The effect of the trivalent framework atoms (Si⁴⁺/M³⁺ = 13-105) in Cu exchanged CHA-type zeolites was investigated for the selective catalytic reduction of NO with NH₃. While the increased hydrophobicity of B-CHA compared to Al-CHA could make it a good candidate for low temperature SCR, the material was too unstable under reaction conditions and the exchanged Cu²⁺ did not remain isolated. Consequently a lower activity and selectivity than for Al-CHA were observed. Ga-CHA on the other hand showed a similar Cu²⁺ speciation as Al-CHA at similar Si⁴⁺/M³⁺ ratios. The difference in catalytic activity was remarkably small. While Ga-CHA was less stable upon hydrothermal aging, this was markedly improved by increasing the Si/Ga ratio and by inserting the Cu²⁺ during the synthesis of the zeolite. Remarkably, the Cu-loaded Ga-CHA catalysts demonstrated a consistently lower selectivity to N₂O by-product formation compared to Al-CHA because of a lower tendency for NO oxidation.

研究了Cu 交换 CHA 型沸石中三价骨架原子 (Si ⁴⁺ /M ³⁺ = 13-105) 对用 NH ₃选择性催化还原 NO 的影响。虽然与 Al-CHA 相比，B-CHA 增加的疏水性使其成为低温 SCR 的良好候选者，但该材料在反应条件下太不稳定，并且交换的 Cu ²⁺不会保持分离。因此，观察到比 Al-CHA 更低的活性和选择性。另一方面，Ga-CHA在相似的 Si ⁴⁺ /M ^{3+ 下}表现出与Al-CHA相似的 Cu ²⁺形态比率。催化活性的差异非常小。虽然Ga-CHA 在水热老化时稳定性较差，但通过增加Si/Ga 比和在沸石合成过程中插入Cu ^{2+ 可以}显着改善这一点。值得注意的是，与 Al-CHA 相比，负载 Cu 的 Ga-CHA 催化剂对 N ₂ O 副产物形成的选择性始终较低，因为 NO 氧化的趋势较低。