Kozo Tanabe

Surface and catalytic properties of ZrO2

Abstract Zirconium oxide is characterized to be the only one metal oxide which possesses explicitly four chemical properties on the surface; acidic and basic properties and oxidizing and reducing properties. Intriguing and sometimes unique catalytic activities of zirconium oxide itself are discussed in connection with the surface properties. It is also pointed out that zirconium oxide is an interesting and useful catalyst support. Generation of super acidity on the addition of a small amount of sulfate ion to zirconium oxide is elucidated. The surface properties of binary oxides containing zirconium oxide are also characterized.

Catalytic application of niobium compounds

Abstract Salient examples of catalytic application of niobium compounds and materials are demonstrated. Niobium oxides, when small amounts are added to known catalysts, markedly enhance catalytic activity and selectivity and prolong catalyst life for various reactions. Moreover, niobium oxides exhibit a pronounced effect as supports of metal or metal oxide catalysts. Hydrated niobium pentoxide (niobic acid, Nb2O5·nH2O) and niobium phosphate which are unusual solid acids show high catalytic activity, selectivity, and stability for acid-catalyzed reactions. Layer compounds containing niobium combined with metal show peculiar photocatalytic activity. These characteristic features of niobium compounds as catalysts and catalyst components are discussed, their potential significance being emphasized.

Aldol Addition of Acetone, Catalyzed by Solid Base Catalysts: Magnesium Oxide, Calcium Oxide, Strontium Oxide, Barium Oxide, Lanthanum (III) Oxide and Zirconium Oxide

Abstract Aldol addition of acetone was studied over alkaline earth oxides, La 2 O 3 , ZrO 2 , SiO 2 Al 2 O 3 and Nb 2 O 5 at 0°C to elucidate the nature of active sites. The activities of catalysts on a unit surface area basis were in the order: BaO > SrO > CaO > MgO > La 2 O 3 > ZrO 2 ≫ SiO 2 Al 2 O 3 > Nb 2 O 5 . The reaction is base-catalyzed, and the oxides of stronger basic sites promote the reaction effectively. The effects of preadsorption of water, ammonia, pyridine and carbon dioxide were investigated with MgO and CaO. For MgO, addition of water and ammonia caused marked increase in activity and selectivity to diacetone alcohol, while pyridine had little effect on the catalytic behavior. Preadsorption of carbon dioxide scarcely inhibited the reaction. For CaO, the effects of preadsorption were small compared with those on MgO. Basic OH − ions, which are either retained on the surfaces or formed by dehydration of diacetone alcohol, are proposed as active sites for aldol addition of acetone.

The acidic properties of TiO2-SiO2 and its catalytic activities for the amination of phenol, the hydration of ethylene and the isomerization of butene

Abstract The generation of strong acid sites was observed on the binary oxide, TiO 2 -SiO 2 , which was obtained by a coprecipitation method. The acidity and acid strength of the mixed oxide of a certain composition were estimated to be higher than those of SiO 2 -Al 2 O 3 containing 20 wt% of Al 2 O 3 by n -butylamine titration and by the adsorption of basic molecules on the surface. The acidity depended both on pretreating temperature and the catalyst composition. The highest acidity per unit weight of catalyst was observed when TiO 2 -SiO 2 (mole ratio = 1) was heated at 500 °C. The binary oxide showed high catalytic activity and selectivity for the amination of phenol with ammonia to produce aniline, but low activity and selectivity for the hydration of ethylene. The isomerizations of butenes were also catalyzed; the products ratio of cis -/ trans -2-butene was 1–2. The catalytic action for three reactions is well interpreted in terms of the acidic property. The mechanism of the generation of acid sites by mixing TiO 2 with SiO 2 is discussed.

Surface properties of zirconium oxide and its catalytic activity for isomerization of 1-butene

Acidic, basic, oxidizing, and reducing properties of ZrO2 were measured by the ir spectra of adsorbed pyridine, by CO2 adsorption or the ESR of diphenylnitroxide radical formed from diphenylamine and O2, by the ESR of adsorbed triphenylamine, and by the ESR of adsorbed nitrobenzene, respectively. The variations of these properties with pretreatment temperature of ZrO2 were independent of each other. The maximum concentrations of these sites and the pretreatment temperatures at which the maxima were obtained were 3.9 × 10−8 mole/m2 and 400 °C for acidic sites, 1.7 × 10−7 mole/m2 and 700 °C for basic sites measured by diphenylamine, 1.5 × 10 mole/m2 and 700 °C for oxidizing sites, and 4.3 × 10−8 mole/m2 and 500 °C for reducing sites. Among these properties, it was the basic property with which the activity for isomerization of 1-butene correlated best. The activity was poisoned not only by CO2 but also by NH3 or triethylamine, indicating that the active sites consist of both basic and acidic sites. The results of the coisomerization of 1-butene-d0d8 showed that the reaction involved primarily an intramolecular hydrogen transfer.

Preparation and characterization of ZrO2 and SO42−-promoted ZrO2

Abstract The acid-base and oxidizing properties and the structures of ZrOn prepared with ammonia or urea and ZrO 2 treated with sulfuric acid or ammonium sulfate have been investigated. The treatment of ZrO 2 with so 4 2− caused the remarkable increases in the phase transition temperature to monoclinic form, the surface area and the acid strength and the appearance of the oxidizing property. The acid strength was higher for ZrO 2 treated with H 2 SO 4 than for ZrO 2 treated with (NH 4 ) 2 SO 4 , though the surface area was the reverse. The difference between ammonia and urea as precipitating reagents caused no difference in crystallography and acid strength, but the surface areas of ZrO 2 -A and ZrO 2 -A-H 2 SO 4 prepared with ammonia were higher than those of ZrO 2 -U and ZrO 2 -U-H 2 SO 4 prepared with urea, respectively.

Solid super acids: Preparation and their catalytic activities for reaction of alkanes

Abstract Preparation of solid super acid catalysts was attempted by treatment of metal oxides with NH 4 F, FSO 3 H, SbCl 5 , SbF 5 , and FSO 3 H-SbF 5 . All treatments with these reagents enhanced the acidic properties of the metal oxides. Among them, SbF 5 was the most effective. Conversions of several alkanes proceeded at room temperature or below, over the metal oxides treated with SbF 5 . The conversion rates of alkanes were in the order: cyclohexane ∼- methylcyclopentane > hexane > pentane ∼- 2-methylbutane > butane ∼- 2-methylpropane > propane ⪢ 2,2-dimethylpropane ∼-ethane ∼- methane. The acid strengths were −13.75 ≥ H 0 > −14.52 for SbF 5 -SiO 2 -Al 2 O 3 and −13.16 ≥ H 0 > −13.75 for SbF 5 -TiO 2 -SiO 2 and SbF 5 -Al 2 O 3 . The ir spectra of pyridine adsorbed on SbF 5 -SiO 2 -Al 2 O 3 showed that both Bronsted and Lewis acid sites were present on the surface when SiO 2 -Al 2 O 3 was treated with SbF 5 at low temperatures below 100 °C, but only Lewis acid sites when treated at 300 °C. The reaction mechanisms are discussed on the basis of the acidic properties, product distributions, and a tracer study.

Application of niobium oxides as catalysts

Abstract Characteristics of niobium oxides as a promoter of various catalysts, a catalyst support, and a unique solid acid catalyst is reviewed. The pronounced effects as a promoter and a support of catalysts for diversified reactions are demonstrated and the strongly acidic nature of hydrated niobium oxide and its application as an unusual solid acid catalyst are discussed.

Hydrogenation of carbon monoxide and carbon dioxide over supported rhodium catalysts

Abstract The formation of hydrocarbons in the reactions of CO + H2 and CO2 + H2 was studied over rhodium catalysts supported on Nb2O2, ZrO2, Al2O3, SiO2 and MgO. Among these catalysts, Rh on Nb2O5 was most active in the reaction of CO + H2 and RhMgO was least active. In the hydrogenation of CO2, RhZrO2 was more reactive than RhNb2O5 and showed measurable activity even at 50°C, in contrast to the inactivity at temperatures up to 130°C in the CO + H2 reaction. The inverse kinetic isotope effect was observed in both reactions of Co + H2(D2) and CO2 + H2(D2) over RhNb2−O5 and RhZrO2. However, the isotope effect was not observed in the CO2 reaction over RhAl2O3, whose effect in the CO reaction was still inverse. The mechanisms of the above reactions are correlated to the IR study of the adsorbed species.

Basic sites and reducing sites of calcium oxide and their catalytic activities

The amounts of basic and reducing sites of calcium oxides prepared by heat-treating the hydroxide at various temperatures were measured, respectively, by titration with benzoic acid, using bromothymol blue, etc., as indicators and by observing ESR, spectra or visible reflectance spectra of adsorbed nitrobenzene or m-dinitrobenzene. The maximum amount of basic sites was found to be 0.57 mmole/g when the hydroxide was calcined at 500 ° in air, while that of reducing sites to be 5 × 1014 and 1016 sites/g, respectively, when calcined at 700 ° in air and at 500 ° in a vacuum. It has been found that the catalytic activity of various calcium oxides for the esterification of benzaldehyde correlates well with the basicities, whereas that for the polymerization of styrene does with the amounts of reducing sites. On the basis of the above results together with infrared spectra of adsorbed benzaldehyde, isopropyl alcohol, and chloroform, the nature of basic and reducing sites was discussed, the reducing sites being shown to be entirely different from the basic sites.