with the characteristic features of the inhibiting action of these compounds in the liquid-phase oxidation of various hydrocarbons. However, in contrast to phenolic antioxidants for hydroquinolines, there is no dependence of the retardation period onE _1/2 ^oxin the oxidation of hydrocarbons at temperatures higher than 100 °C.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 610–613, April, 1994.     

Development of a detailed pyrolysis mechanism for C1–C4 hydrocarbons under a wide range of temperature and pressure

A model of core mechanism of hydrocarbon pyrolysis with good predictive ability is crucial to the development of active cooling technology for advanced aeroengines. In this work, a detailed core kinetic model of pyrolysis of C₁–C₄ hydrocarbon fuels is developed through the combination of a series of potential energy surfaces and validated against a series of experimental results. The kinetic model contains 103 species and 1290 reactions, and most of the kinetic and thermochemical parameters are compiled from recent highly accurate quantum chemical calculations without modification. The pressure-dependent rate constants are considered for the dissociation/association reactions, isomerization reactions, and chemically activated reactions. Simulation results for various alkanes (methane, ethane, propane, n-butane, isobutane), alkenes (ethylene, propene, 1-butene, 2-butene, isobutene, allene, 1,3-butadiene), and alkynes (acetylene, propyne, vinylacetylene) indicate that the major product distributions at various temperatures (800-2300 K) and pressures (0.8-10 atm) can be predicted well by the developed core kinetic model. Thus, the developed pyrolysis mechanism for C₁–C₄ hydrocarbons can be used as a cornerstone to develop the pyrolysis mechanisms of larger hydrocarbon fuels and thus support the development of thermal management in advanced aeroengines.     

Catalytic reduction of NOx and oxidation of dichloroethane over α-MnO2 catalysts: Properties-Reactivity relationship

The reduction ability of NO to N₂ and the oxidation performance of 1,2-dichloroethane (DCE) over α-MnO₂ catalysts were investigated. The results show that α-MnO₂-3 exhibited the highest catalytic activity in 63.5 % conversion of NO_x reduction by C₃H₈ at 250 °C, and 80 % conversion of DCE combustion by O₂ at 338 °C. It is revealed the active phase of α-MnO₂-3 is tetragonal α-MnO₂ with the selectively exposed plane of (2 1 1). It was proposed the high DCE decomposition of α-MnO₂-3 was ascribed to the redox properties. The overall characterization results revealed that α-MnO₂-3 catalyst preserves more active sites of low valence Mn and higher surface adsorbed oxygen (O_ads) /lattice oxygen (O_latt) at the outermost layers, and lower reduction temperature in H₂-TPR profiles than that of other catalysts. Meanwhile, NH₃-TPD profile of α-MnO₂-3 also shows a large number of acid sites promote NO_x reduction.     

Preferential oxidation of carbon monoxide in a hydrogen-rich gas stream over supported gold catalysts: the effect of a mixed ceria–zirconia support composition

Research on Chemical Intermediates - The effect of the ceria–zirconia (CeO2–ZrO2) support composition of a gold (Au) catalyst (Au/Ce1?xZrxO2, where x is the molar ratio), prepared...     

Hydrogenolysis of glycerol to propanediols over supported Ag–Cu catalysts

Hydrogenolysis of glycerol to 1,2-propanediol and 1,3-propanediol has significant scientific importance and commercial interest due to the huge surplus of glycerol and the various application of propanediols. A series of supported Ag–Cu catalysts synthesized by impregnation method were studied for hydrogenolysis of glycerol to propanediols. The catalysts were characterized by H₂-TPR, NH₃-TPD, XRD, BET, N₂O chemisorption, TG, ICP and SEM. It was observed that the loading of 5% Ag–Cu-based catalysts facilitated the reduction, surface acidity and dispersion of the Cu particles, which improved the conversion of glycerol and promoted the generation of propanediols. It was also found that when loading Ag and Cu simultaneously on Al₂O₃, the catalyst had a better performance for the reaction because of the higher acidity, dispersion and surface area of the Cu species on the catalyst surface. In addition, effects of metal concentrations, metal impregnation sequence, reaction temperature, reaction pressure, reaction time, solvent and pH value of the solution on glycerol hydrogenolysis together with the recyclability of catalyst were investigated in detail. The optimal 5Ag–15Cu/Al₂O₃ achieved 66.4% glycerol conversion with 68.2% 1,2-propanediol and 3.1% 1,3-propanediol selectivity at 200 °C under 3.5 MPa in ethanol for 8 h.