The catalyst screening tests for carbon dioxide oxidative coupling of methane (CO2-OCM) have been investigated over ternary and binary metal oxide catalysts. The catalysts are prepared by doping MgO- and CeO2-based so...The catalyst screening tests for carbon dioxide oxidative coupling of methane (CO2-OCM) have been investigated over ternary and binary metal oxide catalysts. The catalysts are prepared by doping MgO- and CeO2-based solids with oxides from alkali (Li2O), alkaline earth (CaO), and transition metal groups (WO3 or MnO). The presence of the peroxide (O2-2) active sites on the Li2O2, revealed by Raman spectroscopy, may be the key factor in the enhanced performance of some of the Li2O/MgO catalysts. The high reducibility of the CeO2 catalyst, an important factor in the CO2-OCM catalyst activity, may be enhanced by the presence of manganese oxide species. The manganese oxide species increases oxygen mobility and oxygen vacancies in the CeO2 catalyst. Raman and Fourier Transform Infra Red (FT-IR) spectroscopies revealed the presence of lattice vibrations of metal-oxygen bondings and active sites in which the peaks corresponding to the bulk crystalline structures of Li2O, CaO, WO3 and MnO are detected. The performance of 5%MnO/15%CaO/CeO2 catalyst is the most potential among the CeO2-based catalysts, although lower than the 2%Li2O/MgO catalyst. The 2%Li2O/MgO catalyst showed the most promising C2+ hydrocarbons selectivity and yield at 98.0% and 5.7%, respectively.展开更多
Glycerol dehydration to acrolein over a series of supported silicotungstic acid catalysts(SiWx‐Al/Zry)was investigated.Characterization results showed that the final catalyst had high thermal stability,a large pore d...Glycerol dehydration to acrolein over a series of supported silicotungstic acid catalysts(SiWx‐Al/Zry)was investigated.Characterization results showed that the final catalyst had high thermal stability,a large pore diameter,strong Lewis acidic sites,and a large specific surface area.X‐ray photoelectron survey spectra clearly showed peaks attributable to W(W4f=35.8eV),Al2O3(Al2p=74.9eV),and ZrO2(Zr3d=182.8eV).The highest acrolein selectivity achieved was87.3%at97%glycerol conversion over the SiW20‐Al/Zr10catalyst.The prepared catalysts were highly active and selective for acrolein formation even after40h because of the presence of high concentrations of Lewis acidic sites,which significantly reduced the amount of coke on the catalyst surface.Response surface methodology optimization showed that87.7%acrolein selectivity at97.0%glycerol conversion could be obtained under the following optimal reaction conditions:0.5wt%catalyst,reaction temperature300°C,and feed glycerol concentration10wt%.Evaluation of a mass‐transfer‐limited regime showed the absence of internal and external diffusions over pellets of diameter dP<20μm.These results show that glycerol dehydration over a strong Lewis acid catalyst is a promising method for acrolein production.展开更多
Thin films of Bismuth Telluride (Bi<sub>2</sub>Te<sub>3</sub>) are prepared by thermal evaporation from nanopowders on the glass substrates. The XRD patterns of films show that all the films ar...Thin films of Bismuth Telluride (Bi<sub>2</sub>Te<sub>3</sub>) are prepared by thermal evaporation from nanopowders on the glass substrates. The XRD patterns of films show that all the films are polycrystalline and the crystalline increased by annealing temperature. Measuring of the thermoelectric power of thin films in the temperature range 300 to 380 K shows that Seebeck Coefficients have both negative and positive values, indicating that the films have both n-type and p-type conductivity. The re-crystallization of films is done by annealing from 130°C to 175°C and Seebeck Coefficient varied from -150 to 100 μV/K.展开更多
This paper deals with thermodynamic chemical equilibrium analysis using the method of direct minimization of Gibbs free energy for all possible CH4 and CO2 reactions. The effects of CO2/CH4 feed ratio, reaction temper...This paper deals with thermodynamic chemical equilibrium analysis using the method of direct minimization of Gibbs free energy for all possible CH4 and CO2 reactions. The effects of CO2/CH4 feed ratio, reaction temperature, and system pressure on equilibrium composition, conversion, selectivity and yield were studied. In addition, carbon and no carbon formation regions were also considered at various reaction temperatures and CO2/CH4 feed ratios in the reaction system at equilibrium. It was found that the reaction temperature above 1100 K and CO2/CH4 ratio=1 were favourable for synthesis gas production with H2/CO ratio unity, while carbon dioxide oxidative coupling of methane （CO2 OCM） reaction to produce ethane and ethylene is less favourable thermodynamically. Numerical results indicated that the no carbon formation region was at temperatures above 1000 K and CO2/CH4 ratio larger than 1.展开更多
A dual-bed catalytic system is proposed for the direct conversion of methane to liquid hydrocarbons. In this system, methane is converted in the first stage to oxidative coupling of methane （OCM） products by selecti...A dual-bed catalytic system is proposed for the direct conversion of methane to liquid hydrocarbons. In this system, methane is converted in the first stage to oxidative coupling of methane （OCM） products by selective catalytic oxidation with oxygen over La-supported MgO catalyst. The second bed, comprising of the HZSM-5 zeolite catalyst, is used for the oligomerization of OCM light hydrocarbon products to liquid hydrocarbons. The effects of temperature （650-800 ℃）, methane to oxygen ratio （4-10）, and SIO2/Al2O3 ratio of the HZSM-5 zeolite catalyst on the process are studied. At higher reaction temperatures, there is considerable dealumination of HZSM-5, and thus its catalytic performance is reduced. The acidity of HZSM-5 in the second bed is responsible for the oligomerization reaction that leads to the formation of liquid hydrocarbons. The activities of the oligomerization sites were unequivocally affected by the SiO2/Al2O3 ratio. The relation between the acidity and the activity of HZSM-5 is studied by means of TPD-NH3 techniques. The rise in oxygen concentration is not beneficial for the C5＋ selectivity, where the combustion reaction of intermediate hydrocarbon products that leads to the formation of carbon oxide （CO＋CO2） products is more dominant than the oligomerization reaction. The dual-bed catalytic system is highly potential for directly converting methane to liquid fuels.展开更多
Mycoparasitic species of Trichoderma are commercially applied as biological control agents against various fungal pathogens. The mycoparasitic interaction is host specific and includes recognition, attack and subseque...Mycoparasitic species of Trichoderma are commercially applied as biological control agents against various fungal pathogens. The mycoparasitic interaction is host specific and includes recognition, attack and subsequent penetration and killing of the host. Investigations on the underlying events revealed that Trichoderma responds to multiple signals from the host (e.g. lectins or other ligands such as low molecular weight components released from the host’s cell wall) and host attack is accompanied by morphological changes and the secretion of hydrolytic enzymes and antibiotics. Degradation of the cell wall of the host fungus is-besides glucanases and proteases-mainly achieved by chitinases. In vivo studies showed that the ech42 gene (encoding endochitinase 42) is expressed before physical contact of Trichoderma with its host, probably representing one of the earliest events in mycoparasitism, whereas Nag1 (N-acetylglucosaminidase) plays a key role in the general induction of the chitinolytic enzyme system of T. atroviride . Investigations on the responsible signal transduction pathways of T. atroviride led to the isolation of several genes encoding key components of the cAMP and MAP kinase signaling pathways, as alpha and β subunits of heterotrimeric G proteins, the regulatory subunit of cAMP-dependent protein kinase, adenylate cyclase, and three MAP kinases. Analysis of knockout mutants, generated by Agrobacterium-mediated transformation, revealed that at least two alpha-subunits of heterotrimeric G proteins are participating in mycoparasitism-related signal transduction. The Tga1 G alpha subunit was shown to be involved in mycoparasitism-related processes such as chitinase expression and overproduction of toxic secondary metabolites, whereas Tga3 was found to be completely avirulent showing defects in chitinase formation and host recognition.展开更多
In this study,activated carbon was synthesized from palm oil empty fruit bunches through two different carbonization and activation processes and was used as carbon-based electrodes for supercapacitor.The activated ca...In this study,activated carbon was synthesized from palm oil empty fruit bunches through two different carbonization and activation processes and was used as carbon-based electrodes for supercapacitor.The activated carbon was produced by a combination of the hydrothermal and pyrolysis methods using melamine as a nitrogen source dopant and potassium chloride as an activating agent.The effect of pyrolysis temperature on the crystalline structure,crystallite size,functional groups,and surface characteristics of the resulting activated carbon,which was applied as electrodes in an electric double-layer capacitor.The performance of the activated carbon-based electrodes was evaluated,suggesting that activated carbon prepared by pyrolysis at 950°C showed the highest specific capacitance of 389.122 F/g at a current density of 1 A/g with energy and power densities of 13.511 and 125 W/kg,respectively.Overall results suggest that palm oil empty fruit bunches are promising cellulosic sources in synthesizing activated carbon-based electrodes for supercapacitors.展开更多
The research focuses on evaluating how well new solvents attract light hydrocarbons,such as propane,methane,and ethane,in natural gas sweetening units.It is important to accurately determine the solubility of hydrocar...The research focuses on evaluating how well new solvents attract light hydrocarbons,such as propane,methane,and ethane,in natural gas sweetening units.It is important to accurately determine the solubility of hydrocarbons in these solvents to effectively manage the sweetening process.To address this challenge,the study proposes using advanced empirical models based on artificial intelligence techniques like Multi-Layer Artificial Neural Network(ML-ANN),Support Vector Machines(SVM),and Least Square Support Vector Machine(LSSVM).The parameters for the SVM and LSSVM models are estimated using optimization methods like Genetic Algorithm(GA),Particle Swarm Optimization(PSO),and Shuffled Complex Evolution(SCE).Data on the solubility of propane,methane,and ethane in various ionic liquids are collected from reliable literature sources to create a comprehensive database.The proposed artificial intelligence models show great accuracy in predicting hydrocarbon solubility in ionic liquids.Among these,the hybrid SVM models perform exceptionally well,with the PSO-SVM hybrid model being particularly efficient computationally.To ensure a comprehensive analysis,different examples of hydrocarbons and their order are included.Additionally,a comparative analysis is conducted to compare the AI models with the thermodynamic COSMO-RS model for solubility analysis.The results demonstrate the superiority of the AI models,as they outperform traditional thermodynamic models across a wide range of data.In conclusion,this study introduces advanced artificial intelligence algorithms such as ML-ANN,SVM,and LSSVM in accurately estimating the solubility of hydrocarbons in ionic liquids.The incorporation of optimization techniques and variations in hydrocarbon examples improves the accuracy,precision,and reliability of these intelligent models.These findings highlight the significant potential of AI-based approaches in solubility analysis and emphasize their superiority over traditional thermodynamic models.展开更多
Recent advances with Pd containing catalysts for the selective hydrogenation of acetylene are described. The overview classifies enhancement of catalytic proper- ties for monometallic and bimetallic Pd catalysts. Acti...Recent advances with Pd containing catalysts for the selective hydrogenation of acetylene are described. The overview classifies enhancement of catalytic proper- ties for monometallic and bimetallic Pd catalysts. Activity/ selectivity of Pd catalysts can be modified by controllingparticle shape/morphology or immobilisation on a support which interacts strongly with Pd particles. In both cases enhanced ethylene selectivity is generally associated with modifying ethylene adsorption strength and/or changes to hydride formation. Inorganic and organic selectivity modifiers （i.e., species adsorbed onto Pd particle surface） have also been shown to enhance ethylene selectivity. Inorganic modifiers such as TiO2 change Pd ensemble size and modify ethylene adsorption strength whereas organic modifiers such as diphenylsulfide are thought to create a surface template effect which favours acetylene adsorption with respect to ethylene. A number of metals and synthetic approaches have been explored to prepare Pd bimetallic catalysts. Examples where enhanced selectivity is observed are generally associated with decreased Pd ensemble size and/or hindering of the ease with which an unselective hydride phase is formed for Pd. A final class of bimetallic catalysts are discussed where Pd is not thought to be the primary reaction site but merely acts as a site where hydrogen dissociation and spillover occurs onto a second metal （Cu or Au） where the reaction takes place more selectively.展开更多
Herein,we report the application of four amino-tris(phenolate)-based metal complexes incorporating Ti(IV)or Zr(IV)centres(2a-3b)as homogeneous catalysts for the conversion of CO_(2)and epoxides into cyclic carbonates....Herein,we report the application of four amino-tris(phenolate)-based metal complexes incorporating Ti(IV)or Zr(IV)centres(2a-3b)as homogeneous catalysts for the conversion of CO_(2)and epoxides into cyclic carbonates.The four complexes were synthesised,characterised and then evaluated in combination with tetrabutylammo-nium iodide,bromide or chloride as binary catalytic systems for the reaction of CO_(2)with 1,2-epoxyhexane as epoxide substrate at 12 bar CO_(2)pressure and 90?C for 2 h.The catalytic systems comprising the two Ti(IV)complexes(2a and 2b)showed similar performance.One notable exception was the catalytic system consisting of titanium complex 2b,bearing an axial Cl-ligand,and tetrabutylammonium chloride,which displayed higher catalytic activity compared to other titanium-based systems.Even higher activity was achieved with Zr(IV)complex 3a,bearing an axial isopropoxide ligand,which reached turnover numbers(TON metal)up to 1920 for the reaction of CO_(2)with 1,2-epoxyhexane at 12 bar CO_(2)pressure and 90?C for 2 h.This performance is comparable with that of state-of-the-art catalysts for this reaction.The catalytic system consisting of complex 3a and tetra-butylammonium bromide was explored further by investigating its applicability with a broad substrate scope,achieving quantitative conversion of several epoxides with CO_(2)into cyclic carbonate products at 90?C and 12 bar CO_(2)pressure for 18 h.The selectivity towards the cyclic carbonate products was?98%for all studied terminal epoxides and?80%for all examined cyclohexene-type epoxides.展开更多
文摘The catalyst screening tests for carbon dioxide oxidative coupling of methane (CO2-OCM) have been investigated over ternary and binary metal oxide catalysts. The catalysts are prepared by doping MgO- and CeO2-based solids with oxides from alkali (Li2O), alkaline earth (CaO), and transition metal groups (WO3 or MnO). The presence of the peroxide (O2-2) active sites on the Li2O2, revealed by Raman spectroscopy, may be the key factor in the enhanced performance of some of the Li2O/MgO catalysts. The high reducibility of the CeO2 catalyst, an important factor in the CO2-OCM catalyst activity, may be enhanced by the presence of manganese oxide species. The manganese oxide species increases oxygen mobility and oxygen vacancies in the CeO2 catalyst. Raman and Fourier Transform Infra Red (FT-IR) spectroscopies revealed the presence of lattice vibrations of metal-oxygen bondings and active sites in which the peaks corresponding to the bulk crystalline structures of Li2O, CaO, WO3 and MnO are detected. The performance of 5%MnO/15%CaO/CeO2 catalyst is the most potential among the CeO2-based catalysts, although lower than the 2%Li2O/MgO catalyst. The 2%Li2O/MgO catalyst showed the most promising C2+ hydrocarbons selectivity and yield at 98.0% and 5.7%, respectively.
基金the Ministry of Science, Technology and Innovation (MOSTI), Malaysia for supporting the project under project no. 03–01–06–SF0963
文摘Glycerol dehydration to acrolein over a series of supported silicotungstic acid catalysts(SiWx‐Al/Zry)was investigated.Characterization results showed that the final catalyst had high thermal stability,a large pore diameter,strong Lewis acidic sites,and a large specific surface area.X‐ray photoelectron survey spectra clearly showed peaks attributable to W(W4f=35.8eV),Al2O3(Al2p=74.9eV),and ZrO2(Zr3d=182.8eV).The highest acrolein selectivity achieved was87.3%at97%glycerol conversion over the SiW20‐Al/Zr10catalyst.The prepared catalysts were highly active and selective for acrolein formation even after40h because of the presence of high concentrations of Lewis acidic sites,which significantly reduced the amount of coke on the catalyst surface.Response surface methodology optimization showed that87.7%acrolein selectivity at97.0%glycerol conversion could be obtained under the following optimal reaction conditions:0.5wt%catalyst,reaction temperature300°C,and feed glycerol concentration10wt%.Evaluation of a mass‐transfer‐limited regime showed the absence of internal and external diffusions over pellets of diameter dP<20μm.These results show that glycerol dehydration over a strong Lewis acid catalyst is a promising method for acrolein production.
文摘Thin films of Bismuth Telluride (Bi<sub>2</sub>Te<sub>3</sub>) are prepared by thermal evaporation from nanopowders on the glass substrates. The XRD patterns of films show that all the films are polycrystalline and the crystalline increased by annealing temperature. Measuring of the thermoelectric power of thin films in the temperature range 300 to 380 K shows that Seebeck Coefficients have both negative and positive values, indicating that the films have both n-type and p-type conductivity. The re-crystallization of films is done by annealing from 130°C to 175°C and Seebeck Coefficient varied from -150 to 100 μV/K.
文摘This paper deals with thermodynamic chemical equilibrium analysis using the method of direct minimization of Gibbs free energy for all possible CH4 and CO2 reactions. The effects of CO2/CH4 feed ratio, reaction temperature, and system pressure on equilibrium composition, conversion, selectivity and yield were studied. In addition, carbon and no carbon formation regions were also considered at various reaction temperatures and CO2/CH4 feed ratios in the reaction system at equilibrium. It was found that the reaction temperature above 1100 K and CO2/CH4 ratio=1 were favourable for synthesis gas production with H2/CO ratio unity, while carbon dioxide oxidative coupling of methane （CO2 OCM） reaction to produce ethane and ethylene is less favourable thermodynamically. Numerical results indicated that the no carbon formation region was at temperatures above 1000 K and CO2/CH4 ratio larger than 1.
文摘A dual-bed catalytic system is proposed for the direct conversion of methane to liquid hydrocarbons. In this system, methane is converted in the first stage to oxidative coupling of methane （OCM） products by selective catalytic oxidation with oxygen over La-supported MgO catalyst. The second bed, comprising of the HZSM-5 zeolite catalyst, is used for the oligomerization of OCM light hydrocarbon products to liquid hydrocarbons. The effects of temperature （650-800 ℃）, methane to oxygen ratio （4-10）, and SIO2/Al2O3 ratio of the HZSM-5 zeolite catalyst on the process are studied. At higher reaction temperatures, there is considerable dealumination of HZSM-5, and thus its catalytic performance is reduced. The acidity of HZSM-5 in the second bed is responsible for the oligomerization reaction that leads to the formation of liquid hydrocarbons. The activities of the oligomerization sites were unequivocally affected by the SiO2/Al2O3 ratio. The relation between the acidity and the activity of HZSM-5 is studied by means of TPD-NH3 techniques. The rise in oxygen concentration is not beneficial for the C5＋ selectivity, where the combustion reaction of intermediate hydrocarbon products that leads to the formation of carbon oxide （CO＋CO2） products is more dominant than the oligomerization reaction. The dual-bed catalytic system is highly potential for directly converting methane to liquid fuels.
文摘Mycoparasitic species of Trichoderma are commercially applied as biological control agents against various fungal pathogens. The mycoparasitic interaction is host specific and includes recognition, attack and subsequent penetration and killing of the host. Investigations on the underlying events revealed that Trichoderma responds to multiple signals from the host (e.g. lectins or other ligands such as low molecular weight components released from the host’s cell wall) and host attack is accompanied by morphological changes and the secretion of hydrolytic enzymes and antibiotics. Degradation of the cell wall of the host fungus is-besides glucanases and proteases-mainly achieved by chitinases. In vivo studies showed that the ech42 gene (encoding endochitinase 42) is expressed before physical contact of Trichoderma with its host, probably representing one of the earliest events in mycoparasitism, whereas Nag1 (N-acetylglucosaminidase) plays a key role in the general induction of the chitinolytic enzyme system of T. atroviride . Investigations on the responsible signal transduction pathways of T. atroviride led to the isolation of several genes encoding key components of the cAMP and MAP kinase signaling pathways, as alpha and β subunits of heterotrimeric G proteins, the regulatory subunit of cAMP-dependent protein kinase, adenylate cyclase, and three MAP kinases. Analysis of knockout mutants, generated by Agrobacterium-mediated transformation, revealed that at least two alpha-subunits of heterotrimeric G proteins are participating in mycoparasitism-related signal transduction. The Tga1 G alpha subunit was shown to be involved in mycoparasitism-related processes such as chitinase expression and overproduction of toxic secondary metabolites, whereas Tga3 was found to be completely avirulent showing defects in chitinase formation and host recognition.
基金Osaka Gas Foundation of International Cultural Exchange grant,Japan(OGFICE),No.NKB-2669/UN2.F4.D/PPM.00.00/2023 for financial support.
文摘In this study,activated carbon was synthesized from palm oil empty fruit bunches through two different carbonization and activation processes and was used as carbon-based electrodes for supercapacitor.The activated carbon was produced by a combination of the hydrothermal and pyrolysis methods using melamine as a nitrogen source dopant and potassium chloride as an activating agent.The effect of pyrolysis temperature on the crystalline structure,crystallite size,functional groups,and surface characteristics of the resulting activated carbon,which was applied as electrodes in an electric double-layer capacitor.The performance of the activated carbon-based electrodes was evaluated,suggesting that activated carbon prepared by pyrolysis at 950°C showed the highest specific capacitance of 389.122 F/g at a current density of 1 A/g with energy and power densities of 13.511 and 125 W/kg,respectively.Overall results suggest that palm oil empty fruit bunches are promising cellulosic sources in synthesizing activated carbon-based electrodes for supercapacitors.
文摘The research focuses on evaluating how well new solvents attract light hydrocarbons,such as propane,methane,and ethane,in natural gas sweetening units.It is important to accurately determine the solubility of hydrocarbons in these solvents to effectively manage the sweetening process.To address this challenge,the study proposes using advanced empirical models based on artificial intelligence techniques like Multi-Layer Artificial Neural Network(ML-ANN),Support Vector Machines(SVM),and Least Square Support Vector Machine(LSSVM).The parameters for the SVM and LSSVM models are estimated using optimization methods like Genetic Algorithm(GA),Particle Swarm Optimization(PSO),and Shuffled Complex Evolution(SCE).Data on the solubility of propane,methane,and ethane in various ionic liquids are collected from reliable literature sources to create a comprehensive database.The proposed artificial intelligence models show great accuracy in predicting hydrocarbon solubility in ionic liquids.Among these,the hybrid SVM models perform exceptionally well,with the PSO-SVM hybrid model being particularly efficient computationally.To ensure a comprehensive analysis,different examples of hydrocarbons and their order are included.Additionally,a comparative analysis is conducted to compare the AI models with the thermodynamic COSMO-RS model for solubility analysis.The results demonstrate the superiority of the AI models,as they outperform traditional thermodynamic models across a wide range of data.In conclusion,this study introduces advanced artificial intelligence algorithms such as ML-ANN,SVM,and LSSVM in accurately estimating the solubility of hydrocarbons in ionic liquids.The incorporation of optimization techniques and variations in hydrocarbon examples improves the accuracy,precision,and reliability of these intelligent models.These findings highlight the significant potential of AI-based approaches in solubility analysis and emphasize their superiority over traditional thermodynamic models.
文摘Recent advances with Pd containing catalysts for the selective hydrogenation of acetylene are described. The overview classifies enhancement of catalytic proper- ties for monometallic and bimetallic Pd catalysts. Activity/ selectivity of Pd catalysts can be modified by controllingparticle shape/morphology or immobilisation on a support which interacts strongly with Pd particles. In both cases enhanced ethylene selectivity is generally associated with modifying ethylene adsorption strength and/or changes to hydride formation. Inorganic and organic selectivity modifiers （i.e., species adsorbed onto Pd particle surface） have also been shown to enhance ethylene selectivity. Inorganic modifiers such as TiO2 change Pd ensemble size and modify ethylene adsorption strength whereas organic modifiers such as diphenylsulfide are thought to create a surface template effect which favours acetylene adsorption with respect to ethylene. A number of metals and synthetic approaches have been explored to prepare Pd bimetallic catalysts. Examples where enhanced selectivity is observed are generally associated with decreased Pd ensemble size and/or hindering of the ease with which an unselective hydride phase is formed for Pd. A final class of bimetallic catalysts are discussed where Pd is not thought to be the primary reaction site but merely acts as a site where hydrogen dissociation and spillover occurs onto a second metal （Cu or Au） where the reaction takes place more selectively.
文摘Herein,we report the application of four amino-tris(phenolate)-based metal complexes incorporating Ti(IV)or Zr(IV)centres(2a-3b)as homogeneous catalysts for the conversion of CO_(2)and epoxides into cyclic carbonates.The four complexes were synthesised,characterised and then evaluated in combination with tetrabutylammo-nium iodide,bromide or chloride as binary catalytic systems for the reaction of CO_(2)with 1,2-epoxyhexane as epoxide substrate at 12 bar CO_(2)pressure and 90?C for 2 h.The catalytic systems comprising the two Ti(IV)complexes(2a and 2b)showed similar performance.One notable exception was the catalytic system consisting of titanium complex 2b,bearing an axial Cl-ligand,and tetrabutylammonium chloride,which displayed higher catalytic activity compared to other titanium-based systems.Even higher activity was achieved with Zr(IV)complex 3a,bearing an axial isopropoxide ligand,which reached turnover numbers(TON metal)up to 1920 for the reaction of CO_(2)with 1,2-epoxyhexane at 12 bar CO_(2)pressure and 90?C for 2 h.This performance is comparable with that of state-of-the-art catalysts for this reaction.The catalytic system consisting of complex 3a and tetra-butylammonium bromide was explored further by investigating its applicability with a broad substrate scope,achieving quantitative conversion of several epoxides with CO_(2)into cyclic carbonate products at 90?C and 12 bar CO_(2)pressure for 18 h.The selectivity towards the cyclic carbonate products was?98%for all studied terminal epoxides and?80%for all examined cyclohexene-type epoxides.
