Benzenoid Aromatics from Renewable Resources

In this Review, all known chemical methods for the conversion of renewable resources into benzenoid aromatics are summarized. The raw materials that were taken into consideration are CO2; lignocellulose and its constituents cellulose, hemicellulose, and lignin; carbohydrates, mostly glucose, fructose, and xylose; chitin; fats and oils; terpenes; and materials that are easily obtained via fermentation, such as biogas, bioethanol, acetone, and many more. There are roughly two directions. One much used method is catalytic fast pyrolysis carried out at high temperatures (between 300 and 700 °C depending on the raw material), which leads to the formation of biochar; gases, such as CO, CO2, H2, and CH4; and an oil which is a mixture of hydrocarbons, mostly aromatics. The carbon selectivities of this method can be reasonably high when defined small molecules such as methanol or hexane are used but are rather low when highly oxygenated compounds such as lignocellulose are used. The other direction is largely based on the multistep conversion of platform chemicals obtained from lignocellulose, cellulose, or sugars and a limited number of fats and terpenes. Much research has focused on furan compounds such as furfural, 5-hydroxymethylfurfural, and 5-chloromethylfurfural. The conversion of lignocellulose to xylene via 5-chloromethylfurfural and dimethylfuran has led to the construction of two large-scale plants, one of which has been operational since 2023.

In Situ Synthesis of Metal-Containing ZSM-5 and Its Catalytic Performance in Aromatization of Methanol

Metal-containing ZSM-5 zeolites, denoted as M/ZSM-5 (M = Ga, Zn, and La), were prepared by an in situ synthetic method. The structural, textural, and surface acid properties of M/ZSM-5 were characterized by XRD, N₂ adsorption-desorption, NH₃-TPD, and FT-IR. The catalyst pore size and the distribution of strong acid and weak acid were affected by the introduction of metal. Considering the methanol-to-aromatics model reaction, the catalytic performance of these samples was investigated in a fixed bed reactor under the conditions of 450 °C and a liquid weight hourly space velocity (WHSV) of 5 h^-1. The results indicated that the Zn/ZSM-5 molecular sieve was most beneficial to aromatization; the relationship between the change of B/L caused by Zn content and aromatics selectivity was further studied. When the B/L value decreased, the selectivity of aromatics showed an initial increase and then a decrease. The B/L value was optimal, and the aromatics yield was the highest when the Zn loading was 0.35%.

Propane dehydrogenation over PtZn localized at Ti sites on TS-1 zeolite

PtZn localized at Ti sites on TS-1 zeolite exhibited high activity (58.09 mol_C3H6 g_Pt⁻¹ h⁻¹) and durability (k_d = 0.0158 h⁻¹, 96.8 h time on stream at 600 °C) for propane dehydrogenation.

Tandem catalysts for the conversion of methanol to aromatics with excellent selectivity and stability

A schematic diagram of the construction methods and reaction paths of different catalysts.

Synthesis, characterization, and catalytic application of hierarchical nano-ZSM-5 zeolite

Hierarchical nano-ZSM-5 zeolites (Z5-X) with different grain sizes were synthesized by varying amounts of 3-glycidoxypropyltrimethoxysilane (KH-560) in the hydrothermal synthesis strategy. Moreover, the conventional ZSM-5zeolite(Z5), which was prepared without KH-560, was used as the reference sample. The crystalline phases, morphologies, porous characteristics, Si/Al molar ratios and acidic properties of all fresh catalysts were characterized using the X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), scanning electron microscopy (SEM), N₂ adsorption–desorption, inductively coupled plasma atomic emission spectroscopy (ICP) and temperature programmed desorption of ammonia (NH₃-TPD) techniques. Results show that the grain size and strong acid amount of zeolite decreased with the increasing amount of KH-560. The micropore surface areas and the corresponding volume of Z5-X changed less compared with Z5. Consequently, the high shape-selectivity of zeolite was preserved well under the addition of KH-560. However, the mesopore surface areas and the corresponding volume increased significantly with the increasing amount of KH-560. Benefiting from the abundant hierarchical structure, the Z5-X catalysts exhibited a larger coke capacity than the Z5 catalyst. The coke depositions of all the deactivated catalysts were characterized by the thermogravimetric technique (TG), and the results are indicative of the decreased average rate of coke deposition with an increasing amount of KH-560, which could result from the gradually reduced strong acid amount and the nano-sized crystallites. The catalytic performance of methanol-to-aromatics (MTA) indicates that the Z5-0.12 catalyst exhibited higher catalytic activity and selectivity of BTX as the reaction was prolonged, which could result from the synergistic effect among the proper strong acid amount, the smaller zeolite grain size, and the abundant hierarchical structure.

The crystal size and strong acid amounts of ZSM-5 decrease and the mesopores increase with increasing of KH-560. High MTA catalytic performance could be obtained under synergistic effect of proper strong acid amount, smaller crystal size and abundant hierarchical structure.

Two-way desorption coupling to enhance the conversion of syngas into aromatics by MnO/H-ZSM-5

We herein report a composite catalyst containing partially reducible and highly active manganese oxide and nano-size H-ZSM-5 with short b-axis, prepared for the direct conversion of syngas into aromatics.

Direct conversion of syngas into light aromatics over Cu-promoted ZSM-5 with ceria–zirconia solid solution

Syngas conversion with 72.1% selectivity to aromatics and 40.8% CO conversion was achieved over a copper and silica-modified ZSM-5 and ceria–zirconia solid solution bifunctional catalyst.

Transformation of Propane over ZnSnPt Modified Defective HZSM-5 Zeolites: The Crucial Role of Hydroxyl Nests Concentration

A series of ZnSnPt supported defective MFI zeolites with different SiO2/Al2O3 ratios (30, 110, 700, and ∞) and hydroxyl nests concentration were prepared and characterized by multiple techniques including scanning electron microscopy (SEM), nitrogen physisorption, NH3-TPD, transmission electron microscopy (TEM), hydrogen temperature programmed reduction (H2-TPR), and Fourier transform infrared spectrometer (FT-IR). It was found that Brønsted acid sites (Si(OH)Al) with strong acid strength and the hydroxyl nests with weak acid strength coexisted over the defective ZSM-5 zeolites and ZnSnPt Lewis acid sites preferentially located on the hydroxyl nests. The increase in the concentration of hydroxyl nests and SiO2/Al2O3 ratios apparently improved the distribution of ZnSnPt Lewis acid sites. The hydroxyl nest incorporated ZnSnPt Lewis acid sites showed extraordinary dehydrogenation ability. Specially, operando dual beam Fourier transform infrared spectrometer (DB-FTIR) was applied to characterize the propane transformation under reaction conditions. At low SiO2/Al2O3 ratios, the propane efficiently transforms into propene and aromatics (total selectivity of 93.37%) by the cooperation of Brønsted acid sites and ZnSnPt Lewis acid sites. While at high SiO2/Al2O3 ratios, the propane mainly transforms into propene (selectivity of above 95%) and hydrogen. This study provides guidance for the preparation of highly efficient propane dehydrogenative transformation catalyst.

A highly active and stable Zn@C/HZSM-5 catalyst using Zn@C derived from ZIF-8 as a template for conversion of glycerol to aromatics

Zn@C/HZSM-5 showed excellent catalytic activity (54.7% aromatics yield) and high catalytic stability (8.5 h lifetime) due to the synergy between ZnOH⁺, intra-crystalline mesopores and HZSM-5 zeolite.

Enhanced ethene to propene ratio over Zn-modified SAPO-34 zeolites in methanol-to-olefin reaction

The enrichment of incorporated Zn-related species and the accommodation of facilitated aromatics impose increased diffusion restriction for bulky hydrocarbons, thus contributing to significant improvements in ethene selectivity and ethene to propene ratio over Zn modified SAPO-34 zeolites.