Naoya Shigemoto

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.

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.

Redox Behaviors of Magnesium Vanadate Catalysts During the Oxidative Dehydrogenation of Propane

In order to examine the mobility of lattice oxygen in magnesium vanadates, these catalysts were employed for the oxidative dehydrogenation of propane in the absence of oxygen for 2.25 h, followed by the addition of gaseous oxygen into the feedstream. Depending on the degree of the abstraction of lattice oxygen from these catalysts during the oxidation in the absence of the gaseous oxidant, oxygen in the effluent was detected at approximately 1.4 and 9 min with Mg3V2O8 and Mg2V2O7 respectively, after the addition of gaseous oxygen under the present reaction conditions. However, no oxygen was detected with MgV2O6 even after 18.5 min from the addition of gaseous oxygen. 51V MAS NMR was also employed for the observation of redox behaviors of vanadium species in these catalysts during the reaction.

X-ray photoelectron spectra for the oxidation state of TeO2-MoO3 catalyst in the vapor-phase selective oxidation of ethyl lactate to pyruvate

X-ray photoelectron spectra of Te 3d5/2 and Mo 3d5/2 core electrons of TeO2-MoO3 provided an evidence for reduction of Te to the metallic state even in the presence of oxygen in the feed, while the component Mo was rather stable under reductive environment, in the vaporphase oxidation of ethyl lactate at 300 °C. Lattice oxygen was supplied to make up for the oxygen-deficit at the surface, and the catalyst should be used under oxidative, oxygen-rich conditions.

Role of surface chlorine species in the oxidative coupling of methane in the presence of tetrachloromethane on magnesium phosphate and sulphate

Abstract The oxidative coupling of methane was carried out over Mg3 (PO4)2 and MgSO4 in the presence of tetrachloromethane (TCM) in order to compare the catalytic activities, the interaction between TCM and each catalyst and the effect of the nature of the anion. The conversion of methane on the sulphate increased with increase in the partial pressure of TCM and of reaction temperature, while with the phosphate the presence of TCM had little effect under the same conditions as those on the sulphate. With both catalysts the addition of TCM increased the selectivities to ethylene. Relatively large quantities of chlorinated species were detected on the catalyst surface of the used phosphate by XPS, although none were detected by XRD analyses. In contrast, only small quantities of chlorinated species were formed on the sulphate catalyst and magnesia was detected by XRD in the bulk phase of the used sulphate. The interactions between TCM and the catalyst and, in particular, the effect of the nature of the anion are discussed.

Formation of an intermetallic compound Pd3Te with deactivation of Te/Pd/C catalysts for selective oxidation of sodium lactate to pyruvate in aqueous phase

The addition of a trace amount of Te promoted the activity of Pd/C in the liquid-phase oxidation of lactic acid, but the Te/Pd/C catalyst, for which Pd3Te crystalline phase extended over the bulk at a higher Te-doping above Te/Pd = 0.3 (atom), was again inactive. A powder XRD evidence for Pd3Te is given.

Selective oxidative coupling of methane catalysed over hydroxyapatite ion-exchanged with lead

Oxidative coupling of methane to ethane and ethene can be effectively catalysed over hydroxyapatite ion-exchanged with lead at reaction temperatures as low at 700 °C, while hydroxyapatite itself catalyses methane oxidation mainly to carbon oxides. The rate of oxygen conversion over the former apatite is almost the same as that with the latter catalyst, suggesting that the oxidation sites on the two apatites are similar. The experimental results suggest that the lead ions on the surface of apatite play an important role in both the activation of methane and stabilization of methyl radicals on the surface.

An alloy phase of Pd3Pb and the activity of Pb/Pd/C catalysts in the liquid-phase oxidation of sodium lactate to pyruvate

Abstract Oxidation of lactic acid was carried out in aqueous phase at 90°C at a controlled pH of 8 in the presence of lead-modified palladium-on-carbon (Pb/Pd/C) catalysts. The only Pd component detected by powder XRD in Pb/Pd/C as prepared was metallic Pd, while an alloy phase of Pd3Pb was identified in catalysts calcined at 500°C for 3 h under nitrogen. A drastic decrease in activity by calcination was observed for Pb/Pd/C, presumably due to the formation of a rigid structure of an alloy phase of Pd3Pb. However, the catalyst activity was regenerated by the recycle use, while unchanged the XRD patterns signifying that Pd3Pb was still present as the bulk phase. Enriched Pb additive at the Pd surface and facile rearrangement of Pb species in metallic Pd have been demonstrated by the XPS depth profile of Pd 3d 5 2 and Pb 4f 7 2 Core electrons, providing a context of interpreting the regeneration of the calcined catalyst in recycle use.

Formation of chlorine species over magnesium oxide in the oxidative coupling of methane in the presence of carbon tetrachloride

The oxidative coupling of methane on magnesium oxide (MgO) has been studied in the presence of carbon tetrachloride (TCM) as a gas-phase additive. Addition of a small amount of TCM to the reactant stream improves the selectivity to C2H4, while the conversion of methane is not influenced by the additive. X-ray photoelectron spectra of the used MgO reveal the formation of chlorine species on the catalyst surface in quantities up to 0.20 of Cl/Mg (atomic ratio), although X-ray diffraction spectra of the catalyst show MgO only and the content of the chlorine species in the bulk phase estimated by X-ray fluorescence analysis is very low. It is concluded that the enhancement of the selectivity to C2H4 primarily results from the presence of surface chlorine species. The chlorinated species on the catalyst has been identified as MgCl2.