Metalloporphyrin-derived carbons:: models for investigating NOx release from coal char combustion

Nitrogen-containing carbons prepared by the co-carbonisation of tetraphenylporphine and acenaphthylene have been used as models to study NO, 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. (C) 1999 Elsevier Science Ltd. All rights reserved.