Effect of Cu content on the catalytic activity of CuSiBEA zeolite in the SCR of NO by ethanol: Nature of the copper species

The effect of Cu content on the catalytic activity of CuxSiBEA zeolites in the selective catalytic reduction (SCR) of NO by ethanol is investigated. The CuxSiBEA zeolites (x = 0.3, 1.5 and 3.3 Cu wt%) are prepared by a two-step postsynthesis method which allows to control the introduction of copper into BEA zeolite and thus to obtain catalysts with isolated tetrahedral Cu(II) species. The incorporation of Cu into the vacant T-sites of SiBEA framework is evidenced by XRD. The presence of isolated tetracoordinated Cu(II) as the main copper species is evidenced by DR UV–vis and XPS investigations. Cu0.3SiBEA, Cu1.5SiBEA and Cu3.3SiBEA with isolated Cu(II) species are active in SCR of NO by ethanol with the maximum NO conversion of 33%, 45.5% and 50% and selectivity towards N2 of 90%, 97% and 75%, respectively. These results indicate that activity of CuxSiBEA in the SCR process increases with Cu content and the main reaction route is the reduction of NO toward N2. The decreases of selectivity toward N2 and increases toward NO2 with Cu content, is probably related to formation of small amount of octacoordinated Cu(II) as suggested by XPS data. A possible pathway for the formation of tetracoordinated Cu(II) in the framework of CuxSiBEA is proposed.