Metalloporphyrin-derived carbons: models for investigating NO x release from coal char combustion

Abstract

Nitrogen-containing carbons prepared by the co-carbonisation of tetraphenylporphine and acenaphthylene have been used as models to study NO x release during coal char combustion. In addition, carbons prepared from metalloporphyrins have been studied in an attempt to examine the role of well-dispersed metal catalysts on nitrogen release during combustion. The nitrogen functionality in some of the carbons was investigated by nitrogen X-ray Absorption Near-Edge Structure Spectroscopy (XANES), and thermogravimetric analysis–mass spectrometry was used as a means of studying the combustion properties. The nitrogen species present in the carbon are similar to those observed in coals and carbons, and there is some indication of a portion of chelated metal still being present for a lower (873 K) heat-treated carbon prepared from tetraphenylporphine cobalt (II). Even so, the effect of nitrogen functionality on NO emission is secondary to the effect of carbon structure on NO reduction. A model is presented which discusses NO emission in terms of the steady-state surface oxygen concentration on the carbon. In the case of catalysed carbon combustion, the NO reduction reaction is also catalysed. Carbons prepared from these types of metal-containing precursors show larger catalytic effects in combustion than transition metal-impregnated carbons.