Catalytic Activity of Cu-Beta Zeolite in NO Decomposition: Effect of Copper and Aluminium Distribution

Catalytic activity in NO decomposition of Cu-Beta zeolites with different Cu/Al/Si composition, diffuse reflectance UV–vis–NIR spectra of Cu ions of hydrated Cu-Beta zeolites, and concentration of Brønsted and Lewis sites in parent Beta zeolites, determined by quantitative analysis of FTIR spectra of adsorbed d3-acetonitrile, were investigated. Cu-Beta zeolites exhibit high and stable activity in NO decomposition in the temperature range 580–750 K and Si/Al ratio 12.7–42. Strong dependence of activity in NO decomposition per Cu ion (TOF) on Cu/Al loading indicates the presence of three Cu species in Cu-Beta zeolites. Cu ions incorporated at low Cu loading are balanced by two framework Al atoms and are inactive in NO decomposition. Species responsible for NO decomposition are formed at medium Cu loading and represent Cu ions balanced by single-framework Al atoms. At high Cu loading, a new type of inactive, noncationic Cu species (small clusters of Cu2O) is formed. Brønsted and Lewis sites themselves do not contribute to the catalytic activity of Cu-Beta zeolites in NO decomposition. However, the presence of Lewis sites in the parent zeolites is connected with the occurrence of the framework sites containing two close Al atoms and bonding the Cu ions which are not active in NO decomposition. A comparison of Cu ion activity in Beta and ZSM-5 is discussed.