Remarkably enhanced density and specific activity of active sites in Al-rich Cu-, Fe- and Co-beta zeolites for selective catalytic reduction of NOx

Abstract

The efficiency of catalysts for abatement of emissions of nitrogen oxides (NOx) from stationary and especially mobile sources using selective catalytic reduction (SCR) is obviously still not sufficient to meet increasingly more stringent environmental limits. We demonstrate that the conversion of NOx to nitrogen under the relevant conditions of the SCR-NOx can be dramatically increased using Al-rich beta zeolite catalysts with a high concentration of transition metal counter-ions, bearing extra-framework oxygen ligand (M/M-oxo, where M=Cu, Co, Fe), particularly in the low-temperature region as well as at high space velocities. The high concentration of framework Al and corresponding high population of AlSiAl sequences in template-free synthesized Al-rich beta zeolite does not result in relative increased binding of bare non-reducible and non-active M(II) ions. To the contrary, the unparalleled high concentration of the atomically dispersed M/M-oxo counter-ions with appropriate redox properties and enhanced specific activities provides 3–12 times higher reaction rates for the SCR-NOx using ammonia, methane and propane as reducing agents compared to state-of-the-art Si-rich zeolite catalysts.