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2017 Volume 38 Issue 8
2017, 38(8):
Abstract:
2017, 38(8): 1295-1306
Abstract:
Rapid industrialization has accordingly increased the demand for energy. This has resulted in the increasingly severe energy and environmental crises. Hydrogen production, based on the photocatalytic water splitting driven by sunlight, is able to directly convert solar energy into a usable or storable energy resource, which is considered to be an ideal alternative energy source to assist in solving the energy crisis and environmental pollution. Unfortunately, the hydrogen production efficiency of single phase photocatalysts is too low to meet the practical requirements. The construction of heterostructured photocatalyst systems, which are comprised of multiple components or multiple phases, is an efficient method to facilitate the separation of electron-hole pairs to minimize the energy-waste, provide more electrons, enhance their redox ability, and hence improve the photocatalytic activity. We summarize the recent progress in the rational design and fabrication of nanoheterostructured photocatalysts. The heterojunction photocatalytic hydrogen generation systems can be divided into type-I, type-Ⅱ, pn-junction and Z-scheme junction, according to the differences in the transfer of the photogenerated electrons and holes. Finally, a summary and some of the challenges and prospects for the future development of heterojunction photocatalytic systems are discussed.
Rapid industrialization has accordingly increased the demand for energy. This has resulted in the increasingly severe energy and environmental crises. Hydrogen production, based on the photocatalytic water splitting driven by sunlight, is able to directly convert solar energy into a usable or storable energy resource, which is considered to be an ideal alternative energy source to assist in solving the energy crisis and environmental pollution. Unfortunately, the hydrogen production efficiency of single phase photocatalysts is too low to meet the practical requirements. The construction of heterostructured photocatalyst systems, which are comprised of multiple components or multiple phases, is an efficient method to facilitate the separation of electron-hole pairs to minimize the energy-waste, provide more electrons, enhance their redox ability, and hence improve the photocatalytic activity. We summarize the recent progress in the rational design and fabrication of nanoheterostructured photocatalysts. The heterojunction photocatalytic hydrogen generation systems can be divided into type-I, type-Ⅱ, pn-junction and Z-scheme junction, according to the differences in the transfer of the photogenerated electrons and holes. Finally, a summary and some of the challenges and prospects for the future development of heterojunction photocatalytic systems are discussed.
2017, 38(8): 1307-1314
Abstract:
We report the construction of a graphene/tourmaline/TiO2 (G/T/TiO2) composite system with enhanced charge-carrier separation, and therefore enhanced photocatalytic properties, based on tailoring the surface-charged state of graphene and/or by introducing an external electric field arising from tourmaline. A simple two-step hydrothermal method was used to synthesize G/T/TiO2 composites and poly(diallyldimethylammonium chloride)-G/T/TiO2 composites. In the photocatalytic degradation of 2-propanol (IPA), the catalytic activity of the composite containing negatively charged graphene was higher than of the composite containing positively charged graphene. The highest acetone evolution rate (223 μmol/h) was achieved using the ternary composite with the optimum composition, i.e., G0.5/T5/TiO2 (0.5 wt% graphene and 5 wt% tourmaline). The involvement of tourmaline and graphene in the composite is believed to facilitate the separation and transportation of electrons and holes photogenerated in TiO2. This synergetic effect could account for the enhanced photocatalytic activity of the G/T/TiO2 composite. A mechanistic study indicated that O2·- radicals and holes were the main reactive oxygen species in photocatalytic degradation of IPA.
We report the construction of a graphene/tourmaline/TiO2 (G/T/TiO2) composite system with enhanced charge-carrier separation, and therefore enhanced photocatalytic properties, based on tailoring the surface-charged state of graphene and/or by introducing an external electric field arising from tourmaline. A simple two-step hydrothermal method was used to synthesize G/T/TiO2 composites and poly(diallyldimethylammonium chloride)-G/T/TiO2 composites. In the photocatalytic degradation of 2-propanol (IPA), the catalytic activity of the composite containing negatively charged graphene was higher than of the composite containing positively charged graphene. The highest acetone evolution rate (223 μmol/h) was achieved using the ternary composite with the optimum composition, i.e., G0.5/T5/TiO2 (0.5 wt% graphene and 5 wt% tourmaline). The involvement of tourmaline and graphene in the composite is believed to facilitate the separation and transportation of electrons and holes photogenerated in TiO2. This synergetic effect could account for the enhanced photocatalytic activity of the G/T/TiO2 composite. A mechanistic study indicated that O2·- radicals and holes were the main reactive oxygen species in photocatalytic degradation of IPA.
2017, 38(8): 1315-1321
Abstract:
The catalytic activity of metal catalysts can be modulated by confinement within the channels of carbon nanotubes (CNTs). Here, we show that the product distribution of cinnamaldehyde hydrogenation can be modified by confinement of Ru nanoparticles in CNTs. A catalyst composed of Ru nanoparticles dispersed on the exterior walls of CNTs gave hydrocinnamaldehyde as product. In contrast, confinement of the Ru nanoparticles within CNT channels facilitated hydrogenation of C=O bonds and complete hydrogenation, and both cinnamyl alcohol and hydrocinnamyl alcohol formed in addition to hydrocinnamaldehyde. High-resolution transmission electron microscopy, Raman spectroscopy, hydrogen temperature-programmed reduction, and hydrogen temperature-programmed desorption were used to investigate the characteristics of the catalysts. The results indicate that the different interactions between the confined Ru nanoparticles and the exterior and interior walls of the CNTs, as well as spatial restriction and enrichment within the narrow channels likely play important roles in modulation of the product distribution.
The catalytic activity of metal catalysts can be modulated by confinement within the channels of carbon nanotubes (CNTs). Here, we show that the product distribution of cinnamaldehyde hydrogenation can be modified by confinement of Ru nanoparticles in CNTs. A catalyst composed of Ru nanoparticles dispersed on the exterior walls of CNTs gave hydrocinnamaldehyde as product. In contrast, confinement of the Ru nanoparticles within CNT channels facilitated hydrogenation of C=O bonds and complete hydrogenation, and both cinnamyl alcohol and hydrocinnamyl alcohol formed in addition to hydrocinnamaldehyde. High-resolution transmission electron microscopy, Raman spectroscopy, hydrogen temperature-programmed reduction, and hydrogen temperature-programmed desorption were used to investigate the characteristics of the catalysts. The results indicate that the different interactions between the confined Ru nanoparticles and the exterior and interior walls of the CNTs, as well as spatial restriction and enrichment within the narrow channels likely play important roles in modulation of the product distribution.
2017, 38(8): 1322-1329
Abstract:
SnO2-supported Pd catalysts were prepared and the effects of the support calcination tempera-ture on the subsequent catalytic activity during methane combustion were investigated. The physicochemical properties of the Pd/SnO2 were characterized by X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, oxygen temperature-programmed desorption and CH4 temperature-programmed surface reaction. Only crystalline Pd species were found on the catalysts fabricated from the supports calcined above 800℃. It was also determined that lattice geometry matching between PdO and SnO2 in the catalyst made with a support calcined at 1200℃ facilitated oxygen activation from SnO2 to vacant oxygen sites on the PdO/Pd surface via the back-spillover of oxygen. This effect in turn enhanced the catalytic combustion process. The activity of this material was clearly increased compared with the catalysts that did not exhibit lattice matching between the PdO and support.
SnO2-supported Pd catalysts were prepared and the effects of the support calcination tempera-ture on the subsequent catalytic activity during methane combustion were investigated. The physicochemical properties of the Pd/SnO2 were characterized by X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, oxygen temperature-programmed desorption and CH4 temperature-programmed surface reaction. Only crystalline Pd species were found on the catalysts fabricated from the supports calcined above 800℃. It was also determined that lattice geometry matching between PdO and SnO2 in the catalyst made with a support calcined at 1200℃ facilitated oxygen activation from SnO2 to vacant oxygen sites on the PdO/Pd surface via the back-spillover of oxygen. This effect in turn enhanced the catalytic combustion process. The activity of this material was clearly increased compared with the catalysts that did not exhibit lattice matching between the PdO and support.
2017, 38(8): 1330-1337
Abstract:
A nanocomposite catalyst with a nonstoichiometric titanium oxide loaded on a special nanotubular alumina (γ-Al2O3-nt) was developed and used to reduce cinnamaldehyde to cinnamyl alcohol with sacrificial isopropanol, i.e., a Meerwein-Ponndorf-Verley type reaction. The deposition process produced a highly disperse layer of titanium oxide on the surface of a γ-Al2O3-nt support. After a reduction treatment, the as-prepared TiOx/γ-Al2O3-nt was a highly efficient catalyst for the hydrogen transfer reaction between isopropanol and cinnamaldehyde. Selectivity for cinnamic alcohol was higher than 99% and the conversion of cinnamaldehyde was higher than 95%. The regular morphology of the γ-Al2O3-nt support with homogeneous surface sites and the uniformly dispersed titanium oxide featured a high concentration surface Ti(Ⅲ) species. These factors contributed to the high performance of the TiOx/γ-Al2O3-nt catalyst.
A nanocomposite catalyst with a nonstoichiometric titanium oxide loaded on a special nanotubular alumina (γ-Al2O3-nt) was developed and used to reduce cinnamaldehyde to cinnamyl alcohol with sacrificial isopropanol, i.e., a Meerwein-Ponndorf-Verley type reaction. The deposition process produced a highly disperse layer of titanium oxide on the surface of a γ-Al2O3-nt support. After a reduction treatment, the as-prepared TiOx/γ-Al2O3-nt was a highly efficient catalyst for the hydrogen transfer reaction between isopropanol and cinnamaldehyde. Selectivity for cinnamic alcohol was higher than 99% and the conversion of cinnamaldehyde was higher than 95%. The regular morphology of the γ-Al2O3-nt support with homogeneous surface sites and the uniformly dispersed titanium oxide featured a high concentration surface Ti(Ⅲ) species. These factors contributed to the high performance of the TiOx/γ-Al2O3-nt catalyst.
2017, 38(8): 1338-1346
Abstract:
Supported Au catalysts have been reported to exhibit high ethylene selectivity in the hydrogenation of acetylene, but the conversion is relatively low. Adding a second metal to Au has proven to be a promising approach to enhance its catalytic performance in acetylene hydrogenation. In this work, SiO2-supported Au-Ni bimetallic catalysts were synthesized and investigated in the selective hydrogenation of acetylene. The Au-Ni bimetallic catalysts exhibited much higher catalytic performance than that of the corresponding monometallic Au or Ni catalysts. By tuning the reduction temperature and/or Ni loading, we obtained an Au-Ni/SiO2 catalyst with optimal performance. The results of transmission electron microscopy imaging revealed that the Au-Ni bimetallic particles were highly dispersed on the SiO2 support. Meanwhile, analysis of the bimetallic catalyst by energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy demonstrated the formation of Au-Ni alloy, which contributed to the synergistic effect between Au and Ni in the hydrogenation of acetylene.
Supported Au catalysts have been reported to exhibit high ethylene selectivity in the hydrogenation of acetylene, but the conversion is relatively low. Adding a second metal to Au has proven to be a promising approach to enhance its catalytic performance in acetylene hydrogenation. In this work, SiO2-supported Au-Ni bimetallic catalysts were synthesized and investigated in the selective hydrogenation of acetylene. The Au-Ni bimetallic catalysts exhibited much higher catalytic performance than that of the corresponding monometallic Au or Ni catalysts. By tuning the reduction temperature and/or Ni loading, we obtained an Au-Ni/SiO2 catalyst with optimal performance. The results of transmission electron microscopy imaging revealed that the Au-Ni bimetallic particles were highly dispersed on the SiO2 support. Meanwhile, analysis of the bimetallic catalyst by energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy demonstrated the formation of Au-Ni alloy, which contributed to the synergistic effect between Au and Ni in the hydrogenation of acetylene.
2017, 38(8): 1347-1359
Abstract:
A series of Al-containing mesostructured cellular silica foams (Al-MCFs) with different Si/Al molar ratios (x; x=10, 20, 30, 40, or 50) were prepared by a post synthetic method using aluminum isopropoxide as an alumina source. The corresponding NiMo catalysts supported on Al-MCFs were prepared and evaluated using dibenzothiophene (DBT) as the probe reactant. All the synthesized samples were characterized by small-angle X-ray scattering, scanning electron microscopy, nitrogen adsorption-desorption, UV-Vis diffuse reflectance spectroscopy, H2 temperature-programmed reduction, 27Al MAS NMR, temperature-programmed desorption of ammonia, pyridine-FTIR, Raman spectroscopy, HRTEM, and X-ray photoelectron spectroscopy to analyze their physicochemical properties and to gain a deeper insight of the interrelationship between the structures and the catalytic performance. The synthesis mechanism was proposed to involve the formation of Brönsted acid and Lewis acid sites through the replacement of Si4+ with Al3+. Aluminum introduced into MCFs by the post synthetic method has a negligible influence on the mesostructure of the parent MCFs but can form silicoaluminate materials with moderate Brönsted acidity. For Al-MCFs(x) materials, the detection of tetrahedrally coordinated Al3+ cations demonstrated that the Al species had been successfully incorporated into the silicon frameworks. Furthermore, the DBT hydrodesulfurization (HDS) catalytic activity of the NiMo/Al-MCFs(x) catalysts increased with increasing Si/Al molar ratio, and reached a maximum at a Si/Al molar ratio of 20. The interaction of Ni and Mo species with the support became stronger when Al was incorporated into the MCFs supports. The high activities of the NiMo/Al-MCFs catalysts for the DBT HDS were attributed to the suitable acidity properties and good dispersions of the Ni and Mo active phases.
A series of Al-containing mesostructured cellular silica foams (Al-MCFs) with different Si/Al molar ratios (x; x=10, 20, 30, 40, or 50) were prepared by a post synthetic method using aluminum isopropoxide as an alumina source. The corresponding NiMo catalysts supported on Al-MCFs were prepared and evaluated using dibenzothiophene (DBT) as the probe reactant. All the synthesized samples were characterized by small-angle X-ray scattering, scanning electron microscopy, nitrogen adsorption-desorption, UV-Vis diffuse reflectance spectroscopy, H2 temperature-programmed reduction, 27Al MAS NMR, temperature-programmed desorption of ammonia, pyridine-FTIR, Raman spectroscopy, HRTEM, and X-ray photoelectron spectroscopy to analyze their physicochemical properties and to gain a deeper insight of the interrelationship between the structures and the catalytic performance. The synthesis mechanism was proposed to involve the formation of Brönsted acid and Lewis acid sites through the replacement of Si4+ with Al3+. Aluminum introduced into MCFs by the post synthetic method has a negligible influence on the mesostructure of the parent MCFs but can form silicoaluminate materials with moderate Brönsted acidity. For Al-MCFs(x) materials, the detection of tetrahedrally coordinated Al3+ cations demonstrated that the Al species had been successfully incorporated into the silicon frameworks. Furthermore, the DBT hydrodesulfurization (HDS) catalytic activity of the NiMo/Al-MCFs(x) catalysts increased with increasing Si/Al molar ratio, and reached a maximum at a Si/Al molar ratio of 20. The interaction of Ni and Mo species with the support became stronger when Al was incorporated into the MCFs supports. The high activities of the NiMo/Al-MCFs catalysts for the DBT HDS were attributed to the suitable acidity properties and good dispersions of the Ni and Mo active phases.
2017, 38(8): 1360-1372
Abstract:
An environmentally friendly Mn-oxide-supported metal-organic framework (MOF), Mn3O4/ZIF-8, was successfully prepared using a facile solvothermal method, with a formation mechanism proposed. The composite was characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron microscopy, and Fourier-transform infrared spectroscopy. After characterization, the MOF was used to activate peroxymonosulfate (PMS) for degradation of the refractory pollutant rhodamine B (RhB) in water. The composite prepared at a 0.5:1 mass ratio of Mn3O4 to ZIF-8 possessed the highest catalytic activity with negligible Mn leaching. The maximum RhB degradation of approximately 98% was achieved at 0.4 g/L 0.5-Mn/ZIF-120, 0.3 g/L PMS, and 10 mg/L initial RhB concentration at a reaction temperature of 23℃. The RhB degradation followed first-order kinetics and was accelerated with increased 0.5-Mn/ZIF-120 and PMS dosages, decreased initial RhB concentration, and increased reaction temperature. Moreover, quenching tests indicated that ·OH was the predominant radical involved in the RhB degradation; the ·OH mainly originated from SO4-·and, hence, PMS. Mn3O4/ZIF-8 also displayed good reusability for RhB degradation in the presence of PMS over five runs, with a RhB degradation efficiency of more than 96% and Mn leaching of less than 5% for each run. Based on these findings, a RhB degradation mechanism was proposed.
An environmentally friendly Mn-oxide-supported metal-organic framework (MOF), Mn3O4/ZIF-8, was successfully prepared using a facile solvothermal method, with a formation mechanism proposed. The composite was characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron microscopy, and Fourier-transform infrared spectroscopy. After characterization, the MOF was used to activate peroxymonosulfate (PMS) for degradation of the refractory pollutant rhodamine B (RhB) in water. The composite prepared at a 0.5:1 mass ratio of Mn3O4 to ZIF-8 possessed the highest catalytic activity with negligible Mn leaching. The maximum RhB degradation of approximately 98% was achieved at 0.4 g/L 0.5-Mn/ZIF-120, 0.3 g/L PMS, and 10 mg/L initial RhB concentration at a reaction temperature of 23℃. The RhB degradation followed first-order kinetics and was accelerated with increased 0.5-Mn/ZIF-120 and PMS dosages, decreased initial RhB concentration, and increased reaction temperature. Moreover, quenching tests indicated that ·OH was the predominant radical involved in the RhB degradation; the ·OH mainly originated from SO4-·and, hence, PMS. Mn3O4/ZIF-8 also displayed good reusability for RhB degradation in the presence of PMS over five runs, with a RhB degradation efficiency of more than 96% and Mn leaching of less than 5% for each run. Based on these findings, a RhB degradation mechanism was proposed.
2017, 38(8): 1373-1381
Abstract:
Development of the high activity, promoter-free catalysts for carbonyl sulfide (COS) hydrolysis is important for the efficient utilization of various feedstocks. In this study, the Cu-based met-al-organic framework HKUST-1 is synthesized by a simple and mild anodic-dissolution electro-chemical method. The physical and chemical properties of the samples are characterized by several techniques, including scanning electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller analysis and X-ray photoelectron spectroscopy. The results reveal that the synthesis voltage plays a crucial role in controlling the morphology of the resulting HKUST-1. The obtained samples function as novel catalysts for the hydrolysis of COS. A high efficiency, approaching 100%, can be achieved for the conversion of COS at 150℃ over the optimal HKUST-1 synthesized at 25 V. This is significantly higher than that of the sample pre-pared by the traditional hydrothermal method. Additionally, the effects of the water temperature and the flow velocity on the hydrolysis of COS are also investigated in detail. Finally, a possible reaction pathway of COS hydrolysis over HKUST-1 is also proposed. This work represents the first example of MOFs applied to the catalytic hydrolysis of COS. The results presented in this study can be anticipated to give a feasible impetus to design novel catalysts for removing the sulfur-containing compounds.
Development of the high activity, promoter-free catalysts for carbonyl sulfide (COS) hydrolysis is important for the efficient utilization of various feedstocks. In this study, the Cu-based met-al-organic framework HKUST-1 is synthesized by a simple and mild anodic-dissolution electro-chemical method. The physical and chemical properties of the samples are characterized by several techniques, including scanning electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller analysis and X-ray photoelectron spectroscopy. The results reveal that the synthesis voltage plays a crucial role in controlling the morphology of the resulting HKUST-1. The obtained samples function as novel catalysts for the hydrolysis of COS. A high efficiency, approaching 100%, can be achieved for the conversion of COS at 150℃ over the optimal HKUST-1 synthesized at 25 V. This is significantly higher than that of the sample pre-pared by the traditional hydrothermal method. Additionally, the effects of the water temperature and the flow velocity on the hydrolysis of COS are also investigated in detail. Finally, a possible reaction pathway of COS hydrolysis over HKUST-1 is also proposed. This work represents the first example of MOFs applied to the catalytic hydrolysis of COS. The results presented in this study can be anticipated to give a feasible impetus to design novel catalysts for removing the sulfur-containing compounds.
2017, 38(8): 1382-1389
Abstract:
The combination of a zinc phthalocyanine (ZnPc) catalyst and a stoichiometric amount of dimethyl formamide (DMF) provided a simple route to formamide derivatives from amines, CO2, and hydrosilanes under mild conditions. We deduced that formation of an active zinc-hydrogen (Zn-H) species promoted hydride transfer from the hydrosilane to CO2. The cooperative activation of the Lewis acidic ZnPc by strongly polar DMF, led to formation of activated amines and hydrosilanes, which promoted the chemical reduction of CO2. Consequently, the binary ZnPc/DMF catalytic system showed excellent yields and superior chemoselectivity, representing a simple and sustainable pathway for the reductive transformation of CO2 into valuable chemicals as an alternative to conventional halogen-containing process.
The combination of a zinc phthalocyanine (ZnPc) catalyst and a stoichiometric amount of dimethyl formamide (DMF) provided a simple route to formamide derivatives from amines, CO2, and hydrosilanes under mild conditions. We deduced that formation of an active zinc-hydrogen (Zn-H) species promoted hydride transfer from the hydrosilane to CO2. The cooperative activation of the Lewis acidic ZnPc by strongly polar DMF, led to formation of activated amines and hydrosilanes, which promoted the chemical reduction of CO2. Consequently, the binary ZnPc/DMF catalytic system showed excellent yields and superior chemoselectivity, representing a simple and sustainable pathway for the reductive transformation of CO2 into valuable chemicals as an alternative to conventional halogen-containing process.
2017, 38(8): 1390-1398
Abstract:
A mild and efficient oxidative synthesis of isoindolinones has been realized by Rh(Ⅲ)-catalyzed C-H activation of benzamides and[4 + 1] coupling with propargyl alcohols. This coupling system proceeds with broad substrate scope and mild conditions and provides a new approach to access the useful skeleton of γ-lactams with a stereogenic center.
A mild and efficient oxidative synthesis of isoindolinones has been realized by Rh(Ⅲ)-catalyzed C-H activation of benzamides and[4 + 1] coupling with propargyl alcohols. This coupling system proceeds with broad substrate scope and mild conditions and provides a new approach to access the useful skeleton of γ-lactams with a stereogenic center.
2017, 38(8): 1399-1405
Abstract:
Vibrational IR spectra and light-off investigations show that NH3 forms via the "hydrogen down" reaction of adsorbed CO and NO with hydroxyl groups on a CeO2 support during the catalytic reduction of NO by CO. The presence of water in the reaction stream results in a significant increase in NH3 selectivity. This result is due to water-induced hydroxylation promoting NH3 formation and the competitive adsorption of H2O and NO at the same sites, which inhibits the reactivity of NO reduction by NH3.
Vibrational IR spectra and light-off investigations show that NH3 forms via the "hydrogen down" reaction of adsorbed CO and NO with hydroxyl groups on a CeO2 support during the catalytic reduction of NO by CO. The presence of water in the reaction stream results in a significant increase in NH3 selectivity. This result is due to water-induced hydroxylation promoting NH3 formation and the competitive adsorption of H2O and NO at the same sites, which inhibits the reactivity of NO reduction by NH3.
2017, 38(8): 1406-1412
Abstract:
LaMnO3 was prepared by citrate sol-gel, coprecipitation, hard template, and hydrothermal methods, respectively, and its catalytic performance for the combustion of vinyl chloride was investigated. N2 adsorption-desorption, X-ray diffraction (XRD), Raman spectroscopy (Raman), O2 temperature programmed desorption (O2-TPD), H2 temperature programmed surface reaction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the physicochemical properties of the LaMnO3 samples. The preparation methods had obvious effects on the distribution of oxygen and manganese species on the catalyst surface. The reaction followed the suprafacial mechanism; the activity corresponded with the high amount of Mn4+ and adsorbed oxygen species. LaMnO3 prepared by the citrate sol-gel method had the best performance for vinyl chloride combustion with T90 of 182℃. The optimal activity was attributed to the improved redox capability of Mn4+/Mn3+. More available adsorbed oxygen and Mn4+ species on the surface were mainly responsible for the remarkable enhancement of the catalytic activity.
LaMnO3 was prepared by citrate sol-gel, coprecipitation, hard template, and hydrothermal methods, respectively, and its catalytic performance for the combustion of vinyl chloride was investigated. N2 adsorption-desorption, X-ray diffraction (XRD), Raman spectroscopy (Raman), O2 temperature programmed desorption (O2-TPD), H2 temperature programmed surface reaction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the physicochemical properties of the LaMnO3 samples. The preparation methods had obvious effects on the distribution of oxygen and manganese species on the catalyst surface. The reaction followed the suprafacial mechanism; the activity corresponded with the high amount of Mn4+ and adsorbed oxygen species. LaMnO3 prepared by the citrate sol-gel method had the best performance for vinyl chloride combustion with T90 of 182℃. The optimal activity was attributed to the improved redox capability of Mn4+/Mn3+. More available adsorbed oxygen and Mn4+ species on the surface were mainly responsible for the remarkable enhancement of the catalytic activity.
2017, 38(8): 1413-1422
Abstract:
A Pd Schiff base complex was immobilized onto the surface of magnetic MCM-41 (Fe3O4@MCM-41@Pd(0)-P2C) as a novel, eco-friendly, and recyclable heterogeneous nanocatalyst and fully characterized by FT-IR, VSM, EDS, transmission electron microscopy, scanning electron microscopy, thermogravimetric analyses, ICP-OES, and X-ray powder diffraction analysis. The Fe3O4@MCM-41@Pd(0)-P2C was investigated as a catalyst for the one-pot Suzuki and Heck reactions in PEG as a green solvent to provide the target products in excellent yields. The main advantages of using this catalyst include a short reaction time, green reaction conditions, a simple experimental procedure, non-use of hazardous organic solvents, low loading of the catalyst, and the ability to use various substrates. More importantly, the catalyst could be easily separated from the reaction mixture with the assistance of an external magnet and could be recovered and reused several times without significant loss of stability and activity.
A Pd Schiff base complex was immobilized onto the surface of magnetic MCM-41 (Fe3O4@MCM-41@Pd(0)-P2C) as a novel, eco-friendly, and recyclable heterogeneous nanocatalyst and fully characterized by FT-IR, VSM, EDS, transmission electron microscopy, scanning electron microscopy, thermogravimetric analyses, ICP-OES, and X-ray powder diffraction analysis. The Fe3O4@MCM-41@Pd(0)-P2C was investigated as a catalyst for the one-pot Suzuki and Heck reactions in PEG as a green solvent to provide the target products in excellent yields. The main advantages of using this catalyst include a short reaction time, green reaction conditions, a simple experimental procedure, non-use of hazardous organic solvents, low loading of the catalyst, and the ability to use various substrates. More importantly, the catalyst could be easily separated from the reaction mixture with the assistance of an external magnet and could be recovered and reused several times without significant loss of stability and activity.
2017, 38(8): 1423-1430
Abstract:
To investigate how the physicochemical properties and NH3-selective catalytic reduction (NH3-SCR) performance of supported ceria-based catalysts are influenced as a function of support type, a series of CeO2/SiO2, CeO2/γ-Al2O3, CeO2/ZrO2, and CeO2/TiO2 catalysts were prepared. The physicochemical properties were probed by means of X-ray diffraction, Raman spectroscopy, Brunauer-Emmett-Teller surface area measurements, X-ray photoelectron spectroscopy, H2-temperature programmed reduction, and NH3-temperature programmed desorption. Furthermore, the supported ceria-based catalysts' catalytic performance and H2O + SO2 tolerance were evaluated by the NH3-SCR model reaction. The results indicate that out of the supported ceria-based catalysts studied, the CeO2/γ-Al2O3 catalyst exhibits the highest catalytic activity as a result of having a high relative Ce3+/Ce4+ ratio, optimum reduction behavior, and the largest total acid site concentration. Finally, the CeO2/γ-Al2O3 catalyst also presents excellent H2O + SO2 tolerance during the NH3-SCR process.
To investigate how the physicochemical properties and NH3-selective catalytic reduction (NH3-SCR) performance of supported ceria-based catalysts are influenced as a function of support type, a series of CeO2/SiO2, CeO2/γ-Al2O3, CeO2/ZrO2, and CeO2/TiO2 catalysts were prepared. The physicochemical properties were probed by means of X-ray diffraction, Raman spectroscopy, Brunauer-Emmett-Teller surface area measurements, X-ray photoelectron spectroscopy, H2-temperature programmed reduction, and NH3-temperature programmed desorption. Furthermore, the supported ceria-based catalysts' catalytic performance and H2O + SO2 tolerance were evaluated by the NH3-SCR model reaction. The results indicate that out of the supported ceria-based catalysts studied, the CeO2/γ-Al2O3 catalyst exhibits the highest catalytic activity as a result of having a high relative Ce3+/Ce4+ ratio, optimum reduction behavior, and the largest total acid site concentration. Finally, the CeO2/γ-Al2O3 catalyst also presents excellent H2O + SO2 tolerance during the NH3-SCR process.
