Tatsuo Tsunoda

Steam Reforming of Methanol Over Cu/CeO2 Catalysts Studied in Comparison with Cu/ZnO and Cu/Zn(Al)O Catalysts

A series of Ce1-xCuxO2-δ mixed oxides were synthesized using a co-precipitation method and tested as catalysts for the steam reforming of methanol. XRD patterns of the Ce1-xCuxO2-δ mixed oxides indicated that Cu2+ ions were dissolved in CeO2 lattices to form a solid solution by calcination at 773K when x < 0.2. A TPR (temperature-programmed reduction) investigation showed that the CeO2 promotes the reduction of the Cu2+ species. Two reduction peaks were observed in the TPR profiles, which suggested that there were two different Cu2+ species in the Ce1-xCuxO2-δ mixed oxides. The TPR peak at low temperature is attributed to the bulk Cu2+ species which dissolved into the CeO2 lattices, and the peak at high temperature is due to the CuO species dispersed on the surface of CeO2. The Ce1-xCuxO2-δ mixed oxides were reduced to form Cu/CeO2 catalysts for steam reforming of methanol, and were compared with Cu/ZnO, Cu/Zn(Al)O and Cu/AL2O3 catalysts. All the Cu-containing catalysts tested in this study showed high selectivities to CO2 (over 97%) and H2. A 3.8wt% Cu/CeO2 catalyst showed a conversion of 53.9% for the steam reforming of methanol at 513K (W/F = 4.9 g h mol-1), which was higher than that over Cu/ZnO (37.9%), Cu/Zn(Al)O (32.3%) and Cu/AL2O3 (11.2%) with the same Cu loading under the same reaction conditions. It is likely that the high activity of the Cu/CeO2 catalysts may be due to the highly dispersed Cu metal particles and the strong metalsupport interaction between the Cu metal and CeO2 support. Slow deactivations were observed over the 3.8wt% Cu/CeO2 catalyst at 493 and 513K. The activity of the deactivated catalysts can be regenerated by calcination in air at 773K followed by reduction in H2 at 673K, which indicated that a carbonaceous deposit on the catalyst surface caused the catalyst deactivation. Using the TPO (temperature-programmed oxidation) method, the amounts of coke on the 3.8wt% Cu/CeO2 catalyst were 0.8wt% at 493K and 1.7wt% at 513K after 24h on stream.

Encapsulation of hemoglobin in mesoporous silica (FSM)- : Enhanced thermal stability and resistance to denaturants

Hemoblogin (Hb), which is a typical oligomeric protein, was introduced into the pores of mesoporous silica (FSM: folded‐sheet mesoporous material) that had a diameter of 7.5 nm. Soret CD spectra of Hb–FSM‐7.5 conjugates showed a peak that was identical to that of free Hb. This suggests that Hb retained its highly ordered structure in the mesoporous silica. In addition, the UV‐visible absorption spectrum showed that Hb had an increased resistance to heat denaturation in the silica. Even after heat treatment at 85 °C, Hb–FSM‐7.5 retained its ligand‐binding activity. The stability of Hb–FSM‐7.5 was examined further by measuring its peroxidase‐like activity. Encapsulation of Hb resulted in the retention of activity in the presence of high NaCl or Gdn‐HCl levels. This suggests that encapsulation prevented dissociation and denaturing. Thus, it seems that the mesopores created a favorable environment for the oligomeric protein to perform its function, even under harsh conditions.

Sustainable Ni/Ca1−xSrxTiO3 catalyst prepared in situ for the partial oxidation of methane to synthesis gas

A series of mixed metal oxides of the compositions Ca1−xSrxTi1−yNiyO (x = 0–1.0, y = 0–1.0) were prepared by the citrate method, and was tested for the oxidation of CH4 to synthesis gas. Analytical results clearly showed the presence of Ca1−xSrxTi1−yNiyO perovskite structure, where Sr substituted all the Ca sites while Ni substituted the Ti sites in the range of y < 0.1. Among the catalysts tested, the compositions of x = y = 0.2 showed the highest activity. Either Ni species in the Ca0.8Sr0.2Ti1−yNiyO perovskite structure or NiO originally separated from the perovskite structure during the preparation was in situ reduced to Ni metal during the CH4 oxidation. The Ni metal thus formed showed high activity for synthesis gas production, where Ca0.8Sr0.2TiO3 perovskite has an important role as a carrier of the Ni catalyst. Three catalysts of the composition Ca0.8Sr0.2Ti1.0Ni0.2O were then prepared by citrate, impregnation and mixing methods. The highest activity was obtained with the citrate, followed by the impregnation of Ni on Ca0.8Sr0.2TiO3 perovskite. The catalyst prepared by the mixing method afforded no perovskite, resulting in low activity. The amount of coke formation over the Ni catalysts after the reaction for 150 h was as follows: citrate < impregnation ⪡ Niγ-Al2O3 as the comparison. Ca0.8Sr0.2TiO3 perovskite was effective as the carrier of the Ni catalyst for the partial oxidation of CH4 to synthesis gas. Ni/Ca0.8Sr0.2TiO3 prepared by the citrate method is the most sustainable against coke formation during the reaction. It is likely that the citrate method gave high Ni dispersion over the perovskite as well as strong metal-support interaction between Ni and the perovskite, resulting in both high activity and high sustainability against coke formation.

Dry reforming of methane over supported noble metals: a novel approach to preparing catalysts

Abstract A simple and effective approach has been developed for the synthesis of precious metal catalysts supported on Mg–Al mixed oxide. It involved reaction of the mixed oxide powder with aqueous solutions of EDTA-chelated precious metals (EDTA 4− =ethylenediaminetetraacetate) to produce the meixnerite-like layered double hydroxides bearing the anionic metal chelates. Highly active and durable metal catalysts for the reforming of methane with carbon dioxide to synthesis gas were in situ generated from such materials, the most efficient being that of ruthenium.

Comparison of density of states of transition metal disilicides and their related compounds systematically calculated by a first-principle pseudopotential method using plane-wave basis

Density of states of transition metal disilicides and their related compounds of the following types of structures have been calculated by a first-principle pseudopotential method using plane-wave basis, CASTEP; CaF2, α- and β-FeSi2, TiSi2, ZrSi2, CrSi2, MoSi2, Mn4Si7, Ru2Si3, and AlB2. The principle of “DOS at Fermi level would be hopefully smaller in energetically-favored structure” is valid in most of silicides except for IIIa elements. The broadening of the energy difference between the bonding and anti-bonding states by promotion to the heavier element in the same group in periodic table is dependent on the crystal structure and this may cause the transition of the structure in the same group. Semiconducting property of ReSi2 is probably due to the vacancies located at silicon sites because DOS at Fermi level has relatively large value for stoichiometric ReSi2. Also, it is pointed out that the formula of Mn11Si19 is not consistent with the intrinsic semiconducting nature.

Stoichiometry of tantalum oxide films prepared by KrF excimer laser-induced chemical vapor deposition

Abstract Tantalum oxide films have been prepared by photolysis of Ta(OCH 3 ) 5 vapor under KrF excimer laser irradiation at various laser fluences (50–450 J m −2 ). The composition and Stoichiometry of the films were determined by X-ray photoelectron spectroscopy (XPS). The variation of the shape of the Ta 4f XPS peak for surface erosion of samples by argon-ion etching indicated that films were deficient in oxygen atoms compared with the composition of the stoichiometric Ta 2 O 5 , though the X-ray diffraction pattern of films obtained at higher laser fluences (more than 300 J m −2 ) corresponded to that of the β-Ta 2 O 5 phase. The deficiency in oxygen increased with increasing laser fluence to reach the maximum value of about 20% in the laser fluence range 150 J m −2 to 250 J m −2 and then decreased. The carbon content in the films was less than the background contamination level (a few %) under the experimental conditions investigated. Various possible reasons for the laser fluence effect on the stoichiometry of films are discussed.

Enhancement in thermal stability and resistance to denaturants of lipase encapsulated in mesoporous silica with alkyltrimethylammonium (CTAB)

We assembled a highly durable conjugate with both a high-density accumulation and a regular array of lipase, by encapsulating it in mesoporous silica (FSM) with alkyltrimethylammonium (CTAB) chains on the surface. The activity for hydrolyzing esters of the lipase immobilized in mesoporous silica was linearly related to the concentration of lipase, whereas that of non-immobilized lipase showed saturation due to self-aggregation at a high concentration. The lipase conjugate also had increased resistance to heating when stayed in the silica coupling with CTAB. In addition, encapsulating the enzyme with FSM coupled CTAB caused the lipase to remain stable even in the presence of urea and trypsin, suggesting that the encapsulation prevented dissociation and denaturing. This conjugate had much higher activity and much higher stability for hydrolyzing esters when compared to the native lipase. These results show that FSM provides suitable support for the immobilization and dispersion of proteins in mesopores with disintegration of the aggregates.

Selective adsorption of bacterial cells onto zeolites

Zeolites adsorb microbial cells on their surfaces and selective adsorption for specific microorganisms was seen with certain zeolites. Tests for the adsorption ability of zeolites were conducted using various established microbial cell lines. Specific cell lines were shown to selectively absorb to certain zeolites, species to species. In order to understand the selectivity of adsorption, we tested adsorption under various pH conditions and determined the zeta-potentials of zeolites and cells. The adsorption of some cell lines depended on the pH, and some microorganisms were preferentially adsorbed at acidic pH. The values of zeta-potentials were used for calculating the electric double layer interaction energy between zeolites and microbial cells. There was a correlation between the experimental adsorption results and the interaction energy. Moreover, we evaluated the surface hydrophobicity of bacterial cells by using the microbial adherence to hydrocarbon (MATH) assay. In addition, we also applied this method for zeolites to quantify relative surface hydrophobicity. As a result, we found a correlation between the adsorption results and the hydrophobicity of bacterial cells and zeolites. These results suggested that adsorption could be explained mainly by electric double layer interactions and hydrophobic interactions. Finally, by using the zeolites Na-BEA and H-Y, we succeeded in clearly separating three representative microbes from a mixture of Escherichia coli, Bacillus subtilis and Staphylococcus aureus. Zeolites could adsorb each of the bacterial cell species with high selectivity even from a mixed suspension. Zeolites can therefore be used as effective carrier materials to provide an easy, rapid and accurate method for cell separation.

Preparation and characterization of CaTiO3-based perovskitic oxides as catalysts for partial oxidation of light hydrocarbons

A series of perovskites of the formula Ca1−xSrxTi1−yMyO3−δ, M=Fe, Co, Cr or Ni,x = 0−1,y = 0−0.6, has been synthesized by a modified sol-gel method using citrate. Several of these materials were proved to be stable under operating conditions in reducing atmospheres of air and hydrocarbons. An outline of the synthesis procedure is given, together with the results of XRD, SEM, BET, TG, DTA and IR characterization before and after catalytic testing. The solubility of Ni and Cr in this perovskite was very limited, and the solubility of Co decreased abruptly above 1173 K. The solubility range of Ca and Sr on alkaline earth sites is 100%.

Thermoelectric properties and defect structure of La0.45Nd0.45Sr0.1FeO3−δ

Abstract A concept for the design of thermoelectric oxides, which is the method to decrease the thermal conductivity without decreasing the electrical conductivity using the complex oxide system, is proposed. The electrical transport properties and the defect structure of La 0.45 Nd 0.45 Sr 0.1 FeO 3− δ , which corresponds to Sr-doped LaFeO 3 –NdFeO 3 solid solution, were investigated to confirm the concept. La 0.45 Nd 0.45 Sr 0.1 FeO 3− δ was found to show a p-type behavior between 1073 and 1273 K at an oxygen partial pressure of 10 −4 to 1 atm. The values of hole mobility in La 0.45 Nd 0.45 Sr 0.1 FeO 3− δ were found to be in good agreement with those of La 0.9 Sr 0.1 FeO 3− δ . The heat of transport of the holes was also discussed using the small-polaron model.