High-Silica Layer-like Zeolites Y from Seeding-Free Synthesis and Their Catalytic Performance in Low-Density Polyethylene Cracking.

Layer-like FAU-type zeolite Y was synthesized by an organosilane-assisted low-temperature hydrothermal method and its catalytic activity was verified in the low-density polyethylene (LDPE) cracking process. The synthesis procedure of high-silica layer-like zeolite Y was based on organosilane as a growth modifier, and for the first time, the seeding step was successfully avoided. The X-ray diffraction and electron microscopy studies, scanning electron microscopy and transmission electron microscopy confirmed the formation of pure FAU structure and zeolite particles of plate-like morphology arranged in the manner of the skeleton of a cuboctahedron. The in situ Fourier transform infrared (FT-IR) spectroscopic studies, low-temperature nitrogen sorption, and electron microscopy results provided detailed information on the obtained layer-like zeolite Y. The acidic and textural properties of layer-like zeolites Y were faced with the catalytic activity and selectivity in the cracking of LDPE. The quantitative assessment of catalyst selectivity performed in FT-IR/GC-MS operando studies pointed out that LDPE cracking over the layer-like material yielded value-added C3-C4 gases and C5-C6 liquid fraction at the expense of C7+ fraction. The detailed analysis of coke residue on the catalyst was also performed by means of FT-IR spectroscopy, thermogravimetric analysis, and thermoprogrammed oxidation coupled with mass spectrometry for the detection of oxidation products. The acidic and textural properties gave a foundation for the catalytic performance and coking of catalysts.

Synthesis and Characterisation of Hierarchically Structured Titanium Silicalite-1 Zeolites with Large Intracrystalline Macropores.

The successful synthesis of hierarchically structured titanium silicalite-1 (TS-1) with large intracrystalline macropores by steam-assisted crystallisation of mesoporous silica particles is reported. The macropore topology was imaged in 3D by using electron tomography and synchrotron radiation-based ptychographic X-ray computed tomography, revealing interconnected macropores within the crystals accounting for about 30 % of the particle volume. The study of the macropore formation mechanism revealed that the mesoporous silica particles act as a sacrificial macropore template during the synthesis. Silicon-to-titanium ratio of the macroporous TS-1 samples was successfully tuned from 100 to 44. The hierarchically structured TS-1 exhibited high activity in the liquid phase epoxidation of 2-octene with hydrogen peroxide. The hierarchically structured TS-1 surpassed a conventional nano-sized TS-1 sample in terms of alkene conversion and showed comparable selectivity to the epoxide. The flexible synthesis route described here can be used to prepare hierarchical zeolites with improved mass transport properties for other selective oxidation reactions.