Dimethyl Carbonate Formation Research Articles

Surface-Dependent Role of Oxygen Vacancies in Dimethyl Carbonate Synthesis from CO2 and Methanol over CeO2 Catalysts.

The conversion of CO2 into value-added commodity chemicals, such as dimethyl carbonate (DMC), represents an environmentally friendly approach to CO2 utilization. This study exhaustively investigates the influence of oxygen vacancies (Ov) on CeO2 catalysts and, in particular, the role of surface structure. By integrating density functional theory calculations with experimental synthesis, we analyze the complex reaction mechanisms involved in DMC synthesis over both oxidized (Sto-(111), Sto-(110), and Sto-(100)) and nonoxidized (Ovsub-(111), Ovsur-(110), and Ovsur-(100)) CeO2 catalysts. Our findings indicate that Ov on the (111) surface inhibits DMC formation, whereas Ov on the (110) and (100) surfaces promotes it. This differential behavior is primarily attributed to Ov's modulation of the microscopic coordination environment on distinct surfaces, which impacts the rate-limiting step of C-O bond formation: CO2 + OCH3 → CH3OCOO (monodentate methyl carbonate, MMC) and CH3OCO + OCH3 → DMC. Additionally, analysis of the highly active Sto-(111) and Ovsur-(110) catalysts shows that their unique surface coordination microenvironments mitigate steric hindrance and facilitate an optimal arrangement of Lewis acid sites in proximity to Lewis base sites, thereby enhancing the DMC activity. This work underscores the pivotal role of surface structure in determining the effects of Ov, paving the way for the rational design of CeO2-based catalysts for the direct synthesis of DMC from CO2 and methanol.

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

AbstractElectrocatalytic 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.

Ga and Ti co-doped CeO2 nanorod catalysts with enhanced activity towards the synthesis of dimethyl carbonate from CO2 and methanol

Ga and Ti co-doped CeO2 nanorod catalysts with enhanced activity for dimethyl carbonate formation from methanol and CO2 compared to Ga-doped CeO2 catalysts have been obtained by introducing Ti during CeGa synthesis.

Influence of the synthesis method of Cu/Y zeolite catalysts for the gas phase oxidative carbonylation of methanol to dimethyl carbonate

Dimethyl carbonate is an environmentally friendly molecule with increasing applications as reactant, solvent, and fuel additive. Oxidative carbonylation of methanol, with reactants in the gas phase and catalyzed by copper-exchanged Y zeolites, is a promising alternative route for dimethyl carbonate production. This work is focused on the improvement of the catalyst formulation and preparation methods. Catalysts were prepared using two methodologies: solid-state ion exchange and liquid-ethanol ion exchange. Five different copper salts were used as precursors and the NH4+ and Na+ forms of the Y zeolite as supports. The Na+ form of the Y zeolite removed the Brønsted acidity of the support and, therefore, the reaction rate of acid-catalyzed undesired dehydration and decomposition reactions was reduced. The use of copper chloride salts as precursors was crucial to obtain suitable catalysts for dimethyl carbonate formation. Among all the tested catalysts, those prepared using CuCl2 precursor and the Na-Y zeolite by the liquid-ethanol ion exchange method showed the best performance (0.72 molDMC/molCu h). This catalyst exhibited the highest surface chloride content and Lewis acidity.

Synthesis of dimethyl carbonate from CO2 and methanol over CeO2 catalysts prepared by soft-template precipitation and hydrothermal method

Direct synthesis of dimethyl carbonate (DMC) from methanol (MeOH) and carbon dioxide (CO2) is a promising environmentally-friendly process for utilizing CO2 as a source of useful chemicals. For this reaction, CeO2 is known as an effective catalyst, and a variety of CeO2 catalysts prepared via various synthetic methods for controlling textural and surface properties of CeO2 such as facets, particle shapes, acidity, basicity, and oxygen vacancies have been employed. In this study, CeO2 catalysts were prepared via the combination of soft-template precipitation and hydrothermal treatment followed by calcination at different temperatures, and their catalytic performance for the DMC synthesis was investigated in the presence of 2-cyanopyridine (2-CP) as a dehydrating agent. CeO2 calcined at 650 °C (CeO2(650)) exhibited the highest DMC yield among the catalysts prepared in this study under the identical conditions. Its catalytic performance represented by the DMC formation rate at 110 °C was 31 mmol gcat−1 h−1 at 5 MPa of CO2 and MeOH/2-CP molar ratio of 1.0, and this rate was comparable to the previously reported highest value of 42 mmol gcat−1 h−1 under the similar reaction conditions consisting of reaction temperature of 110 ± 20 °C, CO2 pressure of 5 ± 1 MPa, and molar ratio of MeOH/2-CP of 0.5–2.0. Among the surface acidity and basicity examined by the temperature-programmed desorption measurements, the amount of base sites with medium strength of the prepared CeO2 catalysts was in the same order as the DMC amount. The infrared spectroscopy for the CO2 species chemisorbed on the CeO2 surfaces suggested the formation of bicarbonate species on the base sites with medium strength.

Dendritic fibrous nano-titanium (DFNT) with highly dispersed poly(ionic liquids) as a nanocatalyst for synthesis of dimethyl carbonate from methanol and carbon dioxide

The simultaneous fabrication of a phase junction and fibrous anatomy is able to ameliorate the separation, catalytic power, and catalytic activity of nano TiO2. However, It's easy and green fabrication is still essentially required. Here, an advanced dandelion-like TiO2 with anatase/TiO2 phase interface and the high particular outer layer was well created by a convenient and eco-friendly deep eutectic solvent-tuning approach. The large specific outer layer is the result of its 3D hierarchical anatomy assembled by 2D ultrathin nanosheets with mesopores. We fabricated Polyoxomolybdate [Mo132] nanospheres with various ionic liquid groups loaded on dendritic fibrous nanotitanium (DFNT@IL/Mo132) employing an unchallenging synthetic path. DFNT could provide abundant hydroxyl groups for uniform loading of IL through chemical bonding interaction, while IL could adjust the appropriate fiber dimension and show the active adsorption sites of amino groups that contribute to chemisorption with CO2. The overall topography of the DFNT@IL/Mo132 composite did not considerably alter after IL/Mo132 loading, and its mesoporous anatomy as well as crystal line shape were still sustained. This catalyst suffers from a low rate of DMC formation for the direct production of dimethyl carbonate (DMC) from methanol and CO2 due to its small specific outer layer and less active sites. In the current paper, we improved the issueby uniform dispersion of doped IL/Mo132 DFNT-based metal–organic frameworks (DFNT@IL/Mo132), which were produced through anamended hydrothermal approach.

Directly synthesis of dimethyl carbonate from CO2 and methanol over UiO-66 @CeO2 Catalyst

In this study, UiO-66 @CeO2 composites was prepared by loading CeO2 nanoparticles on the surface of UiO-66 using precipitation method, and the effect of CeO2 loading on the catalytic direct reaction of CO2 and methanol into dimethyl carbonate (DMC) was investigated. XRD, N2 adsorption-desorption, FT-IR, XPS, SEM and TEM were used to investigate the physical and chemical properties of UiO-66 @CeO2. The results showed that the framework structure of UiO-66 benefit the high dispersion of CeO2, while the loading of CeO2 provided more oxygen vacancies, which promoted the capture and absorb of CO2, thus promoted the reaction synergistically. Among which, UiO-66 @CeO2-60 showed best activity, with the highest DMC formation rate of 2.84 mmol·g−1·h−1 (yield: 2.27%) within 4 h of reaction time under the optimum conditions. In addition, the catalyst also showed favorable reusability, maintaining ∼90% of catalytic efficiency with 4 reuse cycles compared the fresh ones.

DFT Investigations of the Reaction Mechanism of Dimethyl Carbonate Synthesis from Methanol and CO on Various Cu Species in Y Zeolites

In this study, a density functional theory method is employed to investigate the reaction mechanisms of dimethyl carbonate (DMC) formation, through oxidative carbonylation of methanol, on four types of Y zeolites doped with Cu+, Cu2+, Cu2O and CuO, respectively. A common chemical route is found for these zeolites and identified as, first, the adsorbed CH3OH is oxidized to CH3O species; subsequently, CO inserts into CH3O to CH3OCO, which reacts with CH3O to form DMC rapidly; and finally, the adsorbed DMC is released into the gas phase. The rate-limiting step on Cu2+Y zeolite is identified as oxidation of CH3OH to CH3O with activation barrier of 66.73 kJ·mol−1. While for Cu+Y, Cu2O-Y and CuO-Y zeolites, the rate-limiting step is insertion of CO into CH3O, and the corresponding activation barriers are 63.73, 60.01 and 104.64 kJ·mol−1, respectively. For Cu+Y, Cu2+Y and Cu2O-Y zeolites, adsorbed CH3OH is oxidized to CH3O with the presence of oxygen, whereas oxidation of CH3OH on CuO-Y is caused by the lattice oxygen of CuO. The order of catalytic activities of these four types of zeolites with different Cu states follows Cu+Y ≈ Cu2O-Y > Cu2+Y > CuO-Y zeolite. Therefore, CuY catalysts with Cu+ and Cu2O as dominated Cu species are beneficial to the formation of DMC.

Carbon template synthesis of CeO2 catalyst for direct conversion of methanol and carbon dioxide to dimethyl carbonate

Dimethyl carbonate (DMC) is an interesting, value added chemical and a high energy additive to fuels. In this study, several CeO2 catalysts were successfully synthesized through carbon template method using two renewable sources of activated carbon. The structure of catalysts was fully resolved by XRD, SEM, N2-adsorption, NH3-TPD, CO2-TPD and XPS. CeO2 catalysts prepared using coconut shell activated carbon (CAC) template exhibit better surface morphology and improved catalytic performance compared to walnut shell activated carbon (WAC)-supported catalysts. We demonstrated a correlation between the efficiency of DMC synthesis and the abundance of moderately acidic and moderately basic active sites on the catalyst. It was found that the presence of oxygen vacancies (Vo) facilitates carbonyl bond cleavage of CO2. The best-performing catalyst was 4% CeO2/CAC owing to the richest Vo and the optimum acid/base properties. Moreover, a plausible catalytic mechanism of DMC formation was proposed, and includes the interaction between methoxy carbonate (CH3OCO2−) formed with the aid of Vo and moderately basic sites and methyl cation (CH3+) formed on the moderately acidic sites.

Improvement of the Li metal-electrolyte interfacial stability by cis–trans polar conformer formation in a carbonate electrolyte

This work focuses on interfacial engineering by electrolyte modulation, that is, cis–trans polar conformer formation of dimethyl carbonate, as strategy to widen electrochemical stability window, thus improving cycleability of lithium-metal batteries.

Cerium doped Zr-based metal-organic framework as catalyst for direct synthesis of dimethyl carbonate from CO2 and methanol

The disadvantage of Ce/Zr metal oxide as catalyst for direct synthesis dimethyl carbonate (DMC) from CO2 and methanol is low DMC formation rate because of its low specific surface area and active sites. In this work, it can be improved by highly uniform dispersion cerium doped Zr-based metal-organic frameworks (UiO-66 MOFs), which were synthesized via a modified hydrothermal method. The as-prepared catalysts have been extensively characterized using XRD, BET, FT-IR, SEM, TEM, TGA, NH3-TPD, CO2-TPD, XPS techniques. Experimental evaluation results indicated that the highly uniform dispersed Ce-doped UiO-66 MOFs exhibited markedly improved catalytic performance than traditional Ce/Zr metal oxide catalyst. The highest yield of DMC catalyzed by Ce-UiO-66–2 was 0.295% (reaction time was 12 h; reaction temperature was 140 °C; reaction pressure was 11 MPa). Then, it was found that doping of Ce atoms into the zirconium lattice to produce UiO-66 MOFs could effectively increase the number of acidic and medium basic sites than UiO-66 (none Ce), thus could greatly enhance the catalytic performance. Moreover, using 2-cyanopyridine as dehydrating agent, the DMC yield could be further raised greatly. Last, based on reported literature and our results, a possible reaction mechanism over Ce-UiO-66-X was proposed.

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.

Novel Fe‐modified CeO2 Nanorod Catalyst for the Dimethyl Carbonate Formation from CO2 and Methanol

AbstractA series of Fe‐modified CeO2 catalysts with nanoparticle, nanorod, nanocube and nano‐octahedron morphologies were synthesized and applied for direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol. The Fe‐modification shows a remarkably promoting effect on the formation of DMC over Fe‐modified CeO2 nanorod. The DMC yield was improved from 0.202 to 2.568 mmol DMC per gcat by 2 %Fe‐modification of CeO2 nanorod. A synergistic effect among the moderate acid‐basic sites, specific surface area and surface composition resulted from Fe‐modification was proposed to be crucial to obtaining the high reactivity of DMC formation.

Encapsulating phosphotungstic acid within metal-organic framework for direct synthesis of dimethyl carbonate from CO2 and methanol

Direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol is a sustainable pathway for DMC production and CO2 utilization simultaneously. Herein, metal-organic framework MOF-808 with phosphotungstic acid (HPW) encapsulated into the micropore (HPW@MOF-808) prepared by a simple one-pot synthesis method was demonstrated to be an active heterogeneous catalyst for the direct synthesis of DMC with 1,1,1-trimethoxymethane as dehydrate agent. While HPW/MOF-808 sample prepared using impregnation method with HPW mainly aggregated on the surface of MOF-808 matrix was less active. The superior activity of HPW@MOF-808 was attributed to the encapsulation of HPW in the micropore of HPW@MOF-808 enabled more HPW interacting with Zr6 node to generate more additional HPW induced Bronsted acid sites (Zr-OH) and Lewis acid sites (W+) than HPW/MOF-808, which promoted the formation of methyl cation (rate-determine step in DMC synthesis) and subsequently accelerated the formation of DMC. Additionally, HPW@MOF-808 exhibited better reusability than HPW/MOF-808 since the interaction between the encapsulated HPW and Zr6 node inhibited the leaching of HPW during reaction. This work provided a promising strategy for the designing of efficient MOF based catalyst for direct synthesis of organic carbonate from CO2 and alcohol.

Urea methanolysis mechanism: a computational study

Theoretical study of the reactions of urea with methanol with the formation of O-methyl carbamate and reactions of O-methyl carbamate with methanol with the formation of dimethyl carbonate by the B3LYP and M06 methods has shown that these transformations can proceed according to the concert mechanism. Reactions involving methanol monomers cannot be real pathways for the formation of reaction products. In both transformations, reactions involving linear methanol dimers and trimers are kinetically and thermodynamically more preferable than reactions with methanol monomers. The stage that determines the rate of formation of dimethyl carbonate is the interaction of O-methyl carbamate with methanol associates. The interactions of urea with methanol associates with the formation of O-methylcarbamate are almost irreversible. However, the reactions of O-methylcarbamate with methanol associates with the formation of dimethyl carbonate are substantially reversible. This requires the use of measures to shift the equilibrium towards the reaction products in this interaction.

Synthesis of Dimethyl Carbonate by Transesterification of Propylene Carbonate with Methanol on CeO2-La2O3 Oxides Prepared by the Soft Template Method.

In this study, CeO2, La2O3, and CeO2-La2O3 mixed oxide catalysts with different Ce/La molar ratios were prepared by the soft template method and characterized by different techniques, including inductively coupled plasma atomic emission spectrometry, X-ray diffraction, N2 physisorption, thermogravimetric analysis, and Raman and Fourier transform infrared spectroscopies. NH3 and CO2 adsorption microcalorimetry was also used for assessing the acid and base surface properties, respectively. The behavior of the oxides as catalysts for the dimethyl carbonate synthesis by the transesterification of propylene carbonate with methanol, at 160 °C under autogenic pressure, was studied in a stainless-steel batch reactor. The activity of the catalysts was found to increase with an increase in the basic sites density. The formation of dimethyl carbonate was favored on medium-strength and weak basic sites, while it underwent decomposition on the strong ones. Several parasitic reactions occurred during the transformation of propylene carbonate, depending on the basic and acidic features of the catalysts. A reaction pathway has been proposed on the basis of the components identified in the reaction mixture.

In Situ IR Studies on the Mechanism of Dimethyl Carbonate Synthesis from Methanol and Carbon Dioxide

The synthesis of dimethyl carbonate (DMC) from methanol and Carbon dioxide (CO2) has been investigated over 5% Rh/Al2O3 catalyst. Diffuse Reflectance Infrared Fourier Transfer Spectroscopy (DRIFTS) was used to probe the reaction adsorbates which showed that activation of methanol and CO2 involves generation of intermediate methoxy species and formate ingredients, participating in elementary steps of DMC formation. Formation of DMC involves parallel routes comprising interaction of the OH group of Al2O3 through an acid/base mechanism and formate pathway with participation of metal sites. DMC in acid/base pathway is formed via methoxy species to form methoxy carbonate (CH3O)CO2 (active adsorbate), which then reacts with the methyl species to form DMC. The pathway involving metal Rh sites generates an additional elementary step for the involvement of CO2 in the reaction through active formate species. The synergy of parallel pathways determines the performance of the 5% Rh/Al2O3 catalyst. Further improvement of catalyst performance should be based on such a feature of the reaction mechanism.

Formation of Dimethyl Carbonate from CO2 and Methanol Catalyzed by Me2SnO: A Density Functional Theory Approach

The conversion of CO2 into dimethyl carbonate (DMC) is an environmental and industrial appealing topic because it contributes to reduce the emissions of CO2 and to increase its use as raw material. In the present study we employed the CAM-B3LYP/def2-SVP DFT approach to evaluate the thermodynamic and kinetic parameters for the catalytic conversion of CO2 and methanol into DMC. Starting with the activation of four methanol molecules by the [Me2SnO]2 dimer, we computed all the stationary points along the pathway to convert CO2 and methanol into the DMC. The capture of two CO2 molecules is promoted by an alkoxitin intermediate, in an exothermic process, with low activation energy. Formation of a first DMC occurs after an intramolecular rerrangement involving a tetrahedral intermediate. The formation of a second DMC may occur either in a process similar to the first one or by dimerization of the hemicarbonate formed after releasing the first DMC. In this pathway, the [Me2(OH)SnO(OMe)SnMe2]2 complex is formed. This complex is less reactive than [Me2Sn(OMe)2]2 but still conserves the catalytic activity. Identification of this mechanism suggests that the catalytic action of Me2SnO can be improved by modulating the formation of the final [Me2(OH)SnO(OMe)SnMe2]2 complex.

Supplementary Mechanism for Oxycarbonylation of Methanol Over CuY Catalyst: Origin of the Oxygen Atom in Methoxyl and Formation of By-Products

The reaction network of oxidative carbonylation of methanol (CH3OH) over CuY catalyst prepared by solid-state ion exchange of HY zeolite with CuCl was enriched by combination of in-situ diffuse reflectance infrared fourier transform spectroscopy and mass spectrometric. Based on the proposed mechanism of dimethyl carbonate formation on CuY in literature, this study mainly focused on the origin of the O atom in methoxyl and the reaction pathway for by-products formation. The interaction of the catalyst with different reactants and reactant mixtures (CH3OH, CH318OH, HCHO, O2, CH3OH/HCHO and CH318OH/CO/O2) was studied in detail. It was found that in the presence of CuOx or oxygen, methoxide species are generated by breaking of the O–H bond. Reaction of methoxide species with oxygen leads to the formation of formaldehyde (HCHO), followed by the generation of formate species through consecutive oxidation of HCHO.