Formation of carbonaceous deposits from the platinum-iron catalyzed decomposition of acetylene

Abstract

Controlled atmosphere electron microscopy has been used to study the formation of carbonaceous deposits when a platinum-iron alloy was heated in the presence of acetylene and ethylene. When Pt-Fe particles were heated in acetylene carbon filaments were produced at quite low temperatures (690 K). These deposits were formed by an entirely new mode of filament growth in which the filament was extruded from the catalyst particle, which remained in contact with the support surface. The filament growth rate was two orders of magnitude faster than with a pure iron catalyst under similar conditions. In general the diameters of filaments were less than those of the catalyst particles responsible for their growth. Oxidation studies demonstrated that metal particles were taken up in the filaments, probably in the material constituting the skin of the filaments. A possible growth mechanism for this type of extrusion filament is suggested. When Pt-Fe particles were exposed to ethylene this type of deposit was not produced, but at 1175 K, a cluster of nodular deposit collected around the particles and this occasionally took the form of diffuse filaments. The failure to find well formed filaments is attributed to insufficient heat release at the catalyst surface from the olefin decomposition process.