Catalysts For Oxidation Of Hydrocarbons Research Articles

Biologically inspired oxidation catalysis

The development of processes for selective hydrocarbon oxidation is a goal that has long been pursued. An additional challenge is to make such processes environmentally friendly, for example by using non-toxic reagents and energy-efficient catalytic methods. Excellent examples are naturally occurring iron- or copper-containing metalloenzymes, and extensive studies have revealed the key chemical principles that underlie their efficacy as catalysts for aerobic oxidations. Important inroads have been made in applying this knowledge to the development of synthetic catalysts that model enzyme function. Such biologically inspired hydrocarbon oxidation catalysts hold great promise for wide-ranging synthetic applications.

ChemInform Abstract: The Hydrothermal Synthesis of Tetragonal Tungsten Bronze‐Based Catalysts for the Selective Oxidation of Hydrocarbons.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Selective Hydrocarbon Oxidation in Zeolites

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

The hydrothermal synthesis of tetragonal tungsten bronze-based catalysts for the selective oxidation of hydrocarbons

Mixed metal oxides with tetragonal tungsten bronze (TTB) structure, showing high activity and selectivity for the gas phase partial oxidation of olefins, have been prepared by hydrothermal synthesis from Keggin-type heteropolyacids.

Selective Hydrocarbon Oxidation in Zeolites

Zeolites are highly selective catalysts for partial oxidation of hydrocarbons, but practical applications require faster release of the products.

Hydrocarbon oxidation and aldol condensation over basic zeolite catalysts

Ion-exchanged X zeolites, with and without occluded cesium, were tested as catalysts for hydrocarbon oxidation and aldol condensation. Infrared spectroscopy confirmed that combustion products were formed during the oxidation reactions. The reaction profile of 1-butene or butane oxidation over zeolite X in the range of 473–523 K revealed an induction time followed by a maximum in CO 2 production. Ion-exchanged NaX and CsX exhibited a higher maximum CO 2 production rate than MgX during butene oxidation at 473 K. Addition of Cs to CsX above ion-exchange capacity decreased the CO 2 production rate, indicating that basicity was not important for the reaction. Silica, alumina and Cs-doped alumina were several orders of magnitude less active than NaX and CsX for 1-butene oxidation at 523 K. In general, the oxidation of butane was slower than that of 1-butene. The high electric field associated with cations in the zeolite pores is suggested to be important for the oxidation reactions. In contrast to hydrocarbon oxidation, the condensation reaction of propionic acid and formaldehyde to form methacrylic acid at 598 K depended on the basicity of the zeolite, with the activity increasing in the order NaX < KX < CsX. Increasing the basicity of CsX by occluding Cs in the pores beyond ion-exchange capacity further increased the activity.

Selective oxidation of hydrocarbons catalyzed by iron-containing heterogeneous catalysts

Recent studies on iron-based heterogeneous catalysts for selective oxidation of hydrocarbons are reviewed with emphasis on the partial oxidation of methane and the epoxidation of alkenes. High dispersion of iron sites is essentially important for the selective oxidations. The effective catalysts include immobilized or encapsulated iron complexes, iron-doped metal oxides such as Fe3+-doped silica, iron-containing microporous and mesoporous materials, and iron-containing compounds with isolated iron sites typified by iron phosphate. The structure-reactivity relationships and the factors affecting the catalytic performances are discussed with the aim to uncover the requirements of the active iron sites in target-selective oxidation.

FORMATION OF CATALYTICALLY ACTIVE COPPER NANOPARTICLES IN NATURAL ZEOLITES FOR COMPLETE OXIDATION OF HYDROCARBONS

Copper catalysts for complete oxidation of hydrocarbons supported on natural zeolites of different structure and origin were prepared by ion-exchange procedure. The catalytic experiments demonstrate that the temperature of beginning of hydrocarbons conversion is in the range of 170-300 °C, depending on the composition of the catalyst. The complete conversion can be observed for both zeolites, depending (probably) on Si/Al ratio of the zeolite matrix. Different states of the copper have been identified by the methods of UV-VIS and XPS spectroscopies and TPR by hydrogen. Whereas no changes in XRD and 27 Al MAS NMR was observed under condition of catalytic runs, that supports conclusion about stability of bulk material, XPS spectroscopy reveals significant altering in surface composition under different treatments due to appearance of complicated nano-species of copper, which are responsible for catalytic activity.

Strategies for oxidation catalyzed by polyoxometalates at the interface of homogeneous and heterogeneous catalysis

A basic premise behind the use of polyoxometalates in oxidation chemistry is the fact that polyoxometalates are oxidatively stable. This, a priori, leads to the conclusion that for practical purposes polyoxometalates would have distinct advantages over widely investigated organometallic compounds that are vulnerable to decomposition due to oxidation of the ligand bound to the metal center. Since polyoxometalate synthesis is normally carried out in water by mixing the stoichiometrically required amounts of monomeric metal salts and adjusting the pH to a specific acidic value many structure types are accessible by variation of the reaction stoichiometry, replacement of one or more addenda atoms with other transition or main group metals, and pH control. The structural variety available has enabled the use of polyoxometalates as catalysts for oxidation of hydrocarbons and functionalized organic substrates (alcohols, amines, sulfides, etc.) with a wide range of oxygen donors ranging from molecular oxygen, hydrogen peroxide, nitrous oxide, ozone, alkyl hydroperoxides, periodate, sulfoxide and others. The wide purview of oxidation reactions is enabled because the structural variety leads to oxidation through a number of different mechanistic motifs. From a synthetic organic point of view, the most applicable uses of polyoxometalates as catalysts involve the “green” oxygen donors – hydrogen peroxide and molecular oxygen. Since practical applications are in hand in this area, practical considerations concerned with catalyst recycle and/or recovery and the elimination of environmentally problematic solvents are also coming to the forefront. In this paper, we will present some of our activities in the area of “catalyst engineering” for catalytic synthetic applications by polyoxometalates including: (a) catalytic mesoporous solids from organic-polyoxometalate hybrid materials, (b) fluorous phase polyoxometalates with and without fluorous solvents and (c) the use of aqueous biphasic media for oxidation with hydrogen peroxide.

Selective oxidation of hydrocarbons into synthesis gas at short contact times: Design of monolith catalysts and main process parameters

This review summarizes the main achievements of the Boreskov Institute of Catalysis (Siberian Division, Russian Academy of Sciences) in the development of efficient and stable monolith catalysts for selective oxidation of hydrocarbons into synthesis gas at short contact times. Research in this field has included (1) design of new types of active component based on metal oxides, (2) design of new types of monolith support and development of supporting procedures for active components, and (3) optimization of process parameters for different types of fuel (natural gas, isooctane, and gasoline) and oxidant (air oxygen, including its mixtures with water and carbon dioxide), including the start-up regime. Design of active components (platinum, nickel, or their combination) supported on fluorite-like solid solutions based on cerium dioxide and rare-earth (samarium, gadolinium, and praseodymium) or zirconium cations has been aimed at separating hydrocarbon activation (on metal sites) and oxidation (on the support) and conjugating the separated steps of hydrocarbon oxidation at the metal-oxide interface. Optimization of oxygen mobility in the support lattice by varying the nature and concentration of doping cation along with optimization of hydrocarbon activation on supported metal clusters allow hydrocarbons to be completely converted into synthesis gas by selective oxidation or dry or steam reforming at contact times of a few milliseconds, ruling out undesirable carbon build-up on the catalyst surface. The development of new types of monolith support has targeted the enhancement of thermal shock resistance, including testing of supports based on thermally stable metal foils and composites (cermets). The main steps of the production of these supports have been refined, including unique technologies of blast dusting and hydrothermal treatment. The electric conductivity of these systems allows a quick startup of selective oxidation to be performed by passing electric current, and their thermal conductivity minimizes the temperature gradient arising from heat transfer in the bed. Procedures for loading monolith supports with active components have been developed, including impregnation, washcoating, or encapsulation in cermet matrices. The catalysts produced show a high efficiency and an operational stability adequate to the above tasks in the selective oxidation and steam-air autothermal reforming of natural gas (including processes under pressure), isooctane, and gasoline into synthesis gas.

Nanocrystalline LaCoO 3 perovskite particles confined in SBA-15 silica as a new efficient catalyst for hydrocarbon oxidation

Highly crystalline LaCoO 3 perovskite particles were prepared by a novel microwave-assisted process with a La–Co citrate complex precursor in the host pores of mesoporous SBA-15 silica. The resulting material exhibited considerably higher catalytic activity in the complete methane oxidation than a LaCoO 3/SBA-15 sample prepared by a conventional method with a bulk LaCoO 3 perovskite. This suggests that a higher density of lattice defects achieved on the high-surface-area LaCoO 3 nanocrystals synthesized by microwave processing is essential for the superior performance of the catalyst.

First-principles calculations on the surface electronic and reactive properties of M/SnO 2 (M=Ge, Mn) (110)

First-principles calculations based on density functional theory within the generalized gradient approximation (GGA) have been performed for the rutile M/SnO 2 (M=Ge, Mn) (110) surfaces. The difference in the surface electronic and reactive properties between the stoichiometric and reduced surfaces was investigated and compared to the SnO 2 surfaces. It is found that the close heat of formation of the bulk rutile MO 2 to that of bulk SnO 2 provides the energetic favorable substitution of M atoms for the 5-fold coordinated tin cations in both the stoichiometric and reduced surfaces. The semiconducting Ge/SnO 2 and metallic Mn/SnO 2 surfaces suggested by the band calculations show the increasing and decreasing surface energies relative to the SnO 2 surface, respectively. Using the oxidation of nitrogen monoxide (NO) with the topmost-layer bridging oxygen O b to NO 2, the reduced surfaces served as an oxidation catalyst which can easily generate by less than half of the energies of the thermal reduction process, which is specially effective for the Mn/SnO 2 surfaces with loosely bound O b. In addition, the very weak adsorption of methanol on the Mn/SnO 2 surfaces favors the generation of gaseous methanol before further oxidation. It is expected that those results will be useful to design a catalyst for the selective oxidation of hydrocarbons using the oxidative and reductive reactions on the reduced surface at a lower temperature than the one currently in use. The detailed molecular mechanics of the chemisorption of NO and methanol on the surfaces are also discussed.

Metal Ion Incorporated VPO Phases as Novel Catalysts

Vanadium phosphates function as catalysts for the selective oxidation of hydrocarbons with their activity being strongly dependent on their structure. Consequently, attempts have been made to synthesise novel phases in the VPO system through metal ion incorporation and evaluate the catalytic activity of these phases. It is shown that the incorporation of palladium or platinum leads to novel phases which vary according to the method of syntheses. The incorporated metal ions are catalytically active both for oxidation and reduction reactions with the activity varying according to the mode of incorporation. These phases constitute a novel class of compounds in which oxidation centres are substituted or dispersed within a VPO oxidation catalyst.

Catalytic behaviour of BIMEVOX powders in the oxidative dehydrodimerisation of propene

Ionic oxide conductors of the BIMEVOX family are potentially interesting catalysts for selective oxidation of hydrocarbons in which the migration of lattice oxygen plays an important role. The catalytic performance in fixed bed reactor of Bi2Cu0.1V0.9O5.35 (BICUVOX) and Bi2Co0.1V0.9O5.35 (BICOVOX) in the oxidative dehydrodimerisation of propene has been studied. BICOVOX is more active and more selective to 1,5-hexadiene than BICUVOX but hexadiene is found at high temperature only. The characterisation of the catalysts before and after catalysis by XRD, TPD and TGA shows that this particular catalytic behaviour is related to their partial reduction.

The Effect of Support Nature and the Temperature of Preliminary Calcination on the Atomic Catalytic Activity of Supported Palladium Catalysts for the Complete Oxidation of Hydrocarbons

It is shown that for palladium catalysts supported on various supports, there is no effect of thermal activation consisting of an increase in the turnover number (TON) of palladium with an increase in the temperature of sample calcination from 500 to 700°C, as was observed in the case of similar supported platinum catalysts; for two palladium–alumina catalysts calcined at 500°C and differing in the concentration of palladium and dispersity, the TON of low-dispersity palladium is substantially higher than the TON of high-dispersity palladium; all other conditions being the same, the TON of supported palladium is determined by the support nature.

Thermal Chemistry of 2-Propanol and 2-Propyl Iodide on Clean and Oxygen-Pretreated Ni(100) Single-Crystal Surfaces

The thermal chemistry of 2-propanol and 2-propyl iodide on clean and oxygen-pretreated Ni(100) single-crystal surfaces was studied by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and reflection−absorption infrared spectroscopy (RAIRS). 2-Propyl iodide was used as a precursor for the preparation of 2-propyl surface species, in analogy to chemistry reported for other halo hydrocarbons. Those 2-propyl groups were shown to convert to acetone on both oxygen- and hydroxide-covered Ni(100) surfaces by following a two step mechanism, starting with a facile oxygen insertion into the metal−alkyl bond. The resulting 2-propoxide surface moiety, an intermediate that can also be prepared via dehydrogenation of the hydroxyl group in adsorbed 2-propanol, is stable up to about 300 K, at which point it undergoes β-hydride elimination to acetone. Coadsorbed surface hydroxide facilitates the first oxygen insertion reaction, and surface oxygen enhances the latter conversion of 2-propoxide to acetone. Some alcohol dehydration to propene is also observed, presumably by reaction of two hydrogen-bonded alcohol molecules. These results point to the feasibility of designing nickel-based catalysts for the selective partial oxidation of hydrocarbons.

New SO2 Resistant Mesoporous La—Co—Zr Mixed Oxide Catalysts for Hydrocarbon Oxidation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Design and synthesis of heterogeneous catalysts: the thermolytic molecular precursor approach

The use of the thermolytic molecular precursor (TMP) method for the generation of multicomponent oxide materials is reviewed with emphasis on the generation of catalysts and catalyst support materials. Various adaptations of the TMP method that allow manipulation of catalyst compositions are presented. Further, the generation of isolated catalytic centers via grafting techniques is summarized. The implications for syntheses of new catalysts and catalyst formulations are discussed, and specific examples that involve selective hydrocarbon oxidation catalysts are provided.

New SO2resistant mesoporous La–Co–Zr mixed oxide catalysts for hydrocarbon oxidation

A new approach for the synthesis of a new type of ternary mesoporous La–Co–Zr mixed oxides with various atomic (La + Co/La + Co + Zr) ratios is reported. The synthesis method combines the advantages of the preparation of the clear soluble homogeneous metal oxides containing a cationic surfactant in acidic medium followed by the precipitation of this mixture in basic medium and hydrothermal treatment. These solids have high surface area, uniform mesopore size with a worm-hole like pore structure, good thermal stability and high component dispersion. They exhibit unusually high catalytic activity and resistance to SO2 poisoning in the complete methane oxidation as compared to bulk LaCoO3 perovskites.

Catalytic performance of La0.66Sr0.34Co0.2Fe0.8O3 perovskite in propane combustion: Effect of preparation and specific surface area

Several compositions in a system of La1-x SrxCo1-y FeyO3-δ perovskites are known as very good electronic and ionic conductors, as well as excellent catalysts for hydrocarbon oxidation. In this study La0.66Sr0.34Co0.2Fe0.8O3 was selected as possibly the optimum composition. To assess the effect of preparation and calcination conditions on the activity in propane combustion, a series of different samples was prepared by a method based on slurry of reactive component precursors processed by freeze-drying. Three different materials were used as source of iron and the samples were aged at successively higher temperatures (1,153–1,343 K). The specific surface areas varied between 5.9 and 1 m2/g, depending on iron precursor and/or aging. The activity was determined in an integral U-shape reactor, typically for 1 and 2 vol% propane in air, with 1 g catalyst and 200 or 100 ml/min flowrate. Kinetics determined on the basis of a wider range of concentrations (1–4.3 vol% propane; 10 vol%-pure oxygen) for a selected, the least aged sample indicated that the propane catalytic combustion is best represented by a Mars van Krevelen model with 0.5 order in oxygen and the two kinetic constants having E app of 83 and 81 kJ/mol, respectively. For the aged samples, the pseudofirst order E app varied from 85 to 98 kJ/mol.