Bimetal Ni-Pd Immobilizing into the Hierarchical Beta Zeolite synthesized by using Steam Assisted Conversion Method and Mesoporous Silica KIT-6 and its catalytic application in a Tandem Organic Reaction

Zeolite Beta exhibits remarkable catalytic performance in reactions involving relatively bulky compounds as those involved in Fine Chemistry reactions. Nevertheless, when the molecular size of the latter approaches or is even larger than the micropores of Beta zeolite, important diffusional and/or steric hindrances may appear. A high interest has emerged in past years for the development of hierarchical zeolites, featuring mesoporosity and therefore enhanced accessibility. When used as catalysts, hierarchical zeolites present usually lower steric and diffusional limitations [1]. A hierarchical mesoporous network of Beta zeolite with very high micropore as well as mesopore volume has been synthesized by using Steam-Assisted Conversion (SAC) to induce a burst of nucleation in presence of the organic template (tetraethylammonium hydroxide, TEAOH). Moreover, the mesoporous silica KIT-6 has been applied as a silica source. Physicochemical properties of the resulting samples have been investigated by XRD, SEM, BET, TG, FT-IR, DLS, NH3-TPD and DRS-UV. These characterizations show that using the SAC method incorporation with mesoporous silica KIT-6 led to hierarchical crystalline Beta zeolite with a small crystal size. Here, water plays a pivotal role in the crystallization mechanism, providing for a pool of concentrated nutrients affording fast nucleation, as well as for the recrystallization into ordered, more extended crystallite networks. A complete transformation of silica precursors into zeolite beta materials is thus only possible if the amount of water present in the reactor exceeds the requirements for simple saturation because water condensation in the gel is necessary. Thus, the amount of water needs to be adjusted not only for a specific temperature and reactor volume, but also for the sample loading [2]. This zeolite possesses large surface area (630 m2/g) and mesoporous volume (0.59 cm3/g) resulted from the formation of intercrystalline mesopores and the small crystal size. This hierarchical zeolite was used as acid-metal bi-functional heterogeneous catalysts in a tandem Suzuki-reduction reaction. The catalyst showed a superior activity in the water/ethanol solvent with high reusability.