Takayasu Shirasaki

The chemisorption of CO on ruthenium metals and ruthenium-silica catalysts

The chemisorption of CO on Ru-metals and supported RuSiO2 catalysts was studied at 150 °C. The Ru-metal made by Adamss method adsorbed a normal quantity of CO, and the results agreed with those of previous studies. The Ru-metal made by Willstatters method and supported Ru-SiO2 catalyst adsorbed a large quantity of CO, and the volume decreased by a repetition of the adsorption and reduction. The decrease was not caused by the residual CO of the reduction, but the sintering of Ru-metal was considered. In the case of the Ru-metal made by Willstatters method, the volume of CO chemisorbed did not correspond to the specific surface area. In the fresh samples of supported Ru-SiO2 catalyst, the CORu values (g mol/g atom) were more than unity and the ir spectra of the sample agreed with those of Ru3(CO)12 and other previous studies. This suggested that there were Ru-(CO)2, Ru-(CO)3, etc., species in the CO chemisorption.

Tracer studies of catalytic oxidation by bismuth molybdate: II. Propylene reduction of labeled catalysts and catalytic oxidation of propylene

Differently 18O-labeled bismuth molybdate catalysts were prepared by the solid-state reaction from 18O-enriched bismuth and molybdenum oxides. The results of the propylene reduction of the catalysts and the catalytic oxidation of propylene clearly demonstrated that the oxygen atom in the acrolein formed comes from the (Bi2O2)n2+ layer whether or not the gaseous oxygen is present. During the catalytic oxidation, the oxide ions consumed by the reaction seem to be replenished by gaseous oxygen through the (MoO2)n2+ layer.

Correlation Among Methods of Preparation of Solid Catalysts, Their Structures, and Catalytic Activities

Publisher Summary This chapter describes the traditional methods of preparation of supported nickel catalyst, such as superhomogeneous coprecipitation (SHCP) method, cation exchange method, palladium on aluminosilicate by complex-ion exchange, palladium on active charcoal, and nickel-phosphorus alloy. The catalytic activity of a solid catalyst, including its selectivity and life, is one of the attributes inherent to this solid substance itself and, therefore, depends on its physical and chemical structures, which are, in turn, governed by the method of preparation of this solid substance. The catalytic reaction on the solid catalyst is a kind of reaction that occurs between the reactant and the catalyst surface and, therefore, the physical and chemical structures of the surface must be among the main controlling factors of the surface reaction. The surface of the solid catalyst is heterogeneous in the geometrical composition of atoms and also in the distribution of surface energy.

Studies on the reduction-reoxidation of bismuth molybdate catalysts by temperature programmed reoxidation method

Abstract A new method of temperature programmed reoxidation (TPR) which gives a correlation of reoxidation rates with temperature in curved lines was devised and applied to slightly reduced MoO3, Bi2O3 and bismuth molybdate catalysts. Those oxide catalysts are found to be characterized by peaks in TPR. That is, MoO3 and Bi2O3 give TPR peaks at 410 and 180 °C, respectively. An increase in the extent of prereduction results in another peak with both oxides, indicating that reoxidation takes place in two steps. Bismuth molybdate catalysts of different compositions give different peaks which may be identified as composites of three TPR peaks. Every bismuth molybdate catalyst which gives the TPR peak at 320 °C is invariably active for selective oxidation of propylene to acrolein. The addition of phosphoric acid to bismuth molybdate catalysts increases the peak area at 320 °C and consistently enhances the formation of acrolein from propylene. The activation energies were determined for reduction of bismuth molybdate catalysts, reoxidation of slightly reduced catalysts and catalytic oxidation of propylene to acrolein. Those values are correlated to the TPR peak.

The EPR study of CO adsorbed ruthenium-silica catalysts

The adsorption of CO at 25–150 †C on supported Ru-silica and Ru-graphite catalysts was studied by a pulse-flow system. For the CO-adsorbed Ru-silica catalyst, the EPR spectra were observed. The irreversible adsorption of CO showed its maxima at 60–100 °C, and the (CORu)c ratio (g-mole/g-atom), i.e., the ratio of the total amount of adsorbed CO per unit weight of catalyst (g-mole/-catalyst) to the total amount of supported Ru-metal per unit weight of catalyst (g-atom/g-catalyst), for Ru-silica catalysts was more than unity; therefore, the existence of Ru(CO)3, etc. were predicted. On the other hand, there were signals in the EPR spectra at a high adsorption temperature which corresponded to anisotropy in the g tensor. From the perturbation of 2E-2A1 (C3v) and e-b2 (C4v) in a strong-crystal-field model, the g-values were evaluated; the simulation curve agreed satisfactorily with that observed.

Deposition Mechanism of Alkaline Scale on the Heated Surface of the Boiler from the Aqueous Solution Containing Calcium and Magnesium Salts

We studied on the deposition mechanism of alkaline scale substances (CaC0s, Mg(OH)2) on a heated surface. CaCO3 scale deposited on the heated surface by thermal decomposition of HC08-. The deposition rate was represented by the equation, ri=ki[Ca2][H0O2-]2, and the apparent activation energy was 25 kcal/mol. The dissolved CO, concentration was constant through the process of this reaction. These observations imply that the formation of crystalline CaCO3 is the rate-determining step in this reaction.Mg(OH)2 scale deposited on the heated surface by hydro-decomposition of CaCO3 scale in a MgSO4 solution. The deposition rate was represented by the equation, 7-2=k2Mg21/[Ca2]. The dissolved CO, concentration was constant through the process of the reaction, too. These results suggest that the formation of crystalline Mg(OH)2 is the rate-determining step.The experiment of the deposition of alkaline scale in sea water near the boiling temperature showed that CaCO3 scale deposited. initially by thermal decomposition of HCOs-, and successively Mg(OH)2 scale deposited by hydro-decomposition of CaCO3 scale. The other salts in sea water may not affect directly the deposition of Mg(OH)2 scale.

The Physical Structure and the Effect of Silica Xerogel Support on Metal Catalyst

Silica xerogel is used as a support of metal catalysts. This paper deals with the relation between the physical structure and the supporting effect of the silica xerogel on the dispersibility and the heat resistivity of the supported palladium particles. It was found that specific area of metallic palladium (a measure of dispersibility) was a function of the micropores and the rate of sintering of palladium particles (a measure of heat resistivity) was proportional to the mean radius of the micropores. Consequently, it may be concluded that the mean radius of the support may play an important role in the dispersibility and heat resistivity of palladium particles.

Preparing Procedure, Structure and Activity of Copper Catalyst by Precipitation Method

硝酸銅と水酸化ナトリウムとの水溶液反応で生成する沈殿物の製法 (析出条件, 母液 pH) と色調, 化学構造, 物理構造, およびこれを触媒としたときの活性との関係を調べた。沈殿物はつぎの四つの方法で得た。すなわち (1) 硝酸銅に水酸化ナトリウムを加える方法, (2) 水酸化ナトリウムに硝酸を加える方法, (3) 均密沈殿法, (4) 領域沈殿法。(1), (2)の方法で得た沈殿物は青白色の未知構造物 (※ と略記する, 塩基性硝酸銅と推定される) と褐色ないし黒褐色の含水酸化銅との混合物からなっている不均質物であることがわかった。析出母液 pH が約 6.0 より低い場合 ※ を生成し, 約6. 0より高い場合, 青色の沈殿を経て含水酸化銅を生成した。上記青白色の ※ は水酸化ナトリウム溶液中で約 70 時間熟成すると褐色の含水酸化銅に変化した。含水酸化銅は焼成, 水素還元して金属銅触媒にするとアセトンの水素化 (イソプロピルアルロール生成) に高活性を示したが, ※ は同様に処理して触媒にしても上記の反応にほとんど不活性であった。従来, 普通の沈殿法として行なわれるのは上記の (1) または (2) であって, 母液 pH が高低の幅広い領域にわたって変化しているので, 沈殿物は2種以上の異なる化合形態のものを含む。したがってこれを触媒としたものは2種以上の活性種を含むことがわかった。ところが (3) では析出時母液 pH が一定なので均質な沈殿物が得られ, 単一活性種よりなる触媒が得られることが結論された。

Preparing Procedure, Structure and Activity of Copper-Zinc Oxide Two Components Catalyst by Coprecipitation Method

共沈法による銅-酸化亜鉛系2元成分触媒体 (未賦活時酸化物が化合物や固溶体をつくらない場合) の活性が沈殿剤の添加方向と沈殿母液 pH の二つの要因によってどのように変化するかを研究し, つぎの結果を得た。(1) 硝酸銅と硝酸亜鉛の混合水溶液にかくはんしながら水酸化ナトリウム溶液を加えてゆく (A法) とまず銅分が, ついで逐次的に亜鉛分が主として析出する。逆に水酸化ナトリウム溶液に上記の混合溶液を加えてゆく (B法) と両成分のほとんどすべてが混って析出する。(2) A法とB法では生成触媒の諸構造および性状が大きく異なる。均密共沈法によるものとの比較検討の結果によると, この違いをもたらす直接的な原因は沈殿母液 pH と析出物の畜積順序である。(3) 低 pH 領域で沈殿した A法触媒よりも, 高 pH 領域で沈殿した B法触媒の方がアセトン水素化活性が高い。この結果は前報の単味の銅触媒におけるそれと同様であり, 酸化銅と酸化亜鉛とは均密共沈法によってもなお化学的混合物を作らないで機械的混合状態にあることを示している。

Chemical Structure and Catalytic Activity of Titania-Nickel Oxide or Titania-Ferric Oxide Prepared by Super Homogeneous Coprecipitation Method

耐熱性触媒担体の一つであるチタニアと酸化ニッケルまたは酸化鉄との均質な共沈物をつくり, それらの固体反応温度を示差熱分析法,生成複合酸化物の結晶化特性をX線回折法で調べ,特有の触媒活性を流通反応法で検討した。上記の共沈物は350～410℃ で焼成すると無定形の複合酸化物を生成するようである。そのうちチタニア-ニッケル系はトルエンの核水素化能・水素化脱メチル能をもち,150℃ 程度の低温反応でも経時劣化がいちじるしい。またチタニア-ニッケル系,チタニア-鉄系はともにイソプロパノールの脱水能が大きく,その接触能は市販の活性アルミナより優れていた。上の無定形物を520～570℃ で焼成すると結晶性複合酸化物に変化し,上記の触媒活性がいちじるしく低下した。この結晶性複合酸化物は通常法では950℃ 以上ではじめて生成する化合物であって,均質な共沈物では固体反応がはるかに低温でおこることが知られた。