Catalyst For Synthesis Of Dimethyl Carbonate Research Articles

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.

Surface reconstruction induced highly efficient N-doped carbon nanosheet supported copper cluster catalysts for dimethyl carbonate synthesis

N-doped hierarchical porous carbon nanosheets-supported copper catalysts (Cu/NCNS-x) were fabricated to solve the problem of deactivation caused by the leaching, agglomeration and oxidation of Cu nanoparticles (NPs) in the dimethyl carbonate (DMC) synthesis. The optimal Cu/NCNS-12 exhibited superb activity and stability without obvious deactivation after 10 cycles. The nanosheet structure produced new defects resulting in Cu reconstruction during the reaction process, while the strong interaction between Cu0 and N atoms greatly inhibited the oxidation of Cu0. The reconstruction of Cu was stimulated at above 100 °C, regardless of atmosphere, solvent types, pressure and rotation speed. The mechanism was elaborated that the initial Cu NPs (11 nm) migrated and then was trapped into newly created defects, finally formed into clusters (0.91 nm) as well as single-atom sites. This work provides profound potential in understanding metal reconstruction and developing a promising synthetic strategy of metal cluster catalysts.

Copper supported on phenanthroline‐functionalized porous polymer as an active catalyst for the oxidative carbonylation of methanol

Porous organic polymer has recently attracted tremendous interest because of its potential to combine the best features of homogeneous and heterogeneous catalysts. In this study, copper supported on phenanthroline‐functionalized porous polymer (Cu@PCP‐Phen) was prepared by a co‐polymerization method and used as a heterogeneous catalyst for dimethyl carbonate synthesis via the oxidative carbonylation of methanol. The catalyst was characterized by N2 adsorption, scanning electron microscopy, transmission electron microscopy, 13C solid‐state nuclear magnetic resonance, and X‐ray photoelectron spectroscopy, which suggested that it possessed a big surface area, hierarchical porous structure, and strong electron‐donating effect toward copper species. The Cu@PCP‐Phen catalyst showed high catalytic activity, which was significantly higher than those achieved with Cu‐based catalysts under similar reaction conditions. In addition, the catalyst can be easily separated and reused at least six times with only a slight decrease in activity. The salient features of this protocol are the simplicity in handling of the catalyst, high catalytic activity, excellent selectivity, low copper leaching, and good catalyst recyclability.

Hierarchical Porous Carbon-Supported Copper Nanoparticles as an Efficient Catalyst for the Dimethyl Carbonate Synthesis

A series of three-dimensional (3D)-interconnected hierarchical porous carbons (HPCs) were prepared through a “leavening” strategy. α-Cellulose and NaHCO3 were used as a raw material and foaming agent, respectively, to support copper catalysts (Cu/HPC) for dimethyl carbonate (DMC) synthesis by the oxidative carbonylation of methanol. The calcination temperature had a significant influence on the textural properties of the HPC and the catalytic performance of the Cu/HPC. The catalyst calcined at 900 °C exhibited the highest catalytic activity with a DMC space–time yield of 2018 mg/(g h). The characterization results indicated that the outstanding catalytic activity was related to the highest dispersion of copper species and to a high content of surface Cu0 species, which can be attributed mainly to the enhanced anchoring effect of abundant micro- and mesopores of a 3D-interconnected network. In addition, the well-developed 3D-interconnected hierarchical porous structure provided a rapid and efficient channel for reactant and product transport and migration, which enhanced the catalytic performance. This work expands the potential application range of HPC materials and presents a novel procedure to prepare catalysts for DMC synthesis.

ZrO2 Nanocrystals As Catalyst for Synthesis of Dimethylcarbonate from Methanol and Carbon Dioxide: Catalytic Activity and Elucidation of Active Sites.

The catalytic activity of zirconium oxide (ZrO2) nanocrystals for the reaction of carbon dioxide (CO2) with methanol to form dimethylcarbonate (DMC) was investigated. ZrO2 nanocrystals prepared by hydrothermal synthesis at various temperatures were compared. The size of the ZrO2 nanocrystals monotonically increased with the hydrothermal temperature, according to specific surface area, transmission electron microscope measurements, and their X-ray diffraction peak widths. The ZrO2 nanocrystals prepared by hydrothermal synthesis were found to exhibit high catalytic activity owing to their high surface area and catalytically active surfaces arising from their high crystallinity. Next, adsorbed species generated from CO2 on the ZrO2 surfaces were measured using CO2 temperature-programmed desorption (TPD) and in situ FT-IR spectroscopy. The results confirmed the presence of several kinds of adsorbed species including bidentate bicarbonate (b-HCO3-), bidentate carbonate (b-CO32-), and monodentate carbonate (m-CO32-). The relationship between the amounts of these surface species and the catalytic activity of the ZrO2 was investigated for the first time. The amount of the bidentate species (b-HCO3- and b-CO32-) was found to correlate well with the catalytic activity, demonstrating that the surface sites that afford these species contribute to the catalytic activity for this reaction.

Active ceria-calcium oxide catalysts for dimethyl carbonate synthesis by conversion of CO2

Carbon dioxide has generated great interest in recent years because of its potential usage as an alternative to traditional sources of carbon such as natural gas, petroleum and coal. In this paper, CO2 in combination with methanol was used for dimethyl carbonate (DMC) synthesis in presence of cerium-calcium mixed oxide catalysts. Catalysts with different Ce/Ca molar ratios were synthesized using surfactant templating method and characterized by powder X-ray diffraction (XRD), Raman spectroscopy, N2–sorption, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and temperature-programmed desorption (TPD) of CO2 and NH3. The direct conversion of CO2 was found to be highly dependent upon the acidity and basicity of catalysts. Brunauer-Emmett-Teller (BET) surface area of Ce3Ca1, Ce1Ca1 and Ce1Ca3 was found to be 102, 82, 109m2/g, respectively, and the average pore diameter was 9, 12 and 5nm, respectively. The Ce1Ca1 catalyst performed the best due to its combined acidic-basic properties. In addition, the catalyst was reused up to five cycles without significant loss of performance.

Effects of potassium promoter on the performance of PdCl 2 –CuCl 2 /AC catalysts for the synthesis of dimethyl carbonate from CO and methyl nitrite

The effect of potassium (K) promoter on the catalytic performance of activated carbon (AC) supported Wacker-type catalysts (PdCl2–CuCl2/AC) for the synthesis of dimethyl carbonate (DMC) from CO and methyl nitrite (MN) was investigated by means of N2 adsorption, H2-temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The experimental results showed that the space time yield of DMC on Wacker-type catalysts with different K promoters ranked in the following order: KCl > KOH > CH3COOK > K2CO3. Especially, the addition of KCl significantly improved the catalytic activities of PdCl2–CuCl2/AC catalyst for DMC synthesis from CO and MN. N2 adsorption data indicated that the addition of K promoters did not change the textural properties of Wacker-type catalysts greatly. H2-TPR and XPS results demonstrated that the existence of KCl promoted the reducibility of Cu2+ species and increased the proportion of Cu2+ species on catalyst surface, which is favorable for oxidizing Pd0 to active Pd2+. Further, the addition of KCl benefited the reactivity of PdCl2–CuCl2/AC catalyst for DMC synthesis from CO and MN.

Coating with mesoporous silica remarkably enhances the stability of the highly active yet fragile flower-like MgO catalyst for dimethyl carbonate synthesis

Flower-like MgO is a highly effective catalyst for the synthesis of dimethyl carbonate through the transesterification method, and coating the catalyst with mesoporous silica significantly enhances the stability of the MgO catalyst.

Calcined, Rare Earth Modified Hydrotalcite as a Solid, Reusable Catalyst for Dimethyl Carbonate Synthesis

An eco-friendly building block and fuel additive—dimethyl carbonate (DMC)—was synthesized through a benign route by transesterification of propylene carbonate (PC) with methanol. The catalytic activity of a series of calcined, rare earth elements (La3+, Ce3+, Pr3+, Sm3+, and Y3+; 2–10 mol %) incorporated Mg–Al hydrotalcites (HT) was evaluated for this reaction. Among several, the La (8 mol %) modified HT showed the highest activity (PC conversion = 65.4 mol % and DMC selectivity = 88 mol % at 150 °C and in 2 h). Basicity of the catalyst played an important role on the transesterification activity. The influence of reaction parameters and calcination temperature on the catalytic activity of HT was investigated. The La modified HT catalyst was heterogeneous and could be reused with little loss of activity.

CuCl2Immobilized on Amino-Functionalized MCM-41 and MCM-48 as Efficient Heterogeneous Catalysts for Dimethyl Carbonate Synthesis by Vapor-Phase Oxidative Carbonylation of Methanol

Pure silica mesoporous molecular sieves MCM-41 and MCM-48 organofunctionalized with 3-aminopropyltrimethoxysilane and N-[(3-trimethoxysilyl)propyl]ethylene-diamine, respectively, were served as supports to immobilize CuCl2 with conventional impregnation method. The supported copper catalysts showed a considerable enhancement in the reaction rate in heterogeneous vapor-phase oxidative carbonylation of methanol to produce dimethyl carbonate in comparison with that obtained by CuCl2-supported nonfunctionalized mesoporous silicas under identical conditions. The electronic donation of the amino groups, the accessibility and dischargeability of reactants in the regular mesopores probably account for the good catalytic performance as evidenced by the characteristic studies with XRD, BET, FTIR, TG-DTA, and XPS.

Surface properties of CuCl 2/AC catalysts with various Cu contents: XRD, SEM, TG/DSC and CO-TPD analyses

Surface properties of CuCl 2/activated carbon (AC) catalyst for dimethyl carbonate synthesis were studied by CO-TPD, XRD, SEM and thermogravimetry (TG)/differential scanning calorimetry (DSC) with varying Cu contents. CuCl 2/AC catalysts were prepared by impregnating AC with CuCl 2–ethanol solution in the range of Cu content from 2.8 to 18.7 wt.%. CuCl 2·2H 2O crystalline phase as active sites was gradually increased with an increase in Cu content. Appearance of CuCl 2·2H 2O was clearly identified by XRD and SEM. In relatively low Cu contents, 4.6 and 9.9 wt.%, CuCl 2·2H 2O was not detected in XRD. This indicates the formation of good dispersion of CuCl 2 compounds on activated carbon. However, DSC result revealed that CuCl 2·2H 2O was formed in multi-layers for the catalyst with Cu content more than 9.9 wt.%, which limit the catalyst activity. This fact was also strongly supported by CO-TPD experiment. The two CuCl 2/AC catalysts having Cu contents of 4.6 and 9.9 wt.% showed no difference in CO adsorption amount in TPD experiments.

Mesoporous bimetallic PdCl 2-CuCl 2 catalysts for dimethyl carbonate synthesis by vapor phase oxidative carbonylation of methanol

Dimethyl carbonate (DMC) synthesis reaction by oxidative carbonylation of methanol has been studied in a flow reaction system at atmospheric pressure in the presence of quaternary ammonium salt (QAS)-promoted bimetallic PdCl 2-CuCl 2 catalyst system supported on mesoporous HMS silica. The effects of the various QAS promoters, the promoter doping level and the Cu/Pd mole ratio were investigated, as well as the reaction conditions on the catalytic reactivates. The results showed that the tetrabutylammonium bromide (TBAB) promoted PdCl 2-CuCl 2/HMS catalyst system has the best catalytic performance. The characterization of PdCl 2-CuCl 2-TBAB/HMS catalysts was performed by means of BET, X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The essential role of TBAB promoter is to facilitate the Pd(0)/Pd(II) and Cu(II)/Cu(I) redox processes. The formation of substantial amounts of surface stabilized cuprous species on the bimetallic HMS catalysts may account for the significant enhancement of the catalytic performance in DMC synthesis.

Structure of the Active Sites on H3PO4/ZrO2 Catalysts for Dimethyl Carbonate Synthesis from Methanol and Carbon Dioxide

The catalytic properties of H3PO4/ZrO2 catalysts for dimethyl carbonate (DMC) synthesis from CH3OH and CO2 were investigated. The modification of ZrO2 with H3PO4 promoted the activity for selective DMC formation. The characterization of H3PO4/ZrO2 catalysts was performed by means of BET, XRD, 31P MAS NMR, LRS, DRIFT, and NH3-TPD. From the characterization results, it was determined that ZrO2 had Lewis acid sites and did not have Bronsted acid sites. The presence of Bronsted acid sites as well as Lewis acid sites was observed on H3PO4/ZrO2 (P/Zr = 0.05). The acidity of the Bronsted sites is weak, and the site's structure is a bridged OH. Furthermore, this Bronsted site is formed by the interaction between tetragonal Zr and P. In the reaction scheme of DMC formation, the Bronsted acid site can contribute to CH3OH activation and to the enhancement of the catalytic activity.

Kinetics of Dimethyl Carbonate Synthesis From Ethylene Carbonate and Methanol Using Alkali-Metal Compounds as Catalysts

Dimethyl carbonate (DMC) was synthesized by the ester exchange reaction of ethylene carbonate and methanol. K2 CO3 , KOH, LiOH and NaOH were used as catalysts for DMC synthesis and their catalytic abilities were compared in terms of kinetics. LiOH showed the best reaction rate among the catalysts. The rate constant was estimated to be 0.02538 (dm 3 /mol) 0.21 /min at 298 K.

EXAFS study of Cu/C catalysts

A local arrangement of copper in Cu/C catalysts for dimethylcarbonate synthesis was studied by EXAFS. The samples with various Cu content were prepared by impregnating of carbon carrier “Sibunit” with the alcohol solution of CuCl 2. It was determined, that the oxygen atoms from surface groups of carrier always enter into copper surrounding and the relative content of oxygen drops with the increase of Cu content in the samples. The structure of surface copper compounds for initial catalysts was proposed. Thus, samples with low Cu content (9×10 −4 mol/g-cat) possess surface compounds [carrier-COO–CuCl] or [carrier–CO–CuCl], further, by increasing copper content a second surface layer consisting of hydrated CuCl 2 non-bounded with carrier is formed.