Synthesis, structural and acidity characterizations of the large-pore zeolite SSZ-42 for controlling cold-start emissions

Na-SSZ-42 (a boralite with Si/B = 14) was synthesized and ion-exchanged to obtain H-SSZ-42, and both were tested as hydrocarbon traps for reducing cold-start emissions. This investigation was carried out by the temperature-programmed desorption technique using toluene as a heavy (aromatic) and ethylene as a light (olefin) probe molecules present in the exhaust stream at engine cold-start. These solids were also characterized by a variety of techniques including FTIR of adsorbed pyridine and thermodesorption of ammonia to investigate their acidity and XRD, SEM, 11B MAS NMR and BET to study their structural properties. The thermodesorption of ammonia along with FTIR of adsorbed pyridine indicated acid sites with low strength in these two materials due to presence of boron atoms as trivalent element in their lattice. 11B MAS NMR confirmed most of the boron was incorporated as tetrahedral BO4 units in the framework. These two materials showed remarkably high adsorption capacity for both ethylene and toluene, with very special behaviour in presence of H2O and/or CO2 which are present in exhaust gases. Indeed the adsorption capacity of both sorbates was not significantly affected by the presence of H2O and CO2 molecules.