Kazuyuki Nakai

A study on the preparation of supported metal oxide catalysts using JRC-reference catalysts. I. Preparation of a molybdena–alumina catalyst. Part 1. Surface area of alumina

Abstract This is the first report of a group study on the preparation of a MoO 3 /Al 2 O 3 catalyst to find predominant preparation parameters for better and reproducible catalyst preparations. Variously prepared MoO 3 /Al 2 O 3 catalysts possessing 13xa0wt% MoO 3 were subjected to multiprong characterizations and catalytic tests. It was found that the surface area of the support was the most predominant preparation parameter for the dispersion of Mo oxide species; the dispersion increased as the surface area of the support increased. The formation of crystalline MoO 3 was observed at a surface Mo concentration higher than 3.2 Mo nm −2 . With sulfided MoO 3 /Al 2 O 3 , it was established that the dispersion of Mo sulfide species increased with increasing surface area of the support and was in proportion to that of Mo oxide precursor species. The hydrodesulfurization activity of sulfided MoO 3 /Al 2 O 3 was proportional to the NO adsorption capacity. It is suggested that a homogeneous distribution of Mo oxide species is attained by an equilibrium adsorption technique. However, it was revealed that the surface area of the catalyst and Mo distribution were considerably modified by preparation parameters, such as drying processes, other than the surface area.

A study on the preparation of supported metal oxide catalysts using JRC-reference catalysts. I. Preparation of a molybdena-alumina catalyst. Part 2. Volume of an impregnation solution

Abstract Ten types of 13xa0wt% MoO 3 /Al 2 O 3 catalysts were prepared by a conventional impregnation or equilibrium adsorption method using a common extrudate support. These catalysts were subjected to a comprehensive characterization and catalytic reactions to find important preparation parameters in practical preparations. It was demonstrated in the present group study that the formation of crystalline MoO 3 was strongly correlated with the Mo segregation on the outer surface of the extrudate. When the amount of the impregnation solution was large (ca. 10xa0cm 3 g-Al 2 O 3 −1 ), a considerably homogeneous distribution and high dispersion of Mo oxide species were attained irrespective of the other preparation parameters. It is suggested that when a pore volume impregnation or incipient wetness technique is employed, drying processes strongly affect the dispersion and distribution of Mo oxide species. Drying at a reduced pressure is suggested to result in a segregation of Mo oxides on the outer surface of the extrudate, and accordingly a formation of crystalline MoO 3 .

A study on the preparation of supported metal oxide catalysts using JRC-reference catalysts. I. Preparation of a molybdena-alumina catalyst. Part 3. Drying process

Abstract In the present part of the group study on the preparation of 13xa0wt% MoO3/Al2O3, the effects of drying processes were investigated on the physicochemical and catalytic properties. Two series of catalysts were prepared by a conventional impregnation technique and by an equilibrium adsorption method using a common extrudate support. XPS and EPMA results demonstrated that the distribution of Mo oxide species in extrudates was strongly affected by drying processes. A rapid drying, in particular at a reduced pressure, was found to induce a strong segregation of Mo oxides on the outer surface of the extrudates, forming a sharp egg shell type distribution of Mo. On the other hand, drying under static conditions produced a moderate egg shell type distribution, suggesting that a slow drying rate is favorable for a homogeneous distribution of Mo. The equilibrium adsorption technique was found to provide considerably flat Mo profiles inside the extrudates except for the utmost surfaces where Mo concentrations increased steeply.

Dispersion and location of molybdenum sulfides supported on zeolite for hydrodesulfurization

The dispersion and location of zeolite-supported molybdenum sulfide species have been studied by means of XAFS, XPS, XRD, HREM and pore volume measurements. The zeolites used in the present study were NaY, USY and EMT. Molybdenum sulfide catalysts were prepared by Mo(CO)6 adsorption and impregnation techniques, the former catalysts being considerably more active than the latter systems for the hydrodesulfurization of thiophene and hydrogenation of butadiene. It was demonstrated that with NaY-supported catalysts, molybdenum sulfide species derived from Mo(CO)6 were completely sulfide and highly dispersed inside the zeolite pores. The crystal structure of the host zeolite was not destroyed by the accommodation of the molybdenum sulfide species in the pores. The relative activity of the catalyst for the hydrodesulfurization of substituted thiophenes and pore volumes measured using benzene as an adsorbate were in conformity with the HREM observations that the molybdenum sulfide clusters are located inside the zeolite pores. The structure and dispersion of the molybdenum sulfide species prepared using Mo(CO)6 encaged in zeolite were shown to depend on the zeolite composition and crystal structure. Molybdenum sulfide species in the impregnation catalyst were found to be incompletely sulfide and poorly dispersed in contrast to the molybdenum sulfide catalysts prepared from Mo(CO)6.

A study on the preparation of supported metal oxide catalysts using JRC-reference catalysts. I. Preparation of a molybdena-alumina catalyst. Part 4. Preparation parameters and impact index

Abstract The effects of the volume and pH of the impregnation solution and of the calcination conditions were examined on the physicochemical and catalytic properties of a 13xa0wt% MoO3/Al2O3 extrudate catalyst. The Al2O3 support and drying procedures (static conditions without flowing air) were fixed in the preparations. In the present series of catalysts, the amount of crystalline MoO3 was marginally small. It was found that the dispersion of Mo oxide species increased as the volume of the impregnation solution increased, gradually approaching a maximum value. The increase in pH (2–8) of the impregnation solution was found to reduce the dispersion of Mo oxide species. The Mo dispersion increased slightly for the impregnation catalysts as the calcination temperature increased (673–873xa0K), whereas it decreased for the equilibrium adsorption catalysts. The effects of the calcination atmosphere (with or without flowing air, or with flowing humid air) were very small on the dispersion of Mo oxide species under the present preparation conditions. On the other hand, the methanol oxidation activity of MoO3/Al2O3 was sensitive to the preparation parameters examined here. It was demonstrated by means of EPMA and XPS that a considerable migration of Mo took place during the calcination. In the present study on the preparation of a 13xa0wt% MoO3/Al2O3 catalyst, an impact index is proposed to measure the magnitude of the effects of the respective parameter(s) on the physicochemical and catalytic properties. With the Mo dispersion, the effects of the preparation parameter decreased in the order, surface area of the support >> drying process > volume of the impregnation solution > pH, calcination temperature and atmosphere. The size of the impact index for the dispersion of Mo sulfide species is 70–75% of that for the Mo oxide species. The HDS activity of the catalyst was less affected by the preparation parameters than the Mo sulfide dispersion. The preparation parameters affected the segregation of Mo on the outer surface of extrudates in a decreasing order: drying process > volume of the impregnation solution > pH, calcination conditions. It was found that the oxidation of methanol was affected most intensely by the drying procedures. The volume of the impregnation solution, calcination conditions and pH of the impregnation solution also strongly affected the oxidation activity. The impact index suggests that the sensitivity to the preparation variables of the physicochemical and catalytic properties of MoO3/Al2O3 decreases in the order, methanol oxidation activity > surface Mo segregation > Mo oxide dispersion > Mo sulfide dispersion > HDS activity.

Establishment of Evaluation Method for Fundamental Properties of PEM in PEFC

固体高分子型燃料電池 (PEFC) における高分子電解質膜 (PEM) 開発にとって, 実際に稼動している燃料電池の作動条件に合わせて水蒸気収着量ならびにプロトン伝導度を測定することは非常に重要である。従来これらの測定を行う場合, それぞれのデータは別々の装置を利用することによって得られていたため, 多大な時間とコストを要していた。また, これらのデータを取得するにあたり安定したデータを取得するための統一的な方法がなく, プロトン伝導度においては湿度100%以下での測定や膜を水中につけた後, いつ測定を開始すればよいかという点が明確ではないため, 様々な条件下での膜の特性を高い信頼性を持って正確に評価することが困難であった。そこで当社ではこれらの問題を解決し, PEMの統一的な評価方法を達成すべく, 様々な条件 (測定温度; 298-473K, 測定湿度; 0-95%RH, 測定圧力; 大気圧-1.0MPa) での膜の水蒸気収着量ならびにプロトン伝導度の同時測定装置 (MSB-AD-V-FCTM) を開発した。この方法は, 単一チャンバー内で流通式重量法による膜に対する水蒸気収着平衡を確認後, 4端子による周波数挿引法によりインピーダンスを測定しプロトン伝導度を取得することにより安定かつ再現性の高いデータを取得するというものである。この方法により, イオン交換量の異なる膜や, 厚さの異なる膜の伝導度を平衡状態下で測定することができるばかりでなく, 膜の水分平衡収着量および平衡到達時間を同時に把握することができるようになった。また, これらの方法は全自動測定ソフト (BEL-FCETM) で制御されるため, 膜セッティング後, 任意の測定条件設定のみで前処理から測定および結果明示まで全データを取得することができる。