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2019 Volume 40 Issue 9
2019, 40(9):
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2019, 40(9): 1231-1231
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2019, 40(9): 1232-1232
doi: S1872-2067(19)63425-X
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2019, 40(9): 1233-1254
doi: S1872-2067(19)63360-7
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With growing demand for propylene and increasing production of propane from shale gas, the technologies of propylene production, including direct dehydrogenation and oxidative dehydrogenation of propane, have drawn great attention in recent years. In particular, direct dehydrogenation of propane to propylene is regarded as one of the most promising methods of propylene production because it is an on-purpose technique that exclusively yields propylene instead of a mixture of products. In this critical review, we provide the current investigations on the heterogeneous catalysts (such as Pt, CrOx, VOx, GaOx-based catalysts, and nanocarbons) used in the direct dehydrogenation of propane to propylene. A detailed comparison and discussion of the active sites, catalytic mechanisms, influencing factors (such as the structures, dispersions, and reducibilities of the catalysts and promoters), and supports for different types of catalysts is presented. Furthermore, rational designs and preparation of high-performance catalysts for propane dehydrogenation are proposed and discussed.
With growing demand for propylene and increasing production of propane from shale gas, the technologies of propylene production, including direct dehydrogenation and oxidative dehydrogenation of propane, have drawn great attention in recent years. In particular, direct dehydrogenation of propane to propylene is regarded as one of the most promising methods of propylene production because it is an on-purpose technique that exclusively yields propylene instead of a mixture of products. In this critical review, we provide the current investigations on the heterogeneous catalysts (such as Pt, CrOx, VOx, GaOx-based catalysts, and nanocarbons) used in the direct dehydrogenation of propane to propylene. A detailed comparison and discussion of the active sites, catalytic mechanisms, influencing factors (such as the structures, dispersions, and reducibilities of the catalysts and promoters), and supports for different types of catalysts is presented. Furthermore, rational designs and preparation of high-performance catalysts for propane dehydrogenation are proposed and discussed.
2019, 40(9): 1255-1281
doi: S1872-2067(19)63381-4
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Zeolites with ordered porous structure of molecular size are widely employed as commercial adsorbents and catalysts. On the other hand, the zeolite matrix is regarded as an ideal scaffold for hosting coordinatively unsaturated sites. Remarkable achievements have been made dealing with the construction, characterization and catalytic applications of coordinatively unsaturated sites in zeolite matrix. Herein, a literature overview of recent progresses on this important topic is presented from the specific view of coordination chemistry. Different strategies to construction coordinatively unsaturated sites in zeolite matrix, in zeolite framework or extraframework positions, are first introduced and their characteristics are compared. Then, spectroscopic techniques to determine the existing states of cation sites and their transformations in zeolite matrix are discussed. In the last section, the catalytic applications of coordinatively unsaturated sites in zeolite matrix for various important chemical transformations are summarized.
Zeolites with ordered porous structure of molecular size are widely employed as commercial adsorbents and catalysts. On the other hand, the zeolite matrix is regarded as an ideal scaffold for hosting coordinatively unsaturated sites. Remarkable achievements have been made dealing with the construction, characterization and catalytic applications of coordinatively unsaturated sites in zeolite matrix. Herein, a literature overview of recent progresses on this important topic is presented from the specific view of coordination chemistry. Different strategies to construction coordinatively unsaturated sites in zeolite matrix, in zeolite framework or extraframework positions, are first introduced and their characteristics are compared. Then, spectroscopic techniques to determine the existing states of cation sites and their transformations in zeolite matrix are discussed. In the last section, the catalytic applications of coordinatively unsaturated sites in zeolite matrix for various important chemical transformations are summarized.
2019, 40(9): 1282-1297
doi: S1872-2067(19)63361-9
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The electroactive materials used in the counter electrode (CE) are of great concern as they influence the photovoltaic performances of dye-sensitized solar cells. The main functions of CE materials are collecting electrons from the external circuit and transferring them to the electrolyte and realizing the catalytic reduction of the redox species (I3- or Co3+) present in the electrolyte. The research hotspot of CE materials is seeking functional materials that display high efficiency, low cost, and good electrochemical stability and can substitute the benchmark platinum electrode. Chalcogen compounds of cobalt, nickel, and iron have been widely applied as CE materials and exhibit excellent electrocatalytic performances owing to their unique electrical properties, similar energies of adsorption of I atoms as platinum, excellent catalytic activities, and good chemical stabilities. In this review, we trace the developments and performances of chalcogen compounds of iron, cobalt, and nickel as CE materials and present the latest research directions for improving the electrocatalytic performances. We then highlight the optimization strategies for further improving their performances, such as fabrication of architectures, regulation of the components, synthesis of composites containing carbon materials, and elemental doping.
The electroactive materials used in the counter electrode (CE) are of great concern as they influence the photovoltaic performances of dye-sensitized solar cells. The main functions of CE materials are collecting electrons from the external circuit and transferring them to the electrolyte and realizing the catalytic reduction of the redox species (I3- or Co3+) present in the electrolyte. The research hotspot of CE materials is seeking functional materials that display high efficiency, low cost, and good electrochemical stability and can substitute the benchmark platinum electrode. Chalcogen compounds of cobalt, nickel, and iron have been widely applied as CE materials and exhibit excellent electrocatalytic performances owing to their unique electrical properties, similar energies of adsorption of I atoms as platinum, excellent catalytic activities, and good chemical stabilities. In this review, we trace the developments and performances of chalcogen compounds of iron, cobalt, and nickel as CE materials and present the latest research directions for improving the electrocatalytic performances. We then highlight the optimization strategies for further improving their performances, such as fabrication of architectures, regulation of the components, synthesis of composites containing carbon materials, and elemental doping.
2019, 40(9): 1298-1310
doi: S1872-2067(19)63349-8
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Zn-air batteries have attracted extensive attention for their unique features including high energy density, safety, low cost and environmental friendliness. However, due to their poor chargeability and low efficiency, the practical application remains a challenge. The main obstacles are the intrinsic slow reaction kinetics on air cathodes, including oxygen reduction reaction during the discharging process and oxygen evolution reaction during the recharging process. Searching for efficient bifunctional oxygen electrocatalysts is key to solve these problems. In this review, the configuration and fundamental oxygen electrochemical reactions on air cathodes are briefly introduced for Zn-air batteries first. Then, the latest bifunctional oxygen electrocatalysts are summarized in detail. Finally, the perspectives are provided for the future investigations on bifunctional oxygen electrocatalysts.
Zn-air batteries have attracted extensive attention for their unique features including high energy density, safety, low cost and environmental friendliness. However, due to their poor chargeability and low efficiency, the practical application remains a challenge. The main obstacles are the intrinsic slow reaction kinetics on air cathodes, including oxygen reduction reaction during the discharging process and oxygen evolution reaction during the recharging process. Searching for efficient bifunctional oxygen electrocatalysts is key to solve these problems. In this review, the configuration and fundamental oxygen electrochemical reactions on air cathodes are briefly introduced for Zn-air batteries first. Then, the latest bifunctional oxygen electrocatalysts are summarized in detail. Finally, the perspectives are provided for the future investigations on bifunctional oxygen electrocatalysts.
2019, 40(9): 1311-1323
doi: S1872-2067(19)63321-8
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Atomic layer deposition (ALD) attracts great attention nowadays due to its ability for designing and modifying catalytic systems at the molecular level. There are several reported review papers published recently discussing this technique in catalysis. However, the mechanism on how the deposited materials improve the catalyst stability and tune the reaction selectivity is still unclear. Herein, catalytic systems created via ALD on stepwise preparation and/or modification under self-limiting reaction conditions are summarized. The effects of deposited materials in terms of electronic/geometry modification over the catalytic nanoparticles (NPs) are discussed. These effects explain the mechanism of the catalytic stability improvement and the selectivity modification. The unique properties of ALD for designing new catalytic systems are further investigated for building up photocatalytic reaction nanobowls, tandem catalyst and bi-active-component metallic catalytic systems.
Atomic layer deposition (ALD) attracts great attention nowadays due to its ability for designing and modifying catalytic systems at the molecular level. There are several reported review papers published recently discussing this technique in catalysis. However, the mechanism on how the deposited materials improve the catalyst stability and tune the reaction selectivity is still unclear. Herein, catalytic systems created via ALD on stepwise preparation and/or modification under self-limiting reaction conditions are summarized. The effects of deposited materials in terms of electronic/geometry modification over the catalytic nanoparticles (NPs) are discussed. These effects explain the mechanism of the catalytic stability improvement and the selectivity modification. The unique properties of ALD for designing new catalytic systems are further investigated for building up photocatalytic reaction nanobowls, tandem catalyst and bi-active-component metallic catalytic systems.
2019, 40(9): 1324-1338
doi: S1872-2067(19)63341-3
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Three-dimensionally ordered macroporous (3DOM) perovskite materials have attracted the interest from researchers worldwide due to their unique macroporous structure, flexible composition, tailorable physicochemical property, high stability and biocompatibility. In particular, they were widely used in environmental field, such as photocatalysis, catalytic combustion, catalytic oxidation and sensors. In this review, the recent progresses in the synthesis of 3DOM perovskite materials and their environmental applications are summarized. The advantages and the promoting mechanisms of 3DOM perovskite materials for different applications are discussed in detail. Subsequently, the challenges and perspectives on the topic are proposed.
Three-dimensionally ordered macroporous (3DOM) perovskite materials have attracted the interest from researchers worldwide due to their unique macroporous structure, flexible composition, tailorable physicochemical property, high stability and biocompatibility. In particular, they were widely used in environmental field, such as photocatalysis, catalytic combustion, catalytic oxidation and sensors. In this review, the recent progresses in the synthesis of 3DOM perovskite materials and their environmental applications are summarized. The advantages and the promoting mechanisms of 3DOM perovskite materials for different applications are discussed in detail. Subsequently, the challenges and perspectives on the topic are proposed.
2019, 40(9): 1339-1344
doi: S1872-2067(19)63329-2
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A novel 3D bismuth-organic framework (called Bi-TBAPy) single crystal was synthesized by employing 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H4TBAPy) as an organic linker. The study demonstrates that the Bi-TBAPy not only possesses good chemical stability and suitable band edge positions for promising photocatalytic H2 evolution, but it also exhibits a typical ligand-to-metal charge transfer for favorable charge separation. The photocatalytic H2 evolution rates on the as-obtained Bi-TBAPy with different cocatalysts modified were examined with triethanolamine as the sacrificial reagent. Based on this, the hydrogen evolution rate of 140 μmol h-1 g-1 was obtained on the optimized sample with a loading of 2 wt% Pt as a cocatalyst. To the best of our knowledge, this is the first bismuth-based metal-organic framework (MOF) that functions as an effective photocatalyst for photocatalytic water reduction. Our study not only adds a new member to the family of photocatalyst materials, but also reveals the importance of cocatalyst modification in improving photocatalytic activity of MOFs.
A novel 3D bismuth-organic framework (called Bi-TBAPy) single crystal was synthesized by employing 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H4TBAPy) as an organic linker. The study demonstrates that the Bi-TBAPy not only possesses good chemical stability and suitable band edge positions for promising photocatalytic H2 evolution, but it also exhibits a typical ligand-to-metal charge transfer for favorable charge separation. The photocatalytic H2 evolution rates on the as-obtained Bi-TBAPy with different cocatalysts modified were examined with triethanolamine as the sacrificial reagent. Based on this, the hydrogen evolution rate of 140 μmol h-1 g-1 was obtained on the optimized sample with a loading of 2 wt% Pt as a cocatalyst. To the best of our knowledge, this is the first bismuth-based metal-organic framework (MOF) that functions as an effective photocatalyst for photocatalytic water reduction. Our study not only adds a new member to the family of photocatalyst materials, but also reveals the importance of cocatalyst modification in improving photocatalytic activity of MOFs.
2019, 40(9): 1345-1351
doi: S1872-2067(19)63313-9
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Inexpensive and efficient Cu(I) catalysis is reported for the synthesis of α-hydroxy ketones from propargylic alcohols, CO2, and water via tandem carboxylative cyclization and nucleophilic addition reaction. Notably, hydration of propargylic alcohols can be carried out smoothly under atmospheric CO2 pressure, generating a series of α-hydroxy ketones efficiently and selectively. This strategy shows great potential for the preparation of valuable α-hydroxy ketones by using CO2 as a crucial cocatalyst under mild conditions.
Inexpensive and efficient Cu(I) catalysis is reported for the synthesis of α-hydroxy ketones from propargylic alcohols, CO2, and water via tandem carboxylative cyclization and nucleophilic addition reaction. Notably, hydration of propargylic alcohols can be carried out smoothly under atmospheric CO2 pressure, generating a series of α-hydroxy ketones efficiently and selectively. This strategy shows great potential for the preparation of valuable α-hydroxy ketones by using CO2 as a crucial cocatalyst under mild conditions.
2019, 40(9): 1352-1359
doi: S1872-2067(19)63406-6
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In an attempt to develop low-cost, non-noble-metal bifunctional electrocatalysts for water electrolysis in alkaline media, cobalt-doped molybdenum carbide@N-doped carbon nanosheets/nanotubes were fabricated by using C3N4 as the carbon source on a 3D porous nickel foam substrate. Benefiting from the optimized electronic structure and enhanced mass and charge transport, as well as the 3D conducting pathway, MoxCoy@N-CNSs/CNTs shows superior performance towards both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline medium. The optimal electrocatalyst is Mo2Co1@N-CNSs/CNTs, which reveals a current density of 10 mA cm-2 at the low overpotentials of 99 mV and 300 mV for the HER and OER, respectively, and a relatively low cell voltage (1.63 V) for the overall water electrolysis. The method of optimizing the composition and nanostructure of a material provides a new avenue for the development and utilization of high-performance electrocatalysts.
In an attempt to develop low-cost, non-noble-metal bifunctional electrocatalysts for water electrolysis in alkaline media, cobalt-doped molybdenum carbide@N-doped carbon nanosheets/nanotubes were fabricated by using C3N4 as the carbon source on a 3D porous nickel foam substrate. Benefiting from the optimized electronic structure and enhanced mass and charge transport, as well as the 3D conducting pathway, MoxCoy@N-CNSs/CNTs shows superior performance towards both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline medium. The optimal electrocatalyst is Mo2Co1@N-CNSs/CNTs, which reveals a current density of 10 mA cm-2 at the low overpotentials of 99 mV and 300 mV for the HER and OER, respectively, and a relatively low cell voltage (1.63 V) for the overall water electrolysis. The method of optimizing the composition and nanostructure of a material provides a new avenue for the development and utilization of high-performance electrocatalysts.
2019, 40(9): 1360-1365
doi: S1872-2067(19)63380-2
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Molybdenum selenide is a potential alternative to counter electrode of a platinum-free dye-sensitized solar cell (DSSC). In this work, an in situ magnetron sputtering method is developed to prepare MoSe2 electrodes. The MoSe2 electrodes obtained at various temperatures from 300 and 550℃ are used as counter electrode for a dye-sensitized solar cell. Photovoltaic measurement results indicate that the MoSe2 electrodes prepared at 400℃ has the optimized performance, and the corresponding DSSCs provide an energy conversion efficiency of 6.83% which is comparable than that of the reference DSSC with platinum as counter electrode (6.51%). With further increasing the preparation temperature of the MoSe2 electrodes, the corresponding DSSCs decrease gradually to 5.96% for 550℃. Electrochemical impedance spectra (EIS) reveal that charge transfer resistance (Rct) of MoSe2 electrodes is rising with increase of the temperature from 400 to 500℃, suggesting a downward electrocatalytic activity. Though the MoSe2 electrode prepared at 550℃ show a reduced Rct, its series resistance (Rs) and diffusion resistance (Zw) increase obviously. Considering that MoSe2 phase cannot be formed at 300℃, it can be concluded that the prepared temperature as low as possible is favored for its final electrochemical performance. The results are very significant for developing low-cost and responsible counter electrodes for dye-sensitized solar cells.
Molybdenum selenide is a potential alternative to counter electrode of a platinum-free dye-sensitized solar cell (DSSC). In this work, an in situ magnetron sputtering method is developed to prepare MoSe2 electrodes. The MoSe2 electrodes obtained at various temperatures from 300 and 550℃ are used as counter electrode for a dye-sensitized solar cell. Photovoltaic measurement results indicate that the MoSe2 electrodes prepared at 400℃ has the optimized performance, and the corresponding DSSCs provide an energy conversion efficiency of 6.83% which is comparable than that of the reference DSSC with platinum as counter electrode (6.51%). With further increasing the preparation temperature of the MoSe2 electrodes, the corresponding DSSCs decrease gradually to 5.96% for 550℃. Electrochemical impedance spectra (EIS) reveal that charge transfer resistance (Rct) of MoSe2 electrodes is rising with increase of the temperature from 400 to 500℃, suggesting a downward electrocatalytic activity. Though the MoSe2 electrode prepared at 550℃ show a reduced Rct, its series resistance (Rs) and diffusion resistance (Zw) increase obviously. Considering that MoSe2 phase cannot be formed at 300℃, it can be concluded that the prepared temperature as low as possible is favored for its final electrochemical performance. The results are very significant for developing low-cost and responsible counter electrodes for dye-sensitized solar cells.
2019, 40(9): 1366-1374
doi: S1872-2067(19)63363-2
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hemically modified carbonaceous materials have attained utmost attention in the fields of renewable energy storage and conversion, due to the controllable physicochemical properties, tailorable micro-/nanostructures, and respectable stability. Herein, P-doped mesoporous carbons were synthesized by using F127 as the soft template, organophosphonic acid as the P source and phenolic resin as the carbon source. Small amounts of iron species were introduced to act as a graphitization catalyst. The synthesized carbons exhibit the well-defined wormhole-like pore structure featuring high specific surface area and homogenously doped P heteroatoms. Notably, introducing iron species during the synthesis process can optimize the textural properties and the degree of graphitization of carbon materials. The doping amount of P has an important effect on the porous structure and the defect degree, which correspondingly influence the active sites and the oxygen reduction reaction (ORR) activity. The resultant material presents superior catalytic activity for the ORR, together with remarkably enhanced durability and methanol tolerance in comparison with the commercial Platinum catalyst, demonstrating the possibility for its use in electrode materials and electronic nanodevices for metal-air batteries and fuel cells.
hemically modified carbonaceous materials have attained utmost attention in the fields of renewable energy storage and conversion, due to the controllable physicochemical properties, tailorable micro-/nanostructures, and respectable stability. Herein, P-doped mesoporous carbons were synthesized by using F127 as the soft template, organophosphonic acid as the P source and phenolic resin as the carbon source. Small amounts of iron species were introduced to act as a graphitization catalyst. The synthesized carbons exhibit the well-defined wormhole-like pore structure featuring high specific surface area and homogenously doped P heteroatoms. Notably, introducing iron species during the synthesis process can optimize the textural properties and the degree of graphitization of carbon materials. The doping amount of P has an important effect on the porous structure and the defect degree, which correspondingly influence the active sites and the oxygen reduction reaction (ORR) activity. The resultant material presents superior catalytic activity for the ORR, together with remarkably enhanced durability and methanol tolerance in comparison with the commercial Platinum catalyst, demonstrating the possibility for its use in electrode materials and electronic nanodevices for metal-air batteries and fuel cells.
2019, 40(9): 1375-1384
doi: S1872-2067(19)63378-4
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The selective dehydrogenation of ethanol to acetaldehyde is a promising route for acetaldehyde production. Although Cu-based catalysts exhibit high activity in ethanol dehydrogenation, a rapid deactivation due to Cu sintering always occurs. In this study, highly dispersed Cu species were stabilized using the silanol defects in Beta zeolite (denoted as Beta) resulting from dealumination, and applied as robust catalysts for ethanol-to-acetaldehyde conversion. Typically, a long catalyst lifetime of 100 h with an acetaldehyde yield of ~70% could be achieved over 5% Cu/Beta. The presence of Cu+ and Cu0 species and the agglomeration of Cu particles after a long-term reaction for 180 h were revealed by transmission electron microscopy, thermogravimetric analysis, and CO-diffuse-reflectance infrared Fourier transform spectroscopy, and were responsible for the deactivation of the Cu/Beta catalyst in the ethanol-to-acetaldehyde conversion.
The selective dehydrogenation of ethanol to acetaldehyde is a promising route for acetaldehyde production. Although Cu-based catalysts exhibit high activity in ethanol dehydrogenation, a rapid deactivation due to Cu sintering always occurs. In this study, highly dispersed Cu species were stabilized using the silanol defects in Beta zeolite (denoted as Beta) resulting from dealumination, and applied as robust catalysts for ethanol-to-acetaldehyde conversion. Typically, a long catalyst lifetime of 100 h with an acetaldehyde yield of ~70% could be achieved over 5% Cu/Beta. The presence of Cu+ and Cu0 species and the agglomeration of Cu particles after a long-term reaction for 180 h were revealed by transmission electron microscopy, thermogravimetric analysis, and CO-diffuse-reflectance infrared Fourier transform spectroscopy, and were responsible for the deactivation of the Cu/Beta catalyst in the ethanol-to-acetaldehyde conversion.
2019, 40(9): 1385-1394
doi: S1872-2067(19)63334-6
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Nanocarbon materials have been used as important metal-free catalysts for various reactions including alkane dehydrogenation. However, clarifying the active sites and tuning the nanocarbon structure for direct dehydrogenation have always been significantly challenging owing to the lack of fundamental understanding of the structure and surface properties of carbon materials. Herein, mesoporous carbon materials with different pore ordering and surface properties were synthesized through a soft-templating method with different formaldehyde/resorcinol ratios and carbonization temperatures and used for catalytic dehydrogenation of propane to propylene. The highly ordered mesoporous carbons were found to have higher catalytic activities than disordered and ordered mesoporous carbons, mainly because the highly ordered mesopores favor mass transportation and provide more accessible active sites. Furthermore, mesoporous carbons can provide a large amount of surface active sites owing to their high surface areas, which is favorable for propane dehydrogenation reaction. To control the surface oxygenated functional groups, highly ordered mesoporous carbons were carbonized at different temperatures (600, 700, and 800℃). The propylene formation rates exhibit an excellent linear relationship with the number of ketonic C=O groups, suggesting that C=O groups are the most possible active sites.
Nanocarbon materials have been used as important metal-free catalysts for various reactions including alkane dehydrogenation. However, clarifying the active sites and tuning the nanocarbon structure for direct dehydrogenation have always been significantly challenging owing to the lack of fundamental understanding of the structure and surface properties of carbon materials. Herein, mesoporous carbon materials with different pore ordering and surface properties were synthesized through a soft-templating method with different formaldehyde/resorcinol ratios and carbonization temperatures and used for catalytic dehydrogenation of propane to propylene. The highly ordered mesoporous carbons were found to have higher catalytic activities than disordered and ordered mesoporous carbons, mainly because the highly ordered mesopores favor mass transportation and provide more accessible active sites. Furthermore, mesoporous carbons can provide a large amount of surface active sites owing to their high surface areas, which is favorable for propane dehydrogenation reaction. To control the surface oxygenated functional groups, highly ordered mesoporous carbons were carbonized at different temperatures (600, 700, and 800℃). The propylene formation rates exhibit an excellent linear relationship with the number of ketonic C=O groups, suggesting that C=O groups are the most possible active sites.
2019, 40(9): 1395-1404
doi: S1872-2067(19)63403-0
Abstract:
Development of dry reforming of methane and carbon dioxide is an effective route to convert industrial waste gases such as coke-oven gas and coal-to-oil gas into platform syngas. However, this process encounters severe problems of metal particle sintering and coke formation at high temperatures. In this work, we developed a new synthetic method for preparing confined Ni/MCM-41 catalysts, which impede the sintering of metal nanoparticles (NPs) and coke deposition at high temperatures, enabling them to be successfully applied to methane dry reforming. The method results in high activity and stability of the catalyst at 700℃ for 200 h. The Ni precursor is immersed in ethanol and impregnated into MCM-41 by the peculiar capillary action of hexagonal straight mesopores. By this method, 10 wt% Ni NPs (d=2 nm) is equably confined to the mesoporous channels with strong metal-support interactions, as confirmed by HRTEM, TEM mapping, H2-TPR, and XRD measurements. Such a confined structure has a significant effect on the inhibition of metal NP agglomeration and carbon deposition during methane dry reforming, as evidenced by TEM, Raman, TGA, and TPO measurements of used Ni/MCM-41 catalysts. In contrast, unconfined Ni/MCM-41 catalysts, with Ni NPs located on the pore exteriors, are rapidly deactivated after 12 h due to the blocked contact between the active metal centers and the gas feedstock. Additionally, a fast increase in the Ni NP size and the formation of substantial carbon nanotubes on the unconfined catalyst surface are seen. This work offers a facile approach for the synthesis of anti-sintering, carbon-resistant confined Ni catalysts that can operate at high temperatures.
Development of dry reforming of methane and carbon dioxide is an effective route to convert industrial waste gases such as coke-oven gas and coal-to-oil gas into platform syngas. However, this process encounters severe problems of metal particle sintering and coke formation at high temperatures. In this work, we developed a new synthetic method for preparing confined Ni/MCM-41 catalysts, which impede the sintering of metal nanoparticles (NPs) and coke deposition at high temperatures, enabling them to be successfully applied to methane dry reforming. The method results in high activity and stability of the catalyst at 700℃ for 200 h. The Ni precursor is immersed in ethanol and impregnated into MCM-41 by the peculiar capillary action of hexagonal straight mesopores. By this method, 10 wt% Ni NPs (d=2 nm) is equably confined to the mesoporous channels with strong metal-support interactions, as confirmed by HRTEM, TEM mapping, H2-TPR, and XRD measurements. Such a confined structure has a significant effect on the inhibition of metal NP agglomeration and carbon deposition during methane dry reforming, as evidenced by TEM, Raman, TGA, and TPO measurements of used Ni/MCM-41 catalysts. In contrast, unconfined Ni/MCM-41 catalysts, with Ni NPs located on the pore exteriors, are rapidly deactivated after 12 h due to the blocked contact between the active metal centers and the gas feedstock. Additionally, a fast increase in the Ni NP size and the formation of substantial carbon nanotubes on the unconfined catalyst surface are seen. This work offers a facile approach for the synthesis of anti-sintering, carbon-resistant confined Ni catalysts that can operate at high temperatures.
