Dimethyl Carbonate Yield Research Articles

The effect of NaF amount on solid base catalysts derived from F-Ca-Mg-Al layered double hydroxides and dimethyl carbonate synthesis

Versatile and environmentally benign dimethyl carbonate (DMC) synthesized by propylene carbonate (PC) and methanol via transesterification is green and energy efficient. A series of solid base catalysts derived from F-Ca-Mg-Al layered double hydroxides (LDHs) with different NaF amount were prepared, characterized and tested for the transesterification reaction. The properties of the catalysts modified by fluorine have improved obviously. The catalytic activity increases in the order of: FCMA-0.8 > FCMA-0.4 > FCMA-1.2 > FCMA-1.6 > FCMA-0, which is consistent with the total basic sites amount and the strong basic sites amount. FCMA-0.8 has the best catalytic activity as pure CaO catalyst, and the PC conversion, DMC selectivity and DMC yield are 66.8%, 97.4% and 65.1%, respectively. Furthermore, the DMC yield for FCMA-0.8 just decreased 3.9% (33.2% for CaO catalyst) after 10 recycles. FCMA-0.8 has good prospects in the transesterification of PC with methanol to DMC for industrial application.

Excess soluble alkalis to prepare highly efficient MgO with relative low surface oxygen content applied in DMC synthesis

The activities of various MgO catalysts, which were prepared from different methods such as hydration synthesis, thermal decomposition, combustion, sol–gel and co-precipitation, were conducted in dimethyl carbonate (DMC) synthesis via transesterification of ethylene carbonate with methanol. MgO-P-Na2CO3-3.14 synthesized by the excess Na2CO3 precipitation compared the best catalytic activity and stability, which could be reused for seven times without obvious deactivation. The DMC yield was as high as 69.97% at 68 °C. The transesterification reaction could be separated into two steps, and the samples obtained by NaOH precipitant exhibited better ring-opening capability, while the catalysts acquired by Na2CO3 precipitant displayed superior transesterification ability. The structure-performance relationship was evaluated by multiple characterization methods. The results indicated that the as-synthesized catalyst derived from dried precursors with more crystalline magnesium carbonate was favorable for the promotion of DMC yield, and MgO-P-Na2CO3-3.14 with more Mg-O pairs, which were the active center for the transesterification of 2-hydroxyethyl methyl carbonate (HEMC) intermediate with methanol, resulted in more moderately basic sites left that was in accordance with the DMC yield variation. MgO-P-Na2CO3-3.14 with greater BET surface area and mesopore volume, relative low surface oxygen content and larger moderately basic sites amount compared the excellent activity in DMC synthesis.

Facile reflux preparation of defective mesoporous ceria nanorod with superior catalytic activity for direct carbon dioxide conversion into dimethyl carbonate

Nanostructured ceria has drawn a great interest in sustainable catalysis research due to its unique oxygen release/storage capability. However, the conventional hydrothermal method for ceria preparation requires harsh conditions, which restrict its applications. Here we report a facile reflux process that is able to synthesize ceria nanorods in a mild environment. Particularly, it is found that the rapid reflux synthesis enables the formation of defective mesoporous structure in ceria catalysts, which enriches the surface with abundant trivalent Ce ions and oxygen vacancy sites. These features significantly improve the catalytic activity of ceria nanorod in synthesizing dimethyl carbonate (DMC) from methanol carbonation. Our result also reveals that the shorter reflux period for catalyst preparation can lead to a higher DMC yield due to the larger amounts of mesoporous defects and the higher concentrations of oxygen vacancies. Moreover, the reflux-synthesized ceria nanorods exhibit over 3 times higher DMC yield than hydrothermal counterpart, which can be attributed to their superior CO2 adsorption and activation capabilities as evidenced by combined surface characterizations. This study presents a practical strategy to synthesize CeO2 catalysts with exceptional catalytic activity by creating a defective mesoporous surface structure in a highly-efficient manner.

Effect of Cobalt Doping on the Stability of CaO‐Based Catalysts for Dimethyl Carbonate Synthesis via the Transesterification of Propylene Carbonate with Methanol

AbstractTo improve the stability of the a CaO catalyst with high activity in the synthesis of dimethyl carbonate (DMC) at low‐temperatures via the transesterification of propylene carbonate (PC) with methanol, a series of Co‐doped CaO nanoparticles were synthesized with different cobalt contents via the sol‐gel method, and the catalytic performance of these catalysts increased in the order of 0.7Ca0.3Co<0.8Ca0.2Co<CaO<0.95Ca0.05Co<0.9Ca0.1Co. The characterization results of BET, XRD, FT‐IR, SEM, TEM, CO2‐TPD and XPS indicated that the addition of cobalt to CaO could form a novel layered structure of the Ca3Co4O9 carrier, which favoured the formation of strongly basic sites and then improved the activation of PC and methanol. The catalytic activity of traditional metal oxide catalysts is lower than that of pure CaO; however, the initial activity of the novel layered structure of the 0.9Ca0.1Co catalyst reached 72.9 %, which is obviously higher than that of 65.8 % for CaO. Furthermore, the results of long‐term catalytic evaluation showed that the best 0.9Ca0.1Co catalyst exhibited a stable PC conversion of 95.4 % and DMC yield of 93.1 % at 65 °C even after 168 h in the reactive distillation reactor. The deactivation mechanism showed that the layered structure of Ca3Co4O9 could stabilize CaO and prolong the life of the catalyst.

Performance of supported metal catalysts in the dimethyl carbonate production by direct synthesis using CO2 and methanol

CO2 chemical transformation is an exciting way to reduce CO2 concentration in the atmosphere. The use of CO2 to produce dimethyl carbonate (DMC), a linear, biodegradable, low toxicity carbonate via direct synthesis, is one of the most promising routes from the environmental point of view. However, DMC direct synthesis presents obstacles such as unfavorable thermodynamics and catalytic deactivation due to the water produced as a by-product. Therefore, the development and optimization of a catalytic system that can overcome these obstacles are crucial. This study investigated the catalytic activity of iron nitrate (AC-Fe), copper nitrate (AC-Cu), magnesium nitrate (AC-Mg), and nickel nitrate (AC-Ni) impregnated in activated carbon for DMC direct synthesis. Catalysts were synthesized by the impregnation method and characterized by several techniques. Simulation results evidenced the major reaction steps and simplified models of a complex involving metallic catalysts and reactants. The optimization of the catalyst amount, pressure, temperature, and recyclability of the best catalyst under optimized conditions and in the presence of different dehydrating agents was also performed. Results showed that the AC-Fe catalyst is the most efficient in the DMC direct synthesis, with a yield of 23.5 % and a selectivity of 100 % (80 °C, 40 bar, and 24 h). Reaction optimization (120 °C, 40 bar, and 24 h) using (AC-Fe) as catalyst resulted in a DMC yield of approximately 30 %. The catalytic systems recycling proved that using the dehydrating agent right combination (molecular sieve) and catalyst (AC-Fe) can maintain selectivity at 100 %, slightly decreasing yield.

Dimethyl carbonate (DMC) synthesis from methanol and carbon dioxide in the presence of ZrO2 solid solutions and yield improvement by applying a natural convection circulation system

In this study, we conducted an initial screening of ZrO2 and M/ZrO2 (M = Al, Ca, Ce, Pr, and Y) catalysts employing a batch apparatus first and then applied the selected catalyst (Ce0.1Zr0.9O2) into a natural convection circulation system with dehydrating agents, for the direct synthesis of dimethyl carbonate (DMC) from methanol (MeOH) and CO2. During the initial screening, Ce0.1Zr0.9O2 showed the highest DMC yield at ∼ 0.64% with 100% selectivity at 170 °C. The catalytic reactivities of ZrO2 and M/ZrO2 solid solutions followed the order: Ce/ZrO2 > Y/ZrO2 > Pr/ZrO2 ≈ ZrO2 > Al/ZrO2 > Ca/ZrO2. The relationship between physical properties and the activity of the catalysts was evaluated. As a result, the specific surface area and the acidity/basicity were considered to be irrelevant to the catalytic activity. However, a clear relationship between the temperature-programmed desorption (TPD) profile of MeOH and the reactivity was revealed: the increase of the weak affinity sites leads to the increase of reactivity. During the direct DMC synthesis over Ce0.1Zr0.9O2 catalyst employing the natural convection circulation system with molecular sieves 3A, the DMC yield reached up to 14.3% with 100% selectivity, which was the highest yield so far using M/ZrO2 catalysts. Prior to the experiment with the natural convection circulation system, the initial conditions were determined based on the experimental results employing the batch apparatus, previous literature, and estimation results. Moreover, some factors affecting the DMC yield using the circulation system were studied, including the reaction rate, the circulation rate of the flow in the circulation system, and the dehydration rate in the dehydration part.

One-Pot Synthesis of Dimethyl Carbonate over a Binary Catalyst of an Ionic Liquid and an Alkali Carbonate under Low Pressure.

A mild and highly efficient approach has been developed for the one-pot synthesis of dimethyl carbonate (DMC) from epoxide, carbon dioxide, and methanol under low initial pressure. The key to the successful transformation is the use of a bicomponent catalytic system composed of a hydroxyl-functionalized ionic liquid and an alkali carbonate. This bicomponent catalytic system demonstrated excellent reusability in four runs. Under the optimal reaction conditions, a 64% yield of DMC from propylene oxide and an 81% yield of DMC from ethylene oxide were obtained.

The Influence of Iron Group Promoters on the Synthesis of Dimethyl Carbonate over CuY Catalysts Prepared via Modified Vapor Impregnation Method

CuY and CuMY (M = Fe, Co, Ni) catalysts were prepared by modified vapor impregnation using cupric acetylacetonate as copper source and M acetylacetonate as promoter. The catalysts were evaluated in heterogeneous catalytic vapor phase oxidative carbonylation of methanol to dimethyl carbonate (DMC). The catalyst samples were analyzed by XRD, H2-TPR, XPS, CO-TPD, and NH3‑TPD, and their catalytic performance was assessed in a fixed-bed reactor. The experimental results indicate that all introduced species were well dispersed on zeolite Y, and the addition of iron group promoters have effect on the Cu+ contents, acidity and CO adsorption-desorption performance. Finally the influence of various promoters was examined with the aim of increasing space-time yield of DMC from methanol. Space-time yield of DMC was increased with the addition of iron group promoters in the order Fe < Co < Ni, but the selectivity follows the order of Fe < Ni < Co, respectively.

Efficient fixation of CO2 into carbonates by tertiary N-functionalized poly(ionic liquids): Experimental-theoretical investigation

The efficiency and versatility of catalysts in the multi-step reaction of carbonates with carbon dioxide (CO2) as raw material are barely satisfactory. Herein, ternary copolymerized bifunctional poly(ionic liquid)s (TBPILs) rich in hydroxyls, halogen anions and tertiary N were fabricated via free radical copolymerization. Due to the ingenious modification of tertiary N in the polymeric framework to form multi-site activation with hydroxyls and halogen anions, the specific activity of TBPILs reached to 17.87 mmolSC m−2catal h−1 in CO2 cycloaddition reaction. Meanwhile, for the transesterification reaction of cyclic carbonates with methanol, by the introduction of tertiary N, the yield of dimethyl carbonate increased from trace to 80.31 % in the absence of any solvent or co-catalyst. Density functional theory calculations, combined with electrostatic potential and average local ionization energy analyses confirmed the dual roles of tertiary N in the formation of carbonates by CO2. This work provides an originality idea to design high-efficiency catalysts for CO2 insertion into carbonates, and study the effects of basic sites on CO2 conversion.

One-Pot, Metal-Free Synthesis of Dimethyl Carbonate from CO2 at Room Temperature

Herein, we report on the metal-free, one-pot synthesis of industrially important dimethyl carbonate (DMC) from molecular CO2 under ambient conditions. In this process, initially the CO2 was chemisorbed through the formation of a switchable ionic liquid (SIL), [DBUH] [CH3CO3], by the interaction of CO2 with an equivalent mixture of organic superbase 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU) and methanol. The obtained SIL further reacted with methyl iodide (CH3I) to form DMC. The synthesis was carried out in both dimethyl sulfoxide (DMSO) and methanol. Methanol is preferred, as it not only served as a reagent and solvent in CO2 capture and DMC synthesis, but it also assisted in controlling the side reactions between chemical species such as CH3I and [DBUH]+ cation and increased the yield of DMC. Hence, the use of methanol avoided the loss of captured CO2 and favored the formation of DMC with high selectivity. Under the applied reaction conditions, 89% of the captured CO2 was converted to DMC. DBU was obtained, achieving 86% recovery of its salts formed during the synthesis. Most importantly, in this report we describe a simple and renewable solvent-based process for a metal-free approach to DMC synthesis under industrially feasible reaction conditions.

Low-temperature fabrication of K2O supported mesoporous tetragonal ZrO2 solid base for synthesis of dimethyl carbonate

In the present work, a new strategy was developed to fabricate strong basicity on mesoporous zirconia by in-situ preservation of carbon species originated from organic template during the thermal treatment of mesoporous ZrO2. The carbon species was maintained on mesoporous zirconia by calcination in N2 prior to the introduction of base precursor KNO3. The decomposition temperature of KNO3 to strongly basic site K2O was significantly reduced from higher than 650℃ to about 400℃ in the presence of carbon species, which fascinatingly converted the endothermic decomposition reaction to exothermic process. More importantly, the tetragonal ZrO2 support with excellent mesostructure was well stabilized by the carbon species after introduction of K species. Therefore, K2O supported on mesoporous tetragonal zirconia (K2O/M-ZrO2-C) were successfully fabricated. The resultant mesoporous basic material presented good activity in the synthesis of dimethyl carbonate (DMC) and the DMC yield was 60.0 %, apparently higher than that (18.1 %) of the catalyst prepared without preserving carbon species (K2O/M-ZrO2). The strong basicity and the uniform mesopores of the catalyst were suggested to be contributed to the high activity. The obtained results will provide some fundamental understanding and guidance for rational catalyst design.

Effects of surface acid–base properties of ZrO2 on the direct synthesis of DMC from CO2 and methanol: A combined DFT and experimental study

ZrO2 is known as a prospective catalyst for the direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol, which is important for CO2 utilization and green chemicals production. To identify the relationship between catalytic activity and surface acid–base properties, here, hydroxylated tetragonal (t) and monoclinic (m) zirconia are explored using density function theory (DFT) calculations combined with catalytic activity tests, as well as various characterization techniques, including in situ Fourier transform infrared (FTIR) spectra and temperature-programmed desorption of CO2 and NH3. DMC is formed from the combination of methyl and methyl carbonates on both catalysts, and m-ZrO2 exhibits higher DMC yield than t-ZrO2. The amount and strength of surface Brønsted acid sites, rather than Lewis base sites and Lewis acid sites, strongly affect catalytic performance of ZrO2. In addition, compared with t-ZrO2, m-ZrO2 displays a smaller band gap which also facilitates its catalytic activity for DMC synthesis.

Enhancing the Dispersion of Cu-Ni Metals on the Graphene Aerogel Support for Use as a Catalyst in the Direct Synthesis of Dimethyl Carbonate from Carbon Dioxide and Methanol.

Graphene has attracted attention because of its interesting properties in catalyst applications including as a catalyst support; however, it is known that the graphene can be restacked, forming a graphite-like structure that leads to poor specific surface area. Hence, the high-porosity graphene aerogel was used as a Cu–Ni catalyst support to produce dimethyl carbonate (DMC) from carbon dioxide and methanol. In this work, we have introduced a new synthesis route, which can improve the dispersion of metal particles on the graphene aerogel support. Cu–Ni/graphene aerogel catalysts were synthesized by a two-step procedure: forming Cu–Ni/graphene aerogel catalysts via hydrothermal reduction and then Cu–Ni loading by incipient wetness impregnation. It is found that the catalyst prepared by the two-step procedure exhibits higher DMC yield (25%) and MeOH conversion (18.5%) than those of Cu–Ni loading only by an incipient wetness impregnation method. The results prove that this new synthesis route can improve the performance of Cu–Ni/graphene aerogel catalysts for DMC production.

Direct Transformation of Silica from Natural Resources to Form Tetramethoxysilane

Abstract A simple and practical method for direct synthesis of tetramethoxysilane (TMOS) from silica (SiO2) and methanol was achieved using a base catalyst and acetal as a dehydrant under carbon dioxide (CO2). The production of TMOS was strongly influenced by the kind of the acetal used, with 2,2-dimethoxypropane identified as the most effective dehydrant. We observed that the acetal used enabled the production of a high yield of dimethyl carbonate (DMC), which promoted the TMOS production. DMC is an intermediate product from the reaction of CO2 and methanol, which supported the SiO2 depolymerization process. When the reaction is conducted with 2,2-dimethoxypropane at 260 °C for 24 h, TMOS can be produced in up to 59% yield. For practical applications, the TMOS synthesis has been developed on a 250 mL and 1 L-scale reaction with constant yield (&amp;gt;50%) from various silica resources.

Evolution of the pore and framework structure of NaY zeolite during alkali treatment and its effect on methanol oxidative carbonylation over a CuY catalyst

Alkali treatment is widely used on aluminosilicate zeolites with high Si/Al ratios in order to fabricate mesopores in the framework. However, for zeolites with low Si/Al ratios, the effect of alkali treatment on the pore and framework structure needed further study. In this work, Y zeolite is treated with NaOH solutions of different concentrations and is used as the support for Cu-based catalysts for oxidative carbonylation of methanol to dimethyl carbonate. The physicochemical properties of the supports and corresponding catalysts are characterized by N2 adsorption–desorption, X-ray diffraction, X-ray fluorescence, transmission electron microscopy, inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, and H2-temperature-programmed reduction analyses. The results show that no obvious mesopores are formed under alkali treatment, even at high NaOH concentration. However, amorphous species present in the micropores of Y zeolite are removed, which increases the micropore surface area as well as the crystallinity. Simultaneously, the cage structure is partially destroyed, which also leads to a slight increase of the pore volume and surface area. The altered micropore structure eventually increases the content and accessibility of the exchanged Cu species, which is beneficial to the catalytic activity. When the concentration of NaOH is 0.6 M, the space time yield of dimethyl carbonate for the corresponding catalyst was 151.4 mg g−1 h−1 which is 3.3-fold higher than that of the untreated-Y-zeolite-supported Cu catalyst. However, further increasing the alkali treatment strength can seriously destroy the basic aluminosilicate structure of the Y zeolite and decrease its intrinsic ion-exchange capacity. This results in the formation of agglomerated CuO on the catalyst surface, which was not conducive to catalytic activity.

Understanding the synergy between MgO-CeO2 as an effective promoter and ionic liquids for high dimethyl carbonate production from CO2 and methanol

Direct conversion of carbon dioxide (CO2) to dimethyl carbonate (DMC) using methanol (MeOH) is an attractive approach to utilize CO2. However, this reaction is limited by low CO2 solubility and large amount water formation. For now, dehydrating agents are used to solve this problem. Our goal is to substitute to these dehydrating agents with more abundant porous metal oxide/ionic liquids (ILs) hybrid catalysts. Herein, we have prepared a glycol-based symmetrical cation with different anions assisted ILs combined with electrospun MgO-CeO2 metal oxide nanofiber sponge-500 (EMCMONS-500). The hybrid catalyst displays excellent performance towards DMC synthesis. Notably it showed 98.9% selectivity, and 73.1 mmol g−1 cat DMC yield within 3 h reaction time, 3 MPa CO2 pressure, 120 °C, and 1.12 mmol catalyst loading. In addition, the catalyst shows there is no change in yield and selectivity after several recycles. Furthermore, due to a sponge-like morphology of the EMCMONS-500 catalyst, in which the creation of strong heterojunction takes place which is confirmed by electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) measurements. On the other hand, ILs give tunable acidic properties, high thermal stability, less viscosity, and low vapor pressure. Therefore, EMCMONS-500 easily mixed into ILs and form a highly porous network which gives a huge surface to volume ratios to form a nanoconfinement structure which is helpful to capture more CO2. Considering these advantages of ILs-EMCMONS-500 can be suitable catalyst for CO2 utilization.

Highly dispersed Cu supported on mesoporous Al‐KIT‐6 for oxidative carbonylation of methanol to dimethyl carbonate

Microporous NaY zeolite is a common support of Cu catalysts for oxidative carbonylation of methanol, but the dispersion of Cu species on NaY is usually subjected to its micropore size. Here, ordered mesoporous KIT‐6 was employed as the support for Cu catalyst and Al was incorporated into its framework to increase the surface acidity, which eventually improves the surface exchange capacity and Cu dispersion. The evolution of the state of Cu species on KIT‐6 was analyzed combined with control of Cu loading. The physicochemical properties of the supports and corresponding catalysts were characterized by N2 adsorption–desorption, X‐ray diffraction, ammonia temperature programmed desorption, Fourier transform infrared spectra, transmission electron microscopy, hydrogen temperature programmed reduction, and X‐ray photoelectron spectroscopy. It was found that mesoporous KIT‐6 showed better Cu dispersion than microporous NaY zeolite. Agglomerated CuO, dispersed CuO, and Cu2+ are the major Cu species observed on the catalyst surface. The increased surface acidic sites of KIT‐6 by Al incorporation promoted the formation of Cu2+ and dispersion of CuO. With the increase in Cu loading, the Cu2+ content in the catalyst was decreased gradually along with increase in the bulk CuO. It was speculated that some exchanged Cu2+ could be transformed into highly dispersed CuO and even bulk CuO after calcination at a high Cu loading. Combined with the catalyst evaluation results, it was deduced that highly dispersed Cu2+ and CuO particles play significant roles in catalytic activity. The catalyst Cu/Al‐K‐10 achieved the highest space time yield of dimethyl carbonate of 135.4 mg/(g·h), which is 2.7 times the Cu/K‐10 owing to its more dispersed Cu species. This laid the basis for preparing highly dispersed Cu species on mesoporous silica supports.

Synthesis of nitrogen-containing ordered mesoporous carbon materials with tunable nitrogen distributions and their application for metal-free catalytic synthesis of dimethyl carbonates

Dicyandiamide (DCDA) was utilized as a facile nitrogen source for the fabrication of nitrogen-containing ordered mesoporous carbon (NOMC) samples via a one-pot soft-templating approach under aqueous phase. X-ray diffraction, N2 adsorption–desorption, Transmission electron microscopy, Scanning electron microscopy, Raman and X-ray photoelectron spectroscopy have been applied to analyze the physicochemical properties of the synthesized NOMC materials. The characterization results showed that the textural parameters (545–589 m2 g−1), graphitic crystallinity and distribution of various nitrogen species of the synthesized NOMC materials were largely dependent on the adding mass of DCDA. Besides DCDA, NOMC materials have been also successfully fabricated by employing urea and melamine as nitrogen sources. As metal-free heterogeneous catalysts, the NOMC materials showed good catalytic activity and selectivity in the transesterification of ethylene carbonate to dimethyl carbonate, affording a maximum yield of dimethyl carbonate up to 76 % at 3 h under 120 °C.

CeO2-x quantum dots with massive oxygen vacancies as efficient catalysts for the synthesis of dimethyl carbonate.

CeO2-x quantum dots with massive oxygen vacancies are obtained by a one-step single molecular synthesis strategy. The yield of dimethyl carbonate from CO2 and methanol is more than 5 times that for commercial CeO2 nanoparticles.

Greener synthesis of dimethyl carbonate from carbon dioxide and methanol using a tunable ionic liquid catalyst

AbstractSeveral types of ionic liquids (ILs) performance towards dimethyl carbonate (DMC) synthesis using cheap reactant (methanol) and waste CO2 which is abundantly available in the environment are discussed. We synthesized ILs with cheap raw materials such as ethylene glycol. The main aim of this study is to synthesize efficient catalysts for the production of profitable fuel additives. ILs show high thermal stability, less viscosity, and low vapor pressure. In addition, some ILs have high CO2 absorption capacity due to moderate acid-base properties. These ILs reversibly capture more CO2 which is more efficient towards mass transport of methanol at optimum reaction conditions which enhance the DMC yield. This catalytic system is easily reusable for several reactions without decreased performance under the same reaction conditions. These reaction conditions had an effect on the synthesis of DMC. Temperature, pressure, IL loading, and IL/DMAP ratio were fine tuned. We propose a mechanism which the reaction may follow. The synthesized ILs required moderate reaction conditions and reduce waste gases (CO2) from the environments as they have high CO2 absorption capacity compared to the metal oxide catalyst. Therefore, this catalytic system helps and gives new direction to synthesize new catalyst for other application.