Although technological practice should minimize environmental impact, this is not always economically feasible. During the past decade, for example, there has been increasing global concern over th...

CO2 Reforming of CH4

Publisher Summary This chapter describes the essence of the catalytic chemistry of heteropoly compounds in solution and in the solid state. The catalytic properties of heteropoly compounds have drawn wide attention, owing to the versatility of these compounds as catalysts, which has been demonstrated both by successhl large-scale applications and by promising laboratory results. Heteropolyanions are polymeric oxoanions formed by condensation of more than two different mononuclear oxoanions. Heteropolyanions formed from one kind of polyanion are called isopolyanions. Acidic elements such as Mo, W, V, Nb and Ta, which are present as oxoanions in aqueous solution, tend to polymerize by dehydration at low pH, forming polyanions and water.Heteropoly catalysts can be applied in various ways. They are used as acid as well as oxidation catalysts. They are used in various phases, as homogeneous liquids, in two-phase liquids (in phase-transfer catalysis), and in liquid-solid and in gas-solid combinations, etc.

Catalytic Chemistry of Heteropoly Compounds

Hydrogen production by methane decomposition: A review

Alternatives to petroleum-derived fuels and chemicals are being sought in an effort to improve air quality and increase energy security through development of novel technologies for the production of synthetic fuels and chemicals using renewable energy sources such as biomass. In this context, ethanol is being considered as a potential alternative synthetic fuel to be used in automobiles or as a potential source of hydrogen for fuel cells as it can be produced from biomass. Renewable ethanol can also serve as a feedstock for the synthesis of a variety of industrial chemicals and polymers. Currently, ethanol is produced primarily by fermentation of biomass-derived sugars, especially those containing six carbons, whereas 5-carbon sugars and lignin, which are also present in the biomass, remain unusable. Gasification of biomass to syngas (CO + H2), followed by catalytic conversion of syngas, could produce ethanol in large quantities. However, the catalytic conversion of syngas to ethanol remains challenging,...

A Review of Recent Literature to Search for an Efficient Catalytic Process for the Conversion of Syngas to Ethanol

The controlled synthesis of materials by methods that permit their assembly into functional nanoscale structures lies at the crux of the emerging field of nanotechnology. Although only one of several materials families is of interest, carbon-based nanostructured materials continue to attract a disproportionate share of research effort, in part because of their wide-ranging properties. Additionally, developments of the past decade in the controlled synthesis of carbon nanotubes and nanofibers have opened additional possibilities for their use as functional elements in numerous applications. Vertically aligned carbon nanofibers (VACNFs) are a subclass of carbon nanostructured materials that can be produced with a high degree of control using catalytic plasma-enhanced chemical-vapor deposition (C-PECVD). Using C-PECVD the location, diameter, length, shape, chemical composition, and orientation can be controlled during VACNF synthesis. Here we review the CVD and PECVD systems, growth control mechanisms, catalyst preparation, resultant carbon nanostructures, and VACNF properties. This is followed by a review of many of the application areas for carbon nanotubes and nanofibers including electron field-emission sources, electrochemical probes, functionalized sensor elements, scanning probe microscopy tips, nanoelectromechanical systems (NEMS), hydrogen and charge storage, and catalyst support. We end by noting gaps in the understanding of VACNF growth mechanisms and the challenges remaining in the development of methods for an even more comprehensive control of the carbon nanofiber synthesis process.

Vertically Aligned Carbon Nanofibers and Related Structures: Controlled Synthesis and Directed Assembly

Platinum and palladium catalysts supported on γ-Al2O3 were studied by XRD, UV–vis DRS, HRTEM, TPR-H2, XPS together with measurements of their catalytic properties. The properties of the catalysts denoted as Pt(Pd)/Al2O3(X)-Y (X—the calcination temperature of support, °C; Y—the calcination temperature of catalyst, °C) were studied as a function of the temperatures used for calcination of the support and/or the catalyst in oxygen or in a reaction mixture of CO + O2. It was found that the deposition of Pt or Pd on γ-Al2O3 did not alter the structure of the support. Two types of the Pt and Pd particles were typically present on the γ-Al2O3 surface: individual particles with dimensions of 1.5–3 nm and agglomerates about 100 nm in size. In the catalysts calcined at relatively low temperatures (Pt/Al2O3(550)-450), platinum was present in the form of metal clusters. However, in the Pd/Al2O3(550)-450 catalyst, the palladium particles were almost completely decorated with a thin layer of an aluminate phase. These structures are not reduced in hydrogen in the temperature range of −15 to 450 °C, and are stable to treatment in a reaction mixture of CO + O2. Pd deposition on the γ-Al2O3-800 support was found to result in stabilization of the active component in two main forms, Pdo and PdO, with varying degrees of interaction due to the decoration effect. Calcination at the low temperature of 550 °C led to the formation of a so-called “core–shell structure”, where a palladium metal core is covered with a thin shell of an aluminate phase. Depending on the calcination temperature of the catalyst in the range of 450–1000 °C, the morphological form of the active component was converted from the “core-shell” state to a state consisting of two phases, Pdo and PdO, with a gradual decrease of the Pdo/PdO ratio, weakening the interaction with the support and the growth of palladium particles. Under the action of the reaction mixture, the Pd/Al2O3(800)-(450,600,800,1000) catalysts underwent changes in the Pdo/PdO ratio, which regulates the light-off temperature. After catalyst calcination at the highest temperature used in this study, 1200 °C, the palladium particles became much larger due to the loss of the palladium interaction with the support. Only the metal phase of palladium was observed in these catalysts, and their catalytic activity decreases substantially.

Metal–support interactions in Pt/Al2O3 and Pd/Al2O3 catalysts for CO oxidation

Using coprecipitated Ni-alumina and NiCu-alumina catalysts, up to 250 g/gcat of filamentous carbon was produced by methane decomposition at 823 K and a methane pressure of 100 kPa. The process evolved three general stages. In the induction period carbon was dissolved into the Ni particles as evidenced by in situ X-ray powder diffraction measurements. This promoted the formation of large metal particles pear-shaped in Ni catalysts and quasi-octahedral in NiCu ones. The steady-state growth of the filaments occurred on the second stage. Finally, the catalyst was deactivated producing porous granules composed of interlaced long carbon filaments. In deactivated Ni catalysts the nickel was found in metal state, while in NiCu samples about half of the nickel was atomically dispersed in carbon as revealed by extended X-ray absorption fine structure spectroscopy. The deactivation of the catalysts was suggested to include the fragmentation of the metal particles as well as an atomic erosion in NiCu samples. In addition, in both catalysts the filaments growth could also be limited when the close-packed structures of porous carbon were achieved.

Coprecipitated Ni-alumina and NiCu-alumina catalysts of methane decomposition and carbon deposition. II. Evolution of the catalysts in reaction

New Nickel Catalysts for the Formation of Filamentous Carbon in the Reaction of Methane Decomposition

Formation and decomposition of the Cu–Co alloy and Co 2 C were studied using in situ X-ray diffraction (XRD), TG-DTA and TEM techniques. Cu–Co alloy with ratio Cu/Co=1:1 has been obtained under treatment of CuCoO 2 with hydrogen at 230–300°C. Co 2 C was formed from Cu–Co alloy at 280–310°C and decomposed at 390–400°C under CO. It was shown that the role of Cu–Co alloy consisted in formation of cobalt carbide was able to activate CO undissociatively that led to oxygenates synthesis.

Role of the Cu–Co alloy and cobalt carbide in higher alcohol synthesis

Mechanisms for the synthesis of methanol from CO and CO2 and for the hydrogenation of acetone to isopropanol are discussed based on the recent experimental results obtained by the authors. The state of copper-containing compounds in a hydrogen medium at 200–400°C and the nature of their interaction with the reaction components were studied. Hydrogenation of carbon oxides and acetone was proposed to be the result of the ability of copper ions to reversible transformations to generate copper metal and protons. Activation of acetone and CO2 can be achieved through their interaction with Cu0, and activation of CO through its interaction with oxygen-containing sites of Cu+1OCu+1 type which are formed after oxidation of a portion of Cu0 with carbon dioxide.

L. M. Plyasova

Papers

Metal–support interactions in Pt/Al2O3 and Pd/Al2O3 catalysts for CO oxidation

Coprecipitated Ni-alumina and NiCu-alumina catalysts of methane decomposition and carbon deposition. II. Evolution of the catalysts in reaction

New Nickel Catalysts for the Formation of Filamentous Carbon in the Reaction of Methane Decomposition

Role of the Cu–Co alloy and cobalt carbide in higher alcohol synthesis

Mechanisms for hydrogenation of acetone to isopropanol and of carbon oxides to methanol over copper-containing oxide catalysts