Effect of weak base modification on ZSM‐5 catalyst for methanol to aromatics

Abstract

The effect of weak base modification on the catalytic performance of ZSM-5 catalyst for conversion of methanol to aromatics was investigated. The catalysts were characterized using X-ray diffraction, X-ray fluorescence, N 2 adsorptiondesorption, NH 3 temperature-programmed desorption, Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetry. The results showed that catalysts treated with weak base (NaHCO 3 , Na 2 CO 3 and NH 3 ⋅H 2 O) exhibited a pore structure with interconnected micropores and mesopores. The existence of mesopores was beneficial for improving the diffusion of reactants and products, and the coke deposition resistance capacity of treated catalysts was enhanced greatly. Meanwhile, compared to traditional ZSM-5 zeolite, the ratio of Brønsted to Lewis (B/L) acid sites of ZSM-5/NH 3 ⋅H 2 O (B/L = 7.35) zeolite slightly increased but the amount of acid sites reduced, while those of ZSM-5/NaHCO 3 (B/L = 0.127) and ZSM-5/Na 2 CO 3 (B/L = 0.107) significantly reduced. Further, the catalyst treated with NH 3 ⋅H 2 O solution was evaluated in the methanol to aromatics reaction and led to an enhanced aromatization reaction rate. The liquid hydrocarbons product distribution exhibited higher aromatic hydrocarbons yield (56.12%) and selectivity (40.28%) of benzene, toluene and xylene (BTX) with isoparaffin content reducing to 26.17%, which could be explained by appropriate B/L acid sites ratio, higher pore volumes and higher surface area.

Effect of ketene additive and Si/Al ratio on the reaction of methanol over HZSM‐5 catalysts

“…A wide range of mesoporous material contain silicate and aluminosilicate solids such as MCMs, SBA series and zeolites has been developed as useful catalysts for industrial processes . The hydrated aluminosilicate minerals are referred to as zeolites that consist of SiO 4 and AlO 4 tetrahedral as primary building units, connected by sharing one oxygen atom between two tetrahedral to form 3D frameworks.…”

“…The MTG mechanism has been under scrutiny for decades. From theoretical point of view, a series of mechanisms have been proposed for each step of MTG process during these years . Blaszkowski and van Santen considered two different pathways for dimethyl ether formation from surface methoxy intermediate or associative mechanism.…”

Insight into the Selection of the Post-Treatment Strategy for ZSM-5 Zeolites for the Improvement of Catalytic Stability in the Conversion of Methanol to Hydrocarbons

“…On the contrary, the produced extra-framework Al during alkali treatment promoted the isomerization, hydrogen transfer, and cracking reactions to form the coke deposition, leading to the decrease in lifetime. Moreover, the aromatics selectivity decreased because of the decreased B / L ratio of catalysts . In terms of the synthesis of ZSM-5, the synthesis yield of nano-ZSM-5 was low, and alkali treatment would further reduce the yield .…”

State of the Art and Perspectives of Hierarchical Zeolites: Practical Overview of Synthesis Methods and Use in Catalysis

“…Interestingly, the ZSM-5 catalyst also showed a higher selectivity toward benzene-toluene-xylene (BTX). [74] Zhang et al systematically studied desilication with different alkali-metal hydroxides such as LiOH, NaOH, KOH, and CsOH. All of them effectively created mesoporosity.…”