Synthesis of Dimethyl Carbonate from Carbon Dioxide and Methanol over CexZr1-xO2 and [EMIM]Br/Ce0.5Zr0.5O2

Boosting Dimethyl Carbonate Production from CO2 and Methanol using Ceria-Ionic Liquid Catalyst

As a crucial strategy towards a sustainable chemical industry, the direct synthesis of dimethyl carbonate (DMC) from renewable carbon dioxide (CO2) and methanol (MeOH) is studied using CeO2 nanoparticles modified with 1-butyl-3-methylimidazolium hydrogen carbonate ([BMIm][HCO3]) devoid of stoichiometric dehydrating agents. The synthesized CeO2@[BMIm][HCO3] catalyst having high thermal stability harnesses the unique physicochemical properties of CeO2 and the ionic liquid to exhibit a DMC yield of 10.4 % and a methanol conversion of 16.1 % at optimal conditions (pressure of CO2=5 MPa; temperature=130 °C). The catalytic behavior of CeO2@[BMIm][HCO3] studied with a detailed XRD, XPS, CO2 and NH3-TPD, Raman spectroscopy, TGA, FTIR, SEM and TEM suggests that the synergy between the two catalytic components originating from an increased surface oxygen vacancies boosts the overall catalytic performance. After several recycling tests, the catalyst demonstrated no significant reduction in DMC yield and methanol conversion. This platform is an attractive approach to synthesize thermally stable nanoparticle@ionic liquid that retains and merges the physical attributes of both materials for producing useful bulk chemicals from readily available chemical resources.

Polymers without Petrochemicals: Sustainable Routes to Conventional Monomers

Access to a wide range of plastic materials has been rationalized by the increased demand from growing populations and the development of high-throughput production systems. Plastic materials at low costs with reliable properties have been utilized in many everyday products. Multibillion-dollar companies are established around these plastic materials, and each polymer takes years to optimize, secure intellectual property, comply with the regulatory bodies such as the Registration, Evaluation, Authorisation and Restriction of Chemicals and the Environmental Protection Agency and develop consumer confidence. Therefore, developing a fully sustainable new plastic material with even a slightly different chemical structure is a costly and long process. Hence, the production of the common plastic materials with exactly the same chemical structures that does not require any new registration processes better reflects the reality of how to address the critical future of sustainable plastics. In this review, we have highlighted the very recent examples on the synthesis of common monomers using chemicals from sustainable feedstocks that can be used as a like-for-like substitute to prepare conventional petrochemical-free thermoplastics.

Research progress of CO2 oxidative dehydrogenation of propane to propylene over Cr-free metal catalysts

CO₂-assisted oxidative dehydrogenation of propane (CO₂-ODHP) is an attractive strategy to offset the demand gap of propylene due to its potentiality of reducing CO₂ emissions, especially under the demands of peaking CO₂ emissions and carbon neutrality. The introduction of CO₂ as a soft oxidant into the reaction not only averts the over-oxidation of products, but also maintains the high oxidation state of the redox-active sites. Furthermore, the presence of CO₂ increases the conversion of propane by coupling the dehydrogenation of propane (DHP) with the reverse water gas reaction (RWGS) and inhibits the coking formation to prolong the lifetime of catalysts via the reverse Boudouard reaction. An effective catalyst should selectively activate the C-H bond but suppress the C-C cleavage. However, to prepare such a catalyst remains challenging. Chromium-based catalysts are always applied in industrial application of DHP; however, their toxic properties are harmful to the environment. In this aspect, exploring environment-friendly and sustainable catalytic systems with Cr-free is an important issue. In this review, we outline the development of the CO₂-ODHP especially in the last ten years, including the structural information, catalytic performances, and mechanisms of chromium-free metal-based catalyst systems, and the role of CO₂ in the reaction. We also present perspectives for future progress in the CO₂-ODHP.

En Route to CO2-Based (a)Cyclic Carbonates and Polycarbonates from Alcohols Substrates by Direct and Indirect Approaches

This review is dedicated to the state-of-the art routes used for the synthesis of CO2-based (a)cyclic carbonates and polycarbonates from alcohol substrates, with an emphasis on their respective main advantages and limitations. The first section reviews the synthesis of organic carbonates such as dialkyl carbonates or cyclic carbonates from the carbonation of alcohols. Many different synthetic strategies have been reported (dehydrative condensation, the alkylation route, the “leaving group” strategy, the carbodiimide route, the protected alcohols route, etc.) with various substrates (mono-alcohols, diols, allyl alcohols, halohydrins, propargylic alcohols, etc.). The second section reviews the formation of polycarbonates via the direct copolymerization of CO2 with diols, as well as the ring-opening polymerization route. Finally, polycondensation processes involving CO2-based dimethyl and diphenyl carbonates with aliphatic and aromatic diols are described.

Synthesis of Dimethyl Carbonate from CO2 and Methanol over Zr-Based Catalysts with Different Chemical Environments

The adsorption and activation of both CO2 and methanol are mainly affected by the distance of the Lewis acid site, Zr4+, and Lewis base, Zr4+/O2−, of the Zr-based catalysts. In this paper, Zr-incorporated SBA-15 (Zr-SBA-15) and Zr-grafted SBA-15 (Zr/SBA-15) catalysts were prepared with different Zr environments, and were analyzed with N2 adsorption–desorption isotherms, X-ray diffraction, UV-vis spectra, and XPS. It was proposed that Zr-SBA-15 catalyst with Si-O-Zr-OH and Zr-O-Si-OH structure exhibited non-adjacent sites between Zr4+ and Zr4+/O2−, while Zr/SBA-15 catalyst with Zr-O-Zr-OH structure showed neighboring sites between Zr4+ and Zr4+/O2−. Furthermore, the Zr/SBA-15 catalyst exhibited good catalytic activity, while no DMC was detected over the Zr-SBA-15 catalyst at the same reaction conditions. For combined in situ infrared and catalytic performance, it was indicated that the methanol and CO2 could be activated to form DMC, only when the Zr4+ and Zr4+/O2− sites existed and were adjacent to each other in the Zr-O-Zr-OH of Zr/SBA-15 catalyst.

Solid acid catalyzed carboxymethylation of bio-derived alcohols: an efficient process for the synthesis of alkyl methyl carbonates

Acid catalyzed carboxymethylation of alcohols is an emerging organic transformation that has grabbed the attention of scientific community in recent years. In the present study, sulfonated mesoporous polymer (MP-SO₃H) is presented as a highly active solid acid catalyst to convert a wide range of alcohols into alkyl methyl carbonates. The remarkable catalytic activity of MP-SO₃H is comparable to that of reported homogeneous acid catalysts. A good correlation was established between the catalytic activity and textural properties of the material. An exceptional catalytic activity of MP-SO₃H was observed for DMC mediated carboxymethylation of bio-derived alcohols which is unmatchable to conventional resins and zeolites. This superior activity of MP-SO₃H is ascribed to its intrinsic mesoporosity, high acid strength and uniform coverage of surface area by active sites. The catalyst is recyclable, resistant towards leaching and can be used in successive runs without losing the original activity. To the best of our knowledge, MP-SO₃H is the first solid acid catalyst to exemplify highest activity for the synthesis of different alkyl methyl carbonates using DMC. The protocol developed herein opens up new avenues to transform wide range of bio-alcohols into useful organic carbonates in the future.

Monolithic ZnxCe1−xO2 catalysts for catalytic synthesis of dimethyl carbonate from CO2 and methanol

The schematic diagram of reactor module comprised of honeycomb ceramic monolith with the catalysts for the synthesis of DMC.

Discovery of very active catalysts for methanol carboxylation into DMC by screening of a large and diverse catalyst library

The direct synthesis of dimethyl carbonate from methanol and CO₂ is particularly attractive as it provides a green alternative to other routes while allowing CO₂ conversion.

MxOy-ZrO2 (M = Zn, Co, Cu) Solid Solutions Derived from Schiff Base-Bridged UiO-66 Composites as High-Performance Catalysts for CO2 Hydrogenation

Metal-organic frameworks have been exploited as excellent solid precursors and templates for the preparation integrated nanocatalysts with multicomponent and hierarchical structures. Herein, a novel synthetic protocol has been developed to fabricate versatile Zr-based solid solutions (such as ZnO-ZrO₂, Co₃O₄-ZrO₂, and CuO-ZrO₂) via pyrolysis of Schiff base-modified UiO-66 octahedrons (size <100 nm), which were then utilized as efficient catalysts for CO₂ hydrogenation. The Schiff base serves as an effective bridge to dope secondary metal ions into UiO-66 frameworks with controlled amounts of 0.13-8.8 wt %, which are initially hard to achieve. Interestingly, by simply changing the loading metal ions, the selectivity of C₁ hydrogenation products can be facilely tuned. For instance, the maximum CO₂ conversion of ZnO-ZrO₂, Co₃O₄-ZrO₂, and CuO-ZrO₂ solid solutions were 5.8, 11.4, and 22.5%, with the main product selectivity of 70% CH₃OH, 92.5% CH₄, and 86.7% CO, respectively. Moreover, in situ diffuse reflectance infrared Fourier transform spectra characterization reveals that the significant difference in C₁ product selectivity is mainly determined by the balance of *HCOO, *CH₃O, and *CO intermediate species over the Zr-based solid solutions.

Dialkyl Carbonates in the Green Synthesis of Heterocycles

This review focuses on the use of dialkyl carbonates (DACs) as green reagents and solvents for the synthesis of several 5- and 6-membered heterocycles including: tetrahydrofuran and furan systems, pyrrolidines, indolines, isoindolines, 1,4-dioxanes, piperidines, and cyclic carbamates. Depending on the heterocycle investigated, the synthetic approach used was different. Tetrahydrofuran systems, pyrrolidines, indolines, isoindoline, and 1,4-dioxanes were synthesized using dimethyl carbonate (DMC) as sacrificial molecule (BAc2/BAl2 mechanism). Cyclic carbamates, namely 1,3-oxazin-2-ones, were prepared employing DACs as carbonylating agents, either by BAc2/BAl2 mechanism or through a double BAc2 mechanism. Piperidines were synthetized taking advantage of the anchimeric effect of a new family of dialkyl carbonates, i.e., mustard carbonates. Finally, in the case 5-hydroxymethylfurfural (HMF), DMC has been employed as efficient extracting solvent of this extensively investigated bio-based platform chemical from the reaction mixture. These synthetic approaches demonstrate, once again, the great versatility of DACs and their-yet to be fully explored-potential as green reagents and solvents in the synthesis of heterocycles.

Green chemical engineering in China

In China, the rapid development greatly promotes the national economic power and living standard but also inevitably brings a series of environmental problems. In order to resolve these problems fundamentally, Chinese scientists have been undertaking research in the area of green chemical engineering (GCE) for many years and achieved great progresses. In this paper, we reviewed the research progresses related to GCE in China and screened four typical topics related to the Chinese resources characteristics and environmental requirements, i.e. ionic liquids and their applications, biomass utilization and bio-based materials/products, green solvent-mediated extraction technologies, and cold plasmas for coal conversion. Afterwards, the perspectives and development tendencies of GCE were proposed, and the challenges which will be faced while developing available industrial technologies in China were mentioned.

Effect of In-Situ Dehydration on Activity and Stability of Cu–Ni–K2O/Diatomite as Catalyst for Direct Synthesis of Dimethyl Carbonate

An in-situ dehydrating system built in a continuous flow fixed-bed bubbling reactor for direct synthesis of dimethyl carbonate (DMC) was designed. 3A molecular sieve (MS) was selected as the ideal dehydrating agent and the water trapping efficiency was studied. The effect of dehydrating agent/catalyst ratio, the dehydrating temperature and pressure, as well as the space velocity on the direct DMC synthesis catalyzed by K2O-promoted Cu–Ni was further investigated. These results demonstrated that 3A MS could effectively dehydrate the reaction system at the optimal conditions of 120 °C and 1.0 MPa with gas space velocity (GHSV) of 600 h−1, thereby greatly shifting the reaction equilibrium toward high DMC yield. Higher DMC yield of 13% was achieved compared with undehydrated reaction. Moreover, the catalyst can be highly stabilized by 3A MS dehydration with stable performs over 22 h.

Driving dimethyl carbonate synthesis from CO2 and methanol and production of acetylene simultaneously using CaC2

The synthesis of dimethyl carbonate (DMC) from CO2 and methanol is a very interesting reaction, but is thermodynamically limited. In this work, CaC2 was used to consume the water produced in the reaction to shift the reaction equilibrium, and C2H2 was produced at the same time. This is the first work on the combination of driving a thermodynamically unfavorable reaction and producing C2H2 using CaC2.

TiO2-Doped CeO2 Nanorod Catalyst for Direct Conversion of CO2 and CH3OH to Dimethyl Carbonate: Catalytic Performance and Kinetic Study

A new class of TiO₂-doped CeO₂ nanorods was synthesized via a modified hydrothermal method, and these nanorods were first used as catalysts for the direct synthesis of dimethyl carbonate (DMC) from CO₂ and CH₃OH in a fixed-bed reactor. The micromorphologies and physical-chemical properties of nanorods were characterized by transmission electron microscopy, X-ray diffraction, N₂ adsorption, inductively coupled plasma atomic emission spectrometry, X-ray photoelectron spectroscopy, and temperature-programmed desorption of ammonia and carbon dioxide (NH₃-TPD and CO₂-TPD). The effects of the TiO₂ doping ratio on the catalytic performances were fully investigated. By doping TiO₂, the surface acid-base sites of CeO₂ nanorods can be obviously promoted and the catalytic activity can be raised evidently. Ti_0.04Ce_0.96O₂ nanorod catalysts exhibited remarkably high activity with a methanol conversion of 5.38% with DMC selectivity of 83.1%. Furthermore, kinetic and mechanistic investigations based on the initial rate method were conducted. Over the Ti_0.04Ce_0.96O₂ nanorod catalyst, the apparent activation energy of the reaction was 46.3 kJ/mol. The reaction rate law was determined to be of positive first-order to the CO₂ concentration and the catalyst loading amount. These results were practically identical with the prediction of the Langmuir-Hinshelwood mechanism in which the steps of CO₂ adsorption and activation are considered as rate-determining steps.

Synthesis of dimethyl carbonate from CO2 and methanol over a hydrophobic Ce/SBA-15 catalyst

A series of Ce/SBA-15 catalysts with different degrees of hydrophobicities were prepared via a post-grafting method and used for the direct synthesis of dimethyl carbonate (DMC) from CO₂ and methanol. The Ce/SBA-15-6 catalyst exhibited the highest DMC yield of 0.2%, which was close to the equilibrium value under the reaction conditions of 130 °C, 12 h and 12 MPa. The catalysts were characterized via XRD, BET, FT-IR, solid-state ²⁹Si MAS NMR, CA, TEM, XPS and NH₃/CO₂-TPD; the results indicated that the hydrophobicity of the catalysts facilitated the creation of oxygen vacancies, which could act as Lewis acids to activate methanol. Higher amounts of moderate acid sites led to higher yields of DMC. In addition, the hydrophobicity of the catalysts could also reduce the adsorbed water on their surface and increase the DMC yield while shortening the reaction time.

A series of Ce/SBA-15 catalysts with different degrees of hydrophobicities were prepared via a post-grafting method and used for the direct synthesis of dimethyl carbonate (DMC) from CO₂ and methanol.

Direct Synthesis of Dimethyl Carbonate from Carbon Dioxide and Methanol at Room Temperature Using Imidazolium Hydrogen Carbonate Ionic Liquid as a Recyclable Catalyst and Dehydrant

The direct synthesis of dimethyl carbonate (DMC) from CO₂ and CH₃ OH was achieved at room temperature with 74 % CH₃ OH conversion in the presence of an imidazolium hydrogen carbonate ionic liquid ([C_n C_m Im][HCO₃ ]). Experimental and theoretical results reveal that [C_n C_m Im][HCO₃ ] can transform quickly into a CO₂ adduct, which serves as an effective catalyst and dehydrant. Its dehydration ability is reversible. The energy barrier of the rate-determining step for the DMC synthesis is only 21.7 kcal mol^-1 . The ionic liquid can be reused easily without a significant loss of its catalytic and dehydrating ability.

Fixation of carbon dioxide into dimethyl carbonate over titanium-based zeolitic thiophene-benzimidazolate framework

A titanium-based zeolitic thiophene-benzimidazolate framework has been designed for the direct synthesis of dimethyl carbonate (DMC) from methanol and carbon dioxide. The developed catalyst activates carbon dioxide and delivers over 16% yield of DMC without the use of any dehydrating agent or requirement for azeotropic distillation.

Direct synthesis of dimethyl carbonate from CO2 and methanol over CaO–CeO2 catalysts: the role of acid–base properties and surface oxygen vacancies

The addition of CaO to the CeO₂ catalyst had a significant impact on the acid–base properties and amounts of oxygen vacancies on the surface catalyst.

Kinetic and mechanistic investigation for the copolymerization of CO2 and cyclohexene oxide catalyzed by trizinc complexes

The mechanism of CO₂/epoxide copolymerization catalyzed by Schiff base trizinc complexes.

Ionic liquid-based green processes for energy production

To mitigate the growing pressure on resource depletion and environment degradation, the development of green processes for the production of renewable energy is highly required. As a class of novel and promising media, ionic liquids (ILs) have shown infusive potential applications in energy production. Aiming to offer a critical overview regarding the new challenges and opportunities of ILs for developing green processes of renewable energy, this article emphasises the role of ILs as catalysts, solvents, or electrolytes in three broadly interesting energy production processes from renewable resources, such as CO2 conversion to fuels and fuel additives, biomass pretreatment and conversion to biofuels, as well as solar energy and energy storage. It is expected that this article will stimulate a generation of new ideas and new technologies in IL-based renewable energy production.

Continuous synthesis of diethyl carbonate from ethanol and CO2 over Ce–Zr–O catalysts

Continuous synthesis of diethyl carbonate from ethanol and CO₂ at the reaction equilibrium level is possible at low contact times.

Synthesis of cellulose methylcarbonate in ionic liquids using dimethylcarbonate

Dialkylcarbonates are viewed as low-cost, low-toxicity reagents, finding application in many areas of green chemistry. Homogeneous alkoxycarbonylation of cellulose was accomplished by applying dialkycarbonates (dimethyl and diethyl carbonate) in the ionic liquid-electrolyte trioctylphosphonium acetate ([P8881 ][OAc])/DMSO or 1-ethyl-3-methylimidazolium acetate ([emim][OAc]). Cellulose dialkylcarbonates with a moderate degree of substitution (DS∼1) are accessible via this procedure and cellulose methylcarbonate was thoroughly characterized for its chemical and physical properties after regeneration. This included HSQC & HMBC NMR, ATR-IR, molecular weight distribution, morphology, thermal properties, and barrier properties after film formation.

Catalytic CO2conversion to organic carbonates with alcohols in combination with dehydration system

This perspective highlights the direct synthesis of organic carbonates from CO₂and alcohols combined with dehydration systems.

Morphology control of ceria nanocrystals for catalytic conversion of CO2 with methanol

This paper describes the synthesis of ceria catalysts with octahedron, nanorod, nanocube and spindle-like morphologies via a template-free hydrothermal method. The surface morphologies, crystal plane and physical-chemical structures were investigated via field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and temperature-programmed desorption of ammonia and carbon dioxide (NH3-TPD and CO2-TPD). The catalytic performance over these ceria catalysts with different exposed planes were tested for dimethyl carbonate (DMC) synthesis from CO2 and methanol. The results showed that the spindle-like CeO2 showed the highest DMC yields, followed by nano-rods, nano-cubes and nano-octahedrons. A synergism among the exposed (111) plane, defect sites, and acid-basic sites was proposed to be crucial to obtaining the high reactivity of DMC formation.