HZSM-5/MCM-41 composite molecular sieves for the catalytic cracking of endothermic hydrocarbon fuels: nano-ZSM-5 zeolites as the source

Abstract

A series of HZSM-5/MCM-41 composite molecular sieves (HZM-Ns (x)) were prepared by employing nano-ZSM-5 zeolites with the SiO 2 /Al 2 O 3 ratios (x) of 50, 100 and 150 as the source. These materials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, N 2 adsorptiondesorption measurement, and NH 3 temperature-programmed desorption. The catalytic cracking of endothermic hydrocarbon fuels over the HZM-Ns with ndecane as model was evaluated at atmospheric pressure and 500°C. The effect of the parent zeolite, mesopore and SiO 2 /Al 2 O 3 ratio on the structure, acidity, and catalytic performance of HZM-Ns was investigated. The HZM-Ns exhibited a skeletal matrix with nano-sized HZSM-5 particles (200-300 nm) with a controllable acidity well dispersed in and microporous-mesoporous hierarchical pores. The mesoporous structure improved the diffusion of the reactants and products in the pores, and the HZSM-5 nanoparticles uniformly dispersed in the MCM-41 matrix supplied a proper acidity, shorter channels, and a higher specific surface area for reaction. These resulted in a high catalytic activity, a high selectivity to light olefins and a long lifetime for n-decane catalytic cracking. The HZM-N (150) exhibited the excellent conversion, a high selectivity to light olefins and a long lifetime due to low diffusion resistance, high specific surface area, and appropriate acid distribution and strength, with the increasing SiO 2 / Al 2 O 3 ratio.

Bulk and composite catalysts combining BEA topology and mesoporosity for the valorisation of furfural

“…In a different approach, the crystallite sizes of zeolites can be reduced down to the nanometer scale, which is accompanied by enhanced surface area/micropore volume ratios, leading to reduced intracrystalline diffusional pathways, avoiding mass transfer limitations and extensive coke formation. [31][32][33][34][35] Nevertheless, concerns about the health and environmental effects of using nanoparticles 36 , and technical issues (e.g. high pressure drops, clogging of equipments), place demands on the development of effective nano-catalyst formulations.…”

Strategies to Enhance the Catalytic Performance of ZSM-5 Zeolite in Hydrocarbon Cracking: A Review

“…After addition of MCM-41, ZSM-5@MCM-41 composite exhibited more appropriate acid distribution and strength, shorter pathway length and higher external surface area. The conversion of n-decane cracking increased from 61.7 to 93.0% and it maintained at 89.3% after reaction for 170 min, while that of the parent ZSM-5 was just 56.4% [24]. When it was applied in n-dodecane cracking, the conversion increased by 25% and it kept a stable activity within 30 min [35].…”

“…the diffusion of molecule and the accessibility of acid sites in the micropores of ZSM-5 zeolite, thus enhancing the catalytic activity of ZSM-5 zeolite [34]. ZSM-5@MCM-41 composite zeolite was prepared by treating ZSM-5 zeolite with sodium hydroxide solution, and then the dissolved silica and aluminum were recrystallized on the surface of ZSM-5 zeolites in the form of MCM-41 in the presence of cetyltrimethylammonium bromide (CTAB) [23][24][25]35]. After addition of MCM-41, ZSM-5@MCM-41 composite exhibited more appropriate acid distribution and strength, shorter pathway length and higher external surface area.…”

Core‐shell structured HZSM‐5@mesoSiO2 catalysts with tunable shell thickness for efficient n‐butane catalytic cracking

“…[13][14][15][16][17][18] Specific in chemical reactions, boosting the reaction efficiency based on wettability regulation has been successfully demonstrated in photocatalysis, 19 electrocatalysis, 20 organic synthesis, 21 and so on. On this basis, given the nonpolar property of alkanes, the parallel-sequence reaction characteristics of hydrocarbon catalytic cracking, 22,23 and widely-used microporous zeolites, the design of core-shell structure based catalyst is proposed in the present work. In detail, microporous silica-alumina HZSM-5 and mesoporous SiO 2 were used as core and shell, respectively.…”