Mitsuru Komori

Global CO2 recycling : novel materials and prospect for prevention of global warming and abundant energy supply

Abstract CO2 emissions which induce global warming, increase with the growth of the economic activity. It is, therefore, impossible to decrease emissions only by energy savings and by improvements of the energy efficiency. Global CO2 recycling can solve this problem and supply abundant renewable energy. Global CO2 recycling consists of three districts: (i) in deserts, all necessary electricities are generated by solar cells; (ii) on coasts close to the deserts, the electricity is used for production of H2 by seawater electrolysis, H2 is converted to CH4 by the reaction with CO2 and liquefied CH4 is transported to energy consuming districts; (iii) at energy consuming district, after CH4 is used as a fuel, CO2 is recovered, liquefied and transported to the coasts close to the deserts. A CO2 recycling plant for substantiation of our idea has been built on the roof of our Institute (IMR) in 1996, using key materials tailored by us. The key materials necessary for global CO2 recycling are the anode and cathode for seawater electrolysis and the catalyst for CO2 methanation. Since the quantities of CO2 to be converted far exceed an industrial level, the system must be very simple and the rate of conversion must be very fast. These requirements are satisfied in our global CO2 recycling system. When global CO2 recycling is conducted on a large scale, the energies and costs required to form liquefied CH4 in our global CO2 recycling system are almost the same as those for production of LNG from natural gas wells. A project for field experimenting the global CO2 recycling using pilot plants in Egypt has been planned in cooperation with Egyptian scientists, engineers and industries.

CO2 methanation catalysts prepared from amorphous Ni-Zr-Sm and Ni-Zr-misch metal alloy precursors

Abstract Nickel catalysts supported on nano-grained oxides have been prepared from amorphous Ni–Zr–Sm and Ni–Zr–Mm (Mm: misch metal) alloys and crystalline Ni–Sm and Ni–Mm alloys. These catalysts show higher catalytic activity for methanation of carbon dioxide than a conventionally prepared zirconia supported nickel catalyst. The catalytic activity of Ni–Zr–5 at% Sm catalysts increases with increase in nickel content, and is higher than the samarium-free Ni–Zr catalysts containing the same amount of nickel. The stabilization of tetragonal zirconia and the increase in the number of active surface nickel sites by addition of samarium to the nickel-rich catalysts leads to enhancement of catalytic activity. In the Ni–Zr–5 at% Mm catalysts, only the activity of the catalyst containing 60 at% nickel is enhanced in comparison with misch metal-free Ni–Zr catalysts. It is also found that Ni–Sm and Ni–Mm catalysts show activities as high as that of Ni–Zr catalyst, suggesting that samarium and misch metal oxides also act as good catalyst supports for methanation catalysts.

Compositional dependence of the CO2 methanation activity of Ni/ZrO2 catalysts prepared from amorphous NiZr alloy precursors

Abstract Finely grained Ni/ZrO 2 catalysts were prepared from amorphous Ni Zr alloy precursors by oxidation and subsequent reduction pretreatment, and the catalytic activity for CO 2 methanation was examined as a function of precursor alloy composition and temperature. The catalysts thus prepared produce exclusively methane, apart from water as a by-product. The conversion of CO 2 increases with temperature in the range of 373–573 K. Among the catalysts examined, the maximum methanation rate is obtained on the catalysts prepared from the amorphous alloy precursors containing 40 and 50 at% zirconium. Further, the methanation rates of all the catalysts prepared from the amorphous alloy precursors are higher than that of a 3 at% Ni/ZrO 2 catalyst prepared by wet impregnation. The number of surface nickel atoms, determined by hydrogen chemisorption, increases with zirconium content in the catalysts, while, interestingly, the turnover number decreases with increasing zirconium content. In the catalysts prepared from the amorphous alloys, two types of zirconia are present: metastable tetragonal and stable monoclinic zirconia. The former zirconia phase is present predominantly in the catalyst prepared from the Ni-30 at% Zr alloy, but the relative amount of this oxide phase, with respect to the total amounts of zirconia, gradually decreases with an increase in zirconium content of alloys. Thus, the higher turnover number of the catalysts with higher nickel content can be attributed to nickel supported on metastable tetragonal zirconia. Increasing nickel content of the precursor alloys leads to an increase in tetragonal zirconia and to a decrease in the number of surface nickel atoms on the catalysts. This is responsible for the fact that the maximum conversion appears at medium contents of zirconium in the precursor alloys.

Methanation of carbon dioxide on catalysts derived from amorphous Ni-Zr-rare earth element alloys

Abstrct The nano-grained Ni/ZrO 2 catalysts containing rare earth element oxides were prepared by oxidation-reduction pretreatment of amorphous Ni-(40-x) at% Zr-x at% rare earth element (Y, Ce and Sm; x=l – 10) alloy precursors. The conversion of carbon dioxide on the catalysts containing 1 at% rare earth elements was almost the same as that on the rare earth element-free catalyst, but the addition of 5 at% or more rare earth elements increased remarkably the conversion at 473 K. In contrast to the formation of monochnic and tetragonal ZrO 2 during pretreatment of amorphous Ni-Zr alloys containing 1 at% rare earth elements, tetragonal ZrO 2 , which is generally stable only at high temperatures, was predominantly formed during the pretreatment of the catalysts containing 5 at% or more rare earth elements. The surface area of the catalysts increased with the content of rare earth element. Thus, the increase in the surface area and stabilization of tetragonal ZrO 2 seem to be responsible for the improvement of catalytic activity of the Ni-Zr alloy-derived catalysts by the addition of rare earth elements.

Characterization of CO2 methanation catalysts prepared from amorphous Ni-Zr and NI-Zr-rare earth element alloys

Nano-grained Ni/ZrO2 and Ni/ZrO2 -Sm2O3 catalysts were prepared from amorphous Ni-Zr and Ni-Zr-Sm alloys by oxidation-reduction treatment. Their catalytic activity for methanation of carbon dioxide was examined as a function of precursor alloy composition and temperature. The addition of samarium is effective in enhancing the activity of the nickel-rich catalysts, but not effective for the zirconium-rich catalysts. The surface area and hydrogen uptake of the nickel-rich catalysts are increased by the samarium addition. In addition, tetragonal zirconia, the formation of which is beneficial to the catalytic activity, is stabilized and formed predominantly by the addition of samarium to the nickel-rich catalysts, although monoclinic zirconia is also formed in the zirconium-rich catalysts. As a consequence, the higher conversion of carbon dioxide is obtained on the Ni-Zr-Sm catalysts with relatively high nickel contents.

The effect of microcrystallites in the amorphous matrix on the corrosion behavior of amorphous Fe-8Cr-P alloys

Abstract The formation of a single amorphous Fe-Cr-P phase was strongly related to the amount of phosphorus addition. The structure of the melt-spun Fe-8Cr-P alloys containing 16.5 at% or more phosphorus was confirmed to be amorphous by X-ray diffraction (XRD). However, high-resolution transmission electron microscopy (TEM) revealed that a microcrystalline bcc Fe phase was dispersed in the amorphous matrix of the Fe-8Cr-16.5P and Fe-8Cr-18P alloys. The corrosion behavior of Fe-Cr-P alloys is significantly sensitive to the presence of microcrystallites in the amorphous matrix. A thick corroded layer was formed on the Fe-8Cr-16.5P and Fe-8Cr-18P alloys by immersion in 9M H 2 SO 4 . A TEM image for the thick corroded layer of the Fe-8Cr-16.5P alloy showed that the microcrystalline bcc Fe phase was preferentially dissolved away in the solution and that the amorphous Fe-Cr-P phase remained on the surface of the alloy without dissolution. Accordingly, the thick corroded layer corresponds to the amorphous Fe-Cr-P phase which is covered with the passive film. The addition of 20 at% phosphorus is necessary to form an almost complete amorphous structure and to provide the high corrosion resistance even in 9M H 2 SO 4 .

Nitrogen monoxide decomposition catalysts prepared from amorphous Ni-valve metal-Pd alloys

Abstract Surface-activated amorphous Ni-valve metal (Ta, Nb and Zr)-Pd alloys have been used for the decomposition of nitrogen monoxide. The alloys, which are first activated by immersion in hydrofluoric acid and subsequently oxidized by exposure to oxygen at 500 °C, show a high activity for the decomposition of nitrogen monoxide and have superior deterioration resistance. The catalytic activity of the alloy catalysts is affected by the valve metal elements. The tantalum- and niobium-containing alloy catalysts show higher activities and nitrogen formation selectivities than those of the zirconium-containing alloy. Double oxides of NiTa2O6 and NiNb2O6 are formed during the reaction at temperatures higher than 750 °C and, at the same time, the catalytic activity increases sharply. The synergistic effect of palladium and the double oxides seems to contribute to the high catalytic activity of the Ni40Ta1Pd and Ni40Nb1Pd alloys.

Decomposition of nitrogen monoxide over NiTa2O6-supported palladium catalysts prepared from amorphous alloy precursors

Abstract Active catalysts for the direct decomposition of nitrogen monoxide were prepared from amorphous Ni 40Ta Pd alloys by HF-treatment and subsequent pre-oxidation. The pre-oxidized catalyst consists of NiO, Ta 2 O 5 and PdO, and PdO is decomposed to fcc Pd by heating at temperatures higher than 600°C. At further higher temperatures NiO and Ta 2 O 5 are transformed to a very fine grained double oxide NiTa 2 O 6 . The catalysts thus formed consist of three layers and show high catalytic activity for the decomposition of nitrogen monoxide in a wide temperature range from 550 to 850°C. The catalytic behavior is affected by the structural change in the catalyst. With the transformation from NiO and Ta 2 O 5 to NiTa 2 O 6 , the catalytic activity and the nitrogen formation selectivity increase significantly. TEM observation of ultramicrotomed cross-sections revealed that finely dispersed palladium supported on very fine-grained NiTa 2 O 6 is formed in the interface between the outer and intermediate layers. High catalytic activities and high nitrogen formation selectivities of the Ni 40Ta Pd alloys are attributable to the formation of the NiTa 2 O 6 -supported palladium catalyst.

NO decomposition catalysts prepared from amorphous NiTaPd alloys

Abstract The effects of hydrofluoric acid (HF) treatment and bulk structure of precursor alloys on the catalytic decomposition of nitrogen monoxide have been investigated. Alloy catalysts were prepared from Ni 40valve metal (Ta, Nb, Ti and Zr) 1Pd alloys by the HF treatment and subsequent pre-oxidation at 750°C. The tantalum-containing catalyst without previous HF treatment shows the highest activity among the catalysts examined, while the preparation of the active catalysts from other amorphous alloys requires HF treatment for surface roughening and for surface enrichment of palladium prior to the pre-oxidation treatment. The catalyst prepared from the amorphous Ni 40Ta 1Pd alloy is superior to the conventionally prepared Pd/Al2O3 catalyst, in spite of the fact that the BET surface area of the latter catalyst is two orders of magnitude higher than that of the Ni Ta Pd catalyst. The catalyst prepared from the amorphous Ni 40Ta Pd alloy shows a better performance for the NO decomposition in comparison with the catalyst prepared from the crystalline counterpart, because the amorphous precursor becomes a more irregular and more microporous catalyst.