The Synthesis, Characterization And SCR Performance Of Core-shell Structure Cu-Ce-La-SSZ-13

Ammonia selective catalytic reduction?NH₃-SCR?technology is one of the most effective methods to remove nitrogen oxides.In recent years,Cu-SSZ-13 has been widely used in the field of denitrification catalysis due to its excellent catalytic performance and significantly enhanced hydrothermal stability.In this study,Ce and La were used to modify Cu-SSZ-13,and the synergistic effect of metal ions was studied.Meanwhile,the modified zeolites were coated with different shells by two methods and their catalytic activities were also investigated.Cu-SSZ-13,Cu-Ce-SSZ-13 and Cu-Ce-La-SSZ-13 were prepared with Copper amine complex?Cu-TEPA?as a template,and Cu-Ce-La-SSZ-13 shows stronger catalytic performance and stability.It was found that the introduction of Ce and La cations can enhance the activation ability of isolated copper ions in different atmosphere.Besides,the introduction of Ce and La still can make Cu ions occupied for more active in the SCR reaction at a site?and site?,thereby increasing the speed of SCR reaction.The coordination of different ions was studied,and the results showed that the introduction of Ce and La could make the active copper component exist in the state of isolated ions rather than in the form of oxide.By means of secondary crystallization,Cu-Ce-La/SSZ-13@silicalite-1 molecular sieve with both CHA and MFI crystal types was successfully prepared.By controlling the amount of growth fluid of the shell molecular sieve,core-shell molecular sieve with different shell thickness was constructed.The catalytic test and thermogravimetry characterization?TG?proved that silicalite-1 shell can enhance the water resistance of Cu-Ce-La/SSZ-13.In addition,the introduction of silicalite-1 shell allowed the active components to exist in the CHA framework in the form of Cu⁺/Cu²⁺and changed the acidic sites on the catalyst surface,thus affecting the absorption of NH₃.Similarly,Cu-Ce-La/SSZ-13 as the core phase molecular sieve was successfully coated by meso-SiO₂ shell in the ethanol/ammonia water/water system by self-assembly.BET test showed that the catalyst possessed both microporous and mesoporous structures.By changing the amount of ethyl orthosilicalite,Cu-Ce-La/SSZ-13@meso-SiO₂ molecular sieve with different shell thickness were constructed.X-ray diffraction test?XRD?and BET test showed that the order of shell layer decreased continuously and the pore diameter of mesoporous hole decreased continuously with the increase of shell thickness.In addition,high temperature calcination and solution-self-assembly could cause the migration of core-shell molecular sieve ions,while metal ions mostly existed in the framework of SSZ-13.Both TG and catalytic property tests confirmed that meso-SiO₂ enhanced the water resistance of SSZ-13...