Hiromu Hayashi

Selective formation of Na-X zeolite from coal fly ash by fusion with sodium hydroxide prior to hydrothermal reaction

Hydrothermal treatment of fly ash with alkali gives various types of zeolites such as Na-Pl, Na-A and hydroxysodalite, where the zeolite zone was formed like an egg white, covering the central core of fly ash particles, as evinced in the previous paper. By fusion with sodium hydroxide, most of the fly ash particles were converted into sodium salts such as silicate and aluminate, from which hydrothermal reaction without stirring favourably resulted in the formation of Na-X zeolite. Crystallinity of Na-X zeolite as high as 62% was attained at the optimum condition of NaOH/fly ash = 1.2 and a fusion temperature of 823 K. Fly ash contains 14 wt% mullite (3Al2O3·2SiO2), which was revealed to be a less-active crystalline component for zeolite formation. Aluminium-enriched fly ash gave Na-A in place of Na-X zeolite. Scanning electron microscope images of cubic and octahedral crystals characteristic of Na-A and Na-X zeolite, respectively, obtained from fly ash, are given.

The properties of heteropoly acids and the conversion of methanol to hydrocarbons

The properties of the heteropoly acids, 12-molybdophosphoric acid, 12-tungstosilicic acid, and 12-tungstophosphoric acid, and the dimeric 9-tungstophosphoric acid have been examined. The conversion of methanol to hydrocarbons has been employed as a test reaction for the activity and selectivity of these catalysts. The effects of variations in reaction temperature, calcination temperature, and environment (air, helium, hydrogen), and residence time have been studied, and the catalysts have been characterized by measurements of surface area, pore size distributions, X-ray powder diffraction, and the chemisorption of ammonia.

Conversion of methanol into hydrocarbons over ammonium 12-tungstophosphate

Abstract The ammonium salt of 12-tungstophosphoric acid has been prepared and characterized through powder X-ray diffraction, acid strength, chemisorption of ammonia, and thermal and chemical analyses. The adsorptive and cracking properties of the salt with respect to olefins and paraffins has also been examined. The ammonium salt is found to have a considerably higher catalytic activity for the conversion of methanol to hydrocarbons than that of any other heteropoly compounds reported previously. In addition, in contrast to the observations with other heteropoly compounds, the ammonium salt displays a high selectivity for the formation of saturated hydrocarbons rather than olefins.

Oxidation of propylene glycol and lactic acid to pyruvic acid in aqueous phase catalyzed by lead-modified palladium-on-carbon and related systems

Abstract Oxidation of propylene glycol and related compounds to pyruvic acid was carried out in aqueous phase at 90 °C with a controlled pH of 8 in the presence of Pd/C modified by Pb, Bi and/or Te as additives. Oxidation of propylene glycol was observed on Pd/C at both the primary and secondary hydroxyl groups to yield lactic acid, hydroxyacetone and pyruvic acid with low selectivities. Pd/C, which alone was inactive in the oxidation of lactic acid, bound Pb on the metallic Pd with a strong interaction. The resultant Pb/Pd/C revealed activity for the selective conversion of lactic acid into pyruvic acid. A trace amount of the additive Pb as low as the atomic ratio Pb/Pd = 0.05, was enough to afford pyruvic acid, and the initial rate of the oxidation showed a maximum at Pb/Pd=0.3. Similar catalysts gave results as follows: Pb/Pt/C, highly active, but less selective; Te/Pd/C, highly selective to pyruvic acid with mild activity; Bi/Pd/C, moderate in both activity and selectivity. Commercially available Pb/Pd/CaCO 3 (Lindlar catalyst) and Pb/Pd/Al 2 O 3 were also active, giving 60% yield of pyruvic acid.

Methanol conversion over metal salts of 12-tungstophosphoric acid

The sodium, boron, calcium, magnesium, zinc, aluminum, and zirconium salts of 12-tungstophosphoric acid have been prepared and characterized using X-ray diffraction, mercury porosimetry, the chemisorption of ammonia, and Hammett indicators. Methanol conversion at 350 °C and a variety of residence times produced hydrocarbons ranging from C1 to C5 in amounts which varied with the cation. The more strongly acidic salts produced the higher yields of hydrocarbons. The maximum yield of the major product C4 was found with the aluminum salt. The activities were related to the partial change on the oxygen atoms in the various catalysts.

Enhancement of the selectivity to carbon monoxide with feedstream doping by tetrachloromethane in the oxidation of methane on stoichiometric calcium hydroxyapatite

The oxidation of methane on the stoichiometric hydroxyapatite Ca10(PO4)6(OH)2(HAP) has been examined in the presence and absence of tetrachloromethane (TCM). In contrast to the previously observed effects of TCM on the oxidation of methane with other catalysts, the introduction of a small amount of TCM into the feedstream with stoichiometric HAP produced an increased selectivity to carbon monoxide and a decreased conversion of methane with increasing time-on-stream. The selectivity to C2 compounds changed relatively little on addition of TCM. X-Ray analysis showed that the chlorided species was formed not only on the surface but also in the bulk phase and, at least in the latter, was identified as chlorapatite Ca10(PO4)6Cl2. Pretreatment experiments, in which the hydroxyapatite was exposed to a mixture of O2 and TCM before use in the methane conversion process, showed that the chlorinated surface formed by this method possessed distinctly different catalytic properties from that produced during the methane conversion process in the presence of feedstream TCM.

Heavy metal immobilization in aqueous solution using calcium phosphate and calcium hydrogen phosphates

This study examines the possibilities for removing heavy metal cations from water with calcium phosphate, calcium hydrogen phosphate, and calcium dihydrogen phosphate at 293 K. It was reported that immobilization of aqueous heavy metal cations, which is known to be one of the characteristic properties of calcium hydroxyapatite, proceeded favorably with these phosphates. Calcium phosphate, calcium hydrogen phosphate, and calcium dihydrogen phosphate could favorably remove Pb2+ from aqueous solution. Calcium hydrogen phosphate also removed aqueous Cu2+, Co2+, and Cd2+, whereas these cations were not immobilized by calcium phosphate and calcium dihydrogen phosphate. A contribution of the dissolution-precipitation mechanism to immobilization with these phosphates is suggested.

Sorption and ion-exchange properties of barium hydroxyapatite with divalent cations

The properties of barium hydroxyapatite (BaHAp) for ion exchange with Pb2+, Cu2+, Zn2+, Cd2+ and Co2+ have been investigated, with particular emphasis on the former two cations. Under similar conditions the exchange capacities followed the order Cu2+>Pb2+>Zn2+>Cd2+>Co2+. After exchange with Pb2+, lead hydroxyapatite was identified in the solid but with Cu2+ no copper analogue of BaHAp was found, although Ba3(PO4)2 was formed. With solutions containing both Pb2+ and Cu2+ only the former exchanged into BaHAp. With HCl in the exchanging solutions the capacities of BaHAp for both Pb2+ and Cu2+ were enhanced, while copper hydroxyapatite was not found in the solid. Discussions of possible mechanisms are included.

Surface and bulk properties, catalytic activities and selectivities in methane oxidation on near-stoichiometric calcium hydroxyapatites

Various calcium hydroxyapatites [Ca10–z(HPO4)z(PO4)6–z(OH)2–z; z= 0, stoichiometric apatite (Ca/P = 1.67; atomic ratio); 0 Ca/P 1.50)], together with the apatites of Ca/P = 1.72, were analysed by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy and their catalytic properties in the oxidation of methane at 973 K were examined in the presence and absence of tetrachloromethane as a gas-phase additive. The XRD patterns of each hydroxyapatite were the same. However, the nearest-neighbour distances of the Ca–O bond of stoichiometric and non-stoichiometric hydroxyapatites as estimated by EXAFS were 2.41,2.37, 2.38 and 2.39 A for each catalyst of Ca/P = 1.72,1.68,1.64 and 1.58, respectively. In the oxidation of methane on each hydroxyapatite in the absence of CCl4, the conversion of methane was little influenced by the value of Ca/P but the selectivities to C2H6 and CO showed a maximum and minimum, respectively, at Ca/P = 1.68. On addition of CCl4 into the feedstream, the selectivity to CO2 on Ca/P = 1.68 and 1.72 decreased as the time on-stream increased while sharp decreases in conversion were observed with time on-stream on non-stoichiometric hydroxyapatites of Ca/P = 1.64 and 1.53, respectively, without suppression of the selectivity to CO2.

Enhancement of the catalytic activities in propane oxidation and H–D exchangeability of hydroxyl groups by the incorporation with cobalt into strontium hydroxyapatite

The oxidative dehydrogenation of propane to propylene on strontium and cobalt–strontium hydroxyapatites (SrHAp and Co–SrHAp, respectively) and H–D exchangeability of hydroxyl groups in those catalysts with D2O have been studied. Both the yield of C3H6 and H–D exchangeability were found to be enhanced with increasing the cobalt contents in the catalysts, the latter of which was investigated by solid state 1H MAS MNR at 25 kHz. It is suggested that oxygen species, like lattice oxygen in oxide catalysts, as formed from hydrogen desorption from OH groups in the hydroxyapatites, may contribute to the activation of C3H8. The structure of Co–SrHAp, of which the XRD pattern was identical to that of SrHAp, was also identified with extended X-ray absorption fine structure (XAFS) and solid state 31P MAS NMR.