Kohki Ebitani

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.

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.

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.

Highly efficient oxidation of alcohols to carbonyl compounds in the presence of molecular oxygen using a novel heterogeneous ruthenium catalyst

Abstract A ruthenium cation combined with microcrystals of cobalt hydroxide and cerium oxide acted as a highly efficient heterogeneous catalyst for the oxidation of various types of alcohols to carbonyl compounds under atmospheric pressure of molecular oxygen at 60°C. Especially, primary aliphatic alcohols could be oxidized to afford the carboxylic acids in high yields.

Highly efficient dehydrogenation of indolines to indoles using hydroxyapatite-bound Pd catalyst

A hydroxyapatite-bound palladium catalyst was found to be effective for the dehydrogenation of various types of indolines to give the corresponding indoles. Moreover, the catalyst was readily recovered from the reaction mixture, and could be reused without any loss of its catalytic activity.

Efficient heterogeneous oxidation of organosilanes to silanols catalysed by a hydroxyapatite-bound Ru complex in the presence of water and molecular oxygen

RuHAP is a highly selective and reusable catalyst for the oxidation of a wide variety of organosilanes to the corresponding silanols in the presence of water and molecular oxygen.

Highly efficient heterogeneous acetalization of carbonyl compounds catalyzed by a titanium cation-exchanged montmorillonite

Abstract The titanium cation-exchanged montmorillonite efficiently catalyzed the selective acetalization of various carbonyl compounds as a recyclable solid acid. This heterogeneous catalyst has an advantage of a strikingly simple workup procedure over conventional homogeneous acids.

Highly selective oxidation of allylic alcohols catalysed by monodispersed 8-shell Pd nanoclusters in the presence of molecular oxygen

Treatment of Pd4phen2(CO)2(OAc)4 with metal nitrates such as Cu(NO3)2 produced monodispersed Pd nanoclusters with a mean diameter and standard deviation (d±σ) of 38±2.1 A (σ/d=6%). The Pd nanoclusters act as heterogeneous catalysts for the selective oxidation of primary aromatic allylic alcohols using molecular oxygen as an oxidant. This unique catalysis can be ascribed to multiple interactions between the alcohol and specific ensemble sites consisting of Pd0, Pd+, and Pd2+ on the cluster surface.

Environmentally friendly alcohol oxidation using heterogeneous catalyst in the presence of air at room temperature

Abstract Various types of alcohols oxidation can be achieved using air as a sole oxidant at room temperature without any other additives. From the results of Ru K-edge XAFS and XPS characterizations, MnFe 1.5 Ru 0.35 Cu 0.15 O 4 catalyst with possibly coordinatively unsaturation of the isolated RuO species as active sites is an efficient heterogeneous catalyst and can be reused. Besides, the workup procedure is extremely simple.

Catalysis of giant palladium cluster complexes. Highly selective oxidations of primary allylic alcohols to α,β-unsaturated aldehydes in the presence of molecular oxygen

Abstract A giant Pd cluster, Pd 561 phen 60 (OAc) 180 , has high catalytic activity for the selective oxidations of various primary allylic alcohols to the corresponding α,β-unsaturated aldehydes in the presence of molecular oxygen under mild reaction conditions. A Pd cluster anchored on TiO 2 also catalyzes the above oxidations; the heterogeneous Pd 561 cluster catalyst is easily separated from the reaction mixture and is reusable.