Different Sn/H-zeolite (β, MOR, SSZ-13, FER, and Y zeolite) catalysts are prepared with the improved impregnation method. The effects of reaction temperature and the composition of the reaction gas (ammonia, oxygen, and ethane) on the catalytic reaction are investigated. Adjusting the fraction of ammonia and/or ethane in the reaction gas can effectively strengthen the ethane dehydrogenation (ED) route and ethylamine dehydrogenation (EA) route and inhibit the ethylene peroxidation (EO) route, whereas the adjustment of oxygen cannot effectively promote acetonitrile formation because it cannot avoid enhancing the EO route. By comparing the acetonitrile yields on different Sn/H-zeolite catalysts at 600 °C, it is revealed that the ammonia pool effect, the residual Brönsted acid in the zeolite, and the Sn-Lewis acid synergistically catalyze ethane ammoxidation. Moreover, a higher L/B ratio of the Sn/H zeolite is beneficial to the improvement of acetonitrile yield. With a certain application potential, the Sn/H-FER-zeolite catalyst shows an ethane conversion of 35.2% and an acetonitrile yield of 22.9% at 600 °C; although a similar catalytic performance was observed on the best Co-zeolite catalyst in literature, the Sn/H-FER-zeolite catalyst is more selective to ethene and CO than the Co catalyst. In addition, the selectivity to CO2 is less than 2% of that on the Sn-zeolite catalyst. This may be attributed to the special 2D topology and pore/channel system of the FER zeolite, which guarantee an ideal synergistic effect of the ammonia pool, the residual Brönsted acid in the zeolite, and the Sn-Lewis acid for the Sn/H-FER-catalyzed ethane ammoxidation reaction.
Keywords: Lewis acid sites; Sn-zeolite catalysts; ammonia pool; ethane to acetonitrile; reaction mechanism.