Hideshi Hattori

Skeletal isomerization of hydrocarbons over zirconium oxide promoted by platinum and sulfate ion

Abstract The genesis of the high activity of zirconium oxide promoted by platinum and sulfate ion (Pt/SO 4 2− --ZrO 2 ) for skeletal isomerization of butane and pentane in the presence of hydrogen is studied in terms of the interaction of the catalyst with molecular hydrogen. For skeletal isomerization of pentane at 523 K, Pt/SO 4 2− -ZrO 2 showed activity only in the presence of molecular hydrogen, and its activity persisted for a long period. For skeletal isomerization of butane at 523 K, the catalyst showed activity in the absence of hydrogen, but the activity was markedly enhanced in the presence of hydrogen. For pentane and butane skeletal isomerization, the products consisted exclusively of 2-methylbutane and 2-methylpropane, respectively. For a typical acid-catalyzed reaction of cyclopropane ring opening at 373 K, the presence of hydrogen enhanced the activity, but the hydrogen enhancement effect was small. The products consisted exclusively of propene even in the presence of hydrogen: hydrogenation of propene scarcely occurred. Infrared spectroscopic study of adsorbed pyridine showed that by heating the catalyst in the presence of hydrogen in the temperature range 423–623 K, protonic acid sites were formed with concomitant decrease in the number and strength of Lewis acid sites, demonstrating that the protonic acid sites originate from molecular hydrogen. The mechanisms of protonic acid site generation are discussed. It is suggested that molecular hydrogen dissociates on the platinum to hydrogen atoms which undergo spillover on the SO 4 2− -ZrO 2 and convert to an H+ and an e − or H − . The H+ acts as catalytic site for acid-catalyzed reactions.

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.

Solid base catalysts: generation of basic sites and application to organic synthesis

Abstract Studies of solid base catalysts on generation of basic sites and their catalytic behaviors in organic reactions performed in our group are summarized. For most of the materials called solid base, the catalytic activities appear on removal of water and carbon dioxide from the surfaces. The nature of the surface basic sites varies with severity of pre-treatment conditions. Besides removal of water and carbon dioxide, rearrangement of surface and bulk atoms occurs during pre-treatment, which changes the number and nature of the basic sites with increasing the pre-treatment temperature. Therefore, the optimum pre-treatment temperature varies with the type of reaction. Applications of solid base catalysts to the following reactions are described; (1) double bond isomerization, (2) hydrogenation, (3) amination, (4) dehydrocyclodimerization, (5) aldol addition, (6) nitroaldol reaction, (7) Michael addition, (8) conjugate addition of alcohol, (9) cyanoethylation, and (10) Tishchenko reaction. Characteristic features of the solid base catalysts toward these reactions are briefly explained. Finally, selected base-catalyzed reactions which have been industrialized by use of solid base catalyst are exemplified, and short comments on the catalysts used in these processes are made.

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.

Dynamic modification of surface acid properties with hydrogen molecule for zirconium oxide promoted by platinum and sulfate ions

The dynamic nature of the protonic acid sites on Pt/SO42−ZrO2 was studied by IR spectroscopy. The generation and elimination of the protonic acid sites in response to the presence and absence of molecular hydrogen in the gaseous phase were observed by monitoring the IR spectra of adsorbed pyridine. By heating in the presence of molecular hydrogen, the protonic acid sites were generated and the Lewis acid sites were weakened. By evacuation of molecular hydrogen, the surface acidic properties retrieved original states. The generation of the protonic acid sites involves dissociative adsorption of the hydrogen molecule on Pt, spillover of the H atom onto the SO42−ZrO2 surface, and electron transfer from the H atom to Lewis acid sites leaving H+ on the surface. The elimination of the protonic acid sites by evacuation of molecular hydrogen involves combination of the H+ with the electron trapped on Lewis acid sites to form an H atom, reverse spillover of the H atom to Pt, and association of atomic H to form H2 to be desorbed. Essentially the same dynamic nature was observed on the physical mixture containing Pt black and SO42−ZrO2, although the extent of the change in acidic properties with heating in the presence of hydrogen or evacuation of hydrogen was small compared to Pt/SO42−ZrO2.

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.

In-situ XPS study of zirconium oxide promoted by platinum and sulfate ion

In-situ X-ray photoelectron spectroscopy (XPS) and infrared (IR) study of adsorbed CO were performed to characterize the states of the platinum particles supported on the sulfate ion-treated zirconium oxides (SO[sub 4][sup 2] -ZrO[sub 2]) after reduction with hydrogen. Presence of the sulfate ion strongly suppressed the reducibility of the platinum particles as well as the chemisorptive capacity for CO. The platinum particles consisted mainly of platinum cations (mixture of platinum oxide and platinum sulfate) after reduction with hydrogen at 673 K; the concentration of metallic platinum phase was low. The low reducibility of the dispersed platinum particles present as platinum cations on the SO[sub 4][sup 2-] -ZrO[sub 2] support is interpreted by the redox metal-support interaction (RMSI), which is caused by the acidic properties of the SO[sub 4][sup 2-] support and results in a slow nucleation of the platinum particles. The states of sulfur were also measured by XPS, and the partial conversion of the S[sup 6+] (sulfate ion) to S[sup 2[minus]] species on hydrogen treatment is concluded to occur by the metal-catalyzed mechanism involving spiltover hydrogen atoms resulting from the dissociation of a hydrogen molecule on the metallic platinum.

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.

Surface and catalytic properties of cerium oxide

The acid-base and oxidizing-reducing properties of cerium oxide evacuated or treated with hydrogen after evacuation at various temperatures and the catalytic activity for the isomerization of 1-butene were studied. No correlation was found between the oxidizing or reducing property and the catalytic activity. On the other hand, the activity was lost by the additions of both acidic carbon dioxide and basic ammonia molecules. The ratio of cis-2-butene to trans-2-butene was found to be high (4–6). The active sites have been concluded to be acid-base pair sites, though basic sites play a main role. The experiment on coisomerization of cis-2-butene-d0d8 revealed that the isomerization proceeds intramolecularly via π-allylic carbanion intermediates. The two activity maxima appearing on pretreatment at 600 and 800 °C are considered due to the dehydration and/or decarboxylation and the structural change of cerium oxide, respectively.