from first principles PP-I-1

PP-III-60Mechanism of NO-SCR with Methane over In,H- and Co,In,H-ZSM-5CatalystsLónyi F., Solt H.E., Valyon J.Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences,Hungarian Academy of Sciences, Budapest, Hungarylonyi.ferenc@ttk.mta.huMechanism of selective catalytic reduction of NO (NO-SCR) by methane was studied overzeolite In,H-, Co,H-, and Co,In,H-ZSM-5. The results of H 2 -TPR and XPS experimentsshowed that the catalysts contain indium as [InO] + /[InOH] 2+ cations, whereas cobalt was inthe form of Co 2+ /[Co-OH] + cations and/or Co-oxide clusters in amounts controlled by theapplied preparation method. The NO-SCR by methane was shown to proceed in two coupledprocesses on distinctly different catalytic sites. One of the processes is the oxidation of NO toNO 2 by oxygen (NO-COX reaction) over Brønsted acid sites and/or cobalt-oxide speciesgiving NO/NO 2 gas mixture. The other process is the N 2 formation (CH 4 /NO-SCR reaction),which is the result of the reaction of methane and the NO/NO 2 mixture. Operando diffusereflectance infrared Fourier transform spectroscopic (DRIFTS) results suggested thatmolecules of NO and NO 2 became activated together as NO + /NO - 3 ion pair in reaction with[InO] + /[InOH] 2+ or Co 2+ /[Co-OH] + -sites. The reaction of methane and NO 3 generates anunidentified intermediate that rapidly reacts with the NO + to give N 2 . The former methaneactivation on active NO - 3 surface species was confirmed to be the rate determining step. TheIn-bound nitrate has significantly higher reactivity towards methane than Co-bound nitrate,therefore the In-catalysts are more active in the NO-SCR reaction than the Co-catalysts.Co-oxide clusters, if present, showed significant promotional effect, which was related totheir much higher NO-COX activity than that of the Brønsted acid sites. The acceleratedNO-COX reaction speeds up the formation of NO + /NO - 3 species and the rate of the methaneactivation, being the rate-determining step of the NO-SCR reaction. Thus, the connectionbetween NO-COX and CH 4 /NO-SCR reactions was clearly established. It was also shownthat the NO-SCR reaction could proceed, if NO-COX and CH 4 /NO-SCR catalysts wereplaced in the reactor to form consecutive separated beds. However, to avoid rate controllingNO 2 transport between the sites the close proximity of the different catalytic sites is favorable.214