Effect of method of preparation on activity of Pd/Al₂O₃ monolith catalysts

Abstract

monolithic catalyst of different washcoat thicknesses were prepared by two methods and tested for the activity of hydrogenation of˛-methyl styrene. These catalysts were prepared by two methods; either the palladium was impregnated on -alumina and this Pd/Al 2 O 3 powder was used to prepare the slurry for washcoating (Cat 1) or -alumina washcoating was followed by impregnation of palladium (Cat 2). The effect of slurry concentration, pH of the slurry, and addition of binders on the catalyst properties was investigated. The monolithic catalysts were characterised by determination of metal dispersion, surface area, scanning electron microscopy, and weight loss of washcoat during ultrasonication. Well-adhered washcoats were obtained with slurry prepared using milled -alumina, whereas the adhesion of the washcoat prepared using Pd/Al 2 O 3 powders was very poor. Addition of binders significantly improved the adhesion of the washcoats prepared from Pd/Al 2 O 3 . Metal dispersion for Cat 2 decreased with washcoat loading but did not change with loading for Cat 1. The activity tests were conducted at different washcoat loadings and the productivity of the monolithic catalyst prepared in both methods has been compared. Des catalyseurs monolithiques de Pd/Al2O3 et d'épaisseurs de couche lavis différentes ontété préparées par deux méthodes et testées en termes d'activité pour l'hydrogénation du˛-méthyl-styrène. Ces catalyseurs ontété préparés par deux méthodes : 1) du palladium aété enduit sur de la -alumine et cette poudre de Pd/Al2O3était utilisée pour préparer la boue de couche lavis (Cat 1) ou 2) la préparation de la couche lavis de y-alumineétait suivie d'un enduit de palladium (Cat 2). On aétudié l'effet de la concentration de la boue, de son pH et de l'ajout de liants sur les propriétés des catalyseurs. On a déterminé les caractéristiques des catalyseurs monolithiques par détermination de la dispersion métallique, de la surface, par une microscopieélectroniqueà balayage et par la perte de poids de la couche lavis durant l'ultrasonication. Des couches lavis de bonne adhésion ontété obtenues avec des boues préparées en utilisant de la -alumine moulue, tandis que l'adhésion des couches lavis préparées avec des poudres de Pd/Al2O3était très mauvaise. L'ajout de liants améliorait de façon significative l'adhésion des couches lavis préparées avec le Pd/Al2O3. La dispersion métallique du Cat 2 diminuait avec la charge de couche lavis mais pour le Cat 1, cette dispersion n'était pas modifiée avec la charge. Ces tests d'activité ontété effectués pour différentes charges de couche lavis et l'on a comparé la productivité des catalyseurs monolithiques produits par les deux méthodes.

Mechanical Stability of Monolithic Catalysts: The Influence Mechanism of Primer on the Washcoat Adhesion to the Metallic Substrates

“…It can be elucidated by the mechanical failure mechanism contained the adhesive and cohesive failures, while for metallic substrates, the adhesive failure is the mainly threat because of the different characters between the substrate and the washcoat layer. Furthermore, the viscosity of the alumina sol increased with solid content, which can increase the adhere force between the washcoat layer and the metallic substrate ,. That is, the adhesion of washcoat layer will be strengthened with the solid content increasing.…”

Influence of alumina binders on adhesion and cohesion during preparation of Cu‐SAPO‐34/monolith catalysts

“…The adhesion and cohesiveness of the coating were characterized by observing their resistance to ultrasonic vibration. The monolithic catalyst was immersed in petroleum ether in a test tube and then treated in an ultrasonic bath (40 Hz/60 W) for 30 minutes . The samples were removed, dried and weighed.…”

“…The monolithic catalyst was immersed in petroleum ether in a test tube and then treated in an ultrasonic bath (40 Hz/60 W) for 30 minutes. 15,19,21,22,26 The samples were removed, dried and weighed. The weight losses, a, were then calculated, with…”

“…Obtaining a good adhesion between the coating layers and the substrate, and obtaining coherent layers are among the main challenges when preparing high SCR performance catalysts. It has often been reported that washcoat adhesion and cohesion can be improved by adding binders with high specific surface area such as alumina and silica for ceramic monoliths or by optimized thermal and/or chemical pretreatments for metallic monoliths . However, little is known about washcoating application of CHA catalysts.…”

“…It has often been reported that washcoat adhesion and cohesion can be improved by adding binders with high specific surface area such as alumina and silica for ceramic monoliths [16][17][18] or by optimized thermal and/or chemical pretreatments for metallic monoliths. [19][20][21] However, little is known about washcoating application of CHA catalysts. Mitra and Kunzru 22 reported that the washcoat properties depend on the particle size of the zeolites such as ZSM5, b zeolite, mordenite, and zeolite Y, the number of immersions, dispersion concentration and viscosity, and surface tension.…”