DYNAMIC ELECTRON-MICROSCOPY OF COPPER PALLADIUM INTERMETALLIC COMPOUND CATALYSTS

In-situ electron microscopy has been used to probe fundamental aspects of the dynamic state of supported copper-palladium intermetallic catalysts in controlled-reactions conditions, relating to methanol synthesis from hydrogenation of carbon monoxide. The chemical nature of intermetallic surfaces is found to be different in the different gases and is related to gas chemisorption effects. Subnanometer overlayers of palladium have been imaged on individual small particles under reducing carbon monoxide and synthesis gas environments and characterized by a combination of high-precision analytical electron microscopy, high-resolution electron microscopy and image simulations. They are mostly equilibrated Pd-rich (100) surfaces. The nature of catalytically active centers is explored. Diffuse scattering observed in electron diffraction patterns of perfect crystallites is attributed to directional lattice vibrations, with the diffuse streaks resulting primarily from the intersections of {111} reciprocal lattice (rel) walls, and of 〈110〉 rel rods with the Ewald sphere. Coherent bremsstrahlung peaks have been observed in the microanalysis traces of the small intermetallic particles at low incident electron energies. © 1990.