Synthesis of pillared nanosheet HZSM-5 zeolite films for catalytic cracking of supercritical n-dodecane

The chemical heat sink yielded by the catalytic cracking of supercritical hydrocarbons facilitates the thermal management of hypersonic aircraft. The objective of this study was to alleviate the diffusion restriction of su-percritical hydrocarbons in conventional microporous zeolite films. A dual template method involving different n (C22-6-6)/n (TPAOH) values was adopted to prepare pillared nanosheet HZSM-5 zeolite films by using seed assisted secondary growth. Compared with those of the parent nanosheet HZSM-5 zeolite film (ZN) prepared using only C22-6-6 as the structure directing agent (SDA), the zeolite film prepared using n (C22-6-6)/n (TPAOH) of 10/4 (DZN-4) after pillaring exhibited a higher surface area (525 m(2) g(-1)) and mesoporous volume (0.453 cm(3) g(-1)). A larger amount of TPAOH in the synthesized solution (n (C22-6-6)/n (TPAOH) < 10/6) induced the formation of a bulky microporous MFI crystal phase, thereby sacrificing the mesoporous structure. At 550 degrees C and 4 MPa, the DZN-4 zeolite film yielded the highest n-dodecane conversion rate (76.8%) and TOF value (130.9 s(-1)), due to the presence of highly accessible Bronsted acid sites and ordered mesoporous structures, leading to a heat sink of 2.99 MJ kg(-1), which is 32% higher than that under ZN. Restricted secondary reactions, such as hydride transfer and aromatization, were observed in the presence of highly connected mesopores designed by pillaring, leading to high and low selectivities toward olefins and aromatic compounds, respectively. Amorphous coke was detected on the external mesopore surface of DZN-4, and the adhesive strength was significantly enhanced, resulting in a higher catalytic stability.

Automated summary

Pillared nanosheet HZSM-5 zeolite films prepared using a dual template method exhibited higher surface area, mesoporous volume, heat sink, and catalytic stability compared to conventional microporous zeolite films, leading to improved thermal management and high conversion rates.