Tomoyuki Inui

Effect of the property of solid acid upon syngas-to-dimethyl ether conversion on the hybrid catalysts composed of Cu–Zn–Ga and solid acids

Abstract Syngas-to-dimethyl ether (STD) conversion was examined on various hybrid catalysts. The catalyst composed of a methanol-synthesis catalyst and a silica-rich silica–alumina showed high dimethyl ether (DME) yield (55.5%) with a good selectivity (93.5%). The effects of water on the acid property and on the reaction were examined. At atmospheric pressure, Lewis acid–base pairs were major active sites for methanol dehydration. At higher pressures, however, water formed by methanol dehydration was strongly adsorbed on Lewis acid sites, suppressing the DME formation. The solid-acid catalyst having Bronsted acid sites with moderate acid strength was the best catalyst for the STD process. Modification of the methanol-synthesis catalysts with Pd was effective to enhance the STD activity at low temperatures.

Improvement in the catalyst activity for direct synthesis of dimethyl ether from synthesis gas through enhancing the dispersion of CuO/ZnO/γ-Al2O3 in hybrid catalysts

Abstract Based on the knowledge of the mechanisms of methanol synthesis and methanol dehydration, it was predicted that if the dispersion of CuO/ZnO/γ-Al2O3 in hybrid catalysts for direct synthesis of dimethyl ether from synthesis gas was enhanced, the formation rate of dimethyl ether would be increased. In order to justify the prediction, five preparation methods, including two mechanical mixing ones and three co-precipitation ones were used to prepare the catalysts. It was found that co-precipitation impregnation and co-precipitation of Cu/Zn by NaAlO2 provided the catalyst with the highest activity and co-precipitation of Cu/Zn/Al by Na2CO3 resulted in the worst catalyst. Combined with the XRD results it is deduced that the active phases for direct synthesis of dimethyl ether from synthesis gas are highly-dispersed fine crystallites of CuO/ZnO/γ-Al2O3. Calcination temperature of the precursor of γ-alumina used in the methods of mechanical mixing was also studied. It was found that a calcination temperature of 550°C brought about the most active dehydration catalyst with the largest surface area and nearly pure γ-alumina of poor crystallinity. So it might be concluded that the active phase for methanol dehydration is fine crystallites of γ-alumina.

Effective conversion of carbon dioxide and hydrogen to hydrocarbons

Abstract Recent studies on effective catalytic conversion of carbon dioxide to hydrocarbons were summarized. Firstly, requisites of catalyst structure to realize rapid methanation of carbon dioxide were investigated in detail. The support having a meso-macro bimodal pore structure was found to be superior for both diffusion rates of reactants and products and high dispersion of active catalyst substances, respectively. The Ni-based composite catalyst combined with a small amount of La2O3 and a very small amount of Ru exhibited a very high methanation rate. The role of Ru in the composite catalyst was elucidated as the portholes of hydrogen spillover for the active sites in Ni part. Next, CuZnCrAl mixed oxide catalysts were synthesized by the intrinsic uniform gelation method to synthesize methanol with a comparable reaction rate of syngas conversion to methanol. Furthermore, the performance of methanol synthesis catalyst was markedly improved by modification with Pd or Ag as anticipated an effect of spillover. Gasoline synthesis from carbon dioxide and hydrogen was firstly achieved by adopting a two-stage reactor connected in a series manner as follows; in the first reactor the modified methanol synthesis catalyst was packed, and in the second reactor an HFesilicate catalyst, which has the ZSM-5 (MFI) structure and the activity of methanol to gasoline conversion without acceptance of any effect from the unconverted hydrogen, was packed.

Characterization of precursors of methanol synthesis catalysts, copper/zinc/aluminum oxides, precipitated at different pHs and temperatures

Abstract Catalyst precursors for copper/zinc aluminum mixed oxide catalysts with an atomic ratio of 6/3/1 were prepared by co-current precipitation at different pH levels and different temperatures. The precursors, catalysts and reduced catalysts were characterized by means of infrared spectroscopy, X-ray diffraction, thermal analysis, temperature-programmed oxidation and BET surface measurements. The catalysts were also tested for methanol synthesis activity in a synthesis gas containing a small amount of carbon dioxide. When the precipitation was conducted at pH= 7.0, the precipitates mainly consisted of the malachite-like phase and the catalysts therefrom were more active. Precipitation at pH≤ 6 favored the formation of hydroxynitrate, which led to less active catalysts. Although the composition of the precursors obtained at pH= 7.0 and temperatures lower than 50°C was the same as those at pH= 7.0 and T = 70°C, the activity of the catalysts was much lower. It was also found that the aging temperature was an important factor in determining the interdispersion and activity of the final catalysts. Although the effects of both the pH value and the temperature on activity of the catalysts can be ascribed to a similar reason, i.e., the different interdispersion of copper and zinc, it seems that the pH value exerts its effect through altering the phase composition of the precursors, while the temperature functions through the precipitation kinetics of the precursors with a same composition.

Highly selective synthesis of light olefins from methanol on a novel Fe-silicate

Methanol to hydrocarbon conversion on a number of metallosilicates having the pentasil pore-opening structure were investigated to develop a highly selective catalyst for the olefin synthesis from methanol. The metallosilicates were prepared by replacing the Al ingredient with various metal salts at the stage of gel formation in a modified preparation method (the rapid crystallization method) of ZSM-5. The catalysts were active for the methanol to hydrocarbon conversion, and the selectivity to lower olefins, gasoline, or aromatics changed greatly with the kind of metal incorporated. As for the conversion to lower olefins, silicates of Fe, Co, and Pt exhibited the best selectivity. Among them, the Fe-silicate was least active for the formation of aromatics—undesirable products caused by a consecutive reaction of olefins. Further investigations were then made for the preparation, characterization, and methanol to hydrocarbon conversion on Fe-silicates. It was found that various amounts of Fe up to 10 wt% as Fe2O3 are incorporated in the crystal having pentasil pore-opening structure by the rapid crystallization method. The incorporated Fe was highly dispersed in the crystal and a considerable part of Fe was suggested to be in its framework. The incorporated Fe produced both strong and weak acid sites, and their amounts were controlled by changing Fe content in the catalyst. It was also suggested that a part of the Fe ingredient plays a role as nuclei of crystal growth of the high-silica crystal. The selectivity to C2C4 olefins was greatly increased by the incorporation of Fe in the crystal. The total selectivity to C2-C4 olefins was achieved as high as 97.6 C-mol%, and the space-time yield attained 11.9 C-mol/liter · h at 295 °C.

Novel synthesis of microcrystalline titanium(IV) oxide having high thermal stability and ultra-high photocatalytic activity : thermal decomposition of titanium(IV) alkoxide in organic solvents

Thermal decomposition of titanium(IV) tetra-tert-butoxide (TTB) in inert organic solvents at 573 K yielded microcrystalline anatase (titanium(IV) oxide, TiO2) powders with a crystallite size of ca. 9 nm and a surface area of <100 m2 g-1. Primary and secondary alkoxides of titanium(IV), however, were not decomposed under similar conditions, indicating that the thermal stability of C-O bonds in the alkoxides was a decisive factor for their decomposition. The TiO2 prepared from TTB by this manner was thermally stable upon calcination in air and retained high surface area of ca. 100 m2 g-1 even after calcination at 823 K. The as-prepared TiO2 powders, without calcination, exhibited much higher rate of carbon dioxide formation than any other active photocatalysts such as Degussa P-25 and Ishihara ST-01 in the photocatalytic mineralization of acetic acid in aerated aqueous solutions. The higher activity of the present TiO2 photocatalysts is attributed to both high crystallinity and large surface of the present product. The calcination of the as-prepared TiO2 in air reduced the photocatalytic activity, but it was still higher than the other commercially available TiO2s.

Highly effective conversion of carbon dioxide to valuable compounds on composite catalysts

The highly effective catalytic conversion of CO2 into valuable compounds was investigated by multi-functional catalysts composed of base-metal oxides as the main components promoted by a low concentration of precious metals and gallium oxide. The desired reduced state of catalyst metal oxides for exhibiting the optimum catalytic performance could be controlled by both the hydrogen spillover on the precious metal parts and the inverse-spillover from the Ga parts. By applying those principal concepts in the catalyst structure-design, the rapid CO2 reforming of methane, the rapid CO2 methanation, the effective synthesis of methanol and/or ethanol from CO2 and H2, and selective syntheses of high quality gasoline and/or light olefins by means of one-pass conversion of CO2-H2 mixture via methanol as the intermediate product, were respectively realized. Those novel catalytic reactions would have a high potential to moderate the accumulation of CO2 come from fossil fuel combustion, while compensating the cost of hydrogen as the reducing reagent.

Reliable procedure for the synthesis of Ni-SAPO-34 as a highly selective catalyst for methanol to ethylene conversion

Abstract A reliable synthetic procedure of Ni-SAPO-34 crystals having the catalytic performance for methanol to ethylene with a selectivity as high as 88% was investigated. The focus of the study was put on the increase in homogeneity of the mixed gel as the precursor of crystallites. Proper treatments of the mixed gel such as application of ultrasonic waves, addition of a proper amount of the seed crystals and milling were found to be important to obtain a high crystallinity and a sharp distribution of crystal size. Incorporations of the crystal ingredients, P, Si, and Ni, into the framework of SAPO-34 were observed for those crystallites. The crystallites, which were 0.85±0.05μm in size and had a solid acid density 4 μmol/m2 distributed inside the crystallites, exhibited the highest ethylene selectivity, 88%. The total conversion level of methanol was observed at a medium reaction temperature around 425°C. These crystallites exhibited a minor deactivation due to the lower amounts of coke formation.

Glycothermal synthesis of rare earth aluminium garnets

The reaction of a stoichiometric mixture of aluminium isopropoxide and yttrium acetate in 1,4-butanediol at 300 °C yielded crystalline yttrium aluminium garnet having an approximate particle size of 30 nm. No other phases were detected. Similarly, all the lanthanide elements from Nd to Lu gave essentially single-phase aluminium garnets. Samarium and europium aluminium garnets were also formed by this method, but the products contained corresponding lanthanide acetate oxide. The use of ethylene glycol instead of 1,4-butanediol afforded amorphous products.

Structure and function of Cu-based composite catalysts for highly effective synthesis of methanol by hydrogenation of CO2 and CO

Abstract A highly effective catalytic conversion of CO 2 and CO into methanol has been investigated by the multi-functional catalysts composed of CuZn oxides as the main components with the modification of a low concentration of precious metals and gallium oxide. The desired reduced state of the catalyst metal oxides for exhibiting the optimum catalytic performance could be controlled by both the hydrogen spillover through the precious metal parts and the inverse-spillover from the Ga parts. As a result, an extraordinary high space-time yield of methanol, 1300 g/1 · h, could be realized under conditions of 270°C, 80 atm, SV 18800 h −1 with 22.0% CO 2 conversion to methanol. Furthermore, the catalyst also exhibited a very high performance in CO hydrogenation, and gave a space-time yield of methanol as high as 6340 g/l · h under conditions of 270°C, 80 atm, SV 37 600 h −1 with 39.4% CO conversion to methanol.