Sn-MFI as active, sulphur and water tolerant catalysts for selective reduction of NOx

Sn-MFI catalysts with Si/Sn molar ratios from 33 to 133 were synthesized for NOx selective reduction by propane. SEM images of the samples showed that they consist of neat and uniform particles with different morphologies by varying the Si/Sn ratios. XRD, N-2 adsorption-desorption, DRUV-vis, FTIR and XPS analysis confirmed that the samples were of an MFI structure if the Si/Sn ratio is above 20, in which Sn was incorporated into the MFI framework. As a consequence, a large amount of Lewis acidic sites, mesopores and active surface oxygen species have been formed. The mesopores could facilitate the diffusion of the reactants and products, and the Lewis acidic sites are favourable for the formation of active NOx adsorbates. Therefore, compared with the whole silica Si-MFI ( Silicalite-1), all of the Sn-MFI catalysts with an MFI structure show much improved NOx-SCR activity. Furthermore, Sn-MFI catalysts display potent resistance to both sulphur and water vapour deactivation, which makes them potential catalysts for real exhaust control.