Fast selective catalytic reduction mechanism

Bench-scale flow reactor experiments are an effective way of examining the main performance features of the SCR reaction system on various catalysts. In this section, we review these features for Fe-based catalysts as a backdrop to considering more fundamental kinetics and mechanistic studies in Sect. 11.3 and transport effects in Sect. 11.4. The selective catalytic reduction of NOx by ammonia on Fe-ZSM-5 catalyst has been studied in detail by various research groups [19-22, 26, 27, 34-42]. The results from earlier studies of vanadia-based catalysts have underpinned the more recent studies of zeolite-based catalysts. For example, Koebel et al. [3, 6, 43] carried out a detailed study of the SCR chemistry on V-based catalysts. Nova et al. [5, 8, 44, 45] studied the chemistry of SCR over V-based catalyst and proposed a mechanism for the fast SCR reaction. To this end, the data here are by no means unique but are intended to highlight the important trends. 

The correlation between electronic structure and catalytic performance corroborates the assumption that the selectivity of the catalyst is governed by the electronic structure of the surface. The latter in turn appears to be determined by the electronic defect structure of the underlying bulk. In the investigation of the activated H5[PV2Moio04o] catalyst, reaction conditions that favored a conventional redox mechanism with fast reduction and diffusion-limited reoxidation led to low selectivity. 

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