Effect of Co content on the catalytic activity of CoSiBEA zeolites in N2O decomposition and SCR of NO with ammonia

Abstract

A series of CoxSiBEA zeolite catalysts has been prepared by postsynthesis procedure with various Co content (from 1 to 9wt% Co). The catalytic properties of these materials in SCR of NO with ammonia and N2O decomposition were studied. XRD, FTIR, DR UV–vis, TPR and XPS results show that two-step postsynthesis method allows to control the introduction of cobalt into zeolite and to obtain catalyst with specific Co sites. Introduction of cobalt into SiBEA zeolite leads to an increase in unit cell parameters of the BEA matrix and consumption of silanol groups present in vacant T-atom sites of dealuminated BEA as shown by XRD and FTIR spectroscopy. Cobalt is stabilized in CoxSiBEA in the form of two kinds of Co(II) species. They are characterized by an unusually high reduction temperature, which indicates that the cobalt is in strong interaction with the SiBEA support. It is shown by DR UV–vis and XPS that for low content (<2wt% Co) cobalt is successfully incorporated into the framework of zeolite as pseudo-tetrahedral Co(II). For higher cobalt content, framework pseudo-tetrahedral and extra-framework octahedral Co(II) are detected by DR UV–vis and XPS. The catalytic activity of CoxSiBEA zeolites depends on the amount and nature of Co species. The framework pseudo-tetrahedral Co(II) are responsible for catalytic activity of Co1.0SiBEA catalyst. The higher amount of Lewis acidic sites present in Co4.0SiBEA and Co9.0SiBEA than in Co1.0SiBEA seems to be responsible for the higher activity of former than latter in N2O decomposition and SCR of NO with ammonia.