In situ fabrication of core-shell-structured Beta@Silicalite-1 catalysts by a novel steam-assisted crystallization strategy

A green, cost-effective and facile steam-assisted crystallization (SAC) strategy was developed to synthesize core-shell-structured zeolite composites with different frameworks between the core and shell. Chemical incompatibility from different structures has been circumvented by dip-coating Silicalite-1 seeds and an in situ transformation process. Beta@Silicalite-1 zeolites with a nanoscale polycrystal Silicalite-1 shell wrapped around the monocrystal Beta core was synthesized. The crystallization process and synthetic parameters, such as the composition of the core, crystallization temperature and gel composition of the seed solution, were investigated. The results revealed the importance of stability of the core and the crystallization rate of the Silicalite-1 shell. Interestingly, a trace amount of aluminum in the core zeolite could help resist corrosion during crystallization. Further investigation on alkylation and etherification reactions over Beta@Silicalite-1 demonstrated the advantage in selectivity control toward self-etherification versus alkylation.