Dimethyl Ether Carbonylation Reaction Research Articles

Modulation of aluminum species in mordenite zeolite for enhanced dimethyl ether carbonylation

Dimethyl ether (DME) carbonylation is an important intermediate step in the synthesis of methyl acetate (MA) and ethanol. H-form mordenite (MOR) can efficiently catalyze the reaction, in which Brønsted acid sites (BASs) associated with framework Al function as active sites. But the role of other Al species such as exteraframework Al (EFAl) and framework-associated Al still remains unknown. In this study, we have proposed two convenient approaches for controlling the two Al species and investigating their influence on the DME carbonylation reaction. NH3-TPD and Py-IR analyses revealed that the number of BASs increased after the removal of EFAl and the inhibition the formation of framework-associated Al. The reactivity results showed that the elimination of EFAl promoted the DME conversion from 28% to 46%. Additionally, through the implementation of in-situ calcination to impede the presence of framework-associated Al, the DME conversion increased from 28% to 50%. With the understanding that both EFAl and framework-associated Al have a detrimental effect on the reaction, the highest conversion is achieved with these two treatments, leading to 73% DME conversion with 99% selectivity to MA. Our findings provide a systematical strategy to effectively regulate the presence of Al species in zeolite, offering insights of rational design to optimize zeolite catalysts for important industrialized process.

Enhanced Stability of Dimethyl Ether Carbonylation through Pyrazole Tartrate on Tartaric Acid-Complexed Cobalt-Iron-Modified Hydrogen-Type Mordenite.

In this study, pyrazole tartrate (Pya·DL) and tartaric acid (DL) complexed with cobalt-iron bimetallic modified hydrogen-type mordenite (HMOR) were prepared using the ion exchange method. The results demonstrate that the stability of the dimethyl ether (DME) carbonylation reaction to methyl acetate (MA) was significantly improved after the introduction of Pya·DL to HMOR. The Co∙Fe∙DL-Pya·DL-HMOR (0.8) sample exhibited sustainable stability within 400 h DME carbonylation, exhibiting a DME conversion rate of about 70% and MA selectivity of above 99%. Through modification with the DL-complexed cobalt-iron bimetal, the dispersion of cobalt-iron was greatly enhanced, leading to the formation of new metal Lewis acidic sites (LAS) and thus a significant improvement in catalysis activity. Pya·DL effectively eliminated non-framework aluminum in HMOR, enlarged its pore size, and created channels for carbon deposition diffusion, thereby preventing carbon accumulation and pore blockage. Additionally, Pya·DL shielded the Bronsted acid sites (BAS) in the 12 MR channel, effectively suppressing the side reactions of carbon deposition and reducing the formation of hard carbon deposits. These improvements collectively contribute to the enhanced stability of the DME carbonylation reaction.

Insights into the CO-mediated deactivation mechanism for dimethyl ether carbonylation reaction over a H-MOR catalyst

Dimethyl ether (DME) carbonylation to methyl acetate (MAc) catalyzed by H-MOR catalyst has aroused wide interest due to its high efficiency as an emerging method for ethanol production. However, the rapid deactivation of H-MOR catalyst results in great challenges for its industrial application, urging a clear understanding of the intricate carbonylation deactivation mechanism. Herein, we discover a CO-mediated deactivation mechanism over H-MOR catalyst, which is beyond the traditional understanding that deactivation is originated from DME/methanol-to-hydrocarbon (DTH/MTH) chemistry. It is revealed that the coupling reaction of CO or MAc with olefins accelerate the catalyst deactivation, and methyl cyclopentenones (MCPOs) are first identified as the key intermediates for aromatic cokes formation over H-MOR catalyst. A more comprehensive mechanism for DME carbonylation deactivation is proposed based on the understanding. This study would provide valuable insights into understanding the carbonylation process and offer potential directions for developing carbonylation catalysts with enhanced stability.

Designing a Mordenite Catalyst with Enhanced Acidity for Dimethyl Ether Carbonylation by Engineering Open Sn Sites

Due to their tunable acidity, shape selectivity, and excellent stability, zeolites are of great importance as solid acid materials in industrial catalysis. Tuning the properties of the acid sites in zeolites allows for the rational design and fabrication of catalysts for target reactions. Dimethyl ether (DME) carbonylation, a critical chain-growth reaction for C1 resource utilization, is selectively catalyzed by the Brønsted acid sites within the eight-membered rings (8-MRs) of mordenite (MOR). It is anticipated that strengthening the Brønsted acidity—particularly in 8-MRs—will improve the catalytic performance of MOR. In this work, density functional theory (DFT) calculations are first employed and the results used to design a modified MOR with stannum (Sn) and to predict the corresponding changes in acidity. Guided by the theoretical studies, a series of Sn-modified MOR are synthesized via a defect-engineering and subsequent heteroatom-substitution strategy. After partial desilication, isolated tetrahedral Sn species in an open configuration are successfully synthesized for the first time, within which tetrahedrally coordinated Al sites are preserved. An acidic characterization is used to confirm that the acidity of the Brønsted acid sites is enhanced by the introduction of the Sn species; as a result, the sample exhibits excellent activity in DME carbonylation reaction. Kinetic and DFT studies reveal that this strengthened acidity facilitates the adsorption of DME and reduces the activation barriers of DME dissociation and acetyl formation, accounting for the improved activity. The work demonstrates mechanistic insights into the promoting effects of strong acidity on DME carbonylation and offers a promising strategy to precisely control the acidic strength of zeolites.

Selective removal of acid sites in mordenite with the assistance of tetraethylammonium bromide for high performing dimethyl ether carbonylation reaction

The distribution of acid sites in Mordenite (MOR) is crucial for its carbonylation performance. In this paper, MOR was subjected to acid treatment to selectively remove acid sites in 12 member-ring (MR) with the assistance of tetraethylammonium bromide (TEABr) used during synthesis process. The impact of acid treatment on structure, morphology, framework atoms and acidity were systematically studied. The characterization results indicated that the structure of the samples was only slightly impacted while the mesopore volume slightly increased. Due to the excessive removal of acid sites, the sample treated by nitric acid (0.1 mol/L) exhibited lower carbonylation activity whether with or without the protection of templates. However, the acid sites in the 12 MR were selectively removed in the citric acid treatment process by two different ways: the etching effect of H+ and the complexation of citric ions. The protection effect of templates for the acid sites in 8 MR was remarkable. Therefore, selective removal of acid sites in 12 MR was successful realized with assistance of template, leading to considerable improvements in activity for DME carbonylation reaction.

Synthesis of hierarchical mordenite by solvent-free method for dimethyl ether carbonylation reaction.

A series of hierarchical mordenite (MOR) catalysts were synthesized by adding soft templates via the solvent-free method. The influence of different kinds of soft templates on the structure, morphology and acid sites of mordenite were systematically characterized. The characterization results revealed that the addition of soft templates could successfully introduce hierarchical structure into the system while maintaining good crystallinity. The specific surface area and pore volume became larger. Surfactants could also affect the amount and distribution of acid sites, which in turn would affect the dimethyl ether carbonylation activity. Compared with cationic and nonionic surfactants, the addition of anionic surfactants such as sodium dodecyl benzene sulfonate could result in more Al species to preferentially enter into the 8 member ring, thus enhancing the amount of active sites for the carbonylation reaction while weakening the strength. Meanwhile, the addition of sodium dodecyl benzene sulfonate could also reduce the number of strong acid sites in the 12 member ring and obviously improve the carbonylation performance.

Synthesis of mordenite by solvent-free method and its application in the dimethyl ether carbonylation reaction

Mordenite with different Si/Al ratios were synthesized by solvent-free method and used for dimethyl ether (DME) carbonylation reaction. The influence of Si/Al ratio in the feedstock on the structure, porosity and acid sites were systematically investigated. The characterization results showed that with the increase of Si/Al ratio in the feedstock, part of silicon species fail to enter the skeleton and the specific surface area and pore volume of the samples decreased. The amount of weak acid and medium strong acid decreased alongside with the increasing Si/Al ratio, and the amount of strong acid slightly increased. The Al atoms preferentially enter the strong acid sites in the 8 MR channel during the crystallization process. The high Si/Al ratio sample had more acid sites located in the 8 MR channel, leading to more active sites for carbonylation reaction and higher catalytic performance. Appropriately increasing the Si/Al ratio was beneficial for the improvement of carbonylation reaction activity over the MOR catalyst.

Dimethyl Ether Carbonylation on H-MOR Zeolite, Modified Cu, Co, Mg

Mordenite and ferrierite (Zeolyst International, H-form, SiO2/Al2O3 ≈ 20) were used to study the adsorption, thermally programmed desorption, and carbonylation of dimethyl ether (DME). The behavior of mordenite with Cu, Co, and Mg cations introduced by ion exchange has also been studied. DME carbonylation was carried out at 200°C, pressure 3 MPa, space velocity 8000 ml g–1 h–1 in a mixture, vol. %: ⁓2.2 DME, 92.8–95.5 CO, rest. N2. After the induction period, the methyl acetate content is about 4–5 times higher for mordenite compared to ferrierite. The formation of water, methanol and hydrocarbons was observed in small quantities. The introduction of Cu, Co, Mg cations into mordenite by ion exchange (single ion exchange, cation/Al ratio no more than 35%) not only increased the stability, but also increased the activity in the DME carbonylation reaction. It was found that an increase in the content of copper (from 1.19 to 2.23 wt %) and Mg (from 0.62 to 1.8 wt %) differently affects the activity. In the case of copper, an increase in activity was observed, while in the case of magnesium, the activity decreased. Preliminary reduction of copper-exchange mordenite leads to a decrease in activity and the appearance of metallic copper particles on the surface of mordenite crystallites. According to in situ diffuse reflectance infrared spectroscopy, the introduction of magnesium cations by triple ion exchange leads to a noticeable decrease in the number of Brønsted acid sites (BACs) in both the 12-MR and 8-MR channels of mordenite. The catalytic characteristics of ferrierite practically do not change when copper and magnesium are introduced by ion exchange.

Cyclic Oxygenate-Based Deactivation Mechanism in Dimethyl Ether Carbonylation Reaction over a Pyridine-Modified H-MOR Catalyst

Cyclic Oxygenate-Based Deactivation Mechanism in Dimethyl Ether Carbonylation Reaction over a Pyridine-Modified H-MOR Catalyst

Ferrierite nanosheets with preferential Al locations as catalysts for carbonylation of dimethyl ether

Enriching Al atoms in T2 and T4 sites of FER zeolite is decisive for achieving high catalytic activity in the carbonylation reaction of dimethyl ether (DME). Regulating the spatial position of Al atoms in targeted framework sites remains to be a great challenge during the synthesis of FER zeolite. The FER nanosheets with preferential Al-sitting in T2 and T4 sites were successfully synthesized with the assistance of cetyltrimethylammonium bromide (CTAB). The effect of CTAB on the morphology and Al distribution has been investigated in detail. CTAB mostly adsorbed on external surface serving as growth inhibitors, which resulted in nanosheet morphology and changed the length ratio along the b-axis to c-axis of the crystals. A minor portion of CTAB located in the channels may favor the spatial Al location in T2 and T4 sites, indicated by the results from 27Al MAS NMR spectra. The FER nanosheets exhibited improved DME conversion, stability, space–time yield (STY), and lifetime compared to conventional FER in DME carbonylation reaction.

Effects of metal oxide promoters on Cu-ZnO-Al2O3 for one step DME conversion to ethanol by carbonylation and successive hydrogenation

An indirect ethanol synthesis in terms of carbon neutral strategy by consuming synthesis gas consists of three separate steps such as syngas to dimethyl ether (DME), DME carbonylation and methyl acetate (MA) hydrogenation through tandem reactions. For the series reactions, the nanosheet ferrierite (FER) zeolite was used for a gas-phase DME carbonylation reaction to MA and the Cu-ZnO-Al2O3 (CZA)-based catalyst was modified with additional metal oxide promoter (M = Ga, In and Nd) for MA hydrogenation, where the CZA-M catalysts were prepared by a simple coprecipitation method. The CZA-M catalysts hybridized with FER zeolite showed different catalytic activity for the tandem reactions, where the catalytic activity was largely affected by the CZA-M surface properties. The effects of additional metal oxides promoter on the CZA-M were carefully investigated and the CZA-Nd catalyst having larger Cu crystallites showed the best catalytic activity due to the enhanced oxygen vacant sites correspond to their basic sites.

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.

Dynamic Evolution of Aluminum Coordination Environments in Mordenite Zeolite and Their Role in the Dimethyl Ether (DME) Carbonylation Reaction

Part of tetrahedral framework aluminum in a protonic mordenite (HMOR) will convert geometry to distorted tetrahedral and octahedral coordination. High-field 27 Al NMR data show that more framework Al atoms at T3 and T4 sites change geometry to nonframework structures than others. These nonframework Al species preferentially reside in the side pockets, which will decrease the accessibility of acid sites in the 8-membered ring (MR) channel, impairing the dimethyl ether (DME) carbonylation reaction. The arisen octahedrally coordinated Al species are framework-associated, which can be reverted into the zeolite framework. Herein, we find that a facile treatment with pyridine could force the octahedral coordination Al back into a tetrahedral environment, which could increase the number of available active sites and enhance the diffusion of DME, thus improving the reactivity (4 times) of the DME carbonylation reaction and prolonging the lifetime of catalysts.

Dynamic Evolution of Aluminum Coordination Environments in Mordenite Zeolite and Their Role in the Dimethyl Ether (DME) Carbonylation Reaction

AbstractPart of tetrahedral framework aluminum in a protonic mordenite (HMOR) will convert geometry to distorted tetrahedral and octahedral coordination. High‐field 27Al NMR data show that more framework Al atoms at T3 and T4 sites change geometry to nonframework structures than others. These nonframework Al species preferentially reside in the side pockets, which will decrease the accessibility of acid sites in the 8‐membered ring (MR) channel, impairing the dimethyl ether (DME) carbonylation reaction. The arisen octahedrally coordinated Al species are framework‐associated, which can be reverted into the zeolite framework. Herein, we find that a facile treatment with pyridine could force the octahedral coordination Al back into a tetrahedral environment, which could increase the number of available active sites and enhance the diffusion of DME, thus improving the reactivity (4 times) of the DME carbonylation reaction and prolonging the lifetime of catalysts.

Effect of Steam Treatment on the Properties of Mordenite and Its Catalytic Performance in a DME Carbonylation Reaction

A series of dealuminated mordenite (MOR) samples with different acidities and various porosities were prepared through steam treatment of H+/Na+ mordenite. The obtained zeolites were elaborately characterized by X-ray diffraction, N2 adsorption–desorption, scanning electron microscopy, 29Si nuclear magnetic resonance (NMR), 27Al NMR, NH3 temperature-programmed desorption, and Fourier transform infrared spectroscopy, and the catalytic performance for dimethyl ether (DME) carbonylation was investigated. The characterization results revealed that the kind of cation balancing the zeolite charge had a great effect on the crystalline structure and acidity of mordenite zeolite during steam treatment and ion-exchange processes. Dealumination was observed both on Na-MOR and H-MOR, but it was much milder on the Na-MOR zeolite comparatively. After Na-MOR was treated with steam, its structure was well-preserved, but side pockets of mordenite were opened, resulting in an increased microporous volume and strong acid sites. Interestingly, it was found that the removal of framework Al in the 12MR channel was favored over the 8MR channel during steaming of Na-MOR, leading to the mordenite to possess more acid sites in the 8MR channel compared with those in the 12MR channel. As for the steamed H-MOR, both the crystalline structure and porosity were obviously damaged, resulting in a decreased microporous volume and acidity. The influence was more significant in the 8MR channel of H-MOR due to the obvious removal of framework Al and blockage of side pockets. The performance tests revealed that Na-MOR treated with steam was an effective way to enhance the catalytic performance for DME carbonylation reaction. The N-773 catalyst (steamed with Na-MOR at 773 K) showed a methyl acetate product rate of 0.33 gg–1 h–1, which was much higher than that of the parent H-MOR (0.23 gg–1 h–1). Moreover, the dealuminated catalyst exhibited a slow deactivation rate, which was possibly ascribed to the reduced strong acid sites in the 12MR channels. Although the steam treatment of H-MOR resulted in a lower activity in the DME carbonylation reaction, it exhibited a higher MeOAc selectivity and improved stability for its overall decreased acidity.

Study on the Framework Aluminum Distributions of HMOR Zeolite and Identification of Active Sites for Dimethyl Ether Carbonylation Reaction※

Study on the Framework Aluminum Distributions of HMOR Zeolite and Identification of Active Sites for Dimethyl Ether Carbonylation Reaction^※

Zinc enhances catalytic performance of pyridine-adsorbed HMOR: Dimethyl ether carbonylation

Dimethyl ether (DME) carbonylation to methyl acetate (MA) on H-mordenite (HMOR) zeolite is of critical importance for ethanol synthesis from syngas in industry, but it is generally accepted that carbonaceous deposits at Brønsted acid sites (BASs) in the twelve-membered ring (12-MR) lead to rapid deactivation of HMOR. Pyridine (Py) significantly prolong the catalytic lifetime of HMOR by selectively enter into the 12-MR to occupy the BASs. Moreover, loading Zn species into HMOR dramatically improve the MA formation. However, the role, active type and location of Zn species in HMOR are unclear. Herein, we comparatively dissected the catalytic mechanisms of DME carbonlyation in HMOR, pyridine-adsorbed HMOR (Py-HMOR), and three types of Zn-modified Py-HMOR systems by density functional theory (DFT) calculations, and confirmed Zn2+ ion doped Py-HMOR (Zn2+-Py-HMOR) system with the Zn2+ located between T3O31/T3O31′ and T3O33 sites in the 8-MR shows the optimal catalytic activity for DME carbonylation to MA. During the whole cycle of DME carbonylation, only the reaction step of acetyl intermediate with CH3OH is able to restore the active T3O31/T3O31′. Our Bader charge and charge density differences analyses revealed that the catalytic activity improvement of Zn2+-Py-HMOR system for DME decomposition and MA formation is stem from the enhancement of electrostatic interaction, more framework O sites in 8-MR involving in electron transfer, and matched spatial confinement. This work will provide indispensable inspiration for further modification of zeolite catalysts with 8-MR for DME carbonylation reaction.

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.

Effect of N-Methyl-2-pyrrolidone on Al Distribution in MOR and Enhanced Activity in DME Carbonylation Reaction

A biased acid site distribution in mordenite (MOR), which refers to the enrichment of acid sites within 8-membered ring (MR) channels, was observed with the addition of N-methyl-2-pyrrolidone (NMP) in the initial gel and verified by the enhanced activity in dimethyl ether (DME) carbonylation reaction. This is the first time that lactam has been proved effective in regulating acid site distribution, and the possible mechanism was investigated.

Crystal size sensitivity of HMOR zeolite in dimethyl ether carbonylation

The effect of crystal size of HMOR from micro size to 50 nm, with the apparent similar acid site density, on catalytic performance for the dimethyl ether (DME) carbonylation was investigated. The crystal size of HMOR is sensitive to the deactivation rate of DME carbonylation reaction, and the higher stability around 200 nm can be achieved. The characterization studies reveal that the diffusions of MA product play a key role during the induction and deactivation period in DME carbonylation. These will be helpful for guiding the large-scale synthesis of mordenite zeolites catalysts with high efficiencies for DME carbonylation.