In this work, a conceptual DFT investigation is carried out to study the electrophilic aromatic substitution reaction (SEAr) of 1,2-dimethoxybenzene and 3-(p-nitrobenzoyloxy)-but-3-en-2-one (a captodative olefin). Her...In this work, a conceptual DFT investigation is carried out to study the electrophilic aromatic substitution reaction (SEAr) of 1,2-dimethoxybenzene and 3-(p-nitrobenzoyloxy)-but-3-en-2-one (a captodative olefin). Herein, we have studied the regioselectivity of such reactions considering the effect of solvents of different polarities and the presence of BF3 as the catalyst. Understanding the effect of the solvent and the role of the Lewis catalyst on the pathway of Friedel-Crafts reactions is important to further facilitate the introduction of side chains in aromatic rings with captodative olefins, and thus be able to synthesize compounds analogous to natural products, e.g., α-asarone. Global and local reactivity descriptors were obtained, finding a key role when these reactions take place in the presence of nonpolar solvents. In addition, the Intrinsic Reaction Coordinate diagrams (IRCs) were calculated. Such results of the free activation energy (ΔG‡) clearly show that this reaction is entirely regioselective, forming the unique product in the para position, in agreement with our predictions of the local reactivity descriptors obtained from the Parr functions, wherein the first reaction step, the carbon C4 of the aromatic compound 1,2-dimethoxybenzene is favored. Moreover, from the IRCs, we found that the reactivity of the para adduct increases in the presence of nonpolar solvents. Interestingly, considering a polar solvent (MeCN), the intermediate formed (σ-complex) is more stable since it presents a more significant charge transfer with the solvent than the intermediate in the presence of a nonpolar solvent, making a reaction more challenging to reach when the reaction is carried out in the presence of MeCN because of the increasing of the energetic barrier from σ-complex to the TS2 in the intrinsic reactive coordinate diagram. Therefore, the polarity of the solvent plays an important role, particularly in the activation energy of the TS2. Our computational results explained our experimental results quite well, confirming the importance of the solvent’s polarity to this SEAr reaction and explaining why, experimentally, the nonpolar solvent drove the reaction under catalyzed conditions.展开更多
Most olefins （e.g., ethylene and propylene） will continue to be produced through steam cracking （SC） ofhydrocarbons in the coming decade. In an uncertain commodity market, the chemical industry is investingvery li...Most olefins （e.g., ethylene and propylene） will continue to be produced through steam cracking （SC） ofhydrocarbons in the coming decade. In an uncertain commodity market, the chemical industry is investingvery little in alternative technologies and feedstocks because of their current lack of economic viability,despite decreasing crude oil reserves and the recognition of global warming. In this perspective, some of themost promising alternatives are compared with the conventional SC process, and the major bottlenecks ofeach of the competing processes are highlighted. These technologies emerge especially from the abundanceof cheap propane, ethane, and methane from shale gas and stranded gas. From an economic point of view,methane is an interesting starting material, if chemicals can be produced from it. The huge availability ofcrude oil and the expected substantial decline in the demand for fuels imply that the future for proventechnologies such as Fischer-Tropsch synthesis （FFS） or methanol to gasoline is not bright. The abundance ofcheap ethane and the large availability of crude oil, on the other hand, have caused the SC industry to shiftto these two extremes, making room for the on-purpose production of light olefins, such as by the catalyticdehydrogenation of orooane.展开更多
The modified Ce-SAPO-34 catalysts were prepared with three methods, i.e., the liquid ion exchange with air calcination, impregnation with air calcination and impregnation with steam calcination methods. The catalytic ...The modified Ce-SAPO-34 catalysts were prepared with three methods, i.e., the liquid ion exchange with air calcination, impregnation with air calcination and impregnation with steam calcination methods. The catalytic performances of the catalysts for methanol to olefins were investigated. The properties of the catalysts were characterized using XRD, BET, XRF, FT-IR and NH3-TPD. The results indicated that compared to the SAPO-34 catalyst the catalyst prepared with the impregnation and air calcination prolonged the lifetime by 40 min and improved the selectivity to ethylene by 5% （mol） and the catalyst prepared with the impregnation and steam calcination showed the best modification effect, prolonging the lifetime by 70 min and improving the ethylene selectivity by 10% （mol）. The catalyst prepared with the liquid ion exchange showed similar behaviour as the SAPO-34 catalyst. It was verified that the porous structure and surface acidity of these catalysts determined their catalytic behaviors.展开更多
A systematic study was carried out to investigate the promotion effect of manganese on the performance of a coprecipitated iron-manganese bimetallic catalyst for the light olefins synthesis from syngas. The catalyst s...A systematic study was carried out to investigate the promotion effect of manganese on the performance of a coprecipitated iron-manganese bimetallic catalyst for the light olefins synthesis from syngas. The catalyst samples were characterized by N2 physisorption, transmis- sion electron microscopy （TEM）, X-ray photoelectron spectroscopy （XPS）, powder X-ray diffraction （XRD）, Mossbauer spectroscopy, H2- differential thermogravimetric analysis （H2-DTG）, CO temperature-programmed reduction （CO-TPR） and CO2 temperature-programmed des- orption （CO2-TPD）. The Fischer-Tropsch synthesis （FTS） performance of the catalyst was measured at 1.5 MPa, 250 ℃ and syngas with H2/CO ratio of 2.0. The characterization results indicated that the addition of manganese decreases the catalyst crystallite size, and improves the catalyst BET surface area and pore volume. The presence of manganese suppresses the catalyst reduction and carburization in H2, CO and syngas, respectively. The addition of manganese improves the catalytic activity of water-gas shift reaction and suppresses the oxidation of iron carbides in the FTS reaction. The incorporation of manganese improves the catalyst surface basicity and results in a significant improvement in the selectivities to light olefins and heavy hydrocarbons （C5＋）, and furthermore an inhibition of methane formation in FTS. The pure iron catalyst （Mn-00） has the highest initial FTS catalytic activity （65%） and the lowest selectivity （17.35 wt%） to light olefins （C2=-C4=）. The addition of an appropriate amount of manganese can improve the catalyst FTS activity.展开更多
文摘In this work, a conceptual DFT investigation is carried out to study the electrophilic aromatic substitution reaction (SEAr) of 1,2-dimethoxybenzene and 3-(p-nitrobenzoyloxy)-but-3-en-2-one (a captodative olefin). Herein, we have studied the regioselectivity of such reactions considering the effect of solvents of different polarities and the presence of BF3 as the catalyst. Understanding the effect of the solvent and the role of the Lewis catalyst on the pathway of Friedel-Crafts reactions is important to further facilitate the introduction of side chains in aromatic rings with captodative olefins, and thus be able to synthesize compounds analogous to natural products, e.g., α-asarone. Global and local reactivity descriptors were obtained, finding a key role when these reactions take place in the presence of nonpolar solvents. In addition, the Intrinsic Reaction Coordinate diagrams (IRCs) were calculated. Such results of the free activation energy (ΔG‡) clearly show that this reaction is entirely regioselective, forming the unique product in the para position, in agreement with our predictions of the local reactivity descriptors obtained from the Parr functions, wherein the first reaction step, the carbon C4 of the aromatic compound 1,2-dimethoxybenzene is favored. Moreover, from the IRCs, we found that the reactivity of the para adduct increases in the presence of nonpolar solvents. Interestingly, considering a polar solvent (MeCN), the intermediate formed (σ-complex) is more stable since it presents a more significant charge transfer with the solvent than the intermediate in the presence of a nonpolar solvent, making a reaction more challenging to reach when the reaction is carried out in the presence of MeCN because of the increasing of the energetic barrier from σ-complex to the TS2 in the intrinsic reactive coordinate diagram. Therefore, the polarity of the solvent plays an important role, particularly in the activation energy of the TS2. Our computational results explained our experimental results quite well, confirming the importance of the solvent’s polarity to this SEAr reaction and explaining why, experimentally, the nonpolar solvent drove the reaction under catalyzed conditions.
基金supported by the Long-Term Structural Methusalem Funding (BOF09/01M00409)by the Flemish Government and the European Union’s Horizon H2020 Programme (H2020SPIRE-0 4-2016) under grant agreement No. 72370 6+2 种基金financial support from SABIC Geleenfinancial support from a doctoral fellowship from the Fund for Scientific Research Flanders (FWO)
文摘Most olefins （e.g., ethylene and propylene） will continue to be produced through steam cracking （SC） ofhydrocarbons in the coming decade. In an uncertain commodity market, the chemical industry is investingvery little in alternative technologies and feedstocks because of their current lack of economic viability,despite decreasing crude oil reserves and the recognition of global warming. In this perspective, some of themost promising alternatives are compared with the conventional SC process, and the major bottlenecks ofeach of the competing processes are highlighted. These technologies emerge especially from the abundanceof cheap propane, ethane, and methane from shale gas and stranded gas. From an economic point of view,methane is an interesting starting material, if chemicals can be produced from it. The huge availability ofcrude oil and the expected substantial decline in the demand for fuels imply that the future for proventechnologies such as Fischer-Tropsch synthesis （FFS） or methanol to gasoline is not bright. The abundance ofcheap ethane and the large availability of crude oil, on the other hand, have caused the SC industry to shiftto these two extremes, making room for the on-purpose production of light olefins, such as by the catalyticdehydrogenation of orooane.
基金supported by the National Key Basic Research Development Program of China (NO: 2006CB202503)
文摘The modified Ce-SAPO-34 catalysts were prepared with three methods, i.e., the liquid ion exchange with air calcination, impregnation with air calcination and impregnation with steam calcination methods. The catalytic performances of the catalysts for methanol to olefins were investigated. The properties of the catalysts were characterized using XRD, BET, XRF, FT-IR and NH3-TPD. The results indicated that compared to the SAPO-34 catalyst the catalyst prepared with the impregnation and air calcination prolonged the lifetime by 40 min and improved the selectivity to ethylene by 5% （mol） and the catalyst prepared with the impregnation and steam calcination showed the best modification effect, prolonging the lifetime by 70 min and improving the ethylene selectivity by 10% （mol）. The catalyst prepared with the liquid ion exchange showed similar behaviour as the SAPO-34 catalyst. It was verified that the porous structure and surface acidity of these catalysts determined their catalytic behaviors.
基金supported by Natural Science Foundation of Chongqing Three Gorges University (12ZD14)Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, Southeast University
文摘A systematic study was carried out to investigate the promotion effect of manganese on the performance of a coprecipitated iron-manganese bimetallic catalyst for the light olefins synthesis from syngas. The catalyst samples were characterized by N2 physisorption, transmis- sion electron microscopy （TEM）, X-ray photoelectron spectroscopy （XPS）, powder X-ray diffraction （XRD）, Mossbauer spectroscopy, H2- differential thermogravimetric analysis （H2-DTG）, CO temperature-programmed reduction （CO-TPR） and CO2 temperature-programmed des- orption （CO2-TPD）. The Fischer-Tropsch synthesis （FTS） performance of the catalyst was measured at 1.5 MPa, 250 ℃ and syngas with H2/CO ratio of 2.0. The characterization results indicated that the addition of manganese decreases the catalyst crystallite size, and improves the catalyst BET surface area and pore volume. The presence of manganese suppresses the catalyst reduction and carburization in H2, CO and syngas, respectively. The addition of manganese improves the catalytic activity of water-gas shift reaction and suppresses the oxidation of iron carbides in the FTS reaction. The incorporation of manganese improves the catalyst surface basicity and results in a significant improvement in the selectivities to light olefins and heavy hydrocarbons （C5＋）, and furthermore an inhibition of methane formation in FTS. The pure iron catalyst （Mn-00） has the highest initial FTS catalytic activity （65%） and the lowest selectivity （17.35 wt%） to light olefins （C2=-C4=）. The addition of an appropriate amount of manganese can improve the catalyst FTS activity.
基金supported by the Natural Science Foundation of China (21306046)the Open Project of State Key Laboratory of Chemical Engineering (SKL-Che-15C03)+2 种基金the Fundamental Research Funds for the Central Universities (WA1514013)the 111 Project of Ministry of Education of China (B08021)supported by the China Scholarship Council (CSC) for the research at Norwegian University of Science and Technology (NTNU)
