Satoshi Hamakawa

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.

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.

Mg–Al Layered Double Hydroxide Intercalated with [Ni(edta)]2− Chelate as a Precursor for an Efficient Catalyst of Methane Reforming with Carbon Dioxide

Coprecipitation of Mg2+ and Al3+ with pre-synthesized [Ni(edta)]2− chelate at basic pH resulted in formation of a new layered double hydroxide (LDH) where [Ni(edta)]2− species occupied the interlayer space. The synthesized LDH was characterized by X-ray powder diffraction, diffuse reflectance FTIR and thermogravimetry-differential thermal analysis under inert and oxidative atmosphere. Calcination of LDH led to NiMgAl mixed oxide which after reduction with hydrogen exhibited high catalytic function toward the reaction of methane reforming with carbon dioxide to synthesis gas. The catalyst maintained high activity within 150 h time on stream at 800°C and could be used repeatedly after regeneration. Although coke deposition onto the catalyst surface attained 5–10 wt%, it did not diminish reagent conversion and product selectivity.

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.

Oxidative dehydrogenation of ethane by carbon dioxide over sulfate‐modified Cr2O3/SiO2 catalysts

The oxidative dehydrogenation of ethane into ethylene by carbon dioxide over unsupported Cr2O3, Cr2O3/SiO2 and a series of Cr2O3/SiO2 catalysts modified by sulfate was investigated. The results show that Cr2O3/SiO2 is an effective catalyst for dehydrogenation of ethane and CO2 in the feed promotes the catalytic activity. Sulfation of silica will influence the catalytic behavior of Cr2O3/SiO2 in dehydrogenation of ethane with carbon dioxide depending on the amount of sulfate. Cr2O3/6 wt% SO42-–SiO2 catalysts exhibit an excellent performance for this reaction, giving an ethylene yield of 55% at 67% ethane conversion at 650°C. Characterizations indicate that addition of sulfate changes the bulk and surface properties of Cr2O3/SiO2, promoting the reduction of Cr6+ to Cr3+ and favoring the catalytic conversion.

Methanol decomposition to synthesis gas over supported Pd catalysts prepared from synthetic anionic clays

Supported Pd or Rh catalysts were prepared by the solid-phase crystallization method starting from hydrotalcite anionic clay minerals based on [Mg6Al2(OH)16CO22−]·4H2O as the precursors. The precursors were prepared by a coprecipitation method from the raw materials containing Pd2+ and various trivalent metal ions which can replace each site of Mg2+ and Al3+ in the hydrotalcite. Rh3+ was also used for preparing the catalyst as comparison. The precursors were then thermally decomposed and reduced to form supported Pd or Rh catalysts and used for the methanol decomposition to synthesis gas. Among the precursors tested, use of Mg–Cr hydrotalcite containing Pd2+ resulted in the formation of efficient Pd supported catalysts for the production of synthesis gas by selective decomposition of methanol at low temperature. Although Pd2+ cannot well replace the Mg2+ site in the hydrotalcite, the Pd supported catalyst (Pd/Mg–Cr) prepared by the solid-phase crystallization method formed highly dispersed Pd metal particles and showed much higher activity than that prepared by the conventional impregnation method. When the precursor was prepared under mild conditions, more fine particles of Pd metal were formed over the catalyst, resulting in high activity. It is likely that the high activity may be due to the highly dispersed and stable Pd metal particles assisted by the role of Cr as the co-catalyst.

Oxidative dehydrogenation of ethane over La1−xSrxFeO3−δ perovskite oxides

Catalysts of the composition La1−xSrxFeO3−δ, 0⩽x ⩽1, have been tested for the oxidative dehydrogenation of ethane in the temperature range 300–800°C. The catalyst is active above 400°C, giving a maximum yield of 37% ethylene at 650°C. Above 650°C, synthesis gas was formed together with methane, suggesting that the reforming reaction and thermal cracking of ethane took place. The catalytic data are compared to conductivity measurements on the same material, and a good correlation between the activity and p-type conductivity has been found. In the phase diagram for the system LaFeO3-SrFeO3−δ, a phase separation to two types of (La, Sr)FeO3−δ perovskites was observed in the La/Sr binary composition in the temperature range below 800°C. The phase separation can elucidate the dependency of the catalytic activity on its p-type conductivity.

Production of hydrogen by steam reforming of methanol over Cu/CeO2 catalysts derived from Ce1−xCuxO2−x precursors

Abstract The Ce1−xCuxO2−x mixed oxides were synthesized using the coprecipitation method, and were reduced to form the Cu/CeO2 (cop) catalysts for the steam reforming of methanol. All the Cu-containing catalysts tested in this study showed high selectivities to CO2 (over 97%) and H2. A 3.9 wt% Cu/CeO2 (cop) catalyst showed a conversion of 53.9% for the steam reforming of methanol at 513 K, which was higher than those 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 3.9 wt% Cu/CeO2 (cop) catalyst was due to the highly dispersed Cu metal particles and the Cu+ species stabilized by the CeO2 support.

Partial oxidation of methane over aNi/BaTiO3 catalyst prepared by solid phasecrystallization

Ni/BaTiO 3 catalyst has been prepared by solid phase crystallization (SPC) and used successfully for partial oxidation of CH 4 into synthesis gas at 800°C. In the SPC method, Ni/BaTiO 3 catalyst is obtained in situ by the reaction of starting materials with nickel species homogeneously incorporated in the structure. For the starting reagents, materials of two compositional types were employed i.e., perovskite structures BaTi 1-x Ni x O 3- δ (0⩽x⩽0.4) and stoichiometric structures, BaTiO 3 , Ba 2 TiO 4 and BaTi 5 O 11 , with 0.3NiO. The starting materials were tested for oxidation of CH 4 by increasing the reaction temperature from room temperature to 800°C. The catalysts showed the highest activity for synthesis gas formation around 800°C, and the highest value was obtained at a composition of x=0.3 in the former catalysts. Among the latter catalysts, the highest activity was observed over BaTiO 3 ·0.3NiO, which was more active than BaTi 0.7 Ni 0.3 O 3-δ . On the both catalysts, nickel species originally incorporated in the structure were reduced to the metallic state during the reaction. The BaTiO 3 ·0.3NiO catalyst was further tested for 75 hours at 800°C with no observable degradation and negligible coke formation on the catalyst. Thus, Ni/BaTiO 3 prepared in situ from the perovskite precursor, i.e., by the SPC method, was the most active and resistant to coke formation and deactivation during the reaction. This may be due to well dispersed and stable Ni metal particles over the perovskite, where the nickel species thermally evolve from the cations homogeneously distributed inside an inert perovskite matrix as the precursor.

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.