The relationship between metal particle morphology and the structural characteristics of carbon deposits

Abstract

The understanding of the factors controlling the deposition of carbonaceous solids resulting from the decomposition of hydrocarbons over metal particles has a considerable impact on a number of commerical processes including: catalytic steam reforming of methane, catalytic reforming and systems involving carbon monoxide disproportionation reactions. The highest catalytic activity for carbon deposition is exhibited by iron, cobalt and nickel, and alloys containing these metals. During the past few years we have pursued a program designed to achieve conditions where it is possible to control the catalytic properties of a given metal by inducing perturbations to the reactive surfaces of the crystallites. One of the consequences of such an action is to enable one to alter the catalytic reactivity in such a fashion so as to optimize the performance for a desired reaction pathway, while simultaneously suppressing the rate of detrimental side reactions, such as encapsulating forms of carbon deposition. Our strategy has centered around a study of the effect of introducing selected adatoms into the host metal and using the decomposition of ethylene to probe the manner by which the chemistry of the various faces of the crytallites is modified. In this paper a discussion of the information obtained from the use of a combination of controlled atmosphere and high resolution transmission electron microscopy techniques to study the impact of metal particle morphology on the characteristics of the carbon deposit will be given.