Influence of the nature and environment of vanadium in VSiBEA zeolite on selective catalytic reduction of NO with ammonia

Abstract

The influence of the nature and environmental of vanadium on the catalytic properties of VxSiBEA zeolite in selective catalytic reduction of NO with ammonia is investigated. Catalysts containing 1–7.5wt.% of vanadium were prepared by a two-step postsynthesis method which consists, in the first step, of dealumination of TEABEA zeolite to obtain SiBEA support and then, in the second step, of contacting the obtained material with an aqueous solution of NH4VO3 at pH 2.7. XRD and low temperature N2 sorption results show that full dealumination of parent TEABEA zeolite by nitric acid treatment as well as incorporation of vanadium atoms in the framework of SiBEA zeolite do not change the crystallinity of BEA zeolite. The presence of isolated pseudo-tetrahedral V(V) species for low V content and pseudo-tetrahedral and octahedral V(V) species for high V content is evidenced by diffuse reflectance UV–vis, Raman and TPR. The catalytic activity of VxSiBEA in selective catalytic reduction of nitric oxide with ammonia as reducing agent strongly depends on the nature and environmental of vanadium in BEA structure. The single site V1.0SiBEA catalyst with isolated pseudo-tetrahedral V(V) species is active in SCR of NO process, with maximum NO conversion about 60% at 773K and with very low selectivity toward undesired N2O. In contrast, V3.0SiBEA and, especially, V7.5SiBEA catalyst containing mainly extra-framework octahedral V(V) and vanadium oxide species are less active in SCR of NO process at higher temperature and big amount of N2O is observed in the product stream.