Effect of Pd on the stability improvement of Cu/H-MFI for NO removal underhydrothermal pretreatment conditions

The effect of Pd-modification of Cu ion-exchanged H-MFI (Pd/Cu/H-MFI) on it s performance for NO removal was studied. The stability of the catalysts su bjected to hydrothermal treatment with a He stream containing 10% steam at 800 degreesC was investigated. The Cu/H-MFI catalyst markedly lost its acti vity for NO conversion after the hydrothermal pretreatment. The Pd-modifica tion of the Cu/H-MFI resulted in improved stability against the hydrotherma l treatment when loading Pd approximately 0.2-0.3 wt.%. The dealumination o f tetrahedral Al in MFI framework was completely prevented when loading Pd from 0.3 wt,% or higher. Further loading of Pd higher than 0.3% caused the larger crystallite size upon pretreatment as seen from the scanning electro n micrographs (SEM). It has been suggested that there may be some changes i n Pd and Cu on H-MFI, such as alloying and/or palladium oxides formation, l eading to some loss of Cu2+ active species for NO removal. This results in the limitation of NO conversion improvement for the pretreated Pd/Cu/H-MFI with the loading amount of Pd higher than approximately 0.3%. (C) 2001 Else vier Science B.V. All rights reserved.