Controlling the structure of nitrogen-doped zeolite-templated carbon for CO2 capture based on the synthesis conditions

The surface chemistry and the textural properties of nitrogen-doped zeolite-templated carbon materials (N-ZTC) are decisive for their functionality in CO₂ capture. This study analyses how the synthesis conditions affect the structure, formation of N-containing functional groups, thermal stability and CO₂ capture of N-ZTC in comparison with nitrogen-free ZTC. Faujasite as a hard template and chemical vapour depositions (CVD) with propene and acetonitrile were used for the synthesis of ZTC and N-ZTC, respectively. XRD, SEM, N₂ and CO₂ sorption, XPS and TG/DSC analyses showed that the structural ordering and microporous volume in N-ZTC increases with increasing synthesis temperature. Conversely, at higher temperatures, the content of basic pyridinic groups in N-ZTC decreases in favour of stable graphitic nitrogen. The Lewis acid−base interaction of CO₂ with the pyridinic groups provides the highest adsorption heats, the highest affinity for CO₂ compared to N₂ and enhances CO₂/N₂ selectivity (CO₂/N₂ selectivities of 127, 95, 89, and 66 for N-ZTC_750°C, N-ZTC_800°C, N-ZTC_850°C and ZTC, respectively). The maximum adsorption capacity was achieved for N-ZTC_800°C still yielding a high content of basic groups and a larger micropore volume compared to N-ZTC_750°C. The decisive factor for the selectivity is thus the presence of basic centers attainable in N-ZTC at a lower synthesis temperature. The maximum adsorption capacity is associated with a large microporous volume and basic centers in N-ZTC synthesized at medium temperatures. The energy of CO₂ adsorption by Lewis acid−base interactions and well-developed micropores are decisive for high selectivity and large adsorption capacity for efficient CO₂ capture using N-ZTC materials.