The incorporation of nitrogen into isotropic carbons and its release during temperature-programmed combustion

Abstract

The combustion behavior of a suite of isotropic carbons has been investigated using a thermogravimetric analyser mass spectrometer. The carbons were prepared from polyvinylidene chloride (PVDC) and a phenolic resin by carbonisation under argon to 873 K in the pressure range 0.1–7.5 MPa. Nitrogen was introduced into the carbons (HTT 873 K) by both ammonia treatment at the final heat-treatment temperature (1073 K) and during the carbonisation process. Nitrogen was also incorporated into the PVDC and resin carbons by co-carbonisation of the precursor with carbazole. Comparison of the temperature-programmed combustion results obtained for the isotropic carbons with those for the anisotropic acenaphthylene carbons containing nitrogen, introduced by ammonia treatment, showed that there were distinct differences. The reactivities of the carbons were enhanced by the ammonia treatment for the anisotropic acenaphthylene carbons, but reduced for the isotropic phenolic resin and polyvinylidene chloride carbons. The proportions of the two types of nitrogen functionality introduced by ammonia treatment were distinctly different for the isotropic and anisotropic carbons. The results are discussed in terms of the capping of the active sites to form functionalities substituted on the aromatic structures, and nitrogen incorporation into the ring structure of the ‘graphene’ layers. The conversion of char nitrogen to NO during combustion is discussed in relation to char structural characteristics, reactivity, and nitrogen content.