Progress in the synthesis of small-pore zeolites for purifying NOx from motor vehicle exhaust

SSZ-13 and SSZ-39, as eight-member zeolites with small pore size of ∼0.38 nm, show profound development potential in eliminating NOx emitted from lean-burn vehicles. When were loaded with metal active components such as Pd/Co/Cu, they can be applied as PNAs or SCR catalysts due to their excellent NOx adsorption capacity/catalytic activity as well as superior hydrothermal stability. This work systematically reviewed the research progress of getting the pure SSZ-13 and SSZ-39 phases by both traditional hydrothermal synthesis method and the newly-developed trans-crystallization, seed-assisted as well as solvent-free synthesis method. Moreover, the incorporation of Pd and Cu into zeolites via the route of impregnation, ion exchange or one-step synthesis was also summarized. Simultaneously, the existence and distribution state of metal species in SSZ-13 and SSZ-39 zeolites according to different introducing methods were elaborated. In a word, by comparing the advantages and disadvantages of different methods for obtaining pure or the metal-modified SSZ-13, SSZ-39 zeolites, it is sincerely hoped this review could provide some guidance for the large-scale industrial application of these useful zeolites.