Operando Spatially- and Time-Resolved XAS Study on Zeolite Catalysts for Selective Catalytic Reduction of NOx by NH3

详细信息    查看全文

• 作者：Dmitry E. Doronkin ; Maria Casapu ; Tobias G眉nter ; Oliver M眉ller ; Ronald Frahm ; Jan-Dierk Grunwaldt
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：May 15, 2014
• 年：2014
• 卷：118
• 期：19
• 页码：10204-10212
• 全文大小：455K
• 年卷期：v.118,no.19(May 15, 2014)
• ISSN：1932-7455

文摘

The structure of iron and copper sites during the selective catalytic reduction (SCR) of NO_x by NH₃ and related reactions (NH₃ adsorption/oxidation, NO oxidation) has been elucidated by spatially- and time-resolved X-ray absorption spectroscopy (XAS) along the catalyst bed over Fe-containing BEA and ZSM-5 zeolites as well as Cu-SAPO-34 silicoaluminophosphate. Strong gradients of the Fe and Cu oxidation state are present along the catalyst bed for the processes involving NH₃ and NO_x (SCR) and less pronounced for NH₃ oxidation, whereas the catalyst state in the NO_x containing feed resembles that of a catalyst exposed to air. The variation in the oxidation state is strongly correlated to the concentration of NH₃ and is more pronounced in the presence of NO_x. For temperatures higher than 250 掳C the Fe and Cu sites at the beginning of the catalyst bed stay in partially reduced state, whereas they are more oxidized in the later zones where NH₃ and NO concentrations decrease. For temperatures lower than 250 掳C a reverse effect is seen for Fe-zeolites where the beginning of the catalyst bed contained more oxidized iron species than at the end of the catalyst bed. This is attributed to NH₃ inhibition. The obtained data allow to conclude that both NH₃ and NO_x are involved in a reaction over the corresponding transition metal site, and its reoxidation is a rate-limiting step of the NH₃-SCR for these catalysts.