Masahide Shimokawabe

Characterization of copper/zirconia catalysts prepared by an impregnation method

Abstract Copper/zirconia catalysts were prepared by an impregnation method and were characterized by UV—visible—near-infrared (UV—VIS—NIR) spectroscopy, X-ray diffraction (XRD), differential thermal analysis (DTA) and temperature-programmed reduction (TPR). It was concluded that copper-ammine complexes held on the surface of the zirconia support exist in three different states, viz., isolated and clustered copper(II) ions and tetraamminecopper (II) nitrate. These precursor species were transformed into bulky copper (II) oxide through highly dispersed copper (II) oxide at various temperatures, which depend on the calcination temperatures of the catalysts and the zirconia supports. In the TPR experiments, two TPR peaks were observed at 493 K (peak I) and 515–613 K (peak II). In conjunction with the observations by UV—VIS—NIR and XRD, it was concluded that highly dispersed copper(II) oxide and bulky copper (II) oxide were reduced to metallic copper, giving peaks I and II, respectively. The relative amounts of these precursor species were found to depend strongly on the conditions of preparation of both catalysts and supports.

Influence of the preparation history of α-Fe2O3 on its reactivity for hydrogen reduction

Abstract TG experiments on the hydrogen reduction of α-Fe2O3 were carried out to elucidate the influence of the preparation history of the oxide on its reactivity. α-Fe2O3 samples were prepared by the thermal decomposition of seven iron salts in a stream of oxygen, air or nitrogen at temperatures of 500–1200°C for 1 h. Thirteen metal ions such as Cu2+, Ni2+, etc. were used as doping agents. The reactivity of the oxide was indicated by the initial reduction temperature (Ti. α-Fe2O3 prepared at lower temperatures showed lower Ti values and the reduction proceeded stepwise (Fe2O3 → Fe3O4 → Fe). Ti values increased with the rise in the preparation temperature of the oxide. The oxides prepared at higher temperatures showed that two reduction steps (Fe2O3 → Fe3O4 → Fe) proceed simultaneously. the preparation in oxygen gave higher Ti than that in air or nitrogen. The doping by metal ions, except Ti4+, lowered the Ti of α-Fe2O3. The Cu2+ ion showed the lowest Ti, while Ti4+ showed the highest Ti and the inhibition effect. The reduction process was expressed by two equations; Avrami—Erofeevs equation for α-Fe2O3 → Fe3O4 and Mampels equation for Fe3O4 → Fe.

Steam reforming of methanol on copper-silica catalysts; effect of copper loading and calcination temperature on the reaction

Abstract Steam reforming of methanol CH 3 OH + H 2 O = CO 2 + 3H 2 was carried out over a variety of catalysts which contained various amounts of copper loaded on silica. The selectivity and other kinetic parameters, such as activation energy and turnover frequency of the reaction, were found to depend upon copper loading and the calcination temperature of the catalyst. The catalyst precursors, as well as the catalysts which had been employed for the reaction, were characterized with the aid of UV, XRD, TPR and titration with nitrous oxide. It was concluded that metallic copper which was formed under the reaction conditions was highly active and selective for steam reforming. Small clusters of CuO or bulk CuO which were preferentially formed at higher copper loadings or at higher calcination temperatures were effective precursors for the preparation of metallic copper. On the other hand, isolated cupric ions present on silica were not very useful for the formation of metallic copper. The effect of the catalyst preparation on the reaction was discussed on these bases.

Characterization of copper-silica catalysts prepared by ion exchange

Copper-silica catalysts were prepared by ion exchange between the hydroxyl hydrogens on a silica surface and tetraimmine copper (II) ions, and were characterized by a variety of analytical methods. It was concluded that copper amniine complexes held on the surface can exist in three different states, i.e. isolated and clustered diammines and free tetrammine copper (II) nitrate. The relative amounts of these species were strongly dependent upon the amount of copper loaded onto the silica. These ammine complexes decomposed around 300°C. The clustered species transformed into highly dispersed CuO clusters at 300°C in air and then further crystallized into bulk CuO at around 720°C. The isolated species, on the other hand, remained in part as isolated Cu2+ ions on the support after calcination at temperatures above 300°C,while the tetrammini copper(II) nitrate rapidly transformed into bulk CuO at 500°C. Based on these results, a surface phase diagram of the catalyst was tentatively presented as a function of copper loading and calcination temperature.

Methanation of carbon dioxide: preparation of Ni/MgO catalysts and their performance

Abstract Ni/MgO catalysts prepared by impregnation under various conditions were used for methanation of carbon dioxide, and were characterized by UV/VIS diffuse reflectance spectroscopy and temperature-programmed reduction. The nature of the precursor species formed on the MgO support was influenced by the solvents used for impregnation, nickel loading and the calcination temperature. NiO precursors formed on MgO were readily reduced to metallic nickel, while highly dispersed Ni(II) ion precursors were difficult to reduce to metallic nickel. The former precursors provided fairly active and selective methanation catalysts.

Effect of metal oxide additives on the thermal decomposition of perchlorates, oxalates and hydroxides

The effects of α-Fe2O3 and α-Al2O3 additives on the thermal decomposition of perchlorates, oxalates and hydroxides were investigated by means of DTA, TG and X-ray techniques. It was found that the oxide additives catalytically promoted the decomposition of perchlorates (NaClO4, KClO4 and Mg(ClO4)2) and resulted in a lowering of the initial decomposition temperature (Ti). On the other hand, the oxides showed no significant effect on the decomposition of oxalates (FeC2O4 and CuC2O4) and hydroxides (Mg(OH)2 and Al(OH)3). The thermal decomposition of KClO4 was chosen to compare the catalytic effect of twelve metal oxides. The results indicated that the transition metal oxides such as Cr2O3, α-Fe2O3 and CuO markedly accelerated the decomposition; these oxides resulted in a solid-phase decomposition before fusion of KClO4, and the initial decomposition temperature (Ti) of KClO4 with oxides was about 100–200°C lower than that without catalyst. The oxides such as α-Al2O3 and MgO resulted in a slight lowering of the temperature of the fusion and promoted the molten-phase decomposition of KClO4, but their effects were not so remarkable as those of the transition metal oxides. The modified catalytic mechanisms of transition metal oxides were proposed by considering the electron transfer and the oxygen-abstraction models.

Steam reforming of methanol over Cu/ZrO2. Role of ZrO2 support

Cu/ZrO2 was highly active and selective for the title reaction. The activity obtained exceeded greatly that obtained over Cu/SiO2. It was shown that the precursors highly dispersed on zirconia support were readily reduced to very fine particles of metallic copper.AbstractКатализатор Cu/ZrO2 оказался сильно активным и селективным в заглавной реакции. Полученная активность почти достигает активности на Cu/SiO2. Найдено, что прекурзоры, сильно диспергированные на циркониевом носителе, легко восстанавливаются до очень тонких частиц металлической меди.

Characterization of copper/silica catalysts in reduced states

Abstract The valence states of reduced copper/silica catalysts were elucidated with the help of the selective adsorptions of carbon monoxide and nitrous oxide, and XPS, AES and phosphorescence spectroscopies. Monovalent copper was found to be formed by the hydrogen reduction of the catalysts with copper loadings below 0.5–1.0 wt % to an appreciable extent. On the other hand, the catalysts with higher copper loadings could be readily converted to metallic copper by the reduction. In conjunction with the results previously obtained, it was concluded that the isolated Cu2+ precursors were reduced to monovalent copper while small clusters of cupric oxide were reduced to metallic copper.

Effect of α-Fe2O3 additive on the thermal decomposition of salts of halogen oxoacids, oxalates, azide, permanganate, and oxides

Abstract The effect of additives on the thermal decomposition of salts of hoagen oxoacids (KClO 4 , KClO 3 , KIO 4 and KBrO 3 ), oxalates (NiC 2 O 4 ·2 H 2 O, MgC 2 O 4 ·2 H 2 O and CaC 2 O 4 ·H 2 O), azide (NaN 3 ), permanganate (KMnO 4 ), and oxides (MnO 2 and PbO 2 ) was studied by gas-flow type DTA and X-ray diffraction of samples obtained in the course of the decomposition, α-Fe 2 O 3 was mainly employed as the additive, which was prepared from FeC 2 O 4 ·2 H 2 O by calcining it in flowing air (100 ml min −1 ) at 500°C. α-Al 2 O 3 , CuO, Cu 2 O and NiO were also tested as additives in a few cases. DTA experiments were carried out in static air, flowing N 2 and O 2 (50 ml min −1 ) at a heating rate of 5°C min −1 . The additive α-Fe 2 O 3 exhibited a remarkable catalytic acceleration effect on the decomposition of salts of halogen oxoacids. For the decomposition reactions of other substances, α-Fe 2 O 3 did not show the effects detectable with DTA technique. However, it was observed by X-ray analysis that α-Fe 2 O 3 reacted to form MgFe 2 O 4 and CaFe 2 O 4 for oxalates, PbFe 2 O 4 for PbO 2 , and an unknown compound for KMnO 4 .

Characterization of unsupported cupric oxide and cupric oxide/silica catalysts by temperature-programmed desorption of nitrogen monoxide

Abstract The thermal desorption of nitrogen monoxide (NO) adsorbed on unsupported CuO and CuO/SiO 2 was investigated by means of a temperature-programmed method. In both cases, two NO desorption peaks appeared with maxima in the temperature range of 383–573 and 648–753 K. It was concluded that the former peak was the result of NO adsorbed on copper (II) sites, and the latter peak, which was accompanied by oxygen desorption, was the result of nitrate type species formed by the reaction of NO with adsorbed oxygen. Over CuO/SiO 2 , NO was chemisorbed selectively on CuO species formed on the support. The surface area and the percentage exposed (dispersion) of unsupported CuO were calculated on the basis of the amount of NO desorbed. These values closely agreed with the corresponding ones estimated from the BET surface area. In a similar manner, the dispersion and the average particle size of CuO species formed on silica were calculated. It was shown that these species, which were previously characterized as isolated copper (II) species (or isolated CuO), highly dispersed CuO clusters and bulky CuO, are fine particles of CuO with an average diameter of 1.5–2.5,5–13 and over 15–30 nm, respectively.