Low-silica chabazite zeolites for NOx reduction: Tailoring the active center of Cu2+-2Z and [Cu(OH)]+-Z through the regulation of CHA-cages opening

Low-silica chabazite (CHA) catalysts with varying configurations of Cu 2+ -2Z and [Cu(OH)] + -Z active centers are developed through the regulation of the opening of CHA-cages. The catalysts are subsequently applied to the selective catalytic reduction of NO x by NH 3 (NH 3 -SCR) reactions. A series of characterizations and performance evaluations indicate that the density of [Cu(OH)] + -Z in eight-member rings (8MRs) is positively correlated with low-temperature performance. Moreover, the presence of partial Cu 2+ -2Z in six-member rings (6MRs) enhances activity and tolerance at high temperatures. The residual K + ions in the CHA-cages after NH 4 + exchange are retained in the 6MRs. Density functional theory calculations demonstrate that the residual K + ions stabilize the 6MRs structure, ensuring the entry and stable presence of the active Cu 2+ -2Z centers. In situ analysis reveals the reaction intermediates involved in the NH 3 -SCR process on representative catalysts. These findings can further elucidate the active centers of CHA-type catalysts and guide the design of commercial catalysts.