Process and catalysts for the methanation of oxides of carbon

The present invention is directed to catalysts for the conversion of oxides of carbon to methane and/or other hydrocarbons and to precursors of such catalysts. The catalyst precursors include one or more refractory oxides selected from the group consisting of rare earth oxides and rare earth contg. perovskites, the precursor including nickel or nickel cations sufficient for a catalyst obtainable by reducing the precursor to be capable of at least partially reducing an oxide of carbon to a hydrocarbon product. Processes for the prepn. of such catalysts and catalyst precursors are also disclosed, as are processes for the conversion of oxides of carbon to methane and/or other hydrocarbons. [on SciFinder(R)]

In situ Raman studies of the selective oxidation of methanol to formaldehyde and ethene to ethylene oxide on a polycrystalline silver catalyst

The combined techniques of in situ Raman microscopy and scanning electron microscopy (SEM) have been used to study the selective oxidation of methanol to formaldehyde and the ethene epoxidation reaction over polycrystalline silver catalysts. The nature of the oxygen species formed on silver was found to depend critically upon the exact morphology of the catalyst studied. Bands at 640, 780 and 960 cm-1 were identified only on silver catalysts containing a significant proportion of defects. These peaks were assigned to subsurface oxygen species situated in the vicinity of surface dislocations, AgIII=O sites formed on silver atoms modified by the presence of subsurface oxygen and O2 - species stabilized on subsurface oxygen-modified silver sites, respectively. The selective oxidation of methanol to formaldehyde was determined to occur at defect sites, where reaction of methanol with subsurface oxygen initially produced subsurface OH species (451 cm-1) and adsorbed methoxy species. Two distinct forms of adsorbed ethene were identified on oxidised silver sites. One of these was created on silver sites modified by the interaction of subsurface oxygen species, and the other on silver crystal planes containing a surface coverage of atomic oxygen species. The selective oxidation of ethene to ethylene oxide was achieved by the reaction between ethene adsorbed on modified silver sites and electrophilic AgIII=O species, whereas the combustion reaction was perceived to take place by the reaction of adsorbed ethene with nucleophilic surface atomic oxygen species. Defects were determined to play a critical role in the epoxidation reaction, as these sites allowed the rapid diffusion of oxygen into subsurface positions, and consequently facilitated the formation of the catalytically active AgIII=O sites.

The electro-oxidation of carbon monoxide and ethanol on supported Pt nanoparticles: The influence of the support and catalyst microstructure

The sluggish kinetics of ethanol oxidation on Pt-based electrodes is one of the major drawbacks to its use as a liquid fuel in direct ethanol fuel cells, and considerable efforts have been made to improve the reaction kinetics. Herein, we report an investigation on the effect of the Pt microstructure (well-dispersed versus agglomerated nanoparticles) and the catalyst support (carbon Vulcan, SnO2, and RuO2) on the rate of the electrochemical oxidation of ethanol and its major adsorbed intermediate, namely, carbon monoxide. By using several structural characterization techniques such as X-ray diffraction, X-ray absorption spectroscopy, and transmission electron microscopy, along with potentiodynamic and potentiostatic electrochemical experiments, we show that by altering both the Pt microstructure and the support, the rate of the electrochemical oxidation of ethanol can be improved up to a factor of 12 times compared to well-dispersed carbon-supported Pt nanoparticles. As a result of a combined effect, the interaction of Pt agglomerates with SnO2 yielded the highest current densities among all materials studied. The differences in the activity are discussed in terms of structural and electronic properties as well as by mass transport effects, providing valuable insights to the development of more active materials. © 2013 Springer-Verlag Berlin Heidelberg.

Supercritical water gasification of RDF and its components over RuO2/γ-Al2O3 catalyst:new insights into RuO2 catalytic reaction mechanisms

Five samples including a composite refuse derived fuel (RDF) and four combustible components of municipal solid wastes (MSW) have been reacted under supercritical water conditions in a batch reactor. The reactions have been carried out at 450 °C for 60 min reaction time, with or without 20 wt% RuO2/gamma-alumina catalyst. The reactivities of the samples depended on their compositions; with the plastic-rich samples, RDF and mixed waste plastics (MWP), giving similar product yields and compositions, while the biogenic samples including mixed waste wood (MWW) and textile waste (TXT) also gave similar reaction products. The use of the heterogeneous ruthenium-based catalyst gave carbon gasification efficiencies (CGE) of up to 99 wt%, which was up by at least 83% compared to the non-catalytic tests. In the presence of RuO2 catalyst, methane, hydrogen and carbon dioxide became the dominant gas products for all five samples. The higher heating values (HHV) of the gas products increased at least two-fold in the presence of the catalyst compared to non-catalytic tests. Results show that the ruthenium-based catalyst was active in feedstock steam reforming, methanation and possible direct hydrogenolysis of C-C bonds. This work provides new insights into the catalytic mechanisms of RuO2 during SCWG of carbonaceous materials, along with the possibility of producing high yields of methane from MSW fractions.

A combined environmental scanning electron microscopy and Raman microscopy study of methanol oxidation on silver(I) oxide

The techniques of environmental scanning electron microscopy (ESEM) and Raman microscopy have been used to respectively elucidate the morphological changes and nature of the adsorbed species on silver(I) oxide powder, during methanol oxidation conditions. Heating Ag2O in either water vapour or oxygen resulted firstly in the decomposition of silver(I) oxide to polycrystalline silver at 578 K followed by sintering of the particles at higher temperature. Raman spectroscopy revealed the presence of subsurface oxygen and hydroxyl species in addition to surface hydroxyl groups after interaction with water vapour. Similar species were identified following exposure to oxygen in an ambient atmosphere. This behaviour indicated that the polycrystalline silver formed from Ag2O decomposition was substantially more reactive than silver produced by electrochemical methods. The interaction of water at elevated temperatures subsequent to heating silver(I) oxide in oxygen resulted in a significantly enhanced concentration of subsurface hydroxyl species. The reaction of methanol with Ag2O at high temperatures was interesting in that an inhibition in silver grain growth was noted. Substantial structural modification of the silver(I) oxide material was induced by catalytic etching in a methanol/air mixture. In particular, "pin-hole" formation was observed to occur at temperatures in excess of 773 K, and it was also recorded that these "pin- holes" coalesced to form large-scale defects under typical industrial reaction conditions. Raman spectroscopy revealed that the working surface consisted mainly of subsurface oxygen and surface Ag=O species. The relative lack of sub-surface hydroxyl species suggested that it was the desorption of such moieties which was the cause of the "pin-hole" formation.

Carbon dioxide reforming of methane to produce synthesis gas over metal-supported catalysts: State of the art

Carbon dioxide reforming of methane produces synthesis gas with a low hydrogen to carbon monoxide ratio, which is desirable for many industrial synthesis processes. This reaction also has very important environmental implications since both methane and carbon dioxide contribute to the greenhouse effect. Converting these gases into a valuable feedstock may significantly reduce the atmospheric emissions of CO2 and CH4. In this paper, we present a comprehensive review on the thermodynamics, catalyst selection and activity, reaction mechanism, and kinetics of this important reaction. Recently, research has centered on the development of catalysts and the feasible applications of this reaction in industry. Group VIII metals supported on oxides are found to be effective for this reason. However, carbon deposition causing catalyst deactivation is the major problem inhibiting the industrial application of the CO2/CH4 reaction. Ni-based catalysts impregnated on certain supports show carbon-free operation and thus attract much attention. To develop an effective catalyst for CO2 reforming of CH4 and accelerate the commercial application of the reaction, the following are identified to be the most important areas for future work: (1) selection of metal and support and studying the effect of their interaction on catalyst activity; (2) the effect of different promoter on catalyst activity; (3) the reaction mechanism and kinetics; and (4) pilot reactor performance and scale-up operation.

A fourier-transform infrared study of CO2 and CO2/H2 interactions with caesium-doped copper catalysts

FTIR spectra are reported of CO2 and COi/Hi on a silica-supported caesium-doped copper catalyst. Adsorption of COj on a "caesium"/silica surface resulted in the formation of COj and complexed CO species. Exposure of CO2 to' a caesium-doped reduced copper catalyst produced not only these species but also two forms of adsorbed carboxylate giving bands at 1550, 1510, 1365 and 1345 cm"1. Reaction of carboxylate species with hydrogen at 388 K gave formate species on copper and caesium oxide in addition to methoxy groups associated with caesium oxide. Methoxy species were not detected on undoped copper catalyst suggesting that caesium may be a promoter for the methanol synthesis reaction. Methanol decomposition on a caesium-doped copper catalyst produced a small number of formate species on copper and caesium oxide. Methoxy groups on caesium oxide decomposed to CO and U.2, and subsequent reaction between CO and adsorbed oxygen resulted in carboxylate formation. Methoxy species located at interfacial sites appeared to exhibit unusual adsorption properties.

Simulation of carbon arc discharge for the synthesis of nanotubes

Arc discharge ablation with a catalyst-filled carbon anode in a helium background was used for the synthesis of graphene and carbon nanotubes. In this paper, we present the results of the numerical simulation of the distribution of various plasma parameters in discharge, as well as the distribution of carbon flux on the nanotube surface, for the typical discharge with an arc current of 60 A and a background gas pressure of 68 kPa.