Formation of filamentous carbon from 1,3-butadiene over a Ni-Pd/Al2O3 catalyst

The formation of carbon filaments from 1,3-butadiene over a Ni-Pd/Al2O3 cat alyst at 400-450 degrees C was studied by high-resolution electron microsco py and X-ray diffraction analysis. The carbon filaments differ in morpholog y and in the arrangement of active metal inclusions: (1) abundant similar t o 1000 Angstrom thick filaments contain biconical alloy particles in the mi ddle of the filament, (2) thin filaments of a thickness less than 500 Angst rom rolled in helical fashion contain oval-shaped alloy particles in the mi ddle, and (3) in a few filaments that are less than 200 Angstrom thick, all oy particles are positioned at the ends. When the first two types of filame nts grow, decomposition of the hydrocarbon occurs at the active sites of th e surface with the formation of a carbide microphase with a hexagonal struc ture. This phase is called the active microphase. When the reaction stops, the active phase decomposes to form carbon and hexagonal nickel. Extensive defects like grain boundaries and stacking fault dislocations are present i n the bulk of Ni-Pd alloy particles. The origin of these defects is related to the epitaxial effect of the active microphase particles on the alloy.