Effect of the nature and location of copper species on the catalytic nitric oxide selective catalytic reduction performance of the copper/SSZ-13 zeolite

The nature and location of copper in Cu/SSZ-13 zeolites synthesized by using a one-pot hydrothermal approach with Cu-tetraethylenepentamine as a template and by the ion exchange of SSZ-13 were investigated by applying H ₂-temperature-programmed reduction, FTIR, EPR, and in situ Raman spectroscopic techniques. The one-pot synthesized Cu/SSZ-13 zeolite contains predominantly isolated copper ions in the large cages, whereas copper species in the ion-exchanged Cu/SSZ-13 zeolite occupy sites in the large cages of the chabazite (CHA) structure and the six-membered rings of the CHA structure. If the one-pot synthesized Cu/SSZ-13 zeolite is exchanged with the NH ₄NO₃ solution in addition to the removal of a part of copper ions, the remaining copper ions in the CHA structure relocated from the large cages to the six-membered rings. Isolated copper dominated in all Cu/SSZ-13 zeolites. The in situ Raman spectra demonstrated that Cu-O-Cu dimers form at higher copper content. The bis-μ-oxo dicopper(III) complex is observed only in the ion-exchanged sample upon dehydration. The higher NO selective catalytic reduction activity of the one-pot synthesized sample in a wide temperature range appears to be due to the predominance of isolated Cu ²⁺ sites in the large cages, and their higher reactivity is possibly owing to the lower stability of Cu²⁺ at these sites. Copper in uniform: Temperature-programmed reduction of hydrogen and Raman spectroscopy of Cu/SSZ-13 zeolites reveal that copper species are more uniformly speciated in the one-pot synthesized sample (OP; Cu/Al=0.37), which demonstrates higher activity in a wide temperature range than does the ion-exchanged sample (IE; Cu/Al=0.36).