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2016 Volume 37 Issue 3
2016, 37(3): 325-339
doi: 10.1016/S1872-2067(15)61031-2
Abstract:
The methanol-to-propylene (MTP) process is a route of methanol conversion to hydrocarbons, which is in high demand because of limited oil resources. The present paper discusses the effect of catalyst structure on the MTP process conditions, and the role of different zeolite factors, such as acidity, crystal size, mesoporosity, and topology, on the activity and selectivity of the MTP reaction.
The methanol-to-propylene (MTP) process is a route of methanol conversion to hydrocarbons, which is in high demand because of limited oil resources. The present paper discusses the effect of catalyst structure on the MTP process conditions, and the role of different zeolite factors, such as acidity, crystal size, mesoporosity, and topology, on the activity and selectivity of the MTP reaction.
2016, 37(3): 340-348
doi: 10.1016/S1872-2067(15)61020-8
Abstract:
Most current catalyst preparation methods cause pollution to air, water and land with the use of hazardous chemicals, lengthy operation time, high energy input and excessive water usage. The development of green catalyst preparation is necessary to prevent and eliminate waste from each step of the catalyst preparation. We summarize recent progress in the application of cold plasmas for green catalyst preparation. Cold plasma preparation can reduce the catalyst size, improve the dispersion and enhance catalyst-support interaction with the use of less or no hazardous chemicals. These improvements also lead to the enhancement of catalyst activity and stability. An alternative room temperature electron reduction with a non-hydrogen plasma as an electron source was developed for the reduction of noble metal ions in which no hazardous chemical reducing agent or hydrogen was needed. This creates many opportunities for the development of supported catalysts with heat sensitive substrates, including metal organic frameworks (MOFs), covalent organic framework (COFs), high surface area carbon, peptide, DNA, proteins and others. A novel floating metal catalyst on a water (or solution) surface has been established. Template removal using low temperature cold plasmas also leads to the formation of high surface area porous materials with characteristics that are normally only obtainable with high temperature calcination, but sintering can be avoided. Micro combustion has been developed for the removal of carbon template using cold plasma. This is promising for preparing many structured oxides in a simple way with no use of auxiliary chemicals. Many opportunities exist for the use of cold plasmas to make multi-metallic oxides. Some future development ideas are addressed.
Most current catalyst preparation methods cause pollution to air, water and land with the use of hazardous chemicals, lengthy operation time, high energy input and excessive water usage. The development of green catalyst preparation is necessary to prevent and eliminate waste from each step of the catalyst preparation. We summarize recent progress in the application of cold plasmas for green catalyst preparation. Cold plasma preparation can reduce the catalyst size, improve the dispersion and enhance catalyst-support interaction with the use of less or no hazardous chemicals. These improvements also lead to the enhancement of catalyst activity and stability. An alternative room temperature electron reduction with a non-hydrogen plasma as an electron source was developed for the reduction of noble metal ions in which no hazardous chemical reducing agent or hydrogen was needed. This creates many opportunities for the development of supported catalysts with heat sensitive substrates, including metal organic frameworks (MOFs), covalent organic framework (COFs), high surface area carbon, peptide, DNA, proteins and others. A novel floating metal catalyst on a water (or solution) surface has been established. Template removal using low temperature cold plasmas also leads to the formation of high surface area porous materials with characteristics that are normally only obtainable with high temperature calcination, but sintering can be avoided. Micro combustion has been developed for the removal of carbon template using cold plasma. This is promising for preparing many structured oxides in a simple way with no use of auxiliary chemicals. Many opportunities exist for the use of cold plasmas to make multi-metallic oxides. Some future development ideas are addressed.
2016, 37(3): 349-358
doi: 10.1016/S1872-2067(15)61023-3
Abstract:
A series of WO3 samples with different crystalline phases were prepared by the thermal decomposition method from ammonium tungstate hydrate. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy, and N2 adsorption-desorption were used to characterize the crystalline phase, morphology, particle size, chemical composition, and surface area of the WO3 samples. The formation of hexagonal (h-WO3) and monoclinic (m-WO3) crystal structures of WO3 at different temperatures or different times was confirmed by XRD. m-WO3 is formed at 600 ℃, while m-WO3 starts to transform into h-WO3 at 800 ℃. However, h-WO3, which forms at 800 ℃, may transform into m-WO3 by increasing the calcination temperature to 1000 ℃. SEM results indicate that m-WO3 particles exhibit a bulky shape with heavy aggregates, while h-WO3 particles exhibit a rod-like shape. Moreover, m-WO3 crystals are sporadically patched on the surface of the h-WO3 rod-like particles, resulting in the exposure of both m-WO3 and h-WO3 on the surface. It is observed that the monoclinic phase (m-WO3)/hexagonal phase (h-WO3) junction was fabricated by tuning the calcination temperature and calcination time. The relative ratios between m-WO3 and h-WO3 in the phase junction can readily be tailored by control of the calcination time. The photocatalytic activities of WO3 with different crystalline phases were evaluated by the photocatalytic degradation of rhodamine B as a model pollutant. A higher photocatalytic activity was observed in the WO3 sample with the m-WO3/h-WO3 junction as compared with the sample with only m-WO3. The improvement of photocatalytic activity can be attributed to the reduction of the electron-hole recombination rate owing to the formation of the phase junction, whose presence has been confirmed by HRTEM and photoluminescence spectra.
A series of WO3 samples with different crystalline phases were prepared by the thermal decomposition method from ammonium tungstate hydrate. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy, and N2 adsorption-desorption were used to characterize the crystalline phase, morphology, particle size, chemical composition, and surface area of the WO3 samples. The formation of hexagonal (h-WO3) and monoclinic (m-WO3) crystal structures of WO3 at different temperatures or different times was confirmed by XRD. m-WO3 is formed at 600 ℃, while m-WO3 starts to transform into h-WO3 at 800 ℃. However, h-WO3, which forms at 800 ℃, may transform into m-WO3 by increasing the calcination temperature to 1000 ℃. SEM results indicate that m-WO3 particles exhibit a bulky shape with heavy aggregates, while h-WO3 particles exhibit a rod-like shape. Moreover, m-WO3 crystals are sporadically patched on the surface of the h-WO3 rod-like particles, resulting in the exposure of both m-WO3 and h-WO3 on the surface. It is observed that the monoclinic phase (m-WO3)/hexagonal phase (h-WO3) junction was fabricated by tuning the calcination temperature and calcination time. The relative ratios between m-WO3 and h-WO3 in the phase junction can readily be tailored by control of the calcination time. The photocatalytic activities of WO3 with different crystalline phases were evaluated by the photocatalytic degradation of rhodamine B as a model pollutant. A higher photocatalytic activity was observed in the WO3 sample with the m-WO3/h-WO3 junction as compared with the sample with only m-WO3. The improvement of photocatalytic activity can be attributed to the reduction of the electron-hole recombination rate owing to the formation of the phase junction, whose presence has been confirmed by HRTEM and photoluminescence spectra.
2016, 37(3): 359-366
doi: 10.1016/S1872-2067(15)61042-7
Abstract:
The effects of ethanol vapor pretreatment on the performance of CrOx/SiO2 catalysts during the dehydrogenation of propane to propylene were studied with and without the presence of CO2. The catalyst pretreated with ethanol vapor exhibited better catalytic activity than the pristine CrOx/SiO2, generating 41.4% propane conversion and 84.8% propylene selectivity. The various catalyst samples prepared were characterized by X-ray diffraction, transmission electron microscopy, temperature-programmed reduction, X-ray photoelectron spectroscopy and reflectance UV-Vis spectroscopy. The data show that coordinative Cr3+ species represent the active sites during the dehydrogenation of propane and that these species serve as precursors for the generation of Cr3+. Cr3+ is reduced during the reaction, leading to a decrease in catalytic activity. Following ethanol vapor pretreatment, the reduced CrOx in the catalyst is readily re-oxidized to Cr6+ by CO2. The pretreated catalyst thus exhibits high activity during the propane dehydrogenation reaction by maintaining the active Cr3+ states.
The effects of ethanol vapor pretreatment on the performance of CrOx/SiO2 catalysts during the dehydrogenation of propane to propylene were studied with and without the presence of CO2. The catalyst pretreated with ethanol vapor exhibited better catalytic activity than the pristine CrOx/SiO2, generating 41.4% propane conversion and 84.8% propylene selectivity. The various catalyst samples prepared were characterized by X-ray diffraction, transmission electron microscopy, temperature-programmed reduction, X-ray photoelectron spectroscopy and reflectance UV-Vis spectroscopy. The data show that coordinative Cr3+ species represent the active sites during the dehydrogenation of propane and that these species serve as precursors for the generation of Cr3+. Cr3+ is reduced during the reaction, leading to a decrease in catalytic activity. Following ethanol vapor pretreatment, the reduced CrOx in the catalyst is readily re-oxidized to Cr6+ by CO2. The pretreated catalyst thus exhibits high activity during the propane dehydrogenation reaction by maintaining the active Cr3+ states.
2016, 37(3): 367-377
doi: 10.1016/S1872-2067(15)61033-6
Abstract:
N-K2Ti4O9/UiO-66-NH2 composites synthesized by a facile solvothermal method have a core-shell structure with UiO-66-NH2 forming the shell around a N-K2Ti4O9 core. Their photocatalytic activities in the degradation of dyes under visible light irradiation were investigated. The N-K2Ti4O9/UiO-66-NH2 composites exhibited higher photocatalytic activity than the pure components. This synergistic effect was due to the high adsorption capacity of UiO-66-NH2 and that the two components together induced an enhanced separation efficiency of photogenerated electron-hole pairs. The mass ratio of N-K2Ti4O9 to ZrCl4 of 3:7 in the composite exhibited the highest photocatalytic activity. Due to the electrostatic attraction between the negatively charged backbone of UiO-66-NH2 with the positively charged groups of cationic dyes, the composites were more photocatalytically active for cationic dyes than for anionic dyes.
N-K2Ti4O9/UiO-66-NH2 composites synthesized by a facile solvothermal method have a core-shell structure with UiO-66-NH2 forming the shell around a N-K2Ti4O9 core. Their photocatalytic activities in the degradation of dyes under visible light irradiation were investigated. The N-K2Ti4O9/UiO-66-NH2 composites exhibited higher photocatalytic activity than the pure components. This synergistic effect was due to the high adsorption capacity of UiO-66-NH2 and that the two components together induced an enhanced separation efficiency of photogenerated electron-hole pairs. The mass ratio of N-K2Ti4O9 to ZrCl4 of 3:7 in the composite exhibited the highest photocatalytic activity. Due to the electrostatic attraction between the negatively charged backbone of UiO-66-NH2 with the positively charged groups of cationic dyes, the composites were more photocatalytically active for cationic dyes than for anionic dyes.
2016, 37(3): 378-388
doi: 10.1016/S1872-2067(15)61032-4
Abstract:
Methanol synthesis catalysts based on Cu, Zn and Al were prepared by three methods and subsequently mixed with H-ferrierite zeolite in an aqueous suspension to disperse the catalysts over the support. These materials were characterized by X-ray diffraction, N2 adsorption, transmission electron microscopy, temperature programmed reduction, NH3 and H2 temperature-programmed desorption, and X-ray photoelectron spectroscopy. They were also applied to the CO hydrogenation reaction to produce dimethyl ether and hydrocarbons. The catalysts were prepared by coprecipitation under low and high supersaturation conditions and by a homogeneous precipitation method. The preparation technique was found to affect the precursor structural characteristics, such as purity and crystallinity, as well as the particle size distribution of the resulting catalyst. Low supersaturation conditions favored high dispersion of the Cu species, increasing the methanol synthesis catalyst's metallic surface area and resulting in a homogeneous particle size distribution. These effects in turn were found to modify the zeolite properties, promoting both a low micropore volume and blockage of the zeolite acid sites. The effect of the methanol synthesis catalyst on the reaction was verified by the correlation between the Cu surface area and the CO conversion rate.
Methanol synthesis catalysts based on Cu, Zn and Al were prepared by three methods and subsequently mixed with H-ferrierite zeolite in an aqueous suspension to disperse the catalysts over the support. These materials were characterized by X-ray diffraction, N2 adsorption, transmission electron microscopy, temperature programmed reduction, NH3 and H2 temperature-programmed desorption, and X-ray photoelectron spectroscopy. They were also applied to the CO hydrogenation reaction to produce dimethyl ether and hydrocarbons. The catalysts were prepared by coprecipitation under low and high supersaturation conditions and by a homogeneous precipitation method. The preparation technique was found to affect the precursor structural characteristics, such as purity and crystallinity, as well as the particle size distribution of the resulting catalyst. Low supersaturation conditions favored high dispersion of the Cu species, increasing the methanol synthesis catalyst's metallic surface area and resulting in a homogeneous particle size distribution. These effects in turn were found to modify the zeolite properties, promoting both a low micropore volume and blockage of the zeolite acid sites. The effect of the methanol synthesis catalyst on the reaction was verified by the correlation between the Cu surface area and the CO conversion rate.
2016, 37(3): 389-397
doi: 10.1016/S1872-2067(15)61028-2
Abstract:
A magnetically recoverable biocatalyst was successfully prepared through the immobilization of cellulase onto Fe3O4 nanoparticles. The magnetic nanoparticles were synthesized by a hydrothermal method in an aqueous system. The support (Fe3O4 nanoparticles) was modified with (3-aminopropyl)triethoxysilane, and glutaraldehyde was used as the cross-linker to immobilize the cellulose onto the modified support. Different factors that influence the activity of the immobilized enzyme were investigated. The experimental results indicated that the suitable immobilization temperature and pH are 40 ℃ and 6.0, respectively. The optimal glutaraldehyde concentration is ~2.0 wt%, and the appropriate immobilization time is 4 h. Under these optimal conditions, the activity of the immobilized enzyme could be maintained at 99.1% of that of the free enzyme. Moreover, after 15 cyclic runs, the activity of the immobilized enzyme was maintained at ~91.1%. The prepared biocatalyst was used to decompose corncobs, and the maximum decomposition rate achieved was 61.94%.
A magnetically recoverable biocatalyst was successfully prepared through the immobilization of cellulase onto Fe3O4 nanoparticles. The magnetic nanoparticles were synthesized by a hydrothermal method in an aqueous system. The support (Fe3O4 nanoparticles) was modified with (3-aminopropyl)triethoxysilane, and glutaraldehyde was used as the cross-linker to immobilize the cellulose onto the modified support. Different factors that influence the activity of the immobilized enzyme were investigated. The experimental results indicated that the suitable immobilization temperature and pH are 40 ℃ and 6.0, respectively. The optimal glutaraldehyde concentration is ~2.0 wt%, and the appropriate immobilization time is 4 h. Under these optimal conditions, the activity of the immobilized enzyme could be maintained at 99.1% of that of the free enzyme. Moreover, after 15 cyclic runs, the activity of the immobilized enzyme was maintained at ~91.1%. The prepared biocatalyst was used to decompose corncobs, and the maximum decomposition rate achieved was 61.94%.
2016, 37(3): 398-404
doi: 10.1016/S1872-2067(15)61029-4
Abstract:
Transition metal catalysts M-N-C (M = Co, Fe, Mn) were synthesized by a template-free method by heating meso-tetraphenyl porphyrins (i.e. CoTPP, FeTPPCl, MnTPPCl) precursors. The catalysts were characterized by N2 adsorption-desorption, thermogravimetry, high-resolution transmission electron microscopy, and Raman and X-ray photoelectron spectroscopy. The selective oxidation of ethylbenzene with molecular oxygen under a solvent-free condition was carried out to explore the catalytic performance of the M-N-Cs, which exhibited different catalytic performance. That was ascribed to the difference in M (Co, Fe, Mn) and different graphitization degree forming during the heating process, in which M (Co, Fe, Mn) might have different catalytic activity on the formation of the M-N-C catalyst. All the M-N-C composites had remarkable recyclability in the selective oxidation of ethylbenzene.
Transition metal catalysts M-N-C (M = Co, Fe, Mn) were synthesized by a template-free method by heating meso-tetraphenyl porphyrins (i.e. CoTPP, FeTPPCl, MnTPPCl) precursors. The catalysts were characterized by N2 adsorption-desorption, thermogravimetry, high-resolution transmission electron microscopy, and Raman and X-ray photoelectron spectroscopy. The selective oxidation of ethylbenzene with molecular oxygen under a solvent-free condition was carried out to explore the catalytic performance of the M-N-Cs, which exhibited different catalytic performance. That was ascribed to the difference in M (Co, Fe, Mn) and different graphitization degree forming during the heating process, in which M (Co, Fe, Mn) might have different catalytic activity on the formation of the M-N-C catalyst. All the M-N-C composites had remarkable recyclability in the selective oxidation of ethylbenzene.
2016, 37(3): 405-411
doi: 10.1016/S1872-2067(15)61022-1
Abstract:
The neutral palladium(II) complex bis-[1-(5'-diphenylphosphinothiazol-2'-yl)-imidazolyl] dichloropalladium(II) (1A) ligated by thiazolylimidazolyl-based phosphine (L1) in which thiazolylimidazolyl acted as an S-and N-donor provider with weak coordinating nature, and the ionic complex bis-[1-(5'-diphenylphosphinothiazol-2'-yl)-3-methylimidazolium] dichloropalladium(II) trifluoromethanesulfonate (2A) ligated by thiazolylimidazolium-based phosphine (L2) after quaternization of L1 using methyl trifluoromethanesulphonate were synthesized. It was found that the introduced positive charges and strong electron-withdrawing effect in 2A not only led to changes in the configuration and structural stability of the complex, but also lowered its catalytic performance in carbonylative Sonogashira reactions. These effects reveal the important role of the N-donor in 1A. In addition, as an ionic palladium complex, 2A combined with the room-temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate could be recycled eight times as the catalyst in carbonylative Sonogashira reactions without detectable metal leaching.
The neutral palladium(II) complex bis-[1-(5'-diphenylphosphinothiazol-2'-yl)-imidazolyl] dichloropalladium(II) (1A) ligated by thiazolylimidazolyl-based phosphine (L1) in which thiazolylimidazolyl acted as an S-and N-donor provider with weak coordinating nature, and the ionic complex bis-[1-(5'-diphenylphosphinothiazol-2'-yl)-3-methylimidazolium] dichloropalladium(II) trifluoromethanesulfonate (2A) ligated by thiazolylimidazolium-based phosphine (L2) after quaternization of L1 using methyl trifluoromethanesulphonate were synthesized. It was found that the introduced positive charges and strong electron-withdrawing effect in 2A not only led to changes in the configuration and structural stability of the complex, but also lowered its catalytic performance in carbonylative Sonogashira reactions. These effects reveal the important role of the N-donor in 1A. In addition, as an ionic palladium complex, 2A combined with the room-temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate could be recycled eight times as the catalyst in carbonylative Sonogashira reactions without detectable metal leaching.
2016, 37(3): 412-419
doi: 10.1016/S1872-2067(15)61017-8
Abstract:
Micro-mesoporous ZK-1 molecular sieves with different Si/Al ratios were used as supports for binary Co-Mo hydrodesulfurization (HDS) catalysts. The CoMo/ZK-1 catalysts were prepared using an over-loading impregnation method, and characterized using N2 physisorption, X-ray diffraction, temperature-programmed NH3 desorption, temperature-programmed reduction (TPR), ultraviolet-visible diffuse reflectance spectroscopy, and high-resolution transmission electron microscopy (HRTEM). The results show that the CoMo/ZK-1 catalysts have high surface areas (~700 m2/g), large pore volumes, and hierarchical porous structures, which promote the dispersion of Co and Mo oxide phases on the ZK-1 supports. The TPR results show that the interactions between the Co and Mo oxide phases and the ZK-1 support are weaker than those in the CoMo/γ-Al2O3 catalyst. The HRTEM results show that the CoMo/ZK-1 catalysts have better MoS2 dispersion and more active edge sites. The catalysts were tested in HDS of dibenzothiophene. Under mild reaction conditions, the activity of Co and Mo sulfides supported on ZK-1 was higher than those of Co and Mo sulfides supported on ZSM-5, AlKIT-1, and γ-Al2O3.
Micro-mesoporous ZK-1 molecular sieves with different Si/Al ratios were used as supports for binary Co-Mo hydrodesulfurization (HDS) catalysts. The CoMo/ZK-1 catalysts were prepared using an over-loading impregnation method, and characterized using N2 physisorption, X-ray diffraction, temperature-programmed NH3 desorption, temperature-programmed reduction (TPR), ultraviolet-visible diffuse reflectance spectroscopy, and high-resolution transmission electron microscopy (HRTEM). The results show that the CoMo/ZK-1 catalysts have high surface areas (~700 m2/g), large pore volumes, and hierarchical porous structures, which promote the dispersion of Co and Mo oxide phases on the ZK-1 supports. The TPR results show that the interactions between the Co and Mo oxide phases and the ZK-1 support are weaker than those in the CoMo/γ-Al2O3 catalyst. The HRTEM results show that the CoMo/ZK-1 catalysts have better MoS2 dispersion and more active edge sites. The catalysts were tested in HDS of dibenzothiophene. Under mild reaction conditions, the activity of Co and Mo sulfides supported on ZK-1 was higher than those of Co and Mo sulfides supported on ZSM-5, AlKIT-1, and γ-Al2O3.
2016, 37(3): 420-427
doi: 10.1016/S1872-2067(15)61013-0
Abstract:
Metal organic frameworks (MOFs) are an important platform for heterogeneous catalysts. Although MOFs with a smaller particle size exhibit better catalytic performance because of less diffusion limitations, their separation and recycling after catalytic reactions are difficult. The integration of MOFs with magnetic nanoparticles could facilitate their recovery and separation. Especially, the shell thickness of the core-shell structured composites is controllable. In this study, amino-functionalized Fe3O4@Cu3(BTC)2 was fabricated by a stepwise assembly method and its catalytic performance in Knoevenagel condensation was investigated. The results demonstrated that the magnetic hybrid material exhibited a core-shell structure, with a shell thickness of about 200 nm. Furthermore, it not only exhibited high catalytic activity, but remarkably, it could also be easily recovered magnetically and recycled without obvious loss of catalytic efficiency after three cycles.
Metal organic frameworks (MOFs) are an important platform for heterogeneous catalysts. Although MOFs with a smaller particle size exhibit better catalytic performance because of less diffusion limitations, their separation and recycling after catalytic reactions are difficult. The integration of MOFs with magnetic nanoparticles could facilitate their recovery and separation. Especially, the shell thickness of the core-shell structured composites is controllable. In this study, amino-functionalized Fe3O4@Cu3(BTC)2 was fabricated by a stepwise assembly method and its catalytic performance in Knoevenagel condensation was investigated. The results demonstrated that the magnetic hybrid material exhibited a core-shell structure, with a shell thickness of about 200 nm. Furthermore, it not only exhibited high catalytic activity, but remarkably, it could also be easily recovered magnetically and recycled without obvious loss of catalytic efficiency after three cycles.
2016, 37(3): 428-435
doi: 10.1016/S1872-2067(15)61000-2
Abstract:
Ag/LaCoO3 perovskite catalysts for soot combustion were prepared by the impregnation method. The structure and physicochemical properties of the catalysts were characterized using X-ray diffraction, N2 adsorption-desorption, H2 temperature-programmed reduction, soot temperature-programmed reduction, and X-ray photoelectron spectroscopy. The catalytic activity of the catalysts for soot oxidation was tested by temperature-programmed oxidation in air and in a NOx atmosphere. Metallic Ag particles were the main Ag species. Part of the Ag migrated from the surface to the lattice of the LaCoO3 perovskite, to form La1-xAgxCoO3. This increased the amount of oxygen vacancies in the perovskite structure during thermal treatment. Compared with unmodified LaCoO3, the maximum soot oxidation rate temperature (Tp) decreased by 50-70 ℃ in air when LaCoO3 was partially modified by Ag, depending on the thermal treatment temperature. The Tp of the Ag/LaCoO3 catalyst calcined at 400 ℃ in a NOx atmosphere decreased to about 140 ℃, compared with that of LaCoO3. Ag particles and oxygen vacancies in the catalysts contributed to their high catalytic activity for soot oxidation. The stable catalytic activity of the Ag/LaCoO3 catalyst calcined at 700 ℃ in a NOx atmosphere was related to its stable structure.
Ag/LaCoO3 perovskite catalysts for soot combustion were prepared by the impregnation method. The structure and physicochemical properties of the catalysts were characterized using X-ray diffraction, N2 adsorption-desorption, H2 temperature-programmed reduction, soot temperature-programmed reduction, and X-ray photoelectron spectroscopy. The catalytic activity of the catalysts for soot oxidation was tested by temperature-programmed oxidation in air and in a NOx atmosphere. Metallic Ag particles were the main Ag species. Part of the Ag migrated from the surface to the lattice of the LaCoO3 perovskite, to form La1-xAgxCoO3. This increased the amount of oxygen vacancies in the perovskite structure during thermal treatment. Compared with unmodified LaCoO3, the maximum soot oxidation rate temperature (Tp) decreased by 50-70 ℃ in air when LaCoO3 was partially modified by Ag, depending on the thermal treatment temperature. The Tp of the Ag/LaCoO3 catalyst calcined at 400 ℃ in a NOx atmosphere decreased to about 140 ℃, compared with that of LaCoO3. Ag particles and oxygen vacancies in the catalysts contributed to their high catalytic activity for soot oxidation. The stable catalytic activity of the Ag/LaCoO3 catalyst calcined at 700 ℃ in a NOx atmosphere was related to its stable structure.
2016, 37(3): 436-445
doi: 10.1016/S1872-2067(15)61039-7
Abstract:
A novel sensor for the determination of warfarin based on a simple and sensitive method was developed on multiwalled-carbon-nanotube modified ZnCrFeO4 carbon paste electrodes (MWCNT/ZnCrFeO4/CPEs). Cyclic voltammetry, differential pulse voltammetry, chronoamperometry, and electrochemical impedance spectroscopy were used to investigate the electrochemical behavior of warfarin at the chemically modified electrode. According to the results, MWCNT/ZnCrFeO4/CPEs showed high electrocatalytic activity for warfarin oxidation, producing a sharp oxidation peak current at about +0.97 vs Ag/AgCl reference electrode at pH = 4.0. The peak current was linearly dependent on warfarin concentration over the range of 0.02-920.0 µmol/L with a detection limit of 0.003 µmol/L. In addition, chronoamperometry was also used to determine warfarin's catalytic rate constant and diffusion coefficient at MWCNT/ZnCrFeO4/CPEs.
A novel sensor for the determination of warfarin based on a simple and sensitive method was developed on multiwalled-carbon-nanotube modified ZnCrFeO4 carbon paste electrodes (MWCNT/ZnCrFeO4/CPEs). Cyclic voltammetry, differential pulse voltammetry, chronoamperometry, and electrochemical impedance spectroscopy were used to investigate the electrochemical behavior of warfarin at the chemically modified electrode. According to the results, MWCNT/ZnCrFeO4/CPEs showed high electrocatalytic activity for warfarin oxidation, producing a sharp oxidation peak current at about +0.97 vs Ag/AgCl reference electrode at pH = 4.0. The peak current was linearly dependent on warfarin concentration over the range of 0.02-920.0 µmol/L with a detection limit of 0.003 µmol/L. In addition, chronoamperometry was also used to determine warfarin's catalytic rate constant and diffusion coefficient at MWCNT/ZnCrFeO4/CPEs.
