Synthesis And Catalytic Performance Of Hierarchical Beta Nanozeolites Through Controllable Self-assembly

Recently, hierarchical nanozeolites have received much attention for its remarkable acid properties and short diffusion channel length, which is especially appropriate for the diffusion-limited reactions involving bulky molecules. However, controllable synthesis of micro-mesoporous hierarchical beta nanozeolites still remain a great challenge due to unclear understanding about zeolite formation mechanism. In the present work, new routes to design and produce better zeolite materials with desired physical and chemical properties are developed, and the assembly behavioars of zeolite precursors in different routes were investigated based on the zeolite crystal growth mechanism.To uncover the zeolite nucleation and growth mechanisms, we chose a zeolite beta clear solution hydrogel system as a model system and conducted SAXS, TEM, XRD and NMR analysis of the samples with extension of crystallization time. Experimental findings of zeolite crystal evolution revealed that the zeolite nucleation proceeds through condensed-step mechanism, gradually growing in size along three populations of particles and evolving in internal structure. Therefore, it is practical to controllably synthesize hierarchical beta nanozeolites from tailorable seeds.Hierarchical beta nanozeolites(HDZ-W) were controllably synthesized by tailoring seeds grafted with phenylaminopropyltrimethoxysilane(PHAPTMS). There were two roles of organosilane: the more-like mesoporogen agent and the growth inhibitor. In order to synthesize highly “soluble” beta nanocrystals(HDZ-O) for quasi-catalytic cracking, we further develop the synthesis medium by using organic medium. Catalytic cracking of JP-10 showed that suspensions containing HDZ-O and HDZ-W, especially the HDZ-O, can effectively promote the cracking performance, with cracking conversion and alkenes content 3.6 and 1.3, and 2.8 and 1.1 times of thermal cracking at 680 °C and 4 MPa, respectively.Hierarchical beta nanozeolites with intra-mesopore were synthesized by prepared by the flocculating action of a cationic polymer polydiallyldimethylammonium chloride(PDDA). Compared to conventional zeolite, the hierarchical beta nanozeolites exhibited new pore with diameter of 6 nm without loss of acid properties. The structure/acid properties and catalytic performance are also studied. The hierarchical zeolites exhibit an increase in conversion and a high content of gaseous yield, C3= and C4= fractions in n-decane cracking.Highly crystalline hierarchical Beta/MCM-41 composites were prepared through oriented attachment process of nano-objects assemble with CTAB under the assistance of ethanol. After the characteristic Bragg reflections of BEA-type zeolite appeared, the hydrothermal crystallization of the nano-building blocks assembled with CTAB through an oriented attachment mechanism was performed to obtain the bulk composites with beta nanocrystals embedded in MCM-41 mesoporous shell. The structure/acid properties and catalytic performance are also studied. Beta/MCM-41 composite exhibits an increase in conversion and a high content of gaseous yield, C3= and C4= fractions in n-decane cracking.