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.

Opening up ZSM-5 Hierarchical Zeolite's Porosity through Sequential Treatments for Improved Low-Density Polyethylene Cracking.

An adequately tuned acid wash of hierarchical ZSM-5 zeolites offers a levelling up in the catalytic cracking of low-density polyethylene. Identification of crucial and limiting factors governing the activity of the zeolite was extended with studies about the accessibility of acid sites, nature of the realuminated layer and role of Lewis acid sites. The sequential treatment of a ZSM-5 zeolite offered enhanced activity in low-density polyethylene (LDPE) cracking at low and high conversions, as confirmed by a decrease in the temperatures needed to reach 20% and 80% conversion (T20 and T80, respectively). A linear dependence of the T80 on the coupled IHF (indexed hierarchy factor) and AFB (accessibility factor) highlighted the importance of the textural and acidic parameters in the catalytic cracking of LDPE. Operando FT-IR-GC studies confirmed a higher fraction of short-chain hydrocarbons (C3-C5) in the product distribution of hierarchical catalysts resulting from the effective polymer cracking in easily accessible pores.

Evaluation of the Textural Parameters of Zeolite Beta in LDPE Catalytic Degradation: Thermogravimetric Analysis Coupled with FTIR Operando Studies.

Zeolite-based catalysts are globally employed in many industrial processes, such as crude-oil refining and bulk chemical production. In this work, the cracking of low-density polyethylene (LDPE) was thoroughly followed in a FTIR operando study to examine the catalytic efficiency of purely microporous zeolites of various textural characteristics. To provide complementary and valuable information on the catalytic activity of the zeolite studied, the thermogravimetric analysis results were compared with yields of the products generated under operating conditions. The reaction products were analyzed via GC-MS to determine the hydrocarbon chain distribution in terms of paraffin, olefins, and aromatics. The individual impact of textural and acidic parameters on catalytic parameters was assessed. The accumulation of bridging hydroxyls of high strength in the zeolite benefited the decrease in polymer decomposition temperature. Through a strategic comparison of purely microporous zeolites, we showed that the catalytic cracking of LDPE is dominated by the acidic feature inherent to the microporous environment.

Operando Study Reveals the Superior Cracking Activity and Stability of Hierarchical ZSM-5 Catalyst for the Cracking of Low-Density Polyethylene.

A new theoretical and practical framework has been developed through operando study of the zeolite catalytic cracking of low-density polyethylene (as a model reaction) under reaction conditions. Results show that microporous ZSM-5 gives rise to less cracking products. Hierarchical ZSM-5 zeolites are more active cracking catalysts, rendering more C2 -C5 hydrocarbons, with a delayed deactivation due to the secondary porosity. This tool in combination with thermogravimetric analysis provides complementary and valuable information for the study, and design of advanced catalysts.