3D-printed monoliths based on Cu-exchanged SSZ-13 as catalyst for SCR of NOx

The Selective Catalytic Reduction (SCR) with ammonia is the current technology to remove nitrogen oxides (NOx) from lean-burn diesel engine exhaust. The SCR unit is located downstream of the diesel particulate filter (DPF) where the temperature could reach up to 650 °C and the SCR catalyst can be easily damaged in the presence of steam generated from the combustion of diesel fuel. Zeolite based catalysts are tolerant to high temperature and show a good resistance to alkali metal poisoning due to their high surface area and strong acidity. Small-pore zeolites, such as Cu-SSZ-13, have better NH3-SCR performance due to higher concentration of active sites, higher hydrothermal stability, poisoning tolerance and better N2 selectivity than other zeolites. The introduction of a Cu-exchanged ZSM-5 into a geo-polymeric matrix of a monolith sample produced by Direct Ink Writing (DIW) led to very promising results in the SCR process related to the hierarchical porosity generated by the intimate contact between a microporous and a macro-mesoporous material. In this work, a Cu-exchanged commercial SSZ-13 has been preliminary tested as pure powder zeolite in order to define the suitable cation exchange procedure and to assess the intrinsic catalytic activity in the NH3-SCR of NOx. Then, the suitable formulation of the ink to print 3D monoliths containing up to 60% SSZ-13 was investigated and modified with respect to that previously used for ZSM-5. Eventually, the definite copper exchange protocol has been extended to the 3D monolith. Both powder and monolith catalysts have been widely characterized to investigate the stability of the SSZ-13 structure in the geo-polymeric matrix and the nature of copper, determining the properties associated to the best activity and selectivity.