Catalytic cracking of supercritical n-dodecane over macro-meso-HZSM-5 coatings by vertical secondary growth. (15th June 2023)

• Record Type: Journal Article
• Authors: Rong, Di; Zhang, Jiaqi; Li, Hao; Guo, Wen; Sun, De; Diao, Zhenheng
• Is Part Of: Fuel. Volume 342(2023)
• Publication Date: 2023-06-15
• Subjects: Catalytic cracking -- Vertical growth -- Macro-meso-HZSM-5 coating -- Supercritical n-dodecane -- Dehydrogenation; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2023.127822
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: Macro-meso-HZSM-5 coating with grains endwise welding on basal layer was fabricated. NH4 + facilitated macropores formation and the pseudo-c-orientation of coatings. The structure breaks trade-off between diffusion and acidity, and enhances adherence. The coating showed excellent catalytic performance of n -dodecane cracking. The coating with Ga-MFI as seed showed high heat sink due to the dehydrogenation. Abstract: Hierarchical HZSM-5 zeolite coatings are extensively investigated for catalytic cracking of supercritical fuels to benefit the thermal management of hypersonic aircraft. However, there is still a challenge for preparing zeolite coatings combining the high diffusion property, strong mechanical strength and a large amount of Brønsted acid sites. Herein, the macro-meso-HZSM-5 coatings with meso-HZSM-5 grains vertically welding on the compact and randomly oriented zeolite basal layer were fabricated on the inner wall of the stainless-steel tubes by ammonia-assisted vertical secondary growth, using amphiphilic organosilane as a meso-porogen. The structure benefited the breaking of the trade-off between diffusion and acidity of the coating. And by adjusting the dosage of inorganic ammonium salt and the crystallization time, the synthesis mechanism of the coatings was speculated. Inorganic ammonium salt facilitated the formation of macropores and the vertical growth of crystals with ( 00 h )&( 10 h ) orientation (pseudo-c-orientation). The chemical composition of the seed layer was adjusted using Si-MFI, Al-MFI or Ga-MFI as seeds, and the mechanical strength was enhanced by the intergrowth of zeolite phase in the seed layer. The macro-meso-HZSM-5 coating synthesized with Al-MFI as the seed (MZC-Al-2N), exhibited an excellent catalytic conversion and stability for cracking of supercritical n -dodecane (550 °C and 4 MPa), with the initial reaction rate and the deactivation rate being three times and 52 % of the conventional HZSM-5 coating, respectively, due to the combination of the improved diffusion property as well as the suitable acidity. The coating synthesized using Ga-MFI seed showed a lower activity, but a higher heat sink compared with MZC-Al-2N, probably due to the dehydrogenation of light alkanes over the synergistic effect between the Brønsted acid sites and the extra-framework Ga species.