DFT study on the interactions between HCN and NO over char

Abstract

A noteworthy part of HCN conversion is in reference to its potential behavior in NO reduction. In this work, a comprehensive density functional theory (DFT) study was carried out to obtain new insight into the mechanisms of HCNNO reaction on the char surface. A model modified with the hydroxyl group contributes to a better understanding of NO reduction with HCN oxidation. The adsorption modes are found to influence the adsorption energies and reaction paths significantly. For single adsorption, the HCN adsorption in dual-site mode is the most thermally favorable. The co-adsorption of HCN and NO is dramatically more significant than the sum of the corresponding single adsorption, mainly due to the reaction of adsorbates on the surface. In addition, the microscopic reaction paths for CO and N2 formation are summarized based on the most energetically stable adsorption and co-adsorption structures separately. The canonical variational transition-state theory (CVT) is adopted here to provide fruitful kinetic implications in the temperature range of 500–1800 K. The analysis indicates that the occurrence of HCN oxidation decreases the reaction energy barriers evidently, which is also responsible for the rates increasing. The co-adsorption mechanism is favorable for NO conversion, especially for the release of CO. The findings from this work are beneficial for better understanding and illustrating the ultra-low NOx emission processes. The co-adsorption mechanism that was always neglected before is strongly suggested in future computational studies.