Controlled preparation of CoPdSiBEA zeolite catalysts for selective catalytic reduction of NO with methane and their characterisation by XRD, DR UV–vis, TPR, XPS

Abstract

The Pd 0.15SiBEA and Co x Pd 0.15SiBEA zeolites (where x = 1.0 and 3.0 wt.% Co) are prepared by a two-step postsynthesis method which allows to control the introduction of palladium and cobalt into zeolite and thus to obtain catalysts with specific bimetallic Pd and Co sites. The effect of Co content on the catalytic activity of Co x Pd 0.15SiBEA zeolites in the selective catalytic reduction (SCR) of NO with methane is investigated. The nature of the active sites is characterized by diffuse reflectance UV–vis, H 2-TPR and XPS. These techniques allow to show that in both Co 1.0Pd 0.15SiBEA and Co 3.0Pd 0.15SiBEA catalysts the cobalt is present as isolated mononuclear Co(II) species. The catalytic activity of Co x Pd 0.15SiBEA strongly depends on the content of this particular Co(II) species. When Co content increase from 1.0 to 3.0 wt.% the NO conversion in SCR of NO with methane increase from maximum value of 25% to 55%. The conversion of methane is lower than 15% for Co 1.0Pd 0.15SiBEA over a wide temperature range (230–460 °C) but for Co 3.0Pd 0.15SiBEA is much higher at temperature range between 400 and 500 °C reaching maximum value of 35% at 500 °C.