Yoshiyuki Nishiyama

Carbon formation on copper-nickel alloys from benzene

Abstract Carbon formation by the decomposition of benzene on copper-nickel alloy sheets and powders was studied in a temperature range from 580 to 900 °C. Two types of carbon were observed: one (type A) formed at higher temperatures was a flat thin film and the other (type B) formed at lower temperatures was a black powder. The rate of type A formation was small and nickel-rich substrates catalyzed it only at the initial stage. The rate of type B formation was considerably large and the alloys of 80 to 40% nickel had stronger catalytic activity than pure nickel. In this carbon, large amounts of metal particles were present in the same composition as that of substrates. A possible mechanism for the deposition is discussed.

Gas-phase hydrogenation of nitriles by nickel on various supports

Abstract Gas-phase hydrogenation of benzonitrile and acetonitrile was investigated using 5% nickel on various supports at normal pressure and in a temperature range of 170–230°C. The only products obtained were the corresponding primary amines; however, the catalytic activity was strongly influenced by the support used, being in the order of alumina>titania>silica-alumina>silica. The activity was higher for the catalyst having a smaller degree of nickel dispersion measured by temperature programmed desorption of hydrogen.

Catalytic gasification of coals — Features and possibilities

Abstract Catalysis in coal gasification is reviewed in relation to the authors own research. The features of three catalyst groups, alkali, alkaline earth and iron-group metals, are compared and the rate change during gasification is discussed. Effect of substrate properties, especially surface area and state of char, on the activity of catalyst is stated. Steam gasification with catalyst is shown to yield more carbon dioxide when gasification activity is high, except for nickel. Possible applications are briefly mentioned.

Effect of hydrogen on carbon deposition catalyzed by copper-nickel alloys

Abstract Carbon deposition from benzene onto cold-rolled sheets of copper-nickel alloys was studied at temperatures ranging from 570 to 700 °C, in atmospheres of hydrogen, helium, and their mixtures. The deposition rate onto pure nickel was higher in hydrogen than in helium, whereas that onto 80% nickel alloy was higher in helium-rich atmosphere than in hydrogen. In hydrogen-rich atmospheres, the deposition proceeded at a constant rate, which changed reversibly with the composition of the atmosphere. In helium, the deposition rate decreased gradually. Hydrogen seems to affect the catalytic deposition in two ways: (i) by removing surface carbon film which hinders the catalytic action of metal surface, and (ii) by removing the chemisorbed species which are the precursor of the deposition.

Conversion of methane with carbon dioxide into C2 hydrocarbons over metal oxides

Abstract Conversion of methane with carbon dioxide has been performed over seventeen metal oxides using a flow reaction system at 1123 K. The conversion ratio of carbon dioxide to methane is approximately two in most cases. Ethane and ethene (C 2 hydrocarbons) are formed over many oxides, and C 2 yield is higher over yttrium and manganese oxides. Rare earth catalysts such as yttrium, lanthanum, and samarium show higher C 2 selectivities of about 30%. C 2 selectivity is almost unchanged over yttrium and zirconium oxides during reaction while it decreases over samarium oxide. X-ray diffraction analysis reveals that some oxides such as manganese and iron oxides are reduced during reaction. The reaction mechanism for C 2 formation is discussed in terms of both adsorbed oxygen species dissociated from carbon dioxide and the lattice oxygen in metal oxides.

Deposition of carbon and its hydrogenation catalyzed by nickel

Abstract Formation of carbon on nickel sheet from benzene vapor carried by hydrogen was studied at a temperature range from 520 to 730°C. A maximum rate was observed at about 630°C, above which the deposition rate decreased rapidly. The carbon formed was hydrogenated in situ . Methane was the main gaseous product and a maximum rate was observed at about 670°C. Very high reactivity of deposited carbon toward hydrogenation was ascribed to the catalytic action of nickel particles dispersed in the carbon. The hydrogenation rates were divided into three zones and possible interpretations are discussed. A mechanism which is a reverse process to deposition was suggested. The decrease of the hydrogenation rate at higher temperatures was due to the equilibrium among carbon, hydrogen and methane, where carbon was more reactive than graphite.

In situ infrared spectroscopic study of the effects of exchanged cations on thermal decomposition of a brown coal

The thermal decomposition of a brown coal with or without cations up to 500°C was followed by in situ diffuse-reflectance infrared spectroscopy. Part of the spectra obtained were deconvoluted using seven Gaussian absorption profiles. The characteristics of the infrared spectra after exchanging cations varied significantly with the species of cation exchanged. The changes in infrared spectra with increasing temperature also differed markedly. When cations were absent, carboxyl groups could be decomposed easily. Most of the functional groups decomposed and their absorption became small; however, some new functional groups appeared, e.g. aromatic CH groups and esters or anhydride groups. The absorption of the OH stretching mode varied with the valency of the cations exchanged. A shift in the peak position of the aromatic ring stretching mode to a lower wavenumber was observed regardless the presence of cations. The exchanged cations were proved to have a significant influence on the mode of decomposition.

Formation of pyrolytic carbon from benzene over nickel and some properties of the carbon formed

Abstract The rate of carbon formation during the catalytic decomposition of benzene vapor over nickel plates was investigated at temperatures from 600 to 970°C. The rate of carbon deposition on the pure nickel was very slow, whereas the rate became fast upon pretreatment of the nickel surface with air at 760°C. Nickel particles of 200–300 A in diameter were included within the carbon. The nickel contents were 11, 4, 3, and 2 wt% for the carbons deposited at 700, 760, 800, and 900°C for 6 hr, respectively. Direct observations of the deposition process were performed in a scanning electron microscope. The formation of fibrous carbons was observed at the initial stage of the deposition at 760°C. The catalytic activity of this carbon including nickel particles was examined in the hydrogenation reaction of cyclohexene. A high catalytic activity was observed when the nickel-carbon catalyst was pretreated with hydrogen at a high temperature such as 600°C. This fact suggests that the nickel particles were surrounded by carbon, and the carbon was gasified to methane upon treatment with hydrogen at a high temperature.

Interrupted-temperature programmed desorption of hydrogen over silica-supported platinum catalysts: the distribution of activation energy of desorption and the phenomena of spillover and reverse spillover of hydrogen

Abstract The surface heterogeneity of silica-supported platinum catalysts was characterized by interrupted temperature programmed desorption (TPD) of hydrogen. It was suggested that hydrogen spillover occurred and spiltover hydrogen moved from the support to the metal at high temperatures (reverse spillover), influencing the TPD spectrum. The distribution of activation energy of desorption for the surface of the metal was determined by a method that was recently developed by the authors. The results of desorption kinetics for the platinum catalysts were compared with the previous ones for silica-supported nickel catalysts. The reverse spillover was discussed briefly with a simplified model.

Nitrogen removal and carbonization of polyacrylonitrile with ultrafine metal particles at low temperatures

Pyrolysis of polyacrylonitrile (PAN) at temperatures up to 1250 K has been studied in the presence of ultrafine particles of Fe, Ni, and Cu metals. The pyrolysis profile is unchanged by use of Cu. On the other hand, Fe and Ni decrease decomposition rates of PAN at 550–750 K, but by contrast these metals dramatically increase formation rates of N2 at 900–1100 K. Pretreatment at 450 K of PAN with Fe shows almost the same effect as above. These effects lead to increases in both carbon yield and conversion to N2. A higher iron loading gives a larger yield and conversion, and consequently the residual nitrogen in the carbon formed at 1250 K with 13 wt% Fe is as low as 1 wt%, which is one-tenth of that without Fe. Such a considerable enhancement of nitrogen removal by Fe and Ni promotes carbonization reactions of PAN, which results in the formation of graphitized carbons with lower atomic ratios of HC.