The NO SCR (selective catalytic reduction) activity with H-2 in the presence of excess O-2 was investigated over Pd/MFI catalyst prepared by sublimation method. With GHSV = 90 000 h(-1), a very high steady-state conversion of NO to N-2 (70%) is achieved at 100 degreesC. Significant reorganizations take place inside the catalyst upon its first contact with all reactants and products at the reaction temperature. Pd-o, which has a significant role in the NO-H-2-O-2 reaction, is possibly the active site for NO reduction. The formation of Pd-beta hydride deactivates the catalyst for NO reduction. Throughout the entire NO-H-2-O-2 reaction, no N2O or NO2 is formed; N-2 is the only N-containing product. The presence of O-2 inhibits the formation of undesirable NH3. The rate of the NO + H-2 reaction is fast or comparable to that of the H-2 + O-2 reaction. The oxidation of Pd-o and subsequent agglomeration of PdO are responsible for the decreased NO reduction activity at high temperature. (C) 2002 Elsevier Science Ltd. All tights reserved.