Performance of hierarchical HZSM-5 zeolites prepared by NaOH treatments in the aromatization of glycerol

Abstract

A series of hierarchical HZSM-5 zeolites were prepared by post-synthesis modification of conventional bulk crystals of HZSM-5 zeolite with NaOH solution at different concentrations. These micro-mesoporous composite molecular sieves were characterized by powder Xray diffraction (XRD), Transmission electron microscopy (TEM), N 2 adsorption, Fourier transform infrared (FT-IR) spectroscopy techniques and pyridine FT-IR to investigate the changes in crystallinity, acidity, morphology and textural property of HZSM-5 zeolite 10 before and after alkaline treatment. The catalytic performances of these hierarchical HZSM-5 zeolites were evaluated by the aromatization of glycerol with methanol as the solvent, which was a promising route to convert renewable glycerol and methanol into high valuable aromatics. Substantial mesoporosity with sizes centered at around 4 nm could be generated for HZSM-5 zeolites after treated by mild NaOH solution (≤0.4 M), coupled with better retained microporosity, resulting in great improvements in catalytic life time and selectivity to BTX aromatics during the reaction of glycerol to aromatics. Though the larger mesopore surface areas were 15 achieved when treated NaOH concentrations were higher than 0.5 M, the HZSM-5 structure was partly damaged, leading to the reduction of catalytic life time and selectivity to BTX aromatics. The HZSM-5 treated with 0.3 M NaOH solution was found as the optimum catalyst for the transformation of glycerol/methanol to aromatics, producing nearly twofold increase in BTX aromatics (carbon yields of 25.18%) and threefold improvement in catalyst life time (12.5 h) than the parent microporous HZSM-5 (13.9% carbon yields of BTX aromatics and 4h). These improved catalytic performances are mainly attributed to the optimized bimodal micro-mesoporous HZSM-5 20 zeolite during the alkali treatment, which retained sufficient micropores that have the capacity of aromatization while created more mesopores that could shorten the average diffusion path lengths, increase the accessibility to the acid sites and facilitate the transportation of large molecular (e.g. glycerol and carbon precursors) during the aromatization of glycerol.

Kinetics of glycerol conversion to hydrocarbon fuels over Pd/H‐ZSM‐5 catalyst

“…A mechanism of sequential hydrodeoxygenation (HDO) and aromatization was proposed for GTH conversion. Similar works, using catalysts such as PdO/H‐ZSM‐5, Zn/H‐ZSM‐5, and Sn/H‐ZSM‐5, have also been reported …”

Selective Production of Benzene, Toluene and p‐Xylene (BTpX) from Various C1‐3 Feedstocks over ZSM‐5/Silicalite‐1 Core‐Shell Zeolite Catalyst

“…Alkylation and disproportionation of toluene are another route to produce xylenes. So far, zeolite catalysts for BTX synthesis from C 1‐3 feedstocks like methanol (MeOH), dimethyl ether (DME), ethanol (EtOH), acetone and so on have been widely studied . However, separation of p ‐xylene from other isomers is a serious issue because the difference in boiling points between them is too small to separate them by distillation.…”

“…So far, zeolite catalysts for BTX synthesis from C 1-3 feedstocks like methanol (MeOH), dimethyl ether (DME), ethanol (EtOH), acetone and so on have been widely studied. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] However, separation of p-xylene from other isomers is a serious issue because the difference in boiling points between them is too small to separate them by distillation. So far, adsorption and crystallization have been used for separation of p-xylene from isomers.…”

MFI Acid Catalysts with Different Crystal Sizes and Porosity for the Conversion of Furanic Compounds in Alcohol Media

“…For MZS0.6, the ratio of L/B increased slightly relative to that of commZS, whereas L+B did not increase. During the desilication process, the amounts of L and B acid sites may change: for example, L acid sites may be formed during the removal of framework Si species through Si−O−Al scissoring, B acid sites may be destroyed during the elimination of internal Si−OH groups, Al species may be extracted from the original framework and reinserted in more accessible (mesoporous) regions, which leads to accessible B acid sites (Si−OH−Al groups), and B acid sites may suffer dehydroxylation generating L acidity . The molar ratio of (L+B)/(Al concentration measured by ICP‐AES) is the same (0.61) for MZS0.2 and MZS0.6, which is interesting and could lead to postulating some type of compromise between (partial) dealumination and acidity after the post‐synthesis treatments (at this stage, we have no clear explanation).…”