Effect of preparation conditions on the morphology of Cu-SSZ-13 zeolites and their performance in the selective catalytic reduction of NO_x by NH₃

SSZ-13 zeolites were synthesized by conventional hydrothermal method and the Cu-SSZ-13 zeolite catalysts were then prepared by Cu ion-exchange and used in the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR); the effect of various preparation parameters including the organic template agent (OSDA) dosage, silicon source, aluminum source, H₂O/Si ratio, Si/Al ratio and aging time on the morphology, crystal size, acidity, state of Cu²⁺ sites and the catalytic performance of Cu-SSZ-13 in NH₃-SCR were investigated. The results indicate that silica sol (JN25) and Al₂(SO₄)₃ are appropriate as the silicon and aluminum sources, respectively, to prepare SSZ-13 zeolites with small crystals, high crystallinity and high activity in NH₃-SCR. With the increase of Si/Al ratio, the crystal size of SSZ-13 increases and the copper content loaded on Cu-SSZ-13 decreases, leading to the degradation of NH₃-SCR activity. A high H₂O/Si ratio of 88 is conducive to forming larger SSZ-13 crystals, whilst increasing the OSDA dosage is beneficial to improving the crystallinity, reducing the crystal size, and accordingly enhancing the catalytic activity of Cu-SSZ-13 in NH₃-SCR. In addition, a relatively longer aging time can also reduce the crystal size and raise the catalytic activity of Cu-SSZ-13. In particular, the Cu-SZ13-A10 zeolite catalyst synthesized with a Si/Al ratio of 10 (with the gel composition of 1SiO₂ : 0.01Al₂(SO₄)₃ : 0.3NaOH : 0.4SDA : 88H₂O; JN25 as silicon source and aging for 2 h) exhibits high activity in NH₃-SCR; under a high GHSV of 240000 h⁻¹, the NO conversion reaches 60% at 200 ℃ and keeps at 100% in the moderate-high temperature range. These results should be useful for the regulation of SSZ-13 zeolite morphology and the preparation of high efficient Cu-SSZ-13 catalysts for NH₃-SCR.