When hydrogen, nitrogen and CO are exposed to amorphous iron silicate surfaces at temperatures between 500–900 K a carbonaceous coating forms via Fischer-Tropsch type reactions. Under normal circumstances such a coating would impede or stop further reaction. However, we find that this coating is a better catalyst than the amorphous iron silicates that initiate these reactions. Formation of a self-perpetuating catalytic coating on grain surfaces could explain the rich deposits of macromolecular carbon found in primitive meteorites and would imply that protostellar nebulae should be rich in organic material.