Preliminary investigation of the palladium-tungsten-γ-alumina catalyst system by transmission electron microscopy (tem)

• Published in: Journal of molecular catalysis 1983-01, Vol.20 (3), p.251-262
• Main Authors: Plummer, H.K., Shinozaki, S., Adams, K.M., Gandhi, H.S.
• Format: Article
• Language: English
• ISSN: 0304-5102
• DOI: 10.1016/0304-5102(83)80034-0

Preliminary studies comparing the morphology and chemical nature of a Pd/γ-Al 2O 3 catalyst with a Pd-W/γ-Al 2O 3 catalyst have been carried out using transmission electron microscopy. Evidence is presented to indicate that the incorporation of a high concentration of tungsten changes the palladium particle characteristics after calcination in air at 500 °C and also after reduction in hydrogen at 550 °C. When Pd/γ-Al 2O 3 is calcined in air, small palladium particles (⩽ 2 nm) are formed in addition to larger palladium oxide particles (⩽ 7 nm). Both types of particles are thin, essentially two-dimensional, resulting in a high surface to volume ratio. On the other hand, the palladium particles formed during reduction contain a narrow size range ( ca. 3–10 nm) with many particles assuming a three-dimensional symmetry, thus providing a lower surface to volume ratio. Pd-W/γ-Al 2O 3 catalyst, when calcined in air, also produces an essentially two-dimensional bimodal particle size distribution, but in this sytem the particles are all metallic palladium with no oxides detected. After heating this specimen in hydrogen, only a small increase in the particle size range, with a slight decrease in the concentration of small particles, was noted indicating a strong interaction between particles and substrate. Thus a high palladium surface area is retained in this catalyst.