Abstract：Based on the principle that molecular sieve ZSM-5 can be highly hydrophobic by using a high Si/Al2 ratio, a silica rich H-ZSM-5 was used as the NO oxidation catalyst and its catalytic activity under various reaction conditions was investigated: relative humidity from 0 to 100%, reaction temperature from 10 to 90℃, and inlet NO concentration from 0.05% to 0.08%. H-ZSM-5 catalyzed NO oxidation efficiently in the presence of vapor. When the Si/Al2 ratio of H-ZSM-5 increased from 50 to 300, the steady-state NO oxidation conversion in wet NOx gas (H2O concentration was 1.18%) raised from 20% to 56%. The oxidation conversion in dry gas decreased monotonously as reaction temperature increased, and low temperature was favorable for NO oxidation. In wet gas (H2O concentration was 1.18%) the optimal reaction temperature for NO oxidation was 20℃, which was close to the temperature of NOx in exhaust gas. The NO conversion decreased when temperature was below or above. A 200h stability test was conducted at 30℃, with an inlet NO concentration of 0.08% and a space time of 0.5s. The NO oxidation conversion reached to 60% and 50%, when the relative humidity was 50% and 100%, respectively. ZSM-5 catalyst displayed high stability in saturated wet gas and it converted the waste gas into an optimum composition for alkali absorption of NOx.
