Hiromu Watanabe

Bio: Hiromu Watanabe is an academic researcher from University of Tokyo. The author has contributed to research in topics: Catalysis & Cyclohexene. The author has an hindex of 4, co-authored 5 publications receiving 624 citations.

Microstructure of Cesium Hydrogen Salts of 12-Tungstophosphoric Acid Relevant to Novel Acid Catalysis†

Abstract: A comprehensive interpretation of the microstructure and mechanism of the formation of a versatile solid acid catalyst, Cs25H05PW12O40, has been attempted by combining the new results obtained with solid-state NMR, XRD, SEM, and N2 porosimetry with the data reported previously The precipitates of Cs25H05PW12O40 just formed from aqueous solutions of H3PW12O40 and Cs2CO3 consist of ultrafine crystallites in which the acid form, H3PW12O40, is epitaxially deposited on the surface of Cs3PW12O40 crystallites Calcination of the precipitates brings about the migration of H+ and Cs+ in the solid to form a nearly uniform solid solution in which protons distribute randomly through the entire bulk, as revealed by XRD and 31P solid-state NMR Impregnation of Cs3PW12O40 with the aqueous solution of H3PW12O40 also gives the uniform salt after calcination Pore-size distribution evaluated by the analysis of N2 desorption isotherm showed that Cs25H05PW12O40 has mesopores as well as micropores that are interparticl

4.8 Novel Catalysis of Cesium Salt of Heteropoly Acid and its Characterization by Solid-state NMR

Abstract: Acid-catalyzed reactions by acidic cesium salts of 12-tungstophosphoric acid (H3PW12O40) have been studied in relation to the acidities and microstructure of the particles. Liquid-phase alkylation of 1,3,5-trimethylbenzene with cyclohexene, decomposition of cyclohexylacetate and gas-phase skeletal isomerization of n-butane were performed over heteropoly compounds and other typical solid acids such as zeolites, Nafion-H, SO42-/ZrO2, etc. It was found that Cs2.5H0.5PW12O40 showed very high activities for these reactions and the excellent selectivity for the skeletal isomerization. XRD, TEM and N2 adsorption revealed that Cs2.5H0.5PW12O40 consists of ultrafine primary particles (∼8 nm) and therefore has a high surface area. High resolution solid-state NMR demonstrated that the chemical shift of 31P (central atom of the polyanion) is determined by the number of proton which is directly attached to the polyanion and all protons are distributed randomly through the whole bulk of the particles. Owing to this, Cs2.5H0.5PW12O40 possesses a high surface protonic acidity, which is a reason for its high activity. The quantity of acid sites of Cs2.5H0.5PW12O40 was less than those of zeolites and SO42−/ZrO2 and the acid strength was lower than that of SO42−/ZrO2. It is presumed, therefore, that the acid-base bifunctional action together with the high surface acidity brought about the high activity of Cs2.5H0.5PW12O40.

Structure and catalysis of cobalt oxide overlayers prepared on zirconia by low-temperature-plasma oxidation

Abstract: The structure of cobalt oxide overlayers on the surface of ZrO2 powder, i.e., CoOx/ZrO2, prepared by low-temperature-plasma oxidation has been investigated using EXAFS, XPS, XRD and IR spectroscopy. XRD and EXAFS revealed that CoOx on ZrO2 is present as fine particles having the structure of Co3O4(spinel). It was found that CoOx/ZrO2 prepared by plasma oxidation was more active for oxidations of CO and propane that Pt/Al2O3, La0.8Sr0.2CoO3, and CoOx/ZrO2 prepared by impregnation. The dispersion of CoOx estimated by XPS and CO adsorption was higher for CoOx/ZrO2 prepared by plasma oxidation than that prepared by the impregnation. The high dispersion is responsible for the higher activity of CoOx/ZrO2 prepared by plasma oxidation.

Catalytic Chemistry of Heteropoly Compounds

Abstract: Publisher Summary This chapter describes the essence of the catalytic chemistry of heteropoly compounds in solution and in the solid state. The catalytic properties of heteropoly compounds have drawn wide attention, owing to the versatility of these compounds as catalysts, which has been demonstrated both by successhl large-scale applications and by promising laboratory results. Heteropolyanions are polymeric oxoanions formed by condensation of more than two different mononuclear oxoanions. Heteropolyanions formed from one kind of polyanion are called isopolyanions. Acidic elements such as Mo, W, V, Nb and Ta, which are present as oxoanions in aqueous solution, tend to polymerize by dehydration at low pH, forming polyanions and water.Heteropoly catalysts can be applied in various ways. They are used as acid as well as oxidation catalysts. They are used in various phases, as homogeneous liquids, in two-phase liquids (in phase-transfer catalysis), and in liquid-solid and in gas-solid combinations, etc.

Heteropoly Acids and Related Compounds as Catalysts for Fine Chemical Synthesis

Abstract: Catalysis by heteropoly acids (HPAs) and related compounds is a field of growing importance, attracting increasing attention worldwide, in which many new and exciting developments are taking place in both research and technology [1–111, HPAs are polyoxometalates incorporating anions (heteropolyanions) having metal-oxygen octahedra as the basic structural units [ll-141. Among a wide variety of HPAs those belonging to the so-called Keggin series are the most importance for catalysis. They include heteropolyanions (HPANs)