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2015 Volume 36 Issue 3
2015, 36(3):
Abstract:
2015, 36(3): 261-267
doi: 10.1016/S1872-2067(14)60273-4
Abstract:
In many catalytic systems the structure of the catalyst plays a crucial role in the reaction especially for catalytic reduction, organic pollutant oxidation and other organic transfor-mations. Herein, we report a template-free approach to the synthesis of multiple Au cores in CeO2 hollow spheres (MACCHS). This material was fabricated by impregnating CeO2 hollow spheres with a HAuCl4 aqueous solution. NaBH4 was then used to reduce HAuCl4 to Au nano-particles to form multiple Au cores in the CeO2 hollow spheres. We used MACCHS as a catalyst for p-nitrophenol reduction and achieved excellent activity. The catalyst showed enhanced stability toward p-nitrophenol reduction compared with bare Au nanoparticles and CeO2 hollow spheres. This simple method to achieve multi-core-in-shell hollow structures will likely have applications in various biological, medical and energy related fields.
In many catalytic systems the structure of the catalyst plays a crucial role in the reaction especially for catalytic reduction, organic pollutant oxidation and other organic transfor-mations. Herein, we report a template-free approach to the synthesis of multiple Au cores in CeO2 hollow spheres (MACCHS). This material was fabricated by impregnating CeO2 hollow spheres with a HAuCl4 aqueous solution. NaBH4 was then used to reduce HAuCl4 to Au nano-particles to form multiple Au cores in the CeO2 hollow spheres. We used MACCHS as a catalyst for p-nitrophenol reduction and achieved excellent activity. The catalyst showed enhanced stability toward p-nitrophenol reduction compared with bare Au nanoparticles and CeO2 hollow spheres. This simple method to achieve multi-core-in-shell hollow structures will likely have applications in various biological, medical and energy related fields.
2015, 36(3): 268-273
doi: 10.1016/S1872-2067(14)60251-5
Abstract:
The high activity and selectivity of H-Beta and H-ZSM-12 zeolites in the dimerization of norbornene was established. The norbornene conversion reached 100% in chlorinated paraffin and argon gas medium, with a selectivity of dimer formation of 88%-98%. Four stereo-isomers of the bis-2,2'-norbornylidene structure were identified in the dimer fraction, with the (Z)-anti-bis-2,2'- norbornylidene prevailing over the others
The high activity and selectivity of H-Beta and H-ZSM-12 zeolites in the dimerization of norbornene was established. The norbornene conversion reached 100% in chlorinated paraffin and argon gas medium, with a selectivity of dimer formation of 88%-98%. Four stereo-isomers of the bis-2,2'-norbornylidene structure were identified in the dimer fraction, with the (Z)-anti-bis-2,2'- norbornylidene prevailing over the others
2015, 36(3): 274-282
doi: 10.1016/S1872-2067(14)60239-4
Abstract:
The catalytic effect of H2 in the one-step synthesis of ethylene glycol (EG) from methanol dehydrogenation coupling reaction using dielectric barrier discharge (DBD) was studied by in-situ optical emission spectroscopy and online chromatographic analysis. The influence of discharge frequency, methanol and H2 flow rates as well as reaction pressure was investigated systematically. Results show that, in the non-equilibrium plasma produced by DBD, H2 dramatically improved not only the conversion of methanol but also the selectivity for EG. Using the reaction conditions of 300 ℃, 0.1 MPa, input power 11 W, discharge frequency 12.0 kHz, methanol gas flow rate 11.0 mL/min, and H2 flow rate 80-180 mL/min, the reaction of the CH3OH/H2 DBD plasma gave a methanol conversion close to 30% and a selectivity for EG of more than 75%. The change of the EG yield correlated with the intensity of the Hαspectral line. H atoms appear to be the catalytically active species in the reaction. In the DBD plasma, the stable ground state H2 molecule undergoes cumulative collision excitation with electrons before transitioning from higher energy excited states to the first excited state. The spontaneous dissociation of the first excited state H2 molecules generates the catalytically ac-tive H atom. The discharge reaction condition affects the catalytic performance of H2 by influencing the dissociation of H2 molecules into H atoms. The catalytic effect of H2 exhibited in the non-equilibrium plasma may be a new opportunity for the synthesis of chemicals.
The catalytic effect of H2 in the one-step synthesis of ethylene glycol (EG) from methanol dehydrogenation coupling reaction using dielectric barrier discharge (DBD) was studied by in-situ optical emission spectroscopy and online chromatographic analysis. The influence of discharge frequency, methanol and H2 flow rates as well as reaction pressure was investigated systematically. Results show that, in the non-equilibrium plasma produced by DBD, H2 dramatically improved not only the conversion of methanol but also the selectivity for EG. Using the reaction conditions of 300 ℃, 0.1 MPa, input power 11 W, discharge frequency 12.0 kHz, methanol gas flow rate 11.0 mL/min, and H2 flow rate 80-180 mL/min, the reaction of the CH3OH/H2 DBD plasma gave a methanol conversion close to 30% and a selectivity for EG of more than 75%. The change of the EG yield correlated with the intensity of the Hαspectral line. H atoms appear to be the catalytically active species in the reaction. In the DBD plasma, the stable ground state H2 molecule undergoes cumulative collision excitation with electrons before transitioning from higher energy excited states to the first excited state. The spontaneous dissociation of the first excited state H2 molecules generates the catalytically ac-tive H atom. The discharge reaction condition affects the catalytic performance of H2 by influencing the dissociation of H2 molecules into H atoms. The catalytic effect of H2 exhibited in the non-equilibrium plasma may be a new opportunity for the synthesis of chemicals.
2015, 36(3): 283-289
doi: 10.1016/S1872-2067(14)60242-4
Abstract:
Organic compounds containing multiple hydroxyl groups, namely α-cyclodextrin and γ-cyclodextrin, were used as additives for promoting Ni dispersion on supported Ni/SBA-15 catalysts. Catalysts prepared using modified and unmodified impregnation methods were characterized using N2 adsorption-desorption isotherms, X-ray diffraction, transmission electron microscopy, temperature-programmed reduction, and thermogravimetric analysis, and their catalytic performance in the CO2 reforming of methane (CRM) to syngas was evaluated. The results show that compared with Ni/SBA-15 prepared using a conventional impregnation method, the cyclodextrin-modified catalysts had smaller NiO particles. They also exhibited higher catalytic activity and had stronger ability to resist carbon deposition in the CRM. Mechanistic studies showed that for the unmodified catalysts, Ni2+ could migrate into the channels of SBA-15 as a result of concentration differences, and the Ni species were sintered during the following thermal treatment processes, and could not be well dispersed. In contrast, various types of complex were formed between Ni(NO3)2 and the cyclodextrins, and this would be favorable for Ni2+ being taken into the channels of the SBA-15. The presence of cyclodextrins was beneficial to the mutual isolation of Ni species, and finally resulted in better dispersion of Ni species.
Organic compounds containing multiple hydroxyl groups, namely α-cyclodextrin and γ-cyclodextrin, were used as additives for promoting Ni dispersion on supported Ni/SBA-15 catalysts. Catalysts prepared using modified and unmodified impregnation methods were characterized using N2 adsorption-desorption isotherms, X-ray diffraction, transmission electron microscopy, temperature-programmed reduction, and thermogravimetric analysis, and their catalytic performance in the CO2 reforming of methane (CRM) to syngas was evaluated. The results show that compared with Ni/SBA-15 prepared using a conventional impregnation method, the cyclodextrin-modified catalysts had smaller NiO particles. They also exhibited higher catalytic activity and had stronger ability to resist carbon deposition in the CRM. Mechanistic studies showed that for the unmodified catalysts, Ni2+ could migrate into the channels of SBA-15 as a result of concentration differences, and the Ni species were sintered during the following thermal treatment processes, and could not be well dispersed. In contrast, various types of complex were formed between Ni(NO3)2 and the cyclodextrins, and this would be favorable for Ni2+ being taken into the channels of the SBA-15. The presence of cyclodextrins was beneficial to the mutual isolation of Ni species, and finally resulted in better dispersion of Ni species.
2015, 36(3): 290-298
doi: 10.1016/S1872-2067(14)60270-9
Abstract:
The composite support CeZrYLa+LaAl was prepared by a co-precipitation method, and Pt-Rh bimetallic catalysts were fabricated on this support using different preparation procedures. The catalytic activities of these materials were tested in a gas mixture simulating the exhaust from a stoichiometric natural gas vehicle. The as-prepared catalysts were also characterized by X-ray photoelectron spectroscopy, X-ray diffraction, N2 adsorption-desorption and H2-temperature-programmed reduction. It was found that the order of activities for CH4, CO and NO conversion was Cat3 ≈ Cat2 > Cat1, where Cat3 had the lowest light-off temperature (T50) for CO (114 ℃) and NO (149 ℃), the lowest complete conversion temperature (T90) for CH4 (398 ℃) and CO (179 ℃), and the lowest ΔT (T90-T50) for CH4 (34 ℃) and CO (65 ℃). Cat2 showed the lowest T50 for CH4 (342 ℃), the lowest T90 for NO (174 ℃), and the lowest ΔT for NO (17 ℃). Cat1 had the highest T50 and T90 and the largest ΔT out of all three catalysts. Indicating that Pt-Rh bimetallic catalysts (Cat2 and Cat3) prepared by physically mixing Pt and Rh powders exhibited much better catalytic activity than those (Cat1) prepared by co-impregnation, since homogeneous Pt and Rh sites made a significant contribution to CH4/CO/NO conversions. In contrast, strong Pt-Rh interactions in the co-impregnation materials affected the oxidation states of Pt, and the Pt-enriched surface blocked active Rh sites. Moreover, Cat3 was prepared by adding additives (La3+, Zr4+ and Ba2+) into the physically mixed Pt-Rh catalysts. XRD results demonstrated that the additive cation (Zr4+) was incorporated into the CeO2-ZrO2 lattice, thus creating a higher concentration of defects and improving the O2-mobility. XPS results showed that the Cat3 had the highest Ce3+/Ce ratio, suggesting the presence of a significant quantity of oxygen vacancies and cerium in the Ce3+ state. All of these further promoted the three-way catalytic activity and widened the air-to-fuel working-window.
The composite support CeZrYLa+LaAl was prepared by a co-precipitation method, and Pt-Rh bimetallic catalysts were fabricated on this support using different preparation procedures. The catalytic activities of these materials were tested in a gas mixture simulating the exhaust from a stoichiometric natural gas vehicle. The as-prepared catalysts were also characterized by X-ray photoelectron spectroscopy, X-ray diffraction, N2 adsorption-desorption and H2-temperature-programmed reduction. It was found that the order of activities for CH4, CO and NO conversion was Cat3 ≈ Cat2 > Cat1, where Cat3 had the lowest light-off temperature (T50) for CO (114 ℃) and NO (149 ℃), the lowest complete conversion temperature (T90) for CH4 (398 ℃) and CO (179 ℃), and the lowest ΔT (T90-T50) for CH4 (34 ℃) and CO (65 ℃). Cat2 showed the lowest T50 for CH4 (342 ℃), the lowest T90 for NO (174 ℃), and the lowest ΔT for NO (17 ℃). Cat1 had the highest T50 and T90 and the largest ΔT out of all three catalysts. Indicating that Pt-Rh bimetallic catalysts (Cat2 and Cat3) prepared by physically mixing Pt and Rh powders exhibited much better catalytic activity than those (Cat1) prepared by co-impregnation, since homogeneous Pt and Rh sites made a significant contribution to CH4/CO/NO conversions. In contrast, strong Pt-Rh interactions in the co-impregnation materials affected the oxidation states of Pt, and the Pt-enriched surface blocked active Rh sites. Moreover, Cat3 was prepared by adding additives (La3+, Zr4+ and Ba2+) into the physically mixed Pt-Rh catalysts. XRD results demonstrated that the additive cation (Zr4+) was incorporated into the CeO2-ZrO2 lattice, thus creating a higher concentration of defects and improving the O2-mobility. XPS results showed that the Cat3 had the highest Ce3+/Ce ratio, suggesting the presence of a significant quantity of oxygen vacancies and cerium in the Ce3+ state. All of these further promoted the three-way catalytic activity and widened the air-to-fuel working-window.
2015, 36(3): 299-307
doi: 10.1016/S1872-2067(14)60265-5
Abstract:
A novel magnetic acidic catalyst comprising Preyssler (H14[NaP5W30O110]) heteropoly acid supported on silica coated nickel ferrite nanoparticles (NiFe2O4@SiO2) was prepared. The catalyst was characterized by Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive spectrum, VSM and particle size neasurement. Its catalytic activity was investigated for the synthesis of bis(dihydropyrimidinone)benzene and 3,4-dihydropyrimidin-2(1H)-ones derivatives by the Biginelli reaction. With the catalyst, the reactions occurred in less than 1 h with good to excel-lent yields. More importantly, the catalyst was easily separated from the reaction mixture by an external magnet and reused at least five times without degradation in the activity.
A novel magnetic acidic catalyst comprising Preyssler (H14[NaP5W30O110]) heteropoly acid supported on silica coated nickel ferrite nanoparticles (NiFe2O4@SiO2) was prepared. The catalyst was characterized by Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive spectrum, VSM and particle size neasurement. Its catalytic activity was investigated for the synthesis of bis(dihydropyrimidinone)benzene and 3,4-dihydropyrimidin-2(1H)-ones derivatives by the Biginelli reaction. With the catalyst, the reactions occurred in less than 1 h with good to excel-lent yields. More importantly, the catalyst was easily separated from the reaction mixture by an external magnet and reused at least five times without degradation in the activity.
2015, 36(3): 308-313
doi: 10.1016/S1872-2067(14)60259-X
Abstract:
A new method has been developed for the chemoselective acetylation of alcohols with acetic anhydride in the presence of phenols using a novel, recyclable CuO-ZnO nanocatalyst. The catalyst was synthesized using the co-precipitation method and characterized by N2 adsorption-desorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersion scanning analyses. Furthermore, this catalyst could be recycled up to six times without significant loss in its activity.
A new method has been developed for the chemoselective acetylation of alcohols with acetic anhydride in the presence of phenols using a novel, recyclable CuO-ZnO nanocatalyst. The catalyst was synthesized using the co-precipitation method and characterized by N2 adsorption-desorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersion scanning analyses. Furthermore, this catalyst could be recycled up to six times without significant loss in its activity.
2015, 36(3): 314-321
doi: 10.1016/S1872-2067(14)60261-8
Abstract:
A PdO/CeO2 catalyst was prepared by deposition-precipitation method and characterized with X-ray diffraction, high-resolution transmission electron microscopy, N2 adsorption-desorption, X-ray photoelectron spectroscopy and Raman spectroscopy. The results show that the Pd is presented as Pd2+ in the catalyst. The interaction between the deposited PdO and CeO2 increases the Ce3+ content. The catalytic activity of PdO/CeO2 was tested in the heterogeneous Fenton-like degradation of acid orange 7 (AO7) and salicylic acid (SA), both in the dark and under visible irradiation. Deposition of PdO accelerates the Fen-ton-like degradation of SA, which reaches a maximum at 1.0 atom% PdO loading. A dye sensitization effect was seen with AO7 under visible irradiation. Dye sensitization promotes the regeneration of Ce3+ by interfacial peroxides species through interfacial electron injection. Consequently, the combined effects of PdO loading and visible light irradiating enhanced the Fenton-like activity to a reaction rate constant of 3.90 h-1 for the 1.0 PdO/CeO2, a ca. 50-fold improvement.
A PdO/CeO2 catalyst was prepared by deposition-precipitation method and characterized with X-ray diffraction, high-resolution transmission electron microscopy, N2 adsorption-desorption, X-ray photoelectron spectroscopy and Raman spectroscopy. The results show that the Pd is presented as Pd2+ in the catalyst. The interaction between the deposited PdO and CeO2 increases the Ce3+ content. The catalytic activity of PdO/CeO2 was tested in the heterogeneous Fenton-like degradation of acid orange 7 (AO7) and salicylic acid (SA), both in the dark and under visible irradiation. Deposition of PdO accelerates the Fen-ton-like degradation of SA, which reaches a maximum at 1.0 atom% PdO loading. A dye sensitization effect was seen with AO7 under visible irradiation. Dye sensitization promotes the regeneration of Ce3+ by interfacial peroxides species through interfacial electron injection. Consequently, the combined effects of PdO loading and visible light irradiating enhanced the Fenton-like activity to a reaction rate constant of 3.90 h-1 for the 1.0 PdO/CeO2, a ca. 50-fold improvement.
2015, 36(3): 322-327
doi: 10.1016/S1872-2067(14)60258-8
Abstract:
High surface area SiC has been used to prepare a Pd/SiC catalyst using the liquid reduction method, and the resulting catalyst was used for the carbonylative Suzuki coupling reaction of aryl iodides with arylboronic acids. The catalyst was also characterized by X-ray diffraction, inductively coupled plasma-mass spectroscopy and high-resolution transmission electron microscopy. The results of these analyses showed that homogeneous Pd nanoparticles with a mean diameter of 2.8 nm were uniformly dispersed on the SiC surface. Optimization of the reaction conditions for the carbonylative Suzuki coupling reaction, including the solvent, base, pressure, temperature and reaction time, revealed that the model reaction of iodobenzene (1.0 mmol) with phenylboronic acid (1.5 mmol) could reach 90% conversion with a selectivity of 99% towards the diphenyl ketone using 3 wt% Pd/SiC under 1.0 MPa of CO pressure at 100 ℃ for 8 h with K2CO3 (3.0 mmol) as the base and anisole as the solvent. The Pd/SiC catalyst exhibited broad substrate scope towards the carbonylative Suzuki coupling reaction of aryl iodides with arylboronic acids bearing a variety of different substituents. Furthermore, the Pd/SiC catalyst exhibited good recyclability properties and could be recovered and reused up to five times with the conversion of iodobenzene decreasing only slightly from 90% to 76%. The decrease in the catalytic activity after five rounds was attributed to the loss of active Pd during the organic reaction.
High surface area SiC has been used to prepare a Pd/SiC catalyst using the liquid reduction method, and the resulting catalyst was used for the carbonylative Suzuki coupling reaction of aryl iodides with arylboronic acids. The catalyst was also characterized by X-ray diffraction, inductively coupled plasma-mass spectroscopy and high-resolution transmission electron microscopy. The results of these analyses showed that homogeneous Pd nanoparticles with a mean diameter of 2.8 nm were uniformly dispersed on the SiC surface. Optimization of the reaction conditions for the carbonylative Suzuki coupling reaction, including the solvent, base, pressure, temperature and reaction time, revealed that the model reaction of iodobenzene (1.0 mmol) with phenylboronic acid (1.5 mmol) could reach 90% conversion with a selectivity of 99% towards the diphenyl ketone using 3 wt% Pd/SiC under 1.0 MPa of CO pressure at 100 ℃ for 8 h with K2CO3 (3.0 mmol) as the base and anisole as the solvent. The Pd/SiC catalyst exhibited broad substrate scope towards the carbonylative Suzuki coupling reaction of aryl iodides with arylboronic acids bearing a variety of different substituents. Furthermore, the Pd/SiC catalyst exhibited good recyclability properties and could be recovered and reused up to five times with the conversion of iodobenzene decreasing only slightly from 90% to 76%. The decrease in the catalytic activity after five rounds was attributed to the loss of active Pd during the organic reaction.
2015, 36(3): 328-335
doi: 10.1016/S1872-2067(14)60269-2
Abstract:
Aqueous colloidal dispersions containing ZnxCd1-xS quantum dots (QDs) of different x compositions were prepared by precipitating zinc and cadmium acetates with sodium sulphide, in the presence of a cetyltrimethylammonium bromide stabilizer. Ultraviolet-visible absorption spectroscopy was used to determine the transition energies of the QDs, which in turn were used to calculate their sizes, which depended on their composition. The QD size decreased with increasing Zn content. The photocatalytic activity of the ZnxCd1-xS QDs was studied by the decomposition of methylene blue under ultraviolet irradiation, at a maximum intensity at 365 nm (3.4 eV). Three different photocatalytic activity regions were observed, which depended on the Zn content. The quantum levels of the QDs could be excited by incident irradiation, and influenced the resulting photocatalytic activity. Maximum photocatalytic activity was achieved at x=0.6, where the QD transition energy was equal to the irradiation photon energy. The photocatalytic efficiency of the QDs depended on their surface area and arrangement of quantum levels, because of the quantum size effect.
Aqueous colloidal dispersions containing ZnxCd1-xS quantum dots (QDs) of different x compositions were prepared by precipitating zinc and cadmium acetates with sodium sulphide, in the presence of a cetyltrimethylammonium bromide stabilizer. Ultraviolet-visible absorption spectroscopy was used to determine the transition energies of the QDs, which in turn were used to calculate their sizes, which depended on their composition. The QD size decreased with increasing Zn content. The photocatalytic activity of the ZnxCd1-xS QDs was studied by the decomposition of methylene blue under ultraviolet irradiation, at a maximum intensity at 365 nm (3.4 eV). Three different photocatalytic activity regions were observed, which depended on the Zn content. The quantum levels of the QDs could be excited by incident irradiation, and influenced the resulting photocatalytic activity. Maximum photocatalytic activity was achieved at x=0.6, where the QD transition energy was equal to the irradiation photon energy. The photocatalytic efficiency of the QDs depended on their surface area and arrangement of quantum levels, because of the quantum size effect.
2015, 36(3): 336-343
doi: 10.1016/S1872-2067(14)60257-6
Abstract:
Acidic, basic and neutral ionic liquids (ILs) have been used as catalysts in the carbonylation of glycerol with urea. The results show that neutral ILs have high catalytic activity in the reaction. The excellent performance of the catalysts can be attributed to the synergistic effect of the cation and anion. We speculated that the cation with positive charge activates urea, and the anion with negative charge activates glycerol. In addition, the well balanced acid-basic properties of the catalysts are necessary for good catalytic performance. The ILs can be reused at least five times without loss of activity. Using ILs, instead of the traditional metal catalysts, reduces the use of non-renewable resources. It is eco-friendly that two inexpensive and bio-based raw materials were used and the catalytic reaction was carried out without solvent.
Acidic, basic and neutral ionic liquids (ILs) have been used as catalysts in the carbonylation of glycerol with urea. The results show that neutral ILs have high catalytic activity in the reaction. The excellent performance of the catalysts can be attributed to the synergistic effect of the cation and anion. We speculated that the cation with positive charge activates urea, and the anion with negative charge activates glycerol. In addition, the well balanced acid-basic properties of the catalysts are necessary for good catalytic performance. The ILs can be reused at least five times without loss of activity. Using ILs, instead of the traditional metal catalysts, reduces the use of non-renewable resources. It is eco-friendly that two inexpensive and bio-based raw materials were used and the catalytic reaction was carried out without solvent.
2015, 36(3): 344-347
doi: 10.1016/S1872-2067(14)60250-3
Abstract:
A series of CoxBa1.5Ni9 catalysts prepared by a co-precipitation method were investigated for N2O decomposition. Co improved the activity of NiO when BaCO3 was present but had the opposite role when it was absent. This was because Co strengthened the Ni-O bond and decreased the surface area when added into pure NiO without BaCO3, while in the presence of BaCO3, it dramatically increased the surface area and amount of active sites of NiO.
A series of CoxBa1.5Ni9 catalysts prepared by a co-precipitation method were investigated for N2O decomposition. Co improved the activity of NiO when BaCO3 was present but had the opposite role when it was absent. This was because Co strengthened the Ni-O bond and decreased the surface area when added into pure NiO without BaCO3, while in the presence of BaCO3, it dramatically increased the surface area and amount of active sites of NiO.
2015, 36(3): 348-354
doi: 10.1016/S1872-2067(14)60244-8
Abstract:
Halloysite-nanotube-supported Mo salen (HNTs-Mo-SL) catalysts were successfully prepared using a facile chemical surface modification and self-assembly method. The morphologies, sizes, structure, and dispersion of the as-prepared catalysts were investigated by transmission electron microscopy, X-ray diffraction, and Fourier-transform infrared, inductively coupled plasma, and X-ray photoelectron spectroscopy, which confirmed the existence of the Mo salen structure and successful synthesis of the HNTs-Mo-SL catalyst. The immobilized catalyst was found to be highly reactive in the epoxidation of a wide range of alkenes, including linear, cyclic, and aromatic alkenes. The immobilized catalyst exhibited a higher catalytic activity for alkene epoxidation than homogeneous Mo. In contrast experiments, it was determined that the salen structure played an important role in immobilizing MoO(O2)2(DMF)2 and improving the conversion and efficiency of alkene epoxidation, which could not be obtained using other ligands, such as the N atom as a single ligand. Furthermore, the bonding between Mo and the salen ligands and the possible mechanism of alkene epoxidation catalyzed by the catalyst were determined. The catalyst could be reused several times without significant loss of catalytic activity. Given that halloysite nanotubes are cheap and easy to obtain, this catalyst offers a novel alternative for the rational design of catalysts with desired features.
Halloysite-nanotube-supported Mo salen (HNTs-Mo-SL) catalysts were successfully prepared using a facile chemical surface modification and self-assembly method. The morphologies, sizes, structure, and dispersion of the as-prepared catalysts were investigated by transmission electron microscopy, X-ray diffraction, and Fourier-transform infrared, inductively coupled plasma, and X-ray photoelectron spectroscopy, which confirmed the existence of the Mo salen structure and successful synthesis of the HNTs-Mo-SL catalyst. The immobilized catalyst was found to be highly reactive in the epoxidation of a wide range of alkenes, including linear, cyclic, and aromatic alkenes. The immobilized catalyst exhibited a higher catalytic activity for alkene epoxidation than homogeneous Mo. In contrast experiments, it was determined that the salen structure played an important role in immobilizing MoO(O2)2(DMF)2 and improving the conversion and efficiency of alkene epoxidation, which could not be obtained using other ligands, such as the N atom as a single ligand. Furthermore, the bonding between Mo and the salen ligands and the possible mechanism of alkene epoxidation catalyzed by the catalyst were determined. The catalyst could be reused several times without significant loss of catalytic activity. Given that halloysite nanotubes are cheap and easy to obtain, this catalyst offers a novel alternative for the rational design of catalysts with desired features.
2015, 36(3): 355-361
doi: 10.1016/S1872-2067(14)60252-7
Abstract:
The promotional effect of SiO2 on the catalytic synthesis of mixed C1-C18 alcohols from syngas using the Fischer-Tropsch reaction over activated carbon-supported cobalt catalysts was investigated. X-ray diffraction, H2 temperature-programmed reduction, pulsed CO chemisorption and N2 physisorption techniques were all employed to assess the catalyst. Although the addition of SiO2 decreased the reducibility of the Co component, Co dispersion was significantly increased and its aggregation during reaction was inhibited, resulting in greatly enhanced reaction activity. Appropriate amounts of SiO2 also promoted the formation of Co2C, leading to an increased selectivity for C1-C18 alcohols. More importantly, the addition of SiO2 favored the formation of higher molecular mass alcohols (C6-C18) by suppressing Co reduction, thus producing an abundance of Co(II) species capable of facilitating CO insertion.
The promotional effect of SiO2 on the catalytic synthesis of mixed C1-C18 alcohols from syngas using the Fischer-Tropsch reaction over activated carbon-supported cobalt catalysts was investigated. X-ray diffraction, H2 temperature-programmed reduction, pulsed CO chemisorption and N2 physisorption techniques were all employed to assess the catalyst. Although the addition of SiO2 decreased the reducibility of the Co component, Co dispersion was significantly increased and its aggregation during reaction was inhibited, resulting in greatly enhanced reaction activity. Appropriate amounts of SiO2 also promoted the formation of Co2C, leading to an increased selectivity for C1-C18 alcohols. More importantly, the addition of SiO2 favored the formation of higher molecular mass alcohols (C6-C18) by suppressing Co reduction, thus producing an abundance of Co(II) species capable of facilitating CO insertion.
2015, 36(3): 362-366
doi: 10.1016/S1872-2067(14)60238-2
Abstract:
A simple and efficient method for the synthesis of 9,9-dimethyl-9,10-dihydro-8H-benzo-[α]xanthen- 11(12)-one derivatives (DDBXs) was developed by the condensation reaction of various substituted aryl aldehydes with 2-naphthol and dimedone using Fe3O4 magnetic nanoparticles (MNPs) as a heterogeneous catalyst under solvent-free conditions at 90-110℃. The experimental procedure is very simple, the products are formed in high yields and the catalyst is easily separated by applying an external magnetic field.
A simple and efficient method for the synthesis of 9,9-dimethyl-9,10-dihydro-8H-benzo-[α]xanthen- 11(12)-one derivatives (DDBXs) was developed by the condensation reaction of various substituted aryl aldehydes with 2-naphthol and dimedone using Fe3O4 magnetic nanoparticles (MNPs) as a heterogeneous catalyst under solvent-free conditions at 90-110℃. The experimental procedure is very simple, the products are formed in high yields and the catalyst is easily separated by applying an external magnetic field.
2015, 36(3): 367-371
doi: 10.1016/S1872-2067(14)60248-5
Abstract:
Chitosan-supported succinic anhydride-cinchonine (CTS-SA-CN) was synthesized via a two-step route with succinic anhydride as the linker. The catalyst was used to promote the direct asymmetric aldol reaction between cyclohexanone and a variety of aromatic aldehydes in aqueous medium. Aldol adducts were obtained in excellent yields (up to 99%) and good enantioselectivities (up to 96% ee). The CTS-SA-CN catalyst was successfully recycled simply by filtration after use, and was reused 5 times without any significant loss of activity.
Chitosan-supported succinic anhydride-cinchonine (CTS-SA-CN) was synthesized via a two-step route with succinic anhydride as the linker. The catalyst was used to promote the direct asymmetric aldol reaction between cyclohexanone and a variety of aromatic aldehydes in aqueous medium. Aldol adducts were obtained in excellent yields (up to 99%) and good enantioselectivities (up to 96% ee). The CTS-SA-CN catalyst was successfully recycled simply by filtration after use, and was reused 5 times without any significant loss of activity.
2015, 36(3): 372-379
doi: 10.1016/S1872-2067(14)60237-0
Abstract:
A hybrid semiconductor composed of a carbon nitride/cadmium sulfide nanocomposite (C3N4/CdS) was synthesized by a template-free one-step calcination route at high temperature using ammonium thiocyanate and cadmium chloride as starting materials. The crystal structure, composition and morphology of the hybrid samples were studied by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. The photocatalytic degradation of Rhodamine B as a model compound was carried out to evaluate the photocatalytic activity of the nanocomposites under visible light irradiation. Hexagonal CdS nanocrystals were uniformly distributed in the bulk C3N4. After coupling with CdS the basic C3N4 structure was mostly unchanged. The visible light absorption properties of the hybrid materials were enhanced. The as-prepared C3N4/CdS hybrid photocatalyst exhibited superior degradation performance under visible light irradiation compared with pure C3N4. The well-matched band energy improved the transfer efficiency of the photoinduced carriers and this was responsible for the enhanced photocatalytic activity and stability of the hybrid photocatalysts.
A hybrid semiconductor composed of a carbon nitride/cadmium sulfide nanocomposite (C3N4/CdS) was synthesized by a template-free one-step calcination route at high temperature using ammonium thiocyanate and cadmium chloride as starting materials. The crystal structure, composition and morphology of the hybrid samples were studied by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. The photocatalytic degradation of Rhodamine B as a model compound was carried out to evaluate the photocatalytic activity of the nanocomposites under visible light irradiation. Hexagonal CdS nanocrystals were uniformly distributed in the bulk C3N4. After coupling with CdS the basic C3N4 structure was mostly unchanged. The visible light absorption properties of the hybrid materials were enhanced. The as-prepared C3N4/CdS hybrid photocatalyst exhibited superior degradation performance under visible light irradiation compared with pure C3N4. The well-matched band energy improved the transfer efficiency of the photoinduced carriers and this was responsible for the enhanced photocatalytic activity and stability of the hybrid photocatalysts.
2015, 36(3): 380-387
doi: 10.1016/S1872-2067(14)60240-0
Abstract:
The effect of water on the hydrogenation of acetone to isopropanol (IPA) on the Ni/MgAlO catalyst was studied. It was found that small amount of water added in the acetone promoted the conversion of acetone to IPA, while more H2O added (>5%) significantly decreased the conversion of acetone. Microcalorimetric adsorption results showed that the presence of small amount of pre-adsorbed water (4% coverage) enhanced the adsorption of acetone while inhibited the adsorption of IPA on Ni, which might be the important reasons for the promotion effect of some water on the hydrogenation of acetone to IPA. On the other hand, the heats for the adsorption of H2, acetone and IPA on the Ni/MgAlO were significantly decreased when more water was pre-adsorbed, which might explain the inhibition effect of more water on the hydrogenation of acetone. The results of infrared spectroscopy revealed that the presence of water suppressed the dehydrogenation of adsorbed IPA to acetone and the formation of enolate and mesityl oxide species from adsorbed acetone, which might be the other reasons for the positive effect of water on the hydrogenation of acetone to IPA.
The effect of water on the hydrogenation of acetone to isopropanol (IPA) on the Ni/MgAlO catalyst was studied. It was found that small amount of water added in the acetone promoted the conversion of acetone to IPA, while more H2O added (>5%) significantly decreased the conversion of acetone. Microcalorimetric adsorption results showed that the presence of small amount of pre-adsorbed water (4% coverage) enhanced the adsorption of acetone while inhibited the adsorption of IPA on Ni, which might be the important reasons for the promotion effect of some water on the hydrogenation of acetone to IPA. On the other hand, the heats for the adsorption of H2, acetone and IPA on the Ni/MgAlO were significantly decreased when more water was pre-adsorbed, which might explain the inhibition effect of more water on the hydrogenation of acetone. The results of infrared spectroscopy revealed that the presence of water suppressed the dehydrogenation of adsorbed IPA to acetone and the formation of enolate and mesityl oxide species from adsorbed acetone, which might be the other reasons for the positive effect of water on the hydrogenation of acetone to IPA.
2015, 36(3): 389-399
doi: 10.1016/S1872-2067(14)60234-5
Abstract:
Ti3+ self-doped TiO2 nanoparticles were synthesized by hydrothermal treatment of a gel precursor obtained using TiH2 as the Ti source and H2O2 as oxidant. The effects of different states of gel and hydrothermal treatment time on the properties of the samples were studied. The structure, crystallinity, morphology, and optical properties of the nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microcopy, and UV-visible diffuse reflectance spectroscopy. The chemical states of Ti and O were confirmed by X-ray photoelectron spectroscopy and electron spin resonance spectroscopy. Methylene blue (MB) solutions were used as simulated wastewater to evaluate the visible-light photocatalytic activity of the samples. The samples exhibited strong absorption in the visible light region compared with pure TiO2 and an excellent performance in the photocatalytic degradation of MB. When yellow gel was used as the precursor, the sample obtained after hydrothermal treatment at 160 ℃ for 24 h exhibited the best visible light photocatalytic activity with a reaction rate constant of 0.0439 min-1, 18.3 times that of pure TiO2. The samples also showed excellent cyclic stability of the photocatalytic activity.
Ti3+ self-doped TiO2 nanoparticles were synthesized by hydrothermal treatment of a gel precursor obtained using TiH2 as the Ti source and H2O2 as oxidant. The effects of different states of gel and hydrothermal treatment time on the properties of the samples were studied. The structure, crystallinity, morphology, and optical properties of the nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microcopy, and UV-visible diffuse reflectance spectroscopy. The chemical states of Ti and O were confirmed by X-ray photoelectron spectroscopy and electron spin resonance spectroscopy. Methylene blue (MB) solutions were used as simulated wastewater to evaluate the visible-light photocatalytic activity of the samples. The samples exhibited strong absorption in the visible light region compared with pure TiO2 and an excellent performance in the photocatalytic degradation of MB. When yellow gel was used as the precursor, the sample obtained after hydrothermal treatment at 160 ℃ for 24 h exhibited the best visible light photocatalytic activity with a reaction rate constant of 0.0439 min-1, 18.3 times that of pure TiO2. The samples also showed excellent cyclic stability of the photocatalytic activity.
2015, 36(3): 400-407
doi: 10.1016/S1872-2067(14)60231-X
Abstract:
Several unsupported Ru-Zn catalysts were successfully prepared using the coprecipitation method under low alkaline conditions, and their catalytic performance was evaluated for the selective liquid-phase hydrogenation of benzene. The effect of the amount of ZnCl2 added to the coprecipitation solution on the physical and catalytic properties of the Ru-Zn catalysts was studied whilst keeping the amount of the NaOH precipitant constant. The properties of the resulting catalysts were characterized by N2 adsorption, X-ray diffraction, and temperature-programmed reduction. The effects of the stirring rate and the amount of ZnSO4 additive on the catalytic properties of the Ru-Zn catalysts were investigated using the optimal Zn content. The recyclability of the optimal Ru-Zn catalyst was also explored. The results revealed that the optimal Zn content for the Ru-Zn catalysts was 16.7 wt%, and the selectivity for cyclohexene could reach up to 80% (yield > 45%) when the benzene conversion was 57% in an aqueous solution of ZnSO4 (0.45 mol/L) under the optimal reaction conditions (i.e., hastelloy reactor, 1200 r/min, 150 ℃ and 5 MPa of H2 pressure). The presence of ZnO crystals in the Ru catalysts was found to be critical to obtaining high selectivity for cyclohexene (>80%). The Ru-Zn catalysts prepared under the low alkaline conditions also showed good stability, which indicates that they could potentially be used for industrial application.
Several unsupported Ru-Zn catalysts were successfully prepared using the coprecipitation method under low alkaline conditions, and their catalytic performance was evaluated for the selective liquid-phase hydrogenation of benzene. The effect of the amount of ZnCl2 added to the coprecipitation solution on the physical and catalytic properties of the Ru-Zn catalysts was studied whilst keeping the amount of the NaOH precipitant constant. The properties of the resulting catalysts were characterized by N2 adsorption, X-ray diffraction, and temperature-programmed reduction. The effects of the stirring rate and the amount of ZnSO4 additive on the catalytic properties of the Ru-Zn catalysts were investigated using the optimal Zn content. The recyclability of the optimal Ru-Zn catalyst was also explored. The results revealed that the optimal Zn content for the Ru-Zn catalysts was 16.7 wt%, and the selectivity for cyclohexene could reach up to 80% (yield > 45%) when the benzene conversion was 57% in an aqueous solution of ZnSO4 (0.45 mol/L) under the optimal reaction conditions (i.e., hastelloy reactor, 1200 r/min, 150 ℃ and 5 MPa of H2 pressure). The presence of ZnO crystals in the Ru catalysts was found to be critical to obtaining high selectivity for cyclohexene (>80%). The Ru-Zn catalysts prepared under the low alkaline conditions also showed good stability, which indicates that they could potentially be used for industrial application.
2015, 36(3): 408-413
doi: 10.1016/S1872-2067(14)60227-8
Abstract:
A series of Brönsted acid ionic liquids (BAILs) containing a long chain Brönsted acid site in the cationic part and a Lewis basic site in the anionic part were designed, synthesized, and used as catalyst for the coupling of epoxides and carbon dioxide to cyclic carbonates without a co-catalyst or co-solvent. The effects of catalyst structure and other parameters on the catalytic performance were investigated. The long chain 2-(N,N-dimethyldodecylammonium) acetic acid bromide ([(CH2COOH)DMDA]Br) showed high catalytic activity and good reusability. This protocol was expanded to various epoxides, which gave the corresponding cyclic carbonates in good yields. The acidity of the catalyst influenced its catalytic activity.
A series of Brönsted acid ionic liquids (BAILs) containing a long chain Brönsted acid site in the cationic part and a Lewis basic site in the anionic part were designed, synthesized, and used as catalyst for the coupling of epoxides and carbon dioxide to cyclic carbonates without a co-catalyst or co-solvent. The effects of catalyst structure and other parameters on the catalytic performance were investigated. The long chain 2-(N,N-dimethyldodecylammonium) acetic acid bromide ([(CH2COOH)DMDA]Br) showed high catalytic activity and good reusability. This protocol was expanded to various epoxides, which gave the corresponding cyclic carbonates in good yields. The acidity of the catalyst influenced its catalytic activity.
2015, 36(3): 414-424
doi: 10.1016/S1872-2067(14)60223-0
Abstract:
To overcome the prohibitive cost and poor durability of conventional Pt-based catalysts, TiO2/C was prepared by pyrolyzing a novel titanium dioxide/polyaniline (TiO2/PANI) composite. The prepared catalysts were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, cyclic voltammetry (CV), and linear sweep voltammetry. Interaction between PANI and TiO2 was found to inhibit the aggregation of TiO2 and its transformation from anatase to rutile. The catalytic activity of the TiO2/C first increased with increasing PANI content and then decreased; the optimum was achieved when the PANI/TiO2 mass ratio was 35/100. CV and i-t curves showed that the prepared composite has a good catalytic stability.
To overcome the prohibitive cost and poor durability of conventional Pt-based catalysts, TiO2/C was prepared by pyrolyzing a novel titanium dioxide/polyaniline (TiO2/PANI) composite. The prepared catalysts were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, cyclic voltammetry (CV), and linear sweep voltammetry. Interaction between PANI and TiO2 was found to inhibit the aggregation of TiO2 and its transformation from anatase to rutile. The catalytic activity of the TiO2/C first increased with increasing PANI content and then decreased; the optimum was achieved when the PANI/TiO2 mass ratio was 35/100. CV and i-t curves showed that the prepared composite has a good catalytic stability.
2015, 36(3): 425-431
doi: 10.1016/S1872-2067(14)60222-9
Abstract:
Magnetic solid acid catalysts SO42-/Zr(OH)4-Fe3O4 were prepared using magnetic Fe3O4 nanoparticles, ZrOCl2·8H2O, and sulfuric acid as starting materials in the calcination temperature range 110-650 ℃. The properties of the magnetic solid acid, such as loaded SO42- content, acid distribution, surface morphology, and porous structure, were characterized. In the aqueous asymmetric aldol reaction of various benzaldehydes with strong electron-withdrawing groups (R=NO2 and CN), good to excellent catalytic performance (83%-100% yield, 86.0%-95.6% ee anti, and anti/syn=88-96/12-4) was achieved. These nanomagnetic solid acids can be quantitatively recycled from the reaction mixture using an external magnet and reused five times without significant loss of catalytic activity.
Magnetic solid acid catalysts SO42-/Zr(OH)4-Fe3O4 were prepared using magnetic Fe3O4 nanoparticles, ZrOCl2·8H2O, and sulfuric acid as starting materials in the calcination temperature range 110-650 ℃. The properties of the magnetic solid acid, such as loaded SO42- content, acid distribution, surface morphology, and porous structure, were characterized. In the aqueous asymmetric aldol reaction of various benzaldehydes with strong electron-withdrawing groups (R=NO2 and CN), good to excellent catalytic performance (83%-100% yield, 86.0%-95.6% ee anti, and anti/syn=88-96/12-4) was achieved. These nanomagnetic solid acids can be quantitatively recycled from the reaction mixture using an external magnet and reused five times without significant loss of catalytic activity.
2015, 36(3): 432-438
doi: 10.1016/S1872-2067(14)60215-1
Abstract:
Tantalum pentoxide (Ta2O5) nanorods were hydrothermally synthesized using polyethylene glycol (PEG) as a guiding agent. The nanorods were characterized by X-ray diffraction, scanning and transmission electron microscopies, and diffuse reflectance ultraviolet-visible and photoluminescence spectroscopies. The effects of crystallization duration and Ta2O5/Sr(OH)2 ratio on the product morphology were investigated, and a growth mechanism was proposed. Phase-pure Ta2O5 nanorods with controlled morphology were formed in the presence of PEG and Sr(OH)2, which was necessary to form the nanorods. Sr(OH)2 induced the surface dissolution and re-growth of Ta2O5. PEG induced the anisotropic growth of Ta2O5 by acting as a capping agent. The products were used to photocatalytically degrade rhodamine B under ultraviolet irradiation. The catalytic activity directly correlated with the length-diameter ratio of the Ta2O5 nanorods. A maximum apparent reaction rate constant of 0.156 min-1 was obtained. The Ta2O5 nanorods were stable during photocatalytic reaction and could be recycled several times without loss of activity.
Tantalum pentoxide (Ta2O5) nanorods were hydrothermally synthesized using polyethylene glycol (PEG) as a guiding agent. The nanorods were characterized by X-ray diffraction, scanning and transmission electron microscopies, and diffuse reflectance ultraviolet-visible and photoluminescence spectroscopies. The effects of crystallization duration and Ta2O5/Sr(OH)2 ratio on the product morphology were investigated, and a growth mechanism was proposed. Phase-pure Ta2O5 nanorods with controlled morphology were formed in the presence of PEG and Sr(OH)2, which was necessary to form the nanorods. Sr(OH)2 induced the surface dissolution and re-growth of Ta2O5. PEG induced the anisotropic growth of Ta2O5 by acting as a capping agent. The products were used to photocatalytically degrade rhodamine B under ultraviolet irradiation. The catalytic activity directly correlated with the length-diameter ratio of the Ta2O5 nanorods. A maximum apparent reaction rate constant of 0.156 min-1 was obtained. The Ta2O5 nanorods were stable during photocatalytic reaction and could be recycled several times without loss of activity.
2015, 36(3): 439-445
doi: 10.1016/S1872-2067(14)60209-6
Abstract:
Ag nanoparticles were synthesized on the surface of a glassy carbon electrode modified with p-tert-butylcalix[4]arene and p-tert-butylcalix[6]arene by the deposition of Ag+ at an open circuit potential followed by the electrochemical reduction of the Ag+. The presence of the calixarene layer on the electrode surface controlled the particle size and prevented agglomeration. Cyclic voltammetry showed that the Ag nanoparticles on the modified glassy carbon electrode had good catalytic ability for the reduction of flutamide. The effects of calixarene concentration, potential applied for the reduction of Ag+, number of calixarene layers, and pH value on the electrocatalytic activity of the Ag nanoparticles were investigated. The modified electrode had a linear range in differential pulse voltammetry of 10-1000 µmol/L with a detection limit of 9.33 µmol/L for flutamide at an S/N=3. The method was applied to the detection of flutamide in practical samples.
Ag nanoparticles were synthesized on the surface of a glassy carbon electrode modified with p-tert-butylcalix[4]arene and p-tert-butylcalix[6]arene by the deposition of Ag+ at an open circuit potential followed by the electrochemical reduction of the Ag+. The presence of the calixarene layer on the electrode surface controlled the particle size and prevented agglomeration. Cyclic voltammetry showed that the Ag nanoparticles on the modified glassy carbon electrode had good catalytic ability for the reduction of flutamide. The effects of calixarene concentration, potential applied for the reduction of Ag+, number of calixarene layers, and pH value on the electrocatalytic activity of the Ag nanoparticles were investigated. The modified electrode had a linear range in differential pulse voltammetry of 10-1000 µmol/L with a detection limit of 9.33 µmol/L for flutamide at an S/N=3. The method was applied to the detection of flutamide in practical samples.
2015, 36(3): 446-453
doi: 10.1016/S1872-2067(14)60202-3
Abstract:
The hydrothermal stability of FePO4-SBA-15 synthesized using a novel one-pot hydrothermal method (OP) was systematically investigated using two methods: treatment with pure steam at 800 ℃ or with boiling water at 100 ℃. The structural changes in the samples were monitored using small angle X-ray diffraction and N2-physisorption methods. It was found that the hydrothermal stabilities of OP samples remained high and showed little difference over the FePO4-doping range 5-40 wt%. These results differ from previous reports that the loading of heterogeneous metal atoms significantly influences the hydrothermal stability of the host ordered mesoporous material. For comparison, the hydrothermal stabilities of FePO4-SBA-15 synthesized using an impregnation method (IMP) and commercially obtained SBA-15 were also studied. The order of the sample hydrothermal stabilities was OP > IMP >> SBA-15. The formed FePO4 protective layers helped to prevent mesostructure degradation during hydrothermal treatment, therefore modified samples showed superior hydrothermal stabilities compared with pure SBA-15. The superior performance of OP samples over IMP samples is mainly attributed to the formation of stable Si-O-Fe bonds and more micropores in OP samples.
The hydrothermal stability of FePO4-SBA-15 synthesized using a novel one-pot hydrothermal method (OP) was systematically investigated using two methods: treatment with pure steam at 800 ℃ or with boiling water at 100 ℃. The structural changes in the samples were monitored using small angle X-ray diffraction and N2-physisorption methods. It was found that the hydrothermal stabilities of OP samples remained high and showed little difference over the FePO4-doping range 5-40 wt%. These results differ from previous reports that the loading of heterogeneous metal atoms significantly influences the hydrothermal stability of the host ordered mesoporous material. For comparison, the hydrothermal stabilities of FePO4-SBA-15 synthesized using an impregnation method (IMP) and commercially obtained SBA-15 were also studied. The order of the sample hydrothermal stabilities was OP > IMP >> SBA-15. The formed FePO4 protective layers helped to prevent mesostructure degradation during hydrothermal treatment, therefore modified samples showed superior hydrothermal stabilities compared with pure SBA-15. The superior performance of OP samples over IMP samples is mainly attributed to the formation of stable Si-O-Fe bonds and more micropores in OP samples.
