Cobalt supported on carbon nanotubes (CNTs)-covered alumina has been recently developed and successfully utilized as a catalyst in Fischer-Tropsch synthesis (FTS). Problems associated with shaping of Co/CNTs into ...Cobalt supported on carbon nanotubes (CNTs)-covered alumina has been recently developed and successfully utilized as a catalyst in Fischer-Tropsch synthesis (FTS). Problems associated with shaping of Co/CNTs into extrudates or pellets as well as catalyst attrition rendered these materials unfavorable for industrial applications. In this investigation regular γ- and nano-structured (N-S) alumina as well as CNTs-covered regular γ- and N-S-alumina supports were impregnated by cobalt nitrate solution to make new cobalt-based catalysts which were also promoted by Ru. The catalysts were characterized and tested in a micro reactor to evaluate their applicability in FTS. γ-Al2O3 was prepared by calcination of bohemite and N-S-Al2O3 was prepared by sol-gel method using aluminum chloride as starting material. Catalyst evaluations indicated that N-S-Al2O3 was superior to regular γ-Al2O3 and that CNTs-covered alumina supports were favored over non-covered ones in terms of activity and heavy hydrocarbon selectivity. These were justified by porosimetric characteristics of the catalysts and existence of CNTs points of view. CNTs-covered catalysts also showed higher wax selectivity and better resistance to deactivation. Furthermore, TPR analysis indicated that the cobalt aluminate phase, which is responsible for the permanent deactivation of alumina supported Co-based catalysts, did not form on alumina supported Co-based catalysts covered with CNTs due to weaker interactions between cobalt and alumina.展开更多
Nitrogen(N)-doped carbon materials as metal catalyst supports have attracted signifi cant attention,but the eff ect of N dopants on catalytic performance remains unclear,especially for complex reaction processes such ...Nitrogen(N)-doped carbon materials as metal catalyst supports have attracted signifi cant attention,but the eff ect of N dopants on catalytic performance remains unclear,especially for complex reaction processes such as Fischer-Tropsch synthesis(FTS).Herein,we engineered ruthenium(Ru)FTS catalysts supported on N-doped carbon overlayers on TiO_(2)nanoparticles.By regulating the carbonization temperatures,we successfully controlled the types and contents of N dopants to identify their impacts on metal-support interactions(MSI).Our fi ndings revealed that N dopants establish a favorable surface environment for electron transfer from the support to the Ru species.Moreover,pyridinic N demonstrates the highest electron-donating ability,followed by pyrrolic N and graphitic N.In addition to realizing excellent catalytic stability,strengthening the interaction between Ru sites and N dopants increases the Ru^(0)/Ru^(δ+)ratios to enlarge the active site numbers and surface electron density of Ru species to enhance the strength of adsorbed CO.Consequently,it improves the catalyst’s overall performance,encompassing intrinsic and apparent activities,as well as its ability for carbon chain growth.Accordingly,the as-synthesized Ru/TiO_(2)@CN-700 catalyst with abundant pyridine N dopants exhibits a superhigh C_(5+)time yield of 219.4 mol CO/(mol Ru·h)and C_(5+)selectivity of 85.5%.展开更多
The direct oxidation of nitrogen is a potential pathway to achieving the zero-carbon-emission synthesis of nitric acid or nitrate, because it does not involve ammonia synthesis and additional ammonia oxidation process...The direct oxidation of nitrogen is a potential pathway to achieving the zero-carbon-emission synthesis of nitric acid or nitrate, because it does not involve ammonia synthesis and additional ammonia oxidation processes. However, the slow kinetics of nitrogen oxidation and the difficult selective control of oxidation products hinder the development of this process. In this study, a plasma-driven gas-liquid relay reaction system was developed to overcome these limitations. A typical feature of this reaction system is that it can efficiently generate NO_x under plasma exposure;moreover, the specific anions in the absorption solution can be oxidized to strong oxidants capable of relay oxidation of low-valence nitrogen oxides. This feature allows for the deep oxidation of nitrogen, thus enabling the oxidation products of nitrogen to exist in high-valence states in the absorption solution. For experimental verification, we achieved the 100% selective synthesis of nitrate under plasma exposure, with air as the supply gas and a sodium sulfate solution as the absorption solution.展开更多
NH_(3) selective catalytic reduction(SCR) has been widely recognized as a promising technique for reducing nitrogen oxides from diesel vehicle exhausts. High-efficiency SCR catalysts that could perform at low temperat...NH_(3) selective catalytic reduction(SCR) has been widely recognized as a promising technique for reducing nitrogen oxides from diesel vehicle exhausts. High-efficiency SCR catalysts that could perform at low temperatures are essential to denitration. In this work, a series of bimetallic CeCu-SAPO-34 molecular sieves were synthesized by one-step hydrothermal method. The Ce Cu-SAPO-34 maintained good crystallinity and a regular hexahedron appearance of Cu-SAPO-34 after introducing Ce species, while exhibiting a higher specific surface area and pore volume. The as-prepared CeCu-SAPO-34 with 0.02%(mass) Ce constituent exhibited the best catalytic activity below 300℃ and a maximum NO_(x) conversion of 99% was attained;the NO_(x) removal rates of more than 68% and 94% were achieved at 150℃ and 200℃, respectively. And the introduction of cerium species in Cu-SAPO-34 improves the low-temperature hydrothermal stability of the catalyst towards NH_(3)-SCR reaction. Additionally, the introduced Ce species could enhance the formation of abundant weak Br?nsted acid centers and promote the synergistic effect between CuO grains and isolated Cu^(2+) to enhance the redox cycle, which benefit the NH_(3)-SCR reaction.This work provides a facile synthesis method of high-efficiency SCR denitration catalysts towards diesel vehicles exhaust treatment under low temperature.展开更多
The Fischer-Tropsch synthesis is a significant technology for converting coal,natural gas,and biomass into synthetic fuels.In recent years,the use of microchannel reactors for the Fischer-Tropsch synthesis has attract...The Fischer-Tropsch synthesis is a significant technology for converting coal,natural gas,and biomass into synthetic fuels.In recent years,the use of microchannel reactors for the Fischer-Tropsch synthesis has attracted significant attention.Fischer-Tropsch synthesis experiments were carried out in a microchannel reactor and the influences of reaction conditions on the experimental results were investigated in this study.Based on the experimental data,a dynamic multi-component pseudo-homogeneous variable-volume flow model of microchannel reactors for the Fischer-Tropsch synthesis was built to determine the pressure-,velocity-,conversion-and(component-wise)concentration-distributions in reaction channels.The model takes into account the combined effects of gas volume expansion caused by the frictional pressure drop and gas volume contraction caused by reaction consumption.A novel effective method for calculating the pressure and superficial gas velocity values in microchannel reactors was proposed in the model.Besides that,two sets of experimental data were selected from references to evaluate the validity and accuracy of the model.The reaction performances in the microchannels were analyzed carefully based on the calculated results.展开更多
Silica, alumina, and activated carbon supported iron-cobalt catalysts were prepared by incipient wetness impregnation. These catalysts have been characterized by BET, X-ray diffraction (XRD), and temperature-program...Silica, alumina, and activated carbon supported iron-cobalt catalysts were prepared by incipient wetness impregnation. These catalysts have been characterized by BET, X-ray diffraction (XRD), and temperature-programmed reduction (TPR). Activity and selectivity of iron-cobalt supported on different carriers for CO hydrogenation were studied under the conditions of 1.5 MPa, 493 K, 630 h^-1, and H2/CO ratio of 1.6. The results indicate that the activity, C4 olefin/(C4 olefin+C4 paraffin) ratio, and C5 olefin/(C5 olefin+C5 paraffin) decrease in the order of Fe-Co/SiO2, Fe-Co/AC1, Fe-Co/Al2O3 and Fe- Co/AC2. The activity of Fe-Co/SiO2 reached a maximum. The results of TPR show that the Fe-Co/SiO2 catalyst is to some extent different. XRD patterns show that the Fe-Co/SiO2 catalyst differs significantly from the others; it has two diffraction peaks. The active spinel phase is correlated with the supports.展开更多
Fischer-Tropsch synthesis(FTS) is the key step in converting syngas into clean fuels. Traditional supported catalysts for FTS are problematic because the active metal crystalline size is positively related to metal lo...Fischer-Tropsch synthesis(FTS) is the key step in converting syngas into clean fuels. Traditional supported catalysts for FTS are problematic because the active metal crystalline size is positively related to metal loading. Therefore, increasing active metal loading may reduce the cobalt time yield(CTY) since a high CTY is usually obtained when the Co size is 8 nm. Here, a ZIF-67(Zeolitic imidazolate framework-67) with a MOF(Metal organic framework) structure is used as a precursor to prepare the Co@C catalyst with not only high cobalt loading(55.6 wt%) but also with a small cobalt crystal size(as small as 8.6 nm). Coreshell Co@C@SiO2-X catalysts with different SiO2 shell thicknesses were successfully prepared by coating different amounts of TEOS on the outer surface of Co@C to modify product selectivity. Compared with40 wt% Co/SiO2 catalyst, core-shell Co@C@SiO2-X catalysts exhibited improved FTS performance. Furthermore, different gaseous hourly space velocities(GHSVs) were used to obtain CO conversion at similar levels to compare CTY and the turnover frequency(TOF). Among the catalysts, the Co@C@SiO2-1 catalyst, with its better mass transfer ability and suitable hydrophilic property, presented the highest TOF(9.75 × 10-3 s-1) and lowest CH4 selectivity(9.75%). In addition, heavy hydrocarbons were effectively suppressed with the increase in shell thickness due to the increased mass transfer resistance.展开更多
Simple and efficient stereo-selective synthesis of exo-5-norbornene-2-carboxylic acid (NBCA) is reported. Preliminary studies on base promoted isomerization of methyl 5-norbornene-2-carboxylate (MNBC) revealed that ra...Simple and efficient stereo-selective synthesis of exo-5-norbornene-2-carboxylic acid (NBCA) is reported. Preliminary studies on base promoted isomerization of methyl 5-norbornene-2-carboxylate (MNBC) revealed that rapid isomerization was accomplished with sodium tert-butoxide (tBuONa), and the exo-content at the equilibrium was ca. 60%. The hydrolyses of endo-rich MNBC (endo/exo = 80/20) under various conditions were carried out. The exo selectivity for resulting NBCA was improved when the hydrolysis was conducted with equimolar water at room temperature in the presence of the stronger base (tBuONa) (endo/exo: 18/82). Whereas the use of excess amount of water led to rapid and non-selective hydrolysis affording high endo content of the product. The plausible reaction mechanism involving rapid equilibrium of thermodynamic isomerization and kinetically preferred hydrolysis of exo ester is proposed.展开更多
4-hydroxybenzoic acid was synthesized by one pot method using polymer-bonded β-aminopropionic acid-2-β-cyclodextrin as a catalyst.by which the selectivity for 4-hydroxybenzoic acid is 87%. A possible carboxylation m...4-hydroxybenzoic acid was synthesized by one pot method using polymer-bonded β-aminopropionic acid-2-β-cyclodextrin as a catalyst.by which the selectivity for 4-hydroxybenzoic acid is 87%. A possible carboxylation mechanism in the presence of the title catalyst is discussed. Also.the recovery and reusage of the catalyst is studied.展开更多
Carbon nanotube (CNT)-supported Ru nanoparticles with mean sizes ranging from 2.3 to 9.2 nm were prepared by different post-treatments and studied for Fischer-Tropsch (FT) synthesis. The effects of Ru particle siz...Carbon nanotube (CNT)-supported Ru nanoparticles with mean sizes ranging from 2.3 to 9.2 nm were prepared by different post-treatments and studied for Fischer-Tropsch (FT) synthesis. The effects of Ru particle size on catalytic behaviors were investigated at both shorter and longer contact times. At shorter contact time, where the secondary reactions were insignificant, the turnover frequency (TOF) for CO conversion was dependent on the mean size of Ru particles; TOF increased with the mean size of Ru particles from 2.3 to 6.3 nm and then decreased slightly. At the same time, the selectivities to C5+ hydrocarbons increased gradually with the mean size of Ru particles up to 6.3 nm and then kept almost unchanged with a further increase in Ru particle size. At longer contact time, C10-C20 selectivity increased significantly at the expense of C21+ selectivity, suggesting the occurrence of the selective hydrocracking of C21+ to C10-C20 hydrocarbons.展开更多
Catalytic conversion of synthesis gas (CO+H2) into hydrocarbons, also known as Fischer-Tropsch (FT) synthesis, is a crucial reaction for the translbrmation of non-petroleum carbon resources such as coal, natural ...Catalytic conversion of synthesis gas (CO+H2) into hydrocarbons, also known as Fischer-Tropsch (FT) synthesis, is a crucial reaction for the translbrmation of non-petroleum carbon resources such as coal, natural gas, shale gas, coal-bed gas and biogas, as well as biomass into liquid fuels and chemicals. Many factors can influence the catalytic behavior of a FT catalyst. This review highlights recent advances in understanding some key catalyst factors, including the chemical state of active phases, the promoters, the size and the microenvironment of active phase, which determine the CO conversion activity and the product selectivity, particularly the selectivity to C5 + hydrocarbons.展开更多
The effects of Manganese (Mn) incorporation on a precipitated iron-based Fischer-Tropsch synthesis (FTS) catalyst were investigated using N2 physical adsorption, air differential thermal analysis (DTA), H2 tempe...The effects of Manganese (Mn) incorporation on a precipitated iron-based Fischer-Tropsch synthesis (FTS) catalyst were investigated using N2 physical adsorption, air differential thermal analysis (DTA), H2 temperature-programmed reduction (TPR), and Mǒssbauer spectroscopy. The FTS performances of the catalysts were tested in a slurry phase reactor. The characterization results indicated that Mn increased the surface area of the catalyst, and improved the dispersion of (α-Fe2O3 and reduced its crystallite size as a result of the high dispersion effect of Mn and the Fe-Mn interaction. The Fe-Mn interaction also suppressed the reduction of (α-Fe2O3 to Fe3O4, stabilized the FeO phase, and (or) decreased the carburization degree of the catalysts in the H2 and syngas reduction processes. In addition, incorporated Mn decreased the initial catalyst activity, but improved the catalyst stability because Mn restrained the reoxidation of iron carbides to Fe3O4, and improved further carburization of the catalysts. Manganese suppressed the formation of CH4 and increased the selectivity to light olefins (C2-4^=), but it had little effect on the selectivities to heavy (C5+) hydrocarbons. All these results indicated that the strong Fe-Mn interaction suppressed the chemisorptive effect of the Mn as an electronic promoter, to some extent, in the precipitated iron-manganese catalyst system.展开更多
A systematic study was undertaken to investigate the effects of the manganese incorporation manner on the textural properties, bulk and surface phase compositions, reduction/carburization behaviors, and surface basici...A systematic study was undertaken to investigate the effects of the manganese incorporation manner on the textural properties, bulk and surface phase compositions, reduction/carburization behaviors, and surface basicity of an iron-based Fischer-Tropsch synthesis (FTS) catalyst. The catalyst samples were characterized by N2 physisorption, X-ray photoelectron spectroscopy (XPS), H2 (or CO) temperature-programmed reduction (TPR), CO2 temperature-programmed desorption (TPD), and M5ssbauer spectroscopy. The FTS performance of the catalysts was studied in a slurry-phase continuously stirred tank reactor (CSTR). The characterization results indicated that the manganese promoter incorporated by using the coprecipitation method could improve the dispersion of iron oxide, and decrease the size of the iron oxide crystallite. The manganese incorporated with the impregnation method is enriched on the catalyst's surface. The manganese promoter added with the impregnation method suppresses the reduction and carburization of the catalyst in H2, CO, and syngas because of the excessive enrichment of manganese on the catalyst surface. The catalyst added manganese using the coprecipitation method has the highest CO conversion (51.9%) and the lowest selectivity for heavy hydrocarbons (C12+).展开更多
An extensive study of Fischer-Tropsch (FT) synthesis on cobalt nano particles supported on γ-alumina and carbon nanotubes (CNTs) catalysts is reported.20 wt% of cobalt is loaded on the supports by impregnation me...An extensive study of Fischer-Tropsch (FT) synthesis on cobalt nano particles supported on γ-alumina and carbon nanotubes (CNTs) catalysts is reported.20 wt% of cobalt is loaded on the supports by impregnation method.The deactivation of the two catalysts was studied at 220 C,2 MPa and 2.7 L/h feed flow rate using a fixed bed micro-reactor.The calcined fresh and used catalysts were characterized extensively and different sources of catalyst deactivation were identified.Formation of cobalt-support mixed oxides in the form of xCoO yAl2O3 and cobalt aluminates formation were the main sources of the Co/γ-Al2O3 catalyst deactivation.However sintering and cluster growth of cobalt nano particles are the main sources of the Co/CNTs catalyst deactivation.In the case of the Co/γ-Al2O3 catalyst,after 720 h on stream of continuous FT synthesis the average cobalt nano particles diameter increased from 15.9 to 18.4 nm,whereas,under the same reaction conditions the average cobalt nano particles diameter of the Co/CNTs increased from 11.2 to 17.8 nm.Although,the initial FT activity of the Co/CNTs was 26% higher than that of the Co/γ-Al2O3,the FT activity over the Co/CNTs after 720 h on stream decreased by 49% and that over the Co/γ-Al2O3 by 32%.For the Co/γ-Al2O3 catalyst 6.7% of total activity loss and for the Co/CNTs catalyst 11.6% of total activity loss cannot be recovered after regeneration of the catalyst at the same conditions of the first regeneration step.It is concluded that using CNTs as cobalt catalyst support is beneficial in carbon utilization as compared to γ-Al2O3 support,but the Co/CNTs catalyst is more susceptible for deactivation.展开更多
Barium modified Co/Al2O3 catalysts were prepared by incipient wetness impregnation.The catalysts were characterized by XRD,TPD and DRIFTS.The catalytic activity for Fischer-Tropsch synthesis was measured in a continuo...Barium modified Co/Al2O3 catalysts were prepared by incipient wetness impregnation.The catalysts were characterized by XRD,TPD and DRIFTS.The catalytic activity for Fischer-Tropsch synthesis was measured in a continuously stirred tank reactor.It was found that small amounts of BaO(≤2 wt%) improved the cobalt reducibility,which led to more cobalt active sites on the catalyst surface,and then resulted in higher CO conversion and C5+ selectivity.However,for the catalysts with high BaO loadings negative effects on the catalytic activity and selectivity for high hydrocarbons were observed because of low cobalt reducibility.展开更多
Fischer-Tropsch Synthesis(FTS) is an important catalytic chemical reaction that converts a mixture of CO and H2(syngas) derived from biomass, coal or natural gas into ultra-clean fuels or value-added chemicals. Howeve...Fischer-Tropsch Synthesis(FTS) is an important catalytic chemical reaction that converts a mixture of CO and H2(syngas) derived from biomass, coal or natural gas into ultra-clean fuels or value-added chemicals. However, most traditional catalysts used in the Fischer-Tropsch process are faced with the problems of high deactivation rate triggered by sintering, phase changes and oxidation which hamper their catalytic performance. Metal-organic frameworks(MOFs)-derived materials have been a promising alternative in addressing the catalyst deactivation problems in FTS because of the encapsulation of their metal nanoparticles in carbon matrix and absence of large particle size, among other reasons. Therefore, this review emphasizes the most recent research headway in the investigation of MOFs as precursors to achieve high-performance FTS catalysts. Precisely, the design of iron and cobalt-based FTS catalysts from parent MOFs via MOF-mediated synthesis, the catalytic activity of the MOF-derived materials and the promoter effects under FTS operation were outlined and discussed. We have also evaluated the influence of MOF structures on the FTS performance and compared them with traditional/commercially available catalysts to show the importance of this approach. Finally, the challenges and opportunities to further expedite the extensive research efforts and promote their applications in material design and FT technology were mentioned.展开更多
A series of iron-based Fischer-Tropsch synthesis (FTS) catalysts incorporated with Al2O3 binder were prepared by the combination of co-precipitation and spray drying technology. The catalyst samples were characteriz...A series of iron-based Fischer-Tropsch synthesis (FTS) catalysts incorporated with Al2O3 binder were prepared by the combination of co-precipitation and spray drying technology. The catalyst samples were characterized by using N2 physical adsorption, temperature-programmed reduction/desorption (TPR/TPD) and MSssbauer effect spectroscopy (MES) methods. The characterization results indicated that the BET surface area increases with increasing Al2O3 content and passes through a maximum at the Al2O3/Fe ratio of 10/100 (weight basis). After the point, it decreases with further increase in Al2O3 content. The incorporation of Al2O3 binder was found to weaken the surface basicity and suppress the reduction and carburization of iron-based catalysts probably due to the strong K-Al2O3 and Fe-Al2O3 interactions. Furthermore, the H2 adsorption ability of the catalysts is enhanced with increasing Al2O3 content. The FTS performances of the catalysts were tested in a slurry-phase continuously stirred tank reactor (CSTR) under the reaction conditions of 260 ℃, 1.5 MPa, 1000 h^-1 and molar ratio of H2/CO 0.67 for 200 h. The results showed that the addition of small amounts of Al2O3 affects the activity of iron-based catalysts to a little extent. However, with further increase of Al2O3 content, the FTS activity and water gas shift reaction (WGS) activity are decreased severely. The addition of appropriate Al2O3 do not affect the product selectivity, but the catalysts incorporated with large amounts of Al2O3 have higher selectivity for light hydrocarbons and lower selectivity for heavy hydrocarbons.展开更多
基金supported by the Research and Technology Directorate of National Iranian Oil Company
文摘Cobalt supported on carbon nanotubes (CNTs)-covered alumina has been recently developed and successfully utilized as a catalyst in Fischer-Tropsch synthesis (FTS). Problems associated with shaping of Co/CNTs into extrudates or pellets as well as catalyst attrition rendered these materials unfavorable for industrial applications. In this investigation regular γ- and nano-structured (N-S) alumina as well as CNTs-covered regular γ- and N-S-alumina supports were impregnated by cobalt nitrate solution to make new cobalt-based catalysts which were also promoted by Ru. The catalysts were characterized and tested in a micro reactor to evaluate their applicability in FTS. γ-Al2O3 was prepared by calcination of bohemite and N-S-Al2O3 was prepared by sol-gel method using aluminum chloride as starting material. Catalyst evaluations indicated that N-S-Al2O3 was superior to regular γ-Al2O3 and that CNTs-covered alumina supports were favored over non-covered ones in terms of activity and heavy hydrocarbon selectivity. These were justified by porosimetric characteristics of the catalysts and existence of CNTs points of view. CNTs-covered catalysts also showed higher wax selectivity and better resistance to deactivation. Furthermore, TPR analysis indicated that the cobalt aluminate phase, which is responsible for the permanent deactivation of alumina supported Co-based catalysts, did not form on alumina supported Co-based catalysts covered with CNTs due to weaker interactions between cobalt and alumina.
基金the financial support from by the National Key Research and Development Program of China(No.2022YFB4101800)National Natural Science Foundation of China(No.22278298)Program for Introducing Talents of Discipline to Universities of China(No.BP0618007).
文摘Nitrogen(N)-doped carbon materials as metal catalyst supports have attracted signifi cant attention,but the eff ect of N dopants on catalytic performance remains unclear,especially for complex reaction processes such as Fischer-Tropsch synthesis(FTS).Herein,we engineered ruthenium(Ru)FTS catalysts supported on N-doped carbon overlayers on TiO_(2)nanoparticles.By regulating the carbonization temperatures,we successfully controlled the types and contents of N dopants to identify their impacts on metal-support interactions(MSI).Our fi ndings revealed that N dopants establish a favorable surface environment for electron transfer from the support to the Ru species.Moreover,pyridinic N demonstrates the highest electron-donating ability,followed by pyrrolic N and graphitic N.In addition to realizing excellent catalytic stability,strengthening the interaction between Ru sites and N dopants increases the Ru^(0)/Ru^(δ+)ratios to enlarge the active site numbers and surface electron density of Ru species to enhance the strength of adsorbed CO.Consequently,it improves the catalyst’s overall performance,encompassing intrinsic and apparent activities,as well as its ability for carbon chain growth.Accordingly,the as-synthesized Ru/TiO_(2)@CN-700 catalyst with abundant pyridine N dopants exhibits a superhigh C_(5+)time yield of 219.4 mol CO/(mol Ru·h)and C_(5+)selectivity of 85.5%.
基金supported by the National Key R&D Program of China (2021YFB4000402)the National Natural Science Foundation of China (22022503)。
文摘The direct oxidation of nitrogen is a potential pathway to achieving the zero-carbon-emission synthesis of nitric acid or nitrate, because it does not involve ammonia synthesis and additional ammonia oxidation processes. However, the slow kinetics of nitrogen oxidation and the difficult selective control of oxidation products hinder the development of this process. In this study, a plasma-driven gas-liquid relay reaction system was developed to overcome these limitations. A typical feature of this reaction system is that it can efficiently generate NO_x under plasma exposure;moreover, the specific anions in the absorption solution can be oxidized to strong oxidants capable of relay oxidation of low-valence nitrogen oxides. This feature allows for the deep oxidation of nitrogen, thus enabling the oxidation products of nitrogen to exist in high-valence states in the absorption solution. For experimental verification, we achieved the 100% selective synthesis of nitrate under plasma exposure, with air as the supply gas and a sodium sulfate solution as the absorption solution.
基金supported by Project of Central Government for Local Science and Technology Development of China (2022JH6/100100050)the National Natural Science Foundation of China (21776028)Liaoning Key Laboratory of Chemical Additive Synthesis and Separation (ZJKF2001)。
文摘NH_(3) selective catalytic reduction(SCR) has been widely recognized as a promising technique for reducing nitrogen oxides from diesel vehicle exhausts. High-efficiency SCR catalysts that could perform at low temperatures are essential to denitration. In this work, a series of bimetallic CeCu-SAPO-34 molecular sieves were synthesized by one-step hydrothermal method. The Ce Cu-SAPO-34 maintained good crystallinity and a regular hexahedron appearance of Cu-SAPO-34 after introducing Ce species, while exhibiting a higher specific surface area and pore volume. The as-prepared CeCu-SAPO-34 with 0.02%(mass) Ce constituent exhibited the best catalytic activity below 300℃ and a maximum NO_(x) conversion of 99% was attained;the NO_(x) removal rates of more than 68% and 94% were achieved at 150℃ and 200℃, respectively. And the introduction of cerium species in Cu-SAPO-34 improves the low-temperature hydrothermal stability of the catalyst towards NH_(3)-SCR reaction. Additionally, the introduced Ce species could enhance the formation of abundant weak Br?nsted acid centers and promote the synergistic effect between CuO grains and isolated Cu^(2+) to enhance the redox cycle, which benefit the NH_(3)-SCR reaction.This work provides a facile synthesis method of high-efficiency SCR denitration catalysts towards diesel vehicles exhaust treatment under low temperature.
文摘The Fischer-Tropsch synthesis is a significant technology for converting coal,natural gas,and biomass into synthetic fuels.In recent years,the use of microchannel reactors for the Fischer-Tropsch synthesis has attracted significant attention.Fischer-Tropsch synthesis experiments were carried out in a microchannel reactor and the influences of reaction conditions on the experimental results were investigated in this study.Based on the experimental data,a dynamic multi-component pseudo-homogeneous variable-volume flow model of microchannel reactors for the Fischer-Tropsch synthesis was built to determine the pressure-,velocity-,conversion-and(component-wise)concentration-distributions in reaction channels.The model takes into account the combined effects of gas volume expansion caused by the frictional pressure drop and gas volume contraction caused by reaction consumption.A novel effective method for calculating the pressure and superficial gas velocity values in microchannel reactors was proposed in the model.Besides that,two sets of experimental data were selected from references to evaluate the validity and accuracy of the model.The reaction performances in the microchannels were analyzed carefully based on the calculated results.
文摘Silica, alumina, and activated carbon supported iron-cobalt catalysts were prepared by incipient wetness impregnation. These catalysts have been characterized by BET, X-ray diffraction (XRD), and temperature-programmed reduction (TPR). Activity and selectivity of iron-cobalt supported on different carriers for CO hydrogenation were studied under the conditions of 1.5 MPa, 493 K, 630 h^-1, and H2/CO ratio of 1.6. The results indicate that the activity, C4 olefin/(C4 olefin+C4 paraffin) ratio, and C5 olefin/(C5 olefin+C5 paraffin) decrease in the order of Fe-Co/SiO2, Fe-Co/AC1, Fe-Co/Al2O3 and Fe- Co/AC2. The activity of Fe-Co/SiO2 reached a maximum. The results of TPR show that the Fe-Co/SiO2 catalyst is to some extent different. XRD patterns show that the Fe-Co/SiO2 catalyst differs significantly from the others; it has two diffraction peaks. The active spinel phase is correlated with the supports.
基金financial support from the National Natural Science Foundation of China (21506154)the Program of Introducing Talents of Discipline to Universities (B06006)。
文摘Fischer-Tropsch synthesis(FTS) is the key step in converting syngas into clean fuels. Traditional supported catalysts for FTS are problematic because the active metal crystalline size is positively related to metal loading. Therefore, increasing active metal loading may reduce the cobalt time yield(CTY) since a high CTY is usually obtained when the Co size is 8 nm. Here, a ZIF-67(Zeolitic imidazolate framework-67) with a MOF(Metal organic framework) structure is used as a precursor to prepare the Co@C catalyst with not only high cobalt loading(55.6 wt%) but also with a small cobalt crystal size(as small as 8.6 nm). Coreshell Co@C@SiO2-X catalysts with different SiO2 shell thicknesses were successfully prepared by coating different amounts of TEOS on the outer surface of Co@C to modify product selectivity. Compared with40 wt% Co/SiO2 catalyst, core-shell Co@C@SiO2-X catalysts exhibited improved FTS performance. Furthermore, different gaseous hourly space velocities(GHSVs) were used to obtain CO conversion at similar levels to compare CTY and the turnover frequency(TOF). Among the catalysts, the Co@C@SiO2-1 catalyst, with its better mass transfer ability and suitable hydrophilic property, presented the highest TOF(9.75 × 10-3 s-1) and lowest CH4 selectivity(9.75%). In addition, heavy hydrocarbons were effectively suppressed with the increase in shell thickness due to the increased mass transfer resistance.
文摘Simple and efficient stereo-selective synthesis of exo-5-norbornene-2-carboxylic acid (NBCA) is reported. Preliminary studies on base promoted isomerization of methyl 5-norbornene-2-carboxylate (MNBC) revealed that rapid isomerization was accomplished with sodium tert-butoxide (tBuONa), and the exo-content at the equilibrium was ca. 60%. The hydrolyses of endo-rich MNBC (endo/exo = 80/20) under various conditions were carried out. The exo selectivity for resulting NBCA was improved when the hydrolysis was conducted with equimolar water at room temperature in the presence of the stronger base (tBuONa) (endo/exo: 18/82). Whereas the use of excess amount of water led to rapid and non-selective hydrolysis affording high endo content of the product. The plausible reaction mechanism involving rapid equilibrium of thermodynamic isomerization and kinetically preferred hydrolysis of exo ester is proposed.
文摘4-hydroxybenzoic acid was synthesized by one pot method using polymer-bonded β-aminopropionic acid-2-β-cyclodextrin as a catalyst.by which the selectivity for 4-hydroxybenzoic acid is 87%. A possible carboxylation mechanism in the presence of the title catalyst is discussed. Also.the recovery and reusage of the catalyst is studied.
基金supported by the National Basic Research Program of China (No. 2013CB933100)the National Natural Science Foundation of China (21173174, 21161130522, 21033006 and 20923004)+1 种基金the Program for Changjiang Scholars and Innovative Research Team in University (No. IRT1036)the Research Fund for the Doctoral Program of Higher Education (No. 20090121110007)
文摘Carbon nanotube (CNT)-supported Ru nanoparticles with mean sizes ranging from 2.3 to 9.2 nm were prepared by different post-treatments and studied for Fischer-Tropsch (FT) synthesis. The effects of Ru particle size on catalytic behaviors were investigated at both shorter and longer contact times. At shorter contact time, where the secondary reactions were insignificant, the turnover frequency (TOF) for CO conversion was dependent on the mean size of Ru particles; TOF increased with the mean size of Ru particles from 2.3 to 6.3 nm and then decreased slightly. At the same time, the selectivities to C5+ hydrocarbons increased gradually with the mean size of Ru particles up to 6.3 nm and then kept almost unchanged with a further increase in Ru particle size. At longer contact time, C10-C20 selectivity increased significantly at the expense of C21+ selectivity, suggesting the occurrence of the selective hydrocracking of C21+ to C10-C20 hydrocarbons.
基金the National Basic Research Program of China(No.2013CB933100)the National Natural Science Foundation of China(No.21173174,No.21161130522,No.21033006and No.20923004)the Program for Changjiang Scholars and Innovative Research Team in University(No.IRT1036)
文摘Catalytic conversion of synthesis gas (CO+H2) into hydrocarbons, also known as Fischer-Tropsch (FT) synthesis, is a crucial reaction for the translbrmation of non-petroleum carbon resources such as coal, natural gas, shale gas, coal-bed gas and biogas, as well as biomass into liquid fuels and chemicals. Many factors can influence the catalytic behavior of a FT catalyst. This review highlights recent advances in understanding some key catalyst factors, including the chemical state of active phases, the promoters, the size and the microenvironment of active phase, which determine the CO conversion activity and the product selectivity, particularly the selectivity to C5 + hydrocarbons.
基金Foundation item:the National Outstanding Young Scientists Foundation of China(20625620)the National Key Basic Research Program of China(973 Program,2007CB216401)+1 种基金the National Natural Science Foundation of China(20590360)the Natural Science Foundation of Shanxi Province(2006021014).
文摘The effects of Manganese (Mn) incorporation on a precipitated iron-based Fischer-Tropsch synthesis (FTS) catalyst were investigated using N2 physical adsorption, air differential thermal analysis (DTA), H2 temperature-programmed reduction (TPR), and Mǒssbauer spectroscopy. The FTS performances of the catalysts were tested in a slurry phase reactor. The characterization results indicated that Mn increased the surface area of the catalyst, and improved the dispersion of (α-Fe2O3 and reduced its crystallite size as a result of the high dispersion effect of Mn and the Fe-Mn interaction. The Fe-Mn interaction also suppressed the reduction of (α-Fe2O3 to Fe3O4, stabilized the FeO phase, and (or) decreased the carburization degree of the catalysts in the H2 and syngas reduction processes. In addition, incorporated Mn decreased the initial catalyst activity, but improved the catalyst stability because Mn restrained the reoxidation of iron carbides to Fe3O4, and improved further carburization of the catalysts. Manganese suppressed the formation of CH4 and increased the selectivity to light olefins (C2-4^=), but it had little effect on the selectivities to heavy (C5+) hydrocarbons. All these results indicated that the strong Fe-Mn interaction suppressed the chemisorptive effect of the Mn as an electronic promoter, to some extent, in the precipitated iron-manganese catalyst system.
基金Foundation item:the National Natural Science Foundation of China(20590360)the Natural Science Foundation of Shanxi Province(2006021014)+1 种基金the National Outstanding Young Scientists Foundation of China(20625620)National Key Basic Research Program of China(973 Program)(2007CB216401).
文摘A systematic study was undertaken to investigate the effects of the manganese incorporation manner on the textural properties, bulk and surface phase compositions, reduction/carburization behaviors, and surface basicity of an iron-based Fischer-Tropsch synthesis (FTS) catalyst. The catalyst samples were characterized by N2 physisorption, X-ray photoelectron spectroscopy (XPS), H2 (or CO) temperature-programmed reduction (TPR), CO2 temperature-programmed desorption (TPD), and M5ssbauer spectroscopy. The FTS performance of the catalysts was studied in a slurry-phase continuously stirred tank reactor (CSTR). The characterization results indicated that the manganese promoter incorporated by using the coprecipitation method could improve the dispersion of iron oxide, and decrease the size of the iron oxide crystallite. The manganese incorporated with the impregnation method is enriched on the catalyst's surface. The manganese promoter added with the impregnation method suppresses the reduction and carburization of the catalyst in H2, CO, and syngas because of the excessive enrichment of manganese on the catalyst surface. The catalyst added manganese using the coprecipitation method has the highest CO conversion (51.9%) and the lowest selectivity for heavy hydrocarbons (C12+).
文摘An extensive study of Fischer-Tropsch (FT) synthesis on cobalt nano particles supported on γ-alumina and carbon nanotubes (CNTs) catalysts is reported.20 wt% of cobalt is loaded on the supports by impregnation method.The deactivation of the two catalysts was studied at 220 C,2 MPa and 2.7 L/h feed flow rate using a fixed bed micro-reactor.The calcined fresh and used catalysts were characterized extensively and different sources of catalyst deactivation were identified.Formation of cobalt-support mixed oxides in the form of xCoO yAl2O3 and cobalt aluminates formation were the main sources of the Co/γ-Al2O3 catalyst deactivation.However sintering and cluster growth of cobalt nano particles are the main sources of the Co/CNTs catalyst deactivation.In the case of the Co/γ-Al2O3 catalyst,after 720 h on stream of continuous FT synthesis the average cobalt nano particles diameter increased from 15.9 to 18.4 nm,whereas,under the same reaction conditions the average cobalt nano particles diameter of the Co/CNTs increased from 11.2 to 17.8 nm.Although,the initial FT activity of the Co/CNTs was 26% higher than that of the Co/γ-Al2O3,the FT activity over the Co/CNTs after 720 h on stream decreased by 49% and that over the Co/γ-Al2O3 by 32%.For the Co/γ-Al2O3 catalyst 6.7% of total activity loss and for the Co/CNTs catalyst 11.6% of total activity loss cannot be recovered after regeneration of the catalyst at the same conditions of the first regeneration step.It is concluded that using CNTs as cobalt catalyst support is beneficial in carbon utilization as compared to γ-Al2O3 support,but the Co/CNTs catalyst is more susceptible for deactivation.
基金supported by the National Natural Science Foundation of China(Grants No:20590360 and 20773166)
文摘Barium modified Co/Al2O3 catalysts were prepared by incipient wetness impregnation.The catalysts were characterized by XRD,TPD and DRIFTS.The catalytic activity for Fischer-Tropsch synthesis was measured in a continuously stirred tank reactor.It was found that small amounts of BaO(≤2 wt%) improved the cobalt reducibility,which led to more cobalt active sites on the catalyst surface,and then resulted in higher CO conversion and C5+ selectivity.However,for the catalysts with high BaO loadings negative effects on the catalytic activity and selectivity for high hydrocarbons were observed because of low cobalt reducibility.
基金the University of South Africa, National Research Foundation (NRF UID 95983 and 113648)South AfricaHebei University of Science and Technology, China, for the financial support。
文摘Fischer-Tropsch Synthesis(FTS) is an important catalytic chemical reaction that converts a mixture of CO and H2(syngas) derived from biomass, coal or natural gas into ultra-clean fuels or value-added chemicals. However, most traditional catalysts used in the Fischer-Tropsch process are faced with the problems of high deactivation rate triggered by sintering, phase changes and oxidation which hamper their catalytic performance. Metal-organic frameworks(MOFs)-derived materials have been a promising alternative in addressing the catalyst deactivation problems in FTS because of the encapsulation of their metal nanoparticles in carbon matrix and absence of large particle size, among other reasons. Therefore, this review emphasizes the most recent research headway in the investigation of MOFs as precursors to achieve high-performance FTS catalysts. Precisely, the design of iron and cobalt-based FTS catalysts from parent MOFs via MOF-mediated synthesis, the catalytic activity of the MOF-derived materials and the promoter effects under FTS operation were outlined and discussed. We have also evaluated the influence of MOF structures on the FTS performance and compared them with traditional/commercially available catalysts to show the importance of this approach. Finally, the challenges and opportunities to further expedite the extensive research efforts and promote their applications in material design and FT technology were mentioned.
基金The financial support from the National Natural Science Foundation of China (20590361)the National Outstanding Young Scientists Foundation of China (20625620)
文摘A series of iron-based Fischer-Tropsch synthesis (FTS) catalysts incorporated with Al2O3 binder were prepared by the combination of co-precipitation and spray drying technology. The catalyst samples were characterized by using N2 physical adsorption, temperature-programmed reduction/desorption (TPR/TPD) and MSssbauer effect spectroscopy (MES) methods. The characterization results indicated that the BET surface area increases with increasing Al2O3 content and passes through a maximum at the Al2O3/Fe ratio of 10/100 (weight basis). After the point, it decreases with further increase in Al2O3 content. The incorporation of Al2O3 binder was found to weaken the surface basicity and suppress the reduction and carburization of iron-based catalysts probably due to the strong K-Al2O3 and Fe-Al2O3 interactions. Furthermore, the H2 adsorption ability of the catalysts is enhanced with increasing Al2O3 content. The FTS performances of the catalysts were tested in a slurry-phase continuously stirred tank reactor (CSTR) under the reaction conditions of 260 ℃, 1.5 MPa, 1000 h^-1 and molar ratio of H2/CO 0.67 for 200 h. The results showed that the addition of small amounts of Al2O3 affects the activity of iron-based catalysts to a little extent. However, with further increase of Al2O3 content, the FTS activity and water gas shift reaction (WGS) activity are decreased severely. The addition of appropriate Al2O3 do not affect the product selectivity, but the catalysts incorporated with large amounts of Al2O3 have higher selectivity for light hydrocarbons and lower selectivity for heavy hydrocarbons.