Dimethyl Carbonate Selectivity Research Articles

Engineering the Activity and Stability of the Zn-MOF Catalyst via the Interaction of Doped Zr with Zn.

Metallic atoms within metal-organic framework (MOF) materials exhibit a distinctive and adaptable coordination structure. The three-dimensional (3D) pore configuration of MOFs enables the complete exposure of metal active sites, rendering them prevalent in various catalytic reactions. In this study, zinc (Zn) atoms within Zn-based MOF materials, characterized by an abundance of valence electrons, are utilized for the transesterification of dimethyl carbonate (DMC). Additionally, the introduction of zirconium (Zr) effectively addresses the susceptibility of the MOFs' crystal structure to dissolution in organic solvents. The formulated catalyst, Zn-10%Zr-MOF(300), demonstrates remarkable catalytic performance with 91.5% DMC selectivity, 61.9% propylene carbonate (PC) conversion, and 56.6% DMC yield. Impressively, the catalyst maintains its high performance over five cycles. Results indicate that Zr interacts with Zn, forming new coordination bonds and enhancing the catalyst crystal structure stability. Moreover, electron transfer intensifies the alkalinity of the active Zn atoms, enhancing the overall catalyst performance. This research informs the development of transesterification heterogeneous catalysts and broadens the application scope of MOF catalysts.

Mo-promoted Pd/NaY catalyst for indirect oxidative carbonylation of methanol to dimethyl carbonate

A chlorine-free catalyst consisting of zeolite Y modified with Pd (Pd/NaY) catalyst has been prepared and used in the indirect oxidative carbonylation of methanol to dimethyl carbonate (DMC). The activity and stability of the catalyst were further improved by introducing molybdenum into Pd/NaY using a top-down approach (Pd-Mo/NaY catalyst). The Pd-Mo/NaY catalyst exhibited higher stability compared to the Pd/NaY. A high CO conversion of 97% and DMC selectivity of 80% during a 30-hour catalytic test for the Pd-Mo/NaY were obtained. Furthermore, the incorporation of Mo was found to partially heal the silanols and hinder the aggregation of Pd in the Pd-Mo/NaY catalyst. The interactions between Mo and Pd increased the amount of active Pd2+ species and enhanced the adsorption of CO reactant on the Pd-Mo/NaY catalyst. The key reaction intermediate of COOCH3* was captured by in situ diffuse reflectance infrared Fourier transform spectroscopy. The stabilization of active Pd2+ species contributed to the enhanced catalytic activity of the Pd-Mo/NaY catalyst in the indirect oxidative carbonylation of methanol to DMC reaction.

Stabilization of Pd0 by Cu Alloying: Theory‐Guided Design of Pd3Cu Electrocatalyst for Anodic Methanol Carbonylation

Electrocatalytic carbonylation of CO and CH3OH to dimethyl carbonate (DMC) on metallic palladium (Pd) electrode offers a promising strategy for C1 valorization at the anode. However, its broader application is limited by the high working potential and the low DMC selectivity accompanied with severe methanol self‐oxidation. Herein, our theoretical analysis of the intermediate adsorption interactions on both Pd0 and Pd4+ surfaces revealed that inevitable reconstruction of Pd surface under strongly oxidative potential diminishes its CO adsorption capacity, thus damaging the DMC formation. Further theoretical modeling indicates that doping Pd with Cu not only stabilizes low‐valence Pd in oxidative environments but also lowers the overall energy barrier for DMC formation. Guided by this insight, we developed a facile two‐step thermal shock method to prepare PdCu alloy electrocatalysts for DMC. Remarkably, the predicted Pd3Cu demonstrated the highest DMC selectivity among existing Pd‐based electrocatalysts, reaching a peaked DMC selectivity of 93% at 1.0 V versus Ag/AgCl electrode. (Quasi) in‐situ spectra investigations further confirmed the predicted dual role of Cu dopant in promoting Pd‐catalyzed DMC formation.

Stabilization of Pd0 by Cu Alloying: Theory-Guided Design of Pd3Cu Electrocatalyst for Anodic Methanol Carbonylation.

Electrocatalytic carbonylation of CO and CH3OH to dimethyl carbonate (DMC) on metallic palladium (Pd) electrode offers a promising strategy for C1 valorization at the anode. However, its broader application is limited by the high working potential and the low DMC selectivity accompanied with severe methanol self-oxidation. Herein, our theoretical analysis of the intermediate adsorption interactions on both Pd0 and Pd4+ surfaces revealed that inevitable reconstruction of Pd surface under strongly oxidative potential diminishes its CO adsorption capacity, thus damaging the DMC formation. Further theoretical modeling indicates that doping Pd with Cu not only stabilizes low-valence Pd in oxidative environments but also lowers the overall energy barrier for DMC formation. Guided by this insight, we developed a facile two-step thermal shock method to prepare PdCu alloy electrocatalysts for DMC. Remarkably, the predicted Pd3Cu demonstrated the highest DMC selectivity among existing Pd-based electrocatalysts, reaching a peaked DMC selectivity of 93 % at 1.0 V versus Ag/AgCl electrode. (Quasi) in situ spectra investigations further confirmed the predicted dual role of Cu dopant in promoting Pd-catalyzed DMC formation.

Facile one-pot synthesis of niobium-containing carbon nitride and the catalytic application for synthesis of dimethyl carbonate

Dimethyl carbonate (DMC) is a building block in wide chemical-related fields and the transesterification of ethylene carbonate (EC) and methanol/ethanol is a sustainable route for the synthesis of DMC. Herein, in order to explore efficient heterogeneous catalysts, niobium-containing carbon nitride materials were synthesized by a convenient one-pot calcination method. By reserving the main chemical functionalities of carbon nitride, the Nb-CN composites contained both acidic and basic properties, and Nb can be dispersed by carbon nitride. In the transesterification of EC with methanol, under the reaction temperature of 140 °C and reaction time of 4 h, the conversion of EC and the selectivity of DMC reached 53.8% and 100%, respectively, and the activity of the catalyst did not decrease significantly after several recycling runs. Furthermore, the Nb-CN could promote transesterification reactions of other cyclic carbonate and alcohols.

Enhancing DMC Production from CO2: Tuning Oxygen Vacancies and In Situ Water Removal

The direct synthesis of dimethyl carbonate (DMC) from methanol and CO2 presents an attractive route to turn abundant CO2 into value-added chemicals. However, insufficient DMC yields arise due to the inert nature of CO2 and the limitations of reaction equilibrium. Oxygen vacancies are known to facilitate CO2 activation and improve catalytic performance. In this work, we have demonstrated that tuning oxygen vacancies in catalysts and implementing in situ water removal can enable highly efficient DMC production from CO2. CexZryO2 nanorods with abundant oxygen vacancies were synthesized via a hydrothermal method. In liquid-phase DMC synthesis, the Ce10Zr1O2 nanorods exhibited a 1.7- and 1.4-times higher DMC yield compared to CeO2 nanoparticles and undoped CeO2 nanorods, respectively. Zr doping yielded a CeZr solid solution with increased oxygen vacancies, promoting CO2 adsorption and activation. In addition, adding 2-cyanopyridine as an organic dehydrating agent achieved an outstanding 87% methanol conversion and >99% DMC selectivity by shifting the reaction equilibrium to the desired product. Moreover, mixing CeO2 nanoparticles with hydrophobic fumed SiO2 in gas-phase DMC synthesis led to a doubling of DMC yield. This significant increase was attributed to the faster diffusion of water molecules away from the catalyst surface, facilitated by the hydrophobic SiO2. This study illustrates an effective dual strategy of enhancing oxygen vacancies and implementing in situ water removal to boost DMC production from CO2. The strategy can also be applied to other reactions impacted by water accumulation.

Acid–base bifunctional ZnNbCl/eg-C3N4 materials towards catalytic synthesis of dimethyl carbonate via transesterification of ethylene carbonate

The catalytic transesterification reaction between ethylene carbonate (EC) with methanol is a sustainable approach for the production of dimethyl carbonate (DMC). In this work, exfoliated carbon nitride (eg-C3N4) was supported with ZnCl2 and NbCl5. The synthesized materials (ZnNbCl/eg-C3N4) were analyzed by XRD, N2 adsorption–desorption, FT-IR, XPS, SEM, TG, CO2-TPD, and NH3-TPD. The eg-C3N4 could disperse well Zn2+ and Nb5+ species via nitrogen-containing groups. The combined Zn2+ and Nb5+ components enhanced the alkaline strength of eg-C3N4 and introduced acidic sites, enabling ZnNbCl/eg-C3N4 as solid-base bifunctional catalysts. As heterogeneous catalysts, ZnNbCl/eg-C3N4 exhibited superior activity to ZnCl2/eg-C3N4 or NbCl5/eg-C3N4 in the transesterification of EC. At 140 °C of reaction temperature, EC conversion and DMC selectivity reached 80.1% and 100%, respectively. The catalysts showed good recycling performance and were also compared with other recently reported heterogeneous catalysts.

The direct synthesis of dimethyl carbonate out of carbon dioxide and methanol is catalyzed by D-metals supported on various matrices

The chemical transformation of carbon dioxide (CO2) into valuable chemicals is a fascinating way to reduce CO2 concentration in the atmosphere. Dimethyl carbonate (DMC) exhibits low toxicity, biodegradability, and versatile reactivity. DMC production by direct synthesis using CO2 and methanol (CH3OH) may be one of the ever most promising green routes. On the other hand, direct synthesis of DMC shows some drawbacks including unfavorable thermochemistry and quick deactivation of catalysts. The development of new catalytic systems currently represents an urgent agenda to overcome these disadvantages. This study investigates the catalytic activity of iron (Fe) and copper (Cu) catalysts supported on alumina (AL), silica (SI), and eggshells (ES) during the course of DMC production by direct synthesis. The supported catalysts were synthesized using the impregnation method and characterized by TGA, BET, DTP-NH3, XRD, and FESEM/EDS. The contents of the impregnated iron in the matrices are ES-Fe (13%) > AL-Fe (6%) > SI-Fe (4%). The contents of the impregnated copper are ES-Cu (7%) > AL-Cu (3%) = SI-Cu (3%). The DMC conversions equal 8.9 (AL-Cu), 6.2 (SI-Cu), 11.3% (ES-Cu), 6.1 (AL-Fe), 7.2 (SI-Fe), and 12.7% (ES-Fe). The ES-Fe recycle demonstrated stability of the catalytic action in the first and second reuse, maintaining high conversion and selectivity of DMC. All tests reveal a DMC selectivity of over 99%. The reported results suggest that the catalytic DMC production depends both on the nature of d-metal and support, whereas the ES-Fe system exhibits the best performance.

Emerging co-synthesis of dimethyl oxalate and dimethyl carbonate using Pd/silicalite-1 catalyst with synergistic interactions of Pd and silanols

An emerging synthetic route for the co-synthesis of dimethyl oxalate (DMO) and dimethyl carbonate (DMC) via the indirect oxidative carbonylation of CH3OH is presented. The promising co-synthesis process combines the advantages of two separate routes of DMO and DMC syntheses. Herein, palladium containing silicalite-1 zeolite (Pd/S-1) catalyst was first found to be highly active and stable for the co-synthesis of DMO and DMC. The catalytic performance strongly depended on the catalyst activation, as the heat treatment could tune the silanols around the Pd species on the silicalite-1 zeolite. The Pd/S-1 catalyst with abundant silanols exhibited a higher turnover frequency (TOF) of 0.18 s−1 and a lower apparent activation energy of 51 kJ mol−1 in comparison to the catalyst with low silanol sites (0.06 s−1 and 101 kJ mol−1). The best performing catalyst had an average Pd nanoparticle size of 3.2 nm and Pd loading of 0.48 wt%. This catalyst showed a high CO conversion of 78% and DMO + DMC selectivity of 96%, maintaining high stability for at least 200 h. Furthermore, the synergistic interactions of silanols of silicalite-1 zeolite and Pd were confirmed by a series of in situ infrared experiments, and were found to be responsible for the enhanced activity. The silanols of S-1 zeolite played an essential role in forming the Pd active sites and had a very pronounced effect on the adsorption of CO reactant on the Pd species. Understanding the interactions between metal species and silanols of zeolite is critical for the development of high-performance zeolite catalysts.

Local electron-rich structures facilitating the efficient synthesis of dimethyl carbonate from propylene carbonate and methanol over a ZnO/ZrO2 solid solution catalyst

ZnO/ZrO2 solid solution was introduced as the catalyst for synthesizing dimethyl carbonate (DMC) from propylene carbonate (PC) and methanol. Homogeneous catalysts with strong alkaline nature are the current main catalysts for this reaction. Therefore, to supplant the former with a more applicable multiphase one, it is necessary to construct stable and efficient alkaline active centers on the surface of solid catalysts. The ZnO/ZrO2 solid solution created defective structures of coordinative unsaturation in the form of oxygen vacancies (OV) by substituting Zn atoms for Zr atoms in ZrO2 crystals. Characterizations showed that electrons were transferred to the surrounding Zn atoms upon the formation of these OV, leading to a local enrichment of electrons and the formation of basic active centers. The number of oxygen defects and the alkalinity were effectively regulated by changing the ratio of the two metal atoms in the solid solution. Experiments demonstrated that the catalyst had the best DMC selectivity (92.2%) and the highest DMC yield (57.2%) at a 1:1 ratio of Zn to Zr, at 160 °C and 4 h. This superior performance not only establishes the feasibility of solid solution catalysts in synthesizing DMC but also provides a new perspective on the essential understanding of the active centers of such catalysts.

Improvement of surface properties of metal doped-CeO2 nanospindle catalysts for direct synthesis of dimethyl carbonate from CO2 and methanol

To utilize carbon dioxide (CO2) which is the main greenhouse gas, this study developed effective metal doped-CeO2 nanospindle catalysts for conversion of CO2 and methanol into dimethyl carbonate (DMC). Ce0.9M0.1O2 nanospindles (where M is a transition metal, i.e., Zr, Fe, Cu and Co) were prepared by a template-free hydrothermal method. The substitution of different valence and size cations, including Zr4+, Fe3+, Cu2+ and Co2+, for Ce4+ sites in the fluorite CeO2 lattice induced the defect formation of surface-active sites of exposed Ce3+ and oxygen vacancies through the charge compensation and redox pair reactions. Ce0.9Fe0.1O2 solid solution with well-preserved spindle shaped morphology showed the highest catalytic performance by giving DMC yield at 3.56 mmol.gcat−1 with 100% DMC selectivity. The improvement of catalytic activity was attributed to the higher proportion of surface defect sites and variation of acid-base properties caused by the integration of Fe dopants into CeO2 ionic system.

A highly efficient La-modified ZnAl-LDO catalyst and its performance in the synthesis of dimethyl carbonate from methyl carbamate and methanol

In this paper, the highly efficient ZnAlLa layered double oxide (ZnAlLa-LDO) catalyst was evaluated and used in methyl carbamate (MC) alcoholysis synthesis of dimethyl carbonate. Under optimal conditions, the MC conversion was 33.5% and the dimethyl carbonate (DMC) selectivity was up to 92.4% at 443 K and in 9 h. The prepared catalysts were well characterized to investigate the effect on the catalytic performance and reaction catalysis mechanism. The experimental results show that the addition of La adjusted the structure and chemical properties of ZnAl composite oxide and that the synergistic effect among Zn, Al and La play a key role in adjusting the acid-base properties and stability of the catalyst, which definitely improved the DMC selectivity and catalytic stability. Based on the proposed reaction mechanism, two kinetic models of the catalytic reaction were established and modified: Langmuir-Hinshelwood and power-rate law kinetic model. The good agreement between kinetic models and experimental data showed that the power-rate law kinetic model based on the elementary reactions is a suitable model for providing a theoretical basis. The pre-exponential factor and activation energy of the main reaction are 5.77 × 107 and 77.60 kJ·mol−1, respectively.

Selective synthesis of dimethyl carbonate via the coupling reaction of CO2 and alcohols by the synergistic catalysis of silver sulfadiazine and superbase

The three-component coupling of methanol, CO2 and propargyl alcohol to manufacture dimethyl carbonate (DMC) provides a new, thermodynamic favorable and green chemical synthesis route. In this work, to overcome the problems of low DMC yield and slow conversion rate of intermediates, the synergistic catalytic strategy of silver sulfadiazine and superbase is developed to improve the reaction efficiency. The effect of various parameters i.e. catalyst and cocatalyst types, catalyst loading, solvent, temperature, proportion of raw materials, pressure and time on the coupling reactions is investigated in detail. Under the optimal conditions, the selectivity of DMC is 89.5% with the yield of 55.6%. And the effect of alkyne derivative α-monosubstituted propargyl alcohol on the efficiency and selectivity of DMC are studied also. The mechanism study shows that propargyl alcohols with different structures apparently affect the reaction process, and the synergistic catalysis of silver sulfadiazine/1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) is the reason for the high yield and selectivity of DMC.

Rational design of Ga-substituted NaY zeolites with controllable acidity for remarkable carbonylation of methyl nitrite to dimethyl carbonate

Lack of high performance and stability catalysts remains a technical bottleneck for the industrialization of methyl nitrite (MN) carbonylation to dimethyl carbonate (DMC). Lewis acidity is crucial for catalytic performance in MN carbonylation reaction, but the regulation of Lewis acid sites and the effects of Lewis acid strength on catalytic performance have not been clarified. Thus, rational design of NaY zeolites with controllable acidity is an effective strategy to promote their catalytic performance. Herein, we substituted Ga for partial framework Al to produce a series of NaGaY-x (x = 0 ∼ 2) zeolites with different Ga content via direct hydrothermal method and applied in this reaction. The results showed that the Lewis acid strength increased upon an appropriate amount of Ga incorporation, thereby the electron density of Pd2+ could be regulated. The optimal electron density of Pd2+ promotes the carbon monoxide (CO) adsorption and activation, which contribute to the formation of the critical intermediate species *COOCH3. Eventually, the Ga-modified PdCu/NaY catalyst exhibited remarkable catalytic activity for MN carbonylation to DMC with the weight-time yields (WTYDMC) of 1251 g·kgcat−1·h−1, and the CO conversion to DMC (CCO) of 69.2 % as well as the DMC selectivity based on CO (SDMC/CO) up to 100 %. Our work paves the way to further understand the synergistic effect between Pd2+ and Lewis acid, assists in the development of high-performance MN carbonylation catalysts.

Boosting Activity and Selectivity of UiO-66 through Acidity/Alkalinity Functionalization in Dimethyl Carbonate Catalysis.

The acid-base properties of supports have an enormous impact on catalytic reactions to regulate the selectivity and activity of supported catalysts. Herein, a train of Pd-X-UiO-66 (X = NO2 , NH2 , and CH3 ) catalysts with different acidity/alkalinity functional groups and encapsulated Pd(II) species is first developed, whose activities in dimethyl carbonate (DMC) catalysis are then investigated in details. Thereinto, the Pd-NO2 -UiO-66 catalyst with acidity functionalization exhibits the best catalytic behavior: the DMC selectivity stemmed from methyl nitrite (MN) is up to 68%, the conversion of CO is 73.4%. The obtained experimental results demonstrate that the NO2 group not only affected the interaction between X-UiO-66 and Pd(II) active sites but also play an indispensable role in the adsorption and activation of MN and CO, which remarkably promote the formation of the COOCH3 * intermediate and DMC product.

An Intensified Green Process for the Coproduction of DMC and DMO by the Oxidative Carbonylation of Methanol

Dimethyl carbonate (DMC) is an eco-friendly and sustainable compound with widespread industrial applications. Various extensive routes have been exploited in the chemical industry to produce DMC. However, these routes have several environmental and energy drawbacks. In this study, a promising novel industrial scheme for the synthesis of DMC via the oxidative carbonylation of vaporized methanol with dimethyl oxalate (DMO) as a byproduct is investigated. A methanol conversion of 81.86% and a DMC selectivity of 83.47% were achieved using an isothermal fixed-bed reactor at 130 °C. The DMC is withdrawn at a purity of >99 mol% via pressure-swing azeotropic distillations. Heat integration was performed to optimize energy consumption, reducing the energy requirements by 28%. An economic evaluation was performed for estimating the profitability via cash-flow diagrams, predicting a payback period of 3.7 years. The proposed green process exhibits several benefits, including high profitability and being environmentally friendly. It also eliminates the use or production of hazardous materials, and it enhances safety characteristics.

The role of Ce doping on the activity of La2O2CO3 nanosheets catalysts in synthesis of dimethyl carbonate from propylene carbonate and methanol

Dimethyl carbonate (DMC) production from the transesterification reaction of propylene carbonate (PC) and methanol is an eco-friendly and economical process with propylene glycol (PG) as the high value-added co-product. We report herein the synthesis of Ce-doped La2O2CO3 nanosheets (La1Cex) with varying Ce contents through a solvothermol method. La1Ce0.15 catalyst exhibits superior catalytic performance in the production of DMC by the transesterification of methanol and PC. A remarkable improvement in PC conversion (> 85%) and DMC selectivity (> 98%) can be attributed to an increase in surface O2− base sites caused by increased oxygen interstitials and vacancies through Ce doping.

Revealing the roles of hydrogen bond and Al2Cl7− anion species and kinetics for ionic liquid catalyzed transesterification of ethylene carbonate with methanol

The co-production of dimethyl carbonate (DMC) and ethylene glycol (EG) from the transesterification of ethylene carbonate (EC), which is synthesized from CO2 and ethylene oxide, with methanol has received researchers’ attention. Herein, this transformative process catalyzed with metal chloride-based ionic liquids (ILs) was investigated by employing spectroscopic characterizations in combination with kinetic studies. The interaction between cation and methanol via hydrogen bond and activation of carbonyl group in EC (or 2-hydroxyethyl methyl carbonate, HEMC) by metal chloride-contained anion were identified to show synergistic effects on catalytic transesterification. The chain length of alkyl group substituted at the 1-position N atom in imidazole ring affected the reaction rates due to the steric hindrance effect. Not AlCl4− but Al2Cl7− anion species in AlCl3-based IL exhibited activity in this transesterification, and the content of Al2Cl7− species was observed to show linear relationship with the transformative rates of both EC and HEMC. The kinetic studies also elucidated that the rates of both EC (or HEMC) and methanol are first-order dependent on their concentrations, and the formation of HEMC intermediate was the kinetic-relevant step with the activation barrier of 92 kJ/mol. As a result, the yield and selectivity of DMC (or EG) could reach up to around 95 % and 97 % with catalysis of [MDMIM]Cl/AlCl3 with AlCl3 molar fraction of 0.67 after 12 h reaction at 140 °C, which showed higher performance than any other tested metal chloride-based IL. Besides, no decay in catalytic activity and selectivity of this IL was observed after 10 times’ recycling.

Ultrasonically assisted surface modified CeO2 nanospindle catalysts for conversion of CO2 and methanol to DMC

This study developed a facile and effective approach to engineer the surface properties of cerium oxide (CeO2) nanospindle catalysts for the direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol. CeO2 nanospindles were first prepared by a simple precipitation method followed by wet chemical redox etching with sodium borohydride (NaBH4) under high intensity ultrasonication (ultrasonic horn, 20 kHz, 150 W/cm2). The ultrasonically assisted surface modification of the CeO2 nanospindles in NaBH4 led to particle collisions and surface reduction that resulted in an increase in the number of surface-active sites of exposed Ce3+ and oxygen vacancies. The surface modified CeO2 nanospindles showed an improvement of catalytic activity for DMC formation, yielding 17.90 mmol·gcat−1 with 100 % DMC selectivity. This study offers a simple and effective method to modify a CeO2 surface, and it can further be applied for other chemical activities.

Dimethyl Carbonate: Review of Synthesis Routes and Catalysts Used

This review summarizes the performance of potential catalysts for the synthesis of dimethyl carbonate (DMC) using CO2 as a feedstock by two major processes—the direct route of carbonylation of alcohols and the indirect route of alcoholysis of urea. The reaction mechanisms and corresponding catalysts that were previously investigated are discussed. The major challenges associated with the conversion of CO2 to DMC are the low yields, low DMC selectivity, and thermodynamic limitations (alcohol carbonylation) of reversible reactions with low equilibrium constants. This occurs mainly due to the highly stable carbon dioxide molecules. The development of novel catalysts with high yields and high selectivity needs to be studied to overcome these technical challenges. In addition, to enhance the DMC yield, the use of dehydrating agents for water removal from the reaction mixture is recommended and discussed in detail in this article. This review critically examines the different catalysts used by investigators, along with their respective operating conditions and suitability in applications for the commercial synthesis of CO2-based DMC.