Temperature programmed experiment and in-situ IR experiment were performed to study the mechanism of selective catalytic reduction of NO by propylene over Cu-ZSM-5 zeolites and the interaction between the active sites of catalyst and reactants. NO interacts only with copper ion of Cu-ZSM-5, while $C_3H_6$ interacts with copper ion and the acid site of zeolite. After the reaction (NO 3330 ppm, $C_3H_6$ 3330 ppm, $O_2$ 6.67 %, flow rate 30 ㎤/min) at 350℃, TPD (Temperature Programmed Desorption), TPO (Temperature Programmed Oxidation) and TPRX (Temperature Programmed Reaction) of NO experiment were carried out to find out the reactivity between surface intermediates with NO or $O_2$. Not any products were detected after contacting NO or $O_2$ with surface intermediate between 350 and 400℃. In TPO spectrum, the peaks arising from $N_2$ and $CO_2$ were produced after reaction of surface intermediate with $O_2$ at 530℃. In the TPO spectrum of surface intermediate formed after reaction $C_3H_6$ and NO with Cu-ZSM-5 at 350℃, the peaks arising from $N_2$ and $CO_2$ were observed at 400℃. In the TPO spectrum of surface intermediate formed after reaction of $C_3H_6$ with Cu-ZSM-5 at 350℃, the peak arising from $CO_2$ was observed at 400℃. The surface intermediate formed after reaction of propylene and oxygen with Cu-ZSM-5 at 350℃, the $CO_2$ peak observed at 470℃. After SCR reaction with H-ZSM-5 at 350℃, the TPO spectrum shows the continuous increase in $P_CO2$ and $P_N2$ up to 700℃. The data indicates the different surface intermediates are formed at different conditions.
The IR spectrum of surface intermediate after SCR reaction with Cu-ZSM-5 at 350℃ for 1h shows two bands at 2250 and 2165 $cm^{-1}$. In order to verify the reactivity of these peaks with NO or $O_2$, NO and $O_2$ were introduced to the catalyst after SCR reaction respectively, but these peaks existed. Compared with $C_2H_4$ reductant which had no coke on the catalyst after reaction and H-ZSM-5 catalyst which had no copper ion, there were no peaks at 2250 $cm^{-1}$ and 2165 $cm^{-1}$ According to the IR spectrum of propylene at 350℃, $C_3H_6$ was adsorbed molecularly at the reaction temperature. Propylene seemed to be preferentially adsorbed on copper site rather than NO indicated by the IR spectrum of the mixture of $C_3H_6$ and NO adsorbed on Cu-ZSM-5. From the spectra of TPO and IR, it was suggested that the reaction intermediate could be formed from NO and $C_3H_6$.
Based on the results of experiment, the proposed mechanism was discussed.
