Katsuomi Takehira

CO2 reforming of CH4 over Ni/Mg–Al oxide catalysts prepared by solid phase crystallization method from Mg–Al hydrotalcite-like precursors

Ni supported catalysts were prepared by the solid phase crystallization (spc) method starting from hydrotalcite (HT) anionic clay based on [Mg6Al2(OH)16CO32−]⋅H2O as the precursor. The precursors were prepared by the co-precipitation method from nitrates of the metal components, and then thermally decomposed, in situ reduced to form Ni supported catalysts (spc-Ni/Mg–Al) and used for the CO2 reforming of CH4 to synthesis gas. Ni2+ can well replace the Mg2+ site in the hydrotalcite, resulting in the formation of highly dispersed Ni metal particles on spc-Ni/Mg–Al. The spc-catalyst thus prepared showed higher activity than those prepared by the conventional impregnation (imp) method such as Ni/α-Al2O3 and Ni/MgO. When Ni was supported by impregnation of Mg–Al mixed oxide prepared from Mg–Al HT, the activity of imp-Ni/Mg–Al thus prepared was not so low as those of Ni/α-Al2O3 and Ni/MgO but close to that of spc-Ni/Mg–Al. The relatively high activity of imp-Ni/Mg–Al may be due to the regeneration of the Mg–Al HT phase from the mixed oxide during the preparation, resulting in an occurring of the incorporation of Ni2+ in the Mg2+ site in the HT as seen in the spc-method. Such an effect may give rise to the formation of highly dispersed Ni metal species and afford high activity on the imp-Ni/Mg–Al.

Manganese-containing MCM-41 for epoxidation of styrene and stilbene

Mn-MCM-41 is found to be the most effective heterogeneous catalyst for the epoxidation of styrene with tert-butyl hydroperoxide (TBHP) among several metal ion-containing mesoporous molecular sieves including Mn-, V-, Cr-, Fe-, and Mo-MCM-41. ESR, XANES, diffuse reflectance UV–VIS, UV–Raman and XPS are used to characterize the Mn-MCM-41 synthesized by both direct hydrothermal (DHT) and template ion exchange (TIE) methods. The results suggest that Mn2+ and Mn3+ coexist in the Mn-MCM-41 samples synthesized by both methods and a large part of manganese atoms could be incorporated into the framework of MCM-41 obtained by the DHT method. The oxidation of either styrene or stilbene with TBHP as the oxidant over the Mn-MCM-41 produces corresponding epoxide as the main product; the reaction probably proceeds through a radical intermediate. The TIE catalyst shows higher activity, while the DHT catalyst gives higher TBHP efficiency for the epoxidation reactions.

Characterizations and catalytic properties of Cr-MCM-41 prepared by direct hydrothermal synthesis and template-ion exchange

Abstract Cr-MCM-41 prepared by direct hydrothermal synthesis (DHT) and template-ion exchange (TIE) has been characterized by X-ray diffraction (XRD), N 2 adsorption (77 K), diffuse reflectance UV–vis, X-ray absorption (XANES and EXAFS), and UV-Raman spectroscopic measurements. It is suggested that monochromate species mainly exist on the Cr-MCM-41 by the DHT method while several types of chromate species including both monochromates and polychromates coexist on that by the TIE method. The two kinds of samples exhibit similar catalytic property in the dehydrogenation of propane with carbon dioxide. The selectivity to propylene is higher than 90% and the presence of carbon dioxide enhances propane conversion. The chromate species on both types of samples are reduced to aggregated Cr(III) with octahedral coordination during the dehydrogenation reactions. On the other hand, the selectivity to formaldehyde in the partial oxidation of methane with oxygen is remarkably higher over the sample by the DHT method than that by the TIE method. The structure of the chromate species is kept during the oxidation of methane, and the high dispersion of monochromate species probably accounts for the higher selectivity over the sample by the DHT method.

Partial oxidation of methane over Ni/Mg-Al oxide catalysts prepared by solid phase crystallization method from Mg-Al hydrotalcite-like precursors

Ni-supported catalyst was prepared by the solid phase crystallization (spc) method starting from Mg-Al hydrotalcite (HT) anionic clay as the precursor; it was tested for the partial oxidation of CH4 to synthesis gas. The precursor based on [Mg6Al2(OH)16CO32−]·4H2O was prepared by co-precipitation method from nitrates of the metal components. The precursor was then thermally decomposed and reduced to form Ni-supported catalyst (spc-Ni/Mg-Al). Ni2+ can well occupy the Mg2+ sites in the hydrotalcite resulting in the formation of highly dispersed Ni metal particles on spc-Ni/Mg-Al. The spc-Ni/Mg-Al thus prepared, showed high activity and selectivity to synthesis gas even at high space velocity. When Ni was supported by impregnating Mg-Al mixed oxide prepared from Mg-Al HT, the activity of imp-Ni/Mg-Al was higher than those of Ni/α-Al2O3 and Ni/MgO while it was close to that of spc-Ni/Mg-Al. The relatively high activity of the imp-Ni/Mg-Al may be due to the regeneration of Mg-Al HT phase from the mixed oxide during the preparation resulting in incorporation of Ni2+ on the Mg2+ sites in the HT as seen in the spc method.

Partial oxidation of methane to synthesis gas over supported Ni catalysts prepared from Ni–Ca/Al-layered double hydroxide

Abstract The Ni-supported catalysts have been prepared in situ by the solid phase crystallization ( spc ) method starting from layered double hydroxides (LDHs) as the precursor and tested for the partial oxidation of methane to synthesis gas. The spc -Ni/M–Al (M: Mg, Ca and Sr) catalysts were prepared from Ni–M/Al-LDHs as the precursors, and the activities were studied in relation to the structure of the catalysts and compared with those prepared by the impregnation method. Among the catalysts tested, spc -Ni/Ca–Al was easily reduced to form active Ni metal particles during the reaction and showed the highest activity and selectivity to synthesis gas production as well as the highest sustainability against coke formation on the catalyst. The high activity and the high sustainability against coke formation of spc -Ni/Ca–Al may be due to the stable and highly dispersed Ni metal particles in addition to the basic property of Ca–Al mixed oxide as the support.

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.

A convenient synthesis of alkyl-substituted p-benzoquinones from phenols by a H2O2/heteropolyacid system

Abstract Alkyl-substituted p-benzoquinones were easily synthesized in good yields by the oxidation of the corresponding phenols with a hydrogen peroxide/heteropolyacid couple in acetic acid.

Oxidation of isobutane over Mo–V–Sb mixed oxide catalyst

The catalytic performances of Mo–V–Sb mixed oxide catalysts have been studied in the selective oxidation of isobutane into methacrolein. V–Sb mixed oxide showed the activity for oxidative dehydrogenation of isobutane to isobutene. The selectivity to methacrolein increased by the addition of molybdenum species to the V–Sb mixed oxide catalyst. In a series of Mo–V–Sb oxide catalysts, Mo1V1Sb10Ox exhibited the highest selectivity to methacrolein at 440°C. The structure analyses by XRD, laser Raman spectroscopy and XPS showed the coexistence of highly dispersed molybdenum suboxide, VSbO4 and α-Sb2O4 phases in the Mo1V1Sb10Ox. The high catalytic activity of Mo1V1Sb10Ox can be explained by the bifunctional mechanism of highly dispersed molybdenum suboxide and VSbO4 phases. It is likely that the oxidative dehydrogenation of isobutane proceeds on the VSbO4 phase followed by the oxidation of isobutene into methacrolein on the molybdenum suboxide phase.

CO2 absorption properties and characterization of perovskite oxides, (Ba,Ca) (Co,Fe) O3−δ

Abstract Perovskite oxides, Ba 0.95 Ca 0.05 Co 1−x Fe x O 3−δ , were found to be useful as materials for CO 2 absorption at high temperatures between 900 to 1123 K, and CO 2 absorbed perovskite oxides were characterized by Mossbauer spectrometry. Before absorption of CO 2 , a magnetic sextet with sharp peaks and two paramagnetic doublets due to Fe 3+ and Fe 4+ were observed for the cubic oxides with x > 0.4. Perovskite oxides with lattice oxygen vacancies, which were produced at high temperature, easily absorbed CO 2 . After absorption of CO 2 , the paramagnetic peaks disappeared and magnetic fields were produced due to less interaction of lattice oxygens with iron atoms, where CO 2 reacted with lattice oxygen to form CO 3− ions. Finally only one magnetic sextet with sharp peaks remained. It was considered to be due to α-Fe 2 O 3 with a small magnetic field, dispersed in BaCO 3 matrix.

Synthesis of V-MCM-41 by template-ion exchange method and its catalytic properties in propane oxidative dehydrogenation

Vanadium has been introduced to MCM-41 without collapse of the mesoporous structure by exchanging VO2+ ions in the aqueous solution with the template cations in the uncalcined MCM-41. This template-ion exchange (TIE) method provides tetrahedrally coordinated vanadyl species dispersed in the channel of MCM-41. Such synthesized V-MCM-41 shows higher catalytic activity in the oxidative dehydrogenation of propane than that prepared by direct hydrothermal method.