Gas-Phase Carbonylation of Dimethyl Ether on the Stable Seed-Derived Ferrierite

Preparation of Fe-HMOR with a Preferential Iron Location in the 12-MR Channels for Dimethyl Ether Carbonylation

As the Brønsted acid sites in the 8-membered ring (8-MR) of mordenite (MOR) are reported to be the active center for dimethyl ether (DME) carbonylation reaction, it is of great importance to selectively increase the Brønsted acid amount in the 8-MR. Herein, a series of Fe-HMOR was prepared through one-pot hydrothermal synthesis by adding the EDTA-Fe complex into the gel. By combining XRD, FTIR, UV-Vis, Raman and XPS, it was found that the Fe atoms selectively substituted for the Al atoms in the 12-MR channels because of the large size of the EDTA-Fe complex. The NH3-TPD and Py-IR results showed that with the increase in Fe addition from Fe/Si = 0 to 0.02, the Brønsted acid sites derived from Si-OH-Al in the 8-MR first increased and then decreased, with the maximum at Fe/Si = 0.01. The Fe-modified MOR with Fe/Si = 0.01 showed the highest activity in DME carbonylation, which was three times that of HMOR. The TG/DTG results indicated that the carbon deposition and heavy coke formation in the spent Fe-HMOR catalysts were inhibited due to Fe addition. This work provides a practical way to design a catalyst with enhanced catalytic performance.

Improved catalytic performance in gas-phase dimethyl ether carbonylation over facile NH4F etched ferrierite

Gas-phase dimethyl ether (DME) carbonylation to methyl acetate (MA) initiates a promising route for producing ethanol from syngas. Ferrierite (FER, ZSM-35) has received considerable attention as it displays excellent stability in the carbonylation reaction and its modification strategy is to improve its catalytic activity on the premise of maintaining its stability as much as possible. However, conventional post-treatment methods such as dealumination and desilication usually selectively remove framework Al or Si atoms, ultimately altering the intrinsic composition, crystallinity, and acidity of zeolites inevitably. In this study, we successfully prepared a series of hierarchical ZSM-35 materials through post-treatment with NH4F etching, which dissolved framework Al and Si at similar rates and preferentially attacked the defective sites. Interestingly, the produced pore systems effectively penetrated the [100] plane, offering elevated access to both the 8-membered ring (8-MR) and 10-membered ring (10-MR) channels. The physicochemical and acid properties of the pristine and NH4F etched ZSM-35 samples were comprehensively characterized using various techniques, including XRD, XRF, FESEM, HRTEM, Nitrogen adsorption-desorption, NH3-TPD, Py-IR, 27Al MAS NMR, and 29Si MAS NMR. Under moderate treatment conditions, the intrinsic microporous structure, acid properties, and crystallinity of zeolite were retained, leading to superior catalytic activity and stability with respect to the pristine sample. Nonetheless, severe NH4F etching disrupted the crystalline framework and created additional defective sites, bringing about faster deposition of coke precursors on the interior Brønsted acid sites (BAS) and decreased catalytic performance. This technique provides a novel and efficient method to slightly enhance the micropore and mesopore volume of industrially pertinent zeolites through a straightforward post-treatment, thus elevating the catalytic performance of these zeolites.

The Oxygenate-Mediated Conversion of COx to Hydrocarbons─On the Role of Zeolites in Tandem Catalysis

Decentralized chemical plants close to circular carbon sources will play an important role in shaping the postfossil society. This scenario calls for carbon technologies which valorize CO2 and CO with renewable H2 and utilize process intensification approaches. The single-reactor tandem reaction approach to convert COx to hydrocarbons via oxygenate intermediates offers clear benefits in terms of improved thermodynamics and energy efficiency. Simultaneously, challenges and complexity in terms of catalyst material and mechanism, reactor, and process gaps have to be addressed. While the separate processes, namely methanol synthesis and methanol to hydrocarbons, are commercialized and extensively discussed, this review focuses on the zeolite/zeotype function in the oxygenate-mediated conversion of COx to hydrocarbons. Use of shape-selective zeolite/zeotype catalysts enables the selective production of fuel components as well as key intermediates for the chemical industry, such as BTX, gasoline, light olefins, and C3+ alkanes. In contrast to the separate processes which use methanol as a platform, this review examines the potential of methanol, dimethyl ether, and ketene as possible oxygenate intermediates in separate chapters. We explore the connection between literature on the individual reactions for converting oxygenates and the tandem reaction, so as to identify transferable knowledge from the individual processes which could drive progress in the intensification of the tandem process. This encompasses a multiscale approach, from molecule (mechanism, oxygenate molecule), to catalyst, to reactor configuration, and finally to process level. Finally, we present our perspectives on related emerging technologies, outstanding challenges, and potential directions for future research.

Enhancement of the dimethyl ether carbonylation activation via regulating acid sites distribution in FER zeolite framework

The carbonylation of dimethyl ether (DME) with CO is a key step for ethanol synthesis from syngas, but traditional mordenite (MOR) zeolite shows low catalytic stability. Herein, various FER zeolite nanosheets were prepared with four types of organic templates. The catalytic performance of FER in DME carbonylation is strongly dependent on the location of strong acid site in framework, which can be effectively regulated by altering organic template. FER-MORP sample synthesized with morpholine shows the highest DME conversion of 53%, thus, giving a methyl acetate space-time yield (STYMA) of 0.889 mmol g-1 h-1. DFT calculation, NH3-IR, 1H/27Al/29Si MAS NMR, and in situ DRIFTS results indicate that morpholine directs more Al species, or strong Brønsted acid sites (BAS), to locate in 8-membered ring (8-MR) channels, which not only enhances carbonylation activity but also suppresses formation of coke species. The catalytic performance is well maintained within 4 repeated recycles (∼460 h).

Activity Enhancement of Ferrierite in Dimethyl Ether Carbonylation Reactions through Recrystallization with Sodium Oleate

Methyl acetate (MA) has a wide range of applications as an important industrial chemical. Traditional MOR zeolite for carbonylation of DME to MA accumulated carbon easily because of a 12-membered ring (12 MR) channel. In this work, we innovatively developed the method of recrystallization ferrierite (FER) zeolite using special chelating ligand sodium oleate which can affect ions other than alkali metals. The characterization results of N₂ adsorption, transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR) show that hydrothermal recrystallization of ferrierite using sodium oleate resulted in a higher Si/Al ratio, a bigger specific surface area and a larger number of Brønsted acid sites in the eight MR channels, which was more efficient in the reaction of carbonylation of dimethyl ether than ordinary alkali treatment.

Metal Sites in Zeolites: Synthesis, Characterization, and Catalysis

Zeolites with ordered microporous systems, distinct framework topologies, good spatial nanoconfinement effects, and superior (hydro)thermal stability are an ideal scaffold for planting diverse active metal species, including single sites, clusters, and nanoparticles in the framework and framework-associated sites and extra-framework positions, thus affording the metal-in-zeolite catalysts outstanding activity, unique shape selectivity, and enhanced stability and recyclability in the processes of Brønsted acid-, Lewis acid-, and extra-framework metal-catalyzed reactions. Especially, thanks to the advances in zeolite synthesis and characterization techniques in recent years, zeolite-confined extra-framework metal catalysts (denoted as metal@zeolite composites) have experienced rapid development in heterogeneous catalysis, owing to the combination of the merits of both active metal sites and zeolite intrinsic properties. In this review, we will present the recent developments of synthesis strategies for incorporating and tailoring of active metal sites in zeolites and advanced characterization techniques for identification of the location, distribution, and coordination environment of metal species in zeolites. Furthermore, the catalytic applications of metal-in-zeolite catalysts are demonstrated, with an emphasis on the metal@zeolite composites in hydrogenation, dehydrogenation, and oxidation reactions. Finally, we point out the current challenges and future perspectives on precise synthesis, atomic level identification, and practical application of the metal-in-zeolite catalyst system.

Chemocatalytic Conversion of Lignocellulosic Biomass to Ethanol: A Mini-Review

Ethanol has been widely used as a clean fuel, solvent, and hydrogen carrier. Currently, ethanol is generally produced through fermentation of starch- and sugarcane-derived sugars (e.g., glucose and sucrose) or ethylene hydration. Its production from abundant and inexpensive lignocellulosic biomass would facilitate the development of green and sustainable society. Biomass-derived carbohydrates and syngas can serve as important feedstocks for ethanol synthesis via biological and chemical pathways. Nevertheless, the biological pathway for producing ethanol through biomass-derived glucose fermentation has the disadvantages of long production period and carbon loss. These issues can be effectively mitigated by chemocatalytic methods, which can readily convert biomass to ethanol in high yields and high atomic efficiency. In this article, we review the recent advances in chemocatalytic conversion of lignocellulosic biomass to ethanol, with a focus on analyzing the mechanism of chemocatalytic pathways and discussing the issues related to these methods. We hope this mini-review can provide new insights into the development of direct ethanol synthesis from renewable lignocellulosic biomass.

Self-Assembled Nano-Filamentous Zeolite Catalyst to Realize Efficient One-Step Ethanol Synthesis

The non-petroleum synthesis route of ethanol from syngas (H₂ +CO) with methyl acetate (MA) as the core intermediate product has been confirmed as an excellent industrialization route for high purity ethanol production. However, as the central part of this tandem-catalysis path, the carbonylation of dimethyl ether (DME) to MA is limited by the undesirable catalytic activity and stability of zeolite catalysts. Herein, a facile inhibitor-assisted strategy was developed for constructing self-assembled nano-Mordenite (nano-MOR) zeolites without using any expensive or complex template. A nano-filamentous MOR zeolite with only 70 nm crystal diameter was successfully synthesized by selectively controlling the crystal growth orientation with a specific inhibitor. The catalytic performance of self-assembled nano-MOR catalysts was remarkably outstanding in DME carbonylation reaction. The highest Space-Time Yield (STY) of MA was achieved over Nanofilament MOR (NF-MOR), which was significantly improved comparing with that of the traditional Ellipsoid-MOR (ES-MOR) [3780 mmol/(kg ⋅ h) vs. 1368 mmol/(kg ⋅ h)]. One-step ethanol synthesis was realized by combining the MOR catalyst and an innovative self-reduced Cu-ZnO/SiO₂ (CZ/SiO₂ ) catalyst in a rationally designed dual-bed catalysis system. Adopting the tailor-made NF-MOR&CZ/SiO₂ combination, it obtained the highest STY of ethanol, about 4 times of the conventional ES-MOR&CZ combination [1800 mmol/(kg ⋅ h) vs. 476 mmol/(kg ⋅ h)]. The present self-assembled nano-MOR zeolites synthetic strategy opens a new way for the fabrication of high-performance zeolites for practical industrial applications in catalytic conversions of one-carbon (C1) small molecules to high value-added chemicals.

Preferential population of Al atoms at the T4 site of ZSM-35 for the carbonylation of dimethyl ether

ZSM-35, synthesized using dioxane as the structure-directing agent, featured preferential population of Al atoms at the T4 site in the 8-MR pore, and the Brønsted acid site, thus generated, catalyzed DME carbonylation actively and stably.

Molecular Understanding of the Catalytic Consequence of Ketene Intermediates under Confinement

Neutral ketene is a crucial intermediate during zeolite carbonylation reactions. In this work, the roles of ketene and its derivates (viz., acylium ion and surface acetyl) associated with direct C-C bond coupling during the carbonylation reaction have been theoretically investigated under realistic reaction conditions and further validated by synchrotron radiation X-ray diffraction (SR-XRD) and Fourier transformed infrared (FT-IR) studies. It has been demonstrated that the zeolite confinement effect has significant influence on the formation, stability, and further transformation of ketene. Thus, the evolution and the role of reactive and inhibitive intermediates depend strongly on the framework structure and pore architecture of the zeolite catalysts. Inside side pockets of mordenite (MOR), rapid protonation of ketene occurs to form a metastable acylium ion exclusively, which is favorable toward methyl acetate (MA) and acetic acid (AcOH) formation. By contrast, in 12MR channels of MOR, a relatively longer lifetime was observed for ketene, which tends to accelerate deactivation of zeolite due to coke formation by the dimerization of ketene and further dissociation to diene and alkyne. Thus, we resolve, for the first time, a long-standing debate regarding the genuine role of ketene in zeolite catalysis. It is a paradigm to demonstrate the confinement effect on the formation, fate, and catalytic consequence of the active intermediates in zeolite catalysis.

A Carbonylation Zeolite with Specific Nanosheet Structure for Efficient Catalysis

Up to now, the member of zeolite family has expanded to more than 230. However, only little part of them have been reported as catalysts used in reactions. Discovering potential zeolites for reactions is significantly important, especially in industrial applications. A carbonylation zeolite catalyst Al-RUB-41 has special morphology and channel orientation. The 8-MR channel of Al-RUB-41 is just perpendicular to its thin sheet, making a very short mass-transfer distance along 8-MR. This specific nature endows Al-RUB-41 with efficient catalytic ability to dimethyl ether carbonylation reaction with beyond 95% methyl acetate selectivity. Compared with the most widely accepted carbonylation zeolite catalysts, Al-RUB-41 behaves a much better catalytic stability than H-MOR and a greatly enhanced catalytic activity than H-ZSM-35. A space-confined deactivation mechanism over Al-RUB-41 is proposed. By erasing the acid sites on outer surface, Al-RUB-41@SiO₂ catalyst achieves a long-time and high-efficiency activity without any deactivation trend.

Silver-Modified Nano Mordenite for Carbonylation of Dimethyl Ether

Mordenite (H-MOR) catalysts were synthesized by a hydrothermal method, and silver-modified mordenite (Ag-MOR) catalysts were prepared by ion exchange with AgNO3 at different concentrations. The performance of these catalysts in the carbonylation of dimethyl ether (DME) to methyl acetate (MA) was also evaluated. The catalysts were characterized by Ar adsorption/desorption, XRD, ICP-AES, SEM, HRTEM, 27Al NMR, H2-TPR, NH3-TPD, Py-IR, and CO-TPD. According to the characterization results, Ag ion exchange sites were mainly located in the 8-membered ring (8-MR) channels of Ag-MOR; evenly dispersed Ag2O particles were also present. The acid site distribution was changed by the modification of Ag, and the amount of Brønsted acid sites increased in 8-MR and decreased in 12-MR. The CO adsorption performance of the catalyst significantly increased with the modification of Ag. These changes improved the conversion and selectivity of the carbonylation of DME. Over 4Ag-MOR in particular, DME conversion and MA selectivity reached 94% and 100%, respectively.