Shigeru Sugiyama

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.

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.

EFFECTS OF FINE STRUCTURE CHANGES OF STRONTIUM HYDROXYAPATITES ON ION-EXCHANGE PROPERTIES WITH DIVALENT CATIONS

The ion exchange of various strontium hydroxyapatites [SrHAp; stoichiometric form, Sr10(PO4)6(OH)2] of different Sr/P ratios with divalent cations has been investigated and compared with those between the corresponding cations and calcium hydroxyapatites (CaHAp). SrHAp has superior exchange properties for divalent cations in comparison with those of CaHAp and the former solid with Sr/P equal to 1.73 has the highest capacity for ion exchange of the compositions examined. The addition of HCl to the exchanging solution enhanced the exchange of SrHAp with Pb2+, apparently influenced by the formation of strontium and lead chlorapatite during the exchange process. The extended X-ray absorption fine structure (EXAFS) analyses revealed that the ion-exchange characteristics are strongly influenced by the nearest-neighbour distances of the Sr—O bond of SrHAp or the Ca—O bond of CaHAp.

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.

Strontium hydroxyapatites: Catalytic properties in the oxidative dehydrogenation of methane to carbon oxides and hydrogen

Abstract Strontium hydroxyapatite of various Sr/P ratios catalyzes oxidative dehydrogenation of methane to carbon oxides and hydrogen at a reaction temperature of 600°C. Although the selectivities are essentially independent of the composition of the catalyst, the activity decreases with decreasing concentration of strontium. The relatively high ratio of H 2 /CO produced cannot be rationalized either through the oxidation of methanol on the catalyst or the water gas shift reaction, but appears to result primarily from the direct oxidation of methane, with the reaction to produce CO 2 and H 2 proceeding at a rate approximately twice that to CO. New active sites associated with strontium appear to be responsible for the catalytic properties of the hydroxyapatite.

Ketones from carboxylic acids over supported magnesium oxide and related catalysts

Silica-supported alkaline earth oxides revealed excellent activity to convert acetic acid selectively into acetone in a vapor-phase fixed-bed flow system. Acetone was obtained through the cyclic formation of alkaline earth acetate followed by decomposition. Magnesium oxide should be supported on the silica surface without formation of magnesium silicate, which was inactive for the present reaction. Attempted syntheses of benzophenone and acetophenone are also described.