Promoting effect of water on NH3-SCR reaction over Cu-SAPO-34 catalyst: Transient and permanent influences on Cu species
Cu-SAPO-34 catalysts with varied Cu loadings were synthesized through ion exchange to study the influence of water on NH3-SCR reaction. The catalytic activities were evaluated by selective catalytic reduction of NO under reactant feed in the presence/absence of water. Transient experiments were designed to study the response of NO conversion to water presence. H2-TPR and DFT calculations were conducted to study the reducibility of Cu species. NH3-TPD and XPS were conducted to reveal the migration of Cu species. The results show that water could remarkably improve NO reduction activities and the promoting effect is more significant on the catalyst with low Cu loading. Both transient and permanent influences were found in this promoting phenomenon. For transient influence, water has been proved to accelerate the re-oxidation half-cycle. Moreover, water can enhance the promoting effect of SCR feed to the migration of Cu species. Those unanchored Cu ions migrate to defect sites to form active sites, which led to the permanent influence of water.