A Perspective on the Relationship Between Microstructure and Performance of Cu-Based Zeolites for the Selective Catalytic Reduction of NOx

Abstract

Cu-exchanged zeolites are one kind of effective catalysts to eliminate NOx for Selective catalytic reduction with NH3(NH3-SCR) in oxygen-rich exhaust from diesel engines. The microstructure–performance relationships between supports and active sites is crucial to rationally design excellent catalysts for the effective elimination of NOx. Therefore, the effect of topology and element ratio on active species and performance, the new progress in reaction and chemical poisoning mechanism to clarify the nature of the catalytic reactions are reviewed in this article. Furthermore, some new research methods to further promote SCR performance are summarized, which is helping in guiding the rational design of Cu-zeolites catalysts. From the reviewed data, the following important viewpoints emerged: (i) topologies exert different influence on acid properties and the nature of Cu species, which further effect the NH3-SCR performance; (ii) the Si/Al and Cu/Al compositional ratios are key factors in effecting the performance of the Cu-zeolites catalysts; (iii) the degree of chemical inactivation depends on the content and type of impurities; (iv) the common modification methods include the doping of foreign cations or metal oxides and core–shell structures; (v) the active site in the low temperature NH3-SCR catalyst is a mobile transient ion pairs ([(NH3)2CuI-O2-CuI(NH3)2]).Only in the high temperature regime do the NH3-solvated Cu ions decompose to isolated Cu2+ ions that anchor on the zeolite framework and become immobilized.