Detailed Study of Cu Migration in the Course of NH3-Facilitated Solid-State Ion-Exchange into *BEA Zeolites

Abstract

Cu migration into *BEA zeolite in the course of NH3-faciliated solid-state ion exchange (SSIE) was studied using \({\text{Cu}}^{\text{II}} {\text{O}}\) and \({\text{Cu}}^{\text{I}}_{ 2} {\text{O}}\) as the Cu sources. It was found that \({\text{Cu}}^{\text{II}} {\text{O}}\) and \({\text{Cu}}^{\text{I}}_{ 2} {\text{O}}\) are equally effective when SSIE is carried in the presence of 500 ppm NO and 500 ppm NH3. Removal of NO significantly reduces the efficiency of SSIE for [\({\text{Cu}}^{\text{II}} {\text{O }} + {\text{ NH}}_{ 4} {\text{-}}^{*}{\text{BEA}}\)] since the process becomes limited by \({\text{Cu}}^{\text{II}} {\text{O}}\) → \({\text{Cu}}^{\text{I}}_{ 2} {\text{O}}\) reduction. When \({\text{Cu}}^{\text{I}}_{ 2} {\text{O}}\) is used as the Cu source the rate of SSIE is no longer limited by the reduction, but becomes limited by the formation and migration of mobile [Cu(NH3)2]+ complexes. A time-resolved study of SSIE with NH3 and a \({\text{Cu}}^{\text{I}}_{ 2} {\text{O }} + {\text{ NH}}_{ 4} {\text{-}}^{*}{\text{BEA}}\) mixture at 200 and 250 °C reveals two distinctly different stages during Cu migration, which are tentatively attributed to non-random occupation of different cationic positions that the Cu-species occupy upon consecutive exposure to the atmosphere in the selective catalytic reduction of nitrogen oxides with ammonia.