Masaharu Komiyama

Design and Preparation of Impregnated Catalysts

Abstract Solid catalysts in common use are typically in the form of small metal crystallites dispersed on the internal surface of the porous support. Advantages of these supported-metal catalysts lie in their high surface-to-volume ratio and the high thermal stability endowed by the dispersion. Such catalysts are commonly produced by liquid-phase impregnation in which a dry or wet pellet of the porous support is impregnated with a solution of a compound of the desired catalytic constituent. During impregnation and subsequent drying, small crystallites of the catalyst precursors are deposited on the internal surface of the support material. The impregnation and drying steps involve mass and /or heat transfer processes which often do not reach equilibrium, resulting in nonuniform concentration profiles of impregnant, or “impregnation profiles” along the radius of the support pellet.

Structure and catalytic activity of Sb oxide highly dispersed on SnO2 for propene oxidation

Two series of Sbue5f8Sn oxide catalysts having different Sb content and different particle sizes of SnO2 were prepared and their propene oxidation activities were examined. Sb oxide in these Sbue5f8Sn oxide catalysts was noncrystalline in the Sb content range of 5 to 50 at%. The concentration of Sb ions dissolved into SnO2 lattice was estimated to be lower than 10% from the change of IR transmissions. Laser Raman and Auger electron spectroscopic analyses suggested that part of the Sb oxide is present as noncrystalline Sb(III) and Sb(V) oxides dispersed on SnO2, whose proportion depends on the particle size of SnO2. In the propene oxidation, the initial rates of acrylaldehyde formation increased with the increase in surface Sb content and passed through maxima at certain compositions. For both series of catalysts, the high rates and high acrylaldehyde selectivities were obtained at around the surface ratio of SbSn = 12−13. A bifunctional mechanism in propene oxidation over these catalysts is discussed. The differences between SnO2 and TiO2 in their role as a support are also discussed.

Supported metal model catalyst surfaces examined by scanning tunnelling microscopy

Topographic and/or barrier‐height images of ultrafine Pt and Au metal particles supported on a vacuum‐deposited carbon film or titanium oxide thin films grown on titanium metal sheets were obtained. The topographic images of colloidal Au particles (5‐nm diameter) adsorbed on a titanium oxide thin film showed a structure elongated in the direction normal to the x scan, indicating their weak interaction with the support surface. The topographic images of Pt vacuum‐deposited on a carbon film showed c. 4‐nm diameter particles, larger than those observed in electron microscopy. The problems inherent to the STM observation of such dispersed metal systems are identified. In the case of Pt particles vacuum‐deposited on titanium oxide film, its barrier‐height image gave better indication of different phases on the surface than its topographic image. The significance of obtaining barrier‐height images along with topographic images for such sample systems is demonstrated.

Structure of platinum ultrafine particles in Pt/C catalyst observed by scanning tunneling microscopy

Ultrafine platinum metal particles (few nanometers in diameter) dispersed on the surface of a vacuum‐deposited carbon film were examined by scanning tunnelling microscopy. In this system that simulates an industrial Pt/C supported metal catalyst, the observed shape of the Pt particles appeared close to hemispherical, bounded by several relatively flat faces. The particle shapes were fitted well with halves of cubo‐octahedra, providing a model for the structure of ultrafine Pt metal particles in the industrial Pt/C supported metal catalysts.

Preparation of supported rhenium carbonyls and their characterization by IR and XPS studies

Abstract Supported rhenium carbonyls have been prepared by two procedures, viz ; the liquid-phase adsorption of Re 2 (CO) 10 or tricarbonyl species from their tetrahydrofuran solutions on to oxide support surfaces, and direct surface synthesis effected by contacting highly dispersed rhenium metal on the surfaces of oxide supports with CO at elevated temperatures. The former procedure yielded supported deca- and tri-carbonyls, while the latter gave only supported tricarbonyls. The interactions between the supported carbonyls and the various oxide surfaces have been examined by infrared and X-ray photoelectron spectroscopies.

Surface compositions of solid and liquid indium-tin alloys by auger electron spectroscopy using ion bombardment

Abstract Equilibrium surface compositions of solid and liquid Inue5f8Sn alloys of various bulk compositions were examined by Auger electron spectroscopy. The compositional relaxation at the solid surfaces of this alloy system was very fast, and utilizing this the bulk compositions of the solid alloys and the corresponding surface compositions were determined using Xe-ion bombardment in conjunction. Above the temperature 1.2 times the melting point, the surface compositions were constant regardless of temperature, and coincided with the nominal bulk composition. As the temperature was lowered toward the melting point, surface segregation became apparent, and at around the melting point the surface composition nearly coincided with those of the solid alloys. When surface segregation occurred, In segregated to the surfaces of Sn-rich alloys and Sn to the surfaces of In-rich alloys. Under the influence of surface oxygen In segregates to the solid surface at any alloy composition.

A novel method of examining carbonaceous deposits on spent catalyst surfaces

Xenon ion-bombardment used in conjunction with Auger electron spectroscopy was able to discriminate two types of carbonaceous materials accumulated on the surfaces of iron oxide and rhenium/iron-oxide catalysts spent for CO hydrogenation at 250°C and 2.1 MPa. One of the carbonaceous materials was easily eliminated from the surfaces by ion bombardment or by heat-treatment in vacuo at 150°C. On iron oxide only this “soft” carbonaceous material was present. On rhenium/iron oxide, bombardment-resistant “hard” carbonaceous material was also found. The presence of this hard carbonaceous material had little effect on the level of CO hydrogenation activity or the deactivation behavior of this catalytic system.

Mechanism of hydrogen adsorption-induced optical density changes in metal-loaded titania

Abstract The mechanism of the reversible optical density change that occurs when metal-loaded titania comes into contact with hydrogen has been examined by means of high-pressure infrared spectroscopy. The occurrence of this phenomenon requires the presence of supported metal particles as a catalyst, titania as a support and hydrogen in the gas phase. The combination of these three requirements suggests a mechanism that involves hydrogen adsorption and activation at the surface of the supported metal catalyst, followed by its protonation possibly due to its spillover to the support surface, and the donation of electrons to the conduction band of the support titania. The effect of co-adsorbed CO has also been examined.

Scanning tunnelling microscopy images of noble metal fine particles supported on thin titanium oxide film

Abstract Scanning tunnelling microscopy images of Pt fine particles supported on a thin film of titanium oxide spontaneously formed on a titanium metal surface were obtained, for the first time, using a simple STM unit operating under ambient conditions. The examined samples constitute a double-barriered system for STM: one barrier consists of the probe tip-to-metal particle air gap and the other the titanium oxide thin film. The sample also serves as a model for supported metal catalysts. Problems in obtaining and interpreting STM images of fine metal particles supported on thin oxide films are identified and discussed.

Studies on catalysis by molten metals. 14. Catalytic cracking of asphalts at low temperature

Abstract The catalytic effects of liquid metals for low-temperature (336 °C) asphalt-cracking have been examined using a semi-batch reactor. All the liquid metals examined (Bi, Cd, Ga, In, Pb and Sn) effectively catalysed the reduction of molecular weight with minimal gasification (