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2017 Volume 75 Issue 3
2017, 75(3): 257-270
doi: 10.6023/A16090495
Abstract:
Currently, as organic semiconductor materials, thiophene fused ring derivatives and the related polymers have received considerable research and application. Furan has similar chemical structure and electronic properties with thiophene due to the same main group heterocyclic atom in five-membered ring system. But furan and furan derivatives possess smaller aromaticity, higher carrier mobility, higher fluorescence quantum efficiency and better solubility, thus more and more attentions have been paid to the design and synthesis of furan-containing fused rings for the application in organic optoelectronic materials. This paper reviewed the recent research progresses of the synthetic methods, properties and applications of the conjugated organic small molecules and polymers based on the furan-containing fused rings.
Currently, as organic semiconductor materials, thiophene fused ring derivatives and the related polymers have received considerable research and application. Furan has similar chemical structure and electronic properties with thiophene due to the same main group heterocyclic atom in five-membered ring system. But furan and furan derivatives possess smaller aromaticity, higher carrier mobility, higher fluorescence quantum efficiency and better solubility, thus more and more attentions have been paid to the design and synthesis of furan-containing fused rings for the application in organic optoelectronic materials. This paper reviewed the recent research progresses of the synthetic methods, properties and applications of the conjugated organic small molecules and polymers based on the furan-containing fused rings.
2017, 75(3): 271-279
doi: 10.6023/A16100552
Abstract:
Ⅲ-nitrides have attracted huge interest from commercial market of lighting, power electronics and communications due to their unique optoelectronic properties, while their further enlargement is hampered by the limited crystal quality resulting from current heterogeneous epitaxy techniques. Recently, the exotic properties of layered two-dimensional materials have caught wide attention. The weak van der Waals interaction between the layers of two dimensional materials may help Ⅲ-nitrides improving the crystal quality by relieving mismatching between lattice and thermal expansion, reducing costs of preparation by reusing expensive substrate, and realizing the fabrication of flexible devices, which will facilitates their generalization in wearable and foldable applications. This review present a comprehensive summary on the recent progress in regard of the Ⅲ-nitride synthesis on the two-dimensional materials, including graphene, hexagonal boron nitride and transition metal dichalcogenides. Various attempts and their results are presented. Two important aspects in the preparation of GaN and AlN on two-dimensional materials are presented, which are the nucleation on defects and the lateral overgrowth of the nitride islands. A detailed knowledge on the nucleation and lateral overgrowth mechanism and precise controlling on the density and distribution of defects are indispensable for the ultimate realization of this route. The challenges and opportunities are also discussed.
Ⅲ-nitrides have attracted huge interest from commercial market of lighting, power electronics and communications due to their unique optoelectronic properties, while their further enlargement is hampered by the limited crystal quality resulting from current heterogeneous epitaxy techniques. Recently, the exotic properties of layered two-dimensional materials have caught wide attention. The weak van der Waals interaction between the layers of two dimensional materials may help Ⅲ-nitrides improving the crystal quality by relieving mismatching between lattice and thermal expansion, reducing costs of preparation by reusing expensive substrate, and realizing the fabrication of flexible devices, which will facilitates their generalization in wearable and foldable applications. This review present a comprehensive summary on the recent progress in regard of the Ⅲ-nitride synthesis on the two-dimensional materials, including graphene, hexagonal boron nitride and transition metal dichalcogenides. Various attempts and their results are presented. Two important aspects in the preparation of GaN and AlN on two-dimensional materials are presented, which are the nucleation on defects and the lateral overgrowth of the nitride islands. A detailed knowledge on the nucleation and lateral overgrowth mechanism and precise controlling on the density and distribution of defects are indispensable for the ultimate realization of this route. The challenges and opportunities are also discussed.
2017, 75(3): 280-283
doi: 10.6023/A16110587
Abstract:
The Morita-Baylis-Hillman (MBH) reaction of α,β-unsaturated carbonyl compounds with allylic halides or allylic esters has been reported. Compared with allylic halides and allylic esters, allylic alcohols are usually more easily prepared. However, to the best of our knowledge, there is no systematic results on the MBH reaction of α,β-unsaturated carbonyl compounds with allylic alcohols. Our experimental results demonstrated that by the catalysis of 10 mol% Pd (PPh3)4 and the mediation of 100 mol% P (n-Bu)3, various aryl vinyl ketones 1a~1g were able to undergo the MBH reaction smoothly with allylic alcohol 2a in the mixed solvents of toluene/(CF3)2CHOH (V/V=35/1) at 60℃ under nitrogen, affording desired α-allylated products 3aa~3ga in the yields of 57%~80%. The MBH reaction is compatible with a series of functional groups on the benzene ring in 1a~1g, such as fluoro, chloro, trifluoromethyl, methyl, and methoxyl group. Naphthyl group instead of benzene group in aryl vinyl ketone 1h also led to α-coupling product 3ha in a good yield. Various 3-aryl allylic alcohols 2b~2f were also able to undergo the MBH reaction smoothly with vinyl ketone 1b, affording the desired α-allylated products 3bb~3bf in good yields with excellent regioselectivities and E-selectivities. 2-Methylprop-2-en-1-ol (2g), 1-phenylprop-2-en-1-ol (2h) or 1, 3-diphenylprop-2-en-1-ol (2i) also performed the MBH reaction expediently with vinyl ketone 1b to give the corresponding α-coupling product 3bg, 3bb, or 3bi. A plausible mechanism using (CF3)2CHOH to both form phosphonium salt 4 and activate allylic alcohols was also proposed. The MBH reaction has many advantages, such as easy availability of starting materials, good tolerance to many functional groups, excellent regioselectivities and E-stereoselectivities, and satisfactory yields. Thus the MBH reaction of aryl vinyl ketones with allylic alcohols may have practical applications in organic synthesis or industry in the future.
The Morita-Baylis-Hillman (MBH) reaction of α,β-unsaturated carbonyl compounds with allylic halides or allylic esters has been reported. Compared with allylic halides and allylic esters, allylic alcohols are usually more easily prepared. However, to the best of our knowledge, there is no systematic results on the MBH reaction of α,β-unsaturated carbonyl compounds with allylic alcohols. Our experimental results demonstrated that by the catalysis of 10 mol% Pd (PPh3)4 and the mediation of 100 mol% P (n-Bu)3, various aryl vinyl ketones 1a~1g were able to undergo the MBH reaction smoothly with allylic alcohol 2a in the mixed solvents of toluene/(CF3)2CHOH (V/V=35/1) at 60℃ under nitrogen, affording desired α-allylated products 3aa~3ga in the yields of 57%~80%. The MBH reaction is compatible with a series of functional groups on the benzene ring in 1a~1g, such as fluoro, chloro, trifluoromethyl, methyl, and methoxyl group. Naphthyl group instead of benzene group in aryl vinyl ketone 1h also led to α-coupling product 3ha in a good yield. Various 3-aryl allylic alcohols 2b~2f were also able to undergo the MBH reaction smoothly with vinyl ketone 1b, affording the desired α-allylated products 3bb~3bf in good yields with excellent regioselectivities and E-selectivities. 2-Methylprop-2-en-1-ol (2g), 1-phenylprop-2-en-1-ol (2h) or 1, 3-diphenylprop-2-en-1-ol (2i) also performed the MBH reaction expediently with vinyl ketone 1b to give the corresponding α-coupling product 3bg, 3bb, or 3bi. A plausible mechanism using (CF3)2CHOH to both form phosphonium salt 4 and activate allylic alcohols was also proposed. The MBH reaction has many advantages, such as easy availability of starting materials, good tolerance to many functional groups, excellent regioselectivities and E-stereoselectivities, and satisfactory yields. Thus the MBH reaction of aryl vinyl ketones with allylic alcohols may have practical applications in organic synthesis or industry in the future.
2017, 75(3): 284-292
doi: 10.6023/A16110645
Abstract:
Binding energies, geometric and electronic structures for[1+1] (H/[1+1]) and[2+1] (O/[2+1]) additions of H and O atoms on a (5, 5) single-walled carbon nanotube with V1~V4 vacancies are studied using a GGA-PBE method in this work. Defect curvature proposed on the basis of directional curvature theory, including atomic curvature (KM-def) and bond curvature (KD-def), is used to predict the reactivities of different atoms and bonds at the defect structural area. We find that the existence of vacancy defects enhances the H and O adsorption ability on the (5, 5) tube. The calculated results show that in the V1 and V3 defects the C atoms with two-coordination have the strongest chemical activity for[1+1] and[2+1] additions, and among which the C atoms participated into[2+1] additions form carbonyl groups with O. For other atoms and bonds at the defect structural area, the binding energies of one H atom on the (5, 5) tube monotonously increases with the increase of KM-def. When the KD-def of C-C bonds for the O/[2+1] additions are large, the C-C bonds are easily broken, and they are corresponding to adducts with the C-O-C configuration structures and large binding energies. When the KD-def of C-C bonds are small, the C-C bonds are not broken, and they are corresponding to adducts with the closed-3MR (three-member ring) structures. The binding energies for the H/[1+1] and O/[2+1] additions on the (5, 5) tube mainly are determined by the curvature and affected by the electronic density in frontier orbital and partial density of state (PDOS) of C atoms participated in the reactions. The large electronic density in the highest occupied molecular orbital (HOMO) and large PDOS of C atoms near the Fermi level strengthen the adsorption of H and O atoms on the (5, 5) tube. This study will provide a theoretical basis for surface modifications of carbon nanotubes with vacancy defects.
Binding energies, geometric and electronic structures for[1+1] (H/[1+1]) and[2+1] (O/[2+1]) additions of H and O atoms on a (5, 5) single-walled carbon nanotube with V1~V4 vacancies are studied using a GGA-PBE method in this work. Defect curvature proposed on the basis of directional curvature theory, including atomic curvature (KM-def) and bond curvature (KD-def), is used to predict the reactivities of different atoms and bonds at the defect structural area. We find that the existence of vacancy defects enhances the H and O adsorption ability on the (5, 5) tube. The calculated results show that in the V1 and V3 defects the C atoms with two-coordination have the strongest chemical activity for[1+1] and[2+1] additions, and among which the C atoms participated into[2+1] additions form carbonyl groups with O. For other atoms and bonds at the defect structural area, the binding energies of one H atom on the (5, 5) tube monotonously increases with the increase of KM-def. When the KD-def of C-C bonds for the O/[2+1] additions are large, the C-C bonds are easily broken, and they are corresponding to adducts with the C-O-C configuration structures and large binding energies. When the KD-def of C-C bonds are small, the C-C bonds are not broken, and they are corresponding to adducts with the closed-3MR (three-member ring) structures. The binding energies for the H/[1+1] and O/[2+1] additions on the (5, 5) tube mainly are determined by the curvature and affected by the electronic density in frontier orbital and partial density of state (PDOS) of C atoms participated in the reactions. The large electronic density in the highest occupied molecular orbital (HOMO) and large PDOS of C atoms near the Fermi level strengthen the adsorption of H and O atoms on the (5, 5) tube. This study will provide a theoretical basis for surface modifications of carbon nanotubes with vacancy defects.
2017, 75(3): 293-299
doi: 10.6023/A16110593
Abstract:
A rapid and efficient preparation of CPO@ZIF-8 by "one pot " method at 30℃ in aqueous solution is presented in this paper. The structure of zeolitic imidazolate frameworks (ZIF-8) was constructed while chloroperoxidase (CPO) was incorporated into the channel. Mild reaction conditions ensure maintaining the enzyme activity in the preparation of immobilized CPO. The synthesis of CPO@ZIF-8 was performed by mixing zinc nitrate solution and polyvinylpyrrolidone solution (PVP, Mw:10000, 10 mg/mL, 400 μL), chloroperoxidase (CPO) (0.214 mmol/L, 500 μL) and 2-methylimidazole (1.25 mol/L, 25 mL) and stirring for 15 min at 30℃, followed by washing and centrifuging for 3 cycles at 4℃ for 8 min. The structure of CPO@ZIF-8 was characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD), indicating that the incorporation of enzyme molecules did not affect the crystal structure of ZIF-8. To further confirm the incorporation of enzyme into ZIF-8, CPO was labeled by fluorescent probes fluorescein isothiocyanate (FITC) and subjected to the same procedure to synthesize the FITC-CPO@ZIF-8. Confocal laser scanning microscopy (CLSM) proved that CPO was distributed evenly and embedded in the whole framework of CPO@ZIF-8. Compared with the method of preparing ZIF-8 firstly, and then immobilizing enzyme molecule by physical adsorption, the immobilization efficiency of enzyme was enhanced by introducing the enzyme into the whole framework, moreover, the catalytic efficiency of the immobilized CPO was increased due to high specific surface area of ZIF-8. The catalytic performance of the CPO@ZIF-8 was evaluated by the conversion rate of 2, 2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS). The rigid shielding environment provided by the three-dimensional channel of ZIF-8 effectively improved the thermal stability, pH stability, and tolerance to organic solvents of the CPO@ZIF-8 under harsh reaction conditions compared with the free enzyme. When incubated at 50℃, 60℃, 70℃, 80℃ and 90℃ for 1 h, 97.1%, 87.8%, 80.2%, 68.1% and 41.5% of the activity of CPO@ZIF-8 were reserved. When incubated at 50℃, 60℃, 70℃ and 80℃ for 3 h, there were still 91.4%, 77.8%, 64.7% and 50.3% of the activity remained. The tolerance of CPO@ZIF-8 to organic solvent DMF, methanol and methyl cyanide was enhanced to 30%~40%.
A rapid and efficient preparation of CPO@ZIF-8 by "one pot " method at 30℃ in aqueous solution is presented in this paper. The structure of zeolitic imidazolate frameworks (ZIF-8) was constructed while chloroperoxidase (CPO) was incorporated into the channel. Mild reaction conditions ensure maintaining the enzyme activity in the preparation of immobilized CPO. The synthesis of CPO@ZIF-8 was performed by mixing zinc nitrate solution and polyvinylpyrrolidone solution (PVP, Mw:10000, 10 mg/mL, 400 μL), chloroperoxidase (CPO) (0.214 mmol/L, 500 μL) and 2-methylimidazole (1.25 mol/L, 25 mL) and stirring for 15 min at 30℃, followed by washing and centrifuging for 3 cycles at 4℃ for 8 min. The structure of CPO@ZIF-8 was characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD), indicating that the incorporation of enzyme molecules did not affect the crystal structure of ZIF-8. To further confirm the incorporation of enzyme into ZIF-8, CPO was labeled by fluorescent probes fluorescein isothiocyanate (FITC) and subjected to the same procedure to synthesize the FITC-CPO@ZIF-8. Confocal laser scanning microscopy (CLSM) proved that CPO was distributed evenly and embedded in the whole framework of CPO@ZIF-8. Compared with the method of preparing ZIF-8 firstly, and then immobilizing enzyme molecule by physical adsorption, the immobilization efficiency of enzyme was enhanced by introducing the enzyme into the whole framework, moreover, the catalytic efficiency of the immobilized CPO was increased due to high specific surface area of ZIF-8. The catalytic performance of the CPO@ZIF-8 was evaluated by the conversion rate of 2, 2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS). The rigid shielding environment provided by the three-dimensional channel of ZIF-8 effectively improved the thermal stability, pH stability, and tolerance to organic solvents of the CPO@ZIF-8 under harsh reaction conditions compared with the free enzyme. When incubated at 50℃, 60℃, 70℃, 80℃ and 90℃ for 1 h, 97.1%, 87.8%, 80.2%, 68.1% and 41.5% of the activity of CPO@ZIF-8 were reserved. When incubated at 50℃, 60℃, 70℃ and 80℃ for 3 h, there were still 91.4%, 77.8%, 64.7% and 50.3% of the activity remained. The tolerance of CPO@ZIF-8 to organic solvent DMF, methanol and methyl cyanide was enhanced to 30%~40%.
2017, 75(3): 300-306
doi: 10.6023/A16100543
Abstract:
InP quantum dots (QDs) are regarded as the most desirable candidate to replace the role of CdSe QDs in the applications of bio-labeling, LEDs, solar cells, etc, because InP is more environmentally friendly compared to Cd based QDs, and could also offer a tunable emission from blue to near-infrared. Nevertheless, the studies and applications of InP QDs are rather sparse in comparison with CdSe QDs, which are principally caused by significant difficulties in its synthesis. In this report, we developed a novel method for the synthesis of InPZnS/ZnS QDs by using zinc phosphide as phosphorus precursor, and the zinc and sulfur precursors were also added at the start of reaction, which allows the continuous injection of phosphine gas into the reaction, resulting in high quality InPZnS/ZnS quantum dots with emission up to 680 nm. The core synthesis and shell coating were separated by controlling the reaction temperature. During the first 30 minutes, the temperature of reaction solution was kept at 250℃ to grow the InPZnS core QDs. Then, the coating of ZnS shell was happened and kept about 1 hour to guarantee the complete decomposition of 1-dodecanethiol (DDT) after the reaction temperature was increased to 300℃. The biggest advantage of this synthetic method is the tunable emission region from blue to near-infrared. The effects of reaction parameters were systematically investigated. We observed that the molar ratio of In:myristic acid (MA) and that of In:Zn (S) had significant influences on the size of the InP QDs. The structure of InPZnS/ZnS QDs was confirmed by transmission electron microscope (TEM), X-ray powder diffraction (XRD), and energy dispersive X-ray analyzer (EDX). TEM characterization indicated the final core/shell InPZnS/ZnS QDs were good monodispersity with an average size of 7 nm. Furthermore, we investigated the versatility of this method by using other phosphorus precursor. The injection pump leaded to a continuous supply of phosphorus precursor on a timescale and reacted with indium precursor to form InP QDs. The final sample showed an emission at 710 nm. The present method gives access to larger sized InP QDs, making it prosperous for applications in biological labeling.
InP quantum dots (QDs) are regarded as the most desirable candidate to replace the role of CdSe QDs in the applications of bio-labeling, LEDs, solar cells, etc, because InP is more environmentally friendly compared to Cd based QDs, and could also offer a tunable emission from blue to near-infrared. Nevertheless, the studies and applications of InP QDs are rather sparse in comparison with CdSe QDs, which are principally caused by significant difficulties in its synthesis. In this report, we developed a novel method for the synthesis of InPZnS/ZnS QDs by using zinc phosphide as phosphorus precursor, and the zinc and sulfur precursors were also added at the start of reaction, which allows the continuous injection of phosphine gas into the reaction, resulting in high quality InPZnS/ZnS quantum dots with emission up to 680 nm. The core synthesis and shell coating were separated by controlling the reaction temperature. During the first 30 minutes, the temperature of reaction solution was kept at 250℃ to grow the InPZnS core QDs. Then, the coating of ZnS shell was happened and kept about 1 hour to guarantee the complete decomposition of 1-dodecanethiol (DDT) after the reaction temperature was increased to 300℃. The biggest advantage of this synthetic method is the tunable emission region from blue to near-infrared. The effects of reaction parameters were systematically investigated. We observed that the molar ratio of In:myristic acid (MA) and that of In:Zn (S) had significant influences on the size of the InP QDs. The structure of InPZnS/ZnS QDs was confirmed by transmission electron microscope (TEM), X-ray powder diffraction (XRD), and energy dispersive X-ray analyzer (EDX). TEM characterization indicated the final core/shell InPZnS/ZnS QDs were good monodispersity with an average size of 7 nm. Furthermore, we investigated the versatility of this method by using other phosphorus precursor. The injection pump leaded to a continuous supply of phosphorus precursor on a timescale and reacted with indium precursor to form InP QDs. The final sample showed an emission at 710 nm. The present method gives access to larger sized InP QDs, making it prosperous for applications in biological labeling.
2017, 75(3): 307-320
doi: 10.6023/A16110578
Abstract:
Recently, transition metal sulfides (TMS) have played an important role in many catalytic reactions. In particular, they are widely used in the petrochemical industry, such as the hydrodesulfurization (HDS) and the hydrodenitrogenation (HDN) processes. In this work, density functional theory (DFT) and coupled cluster theory[CCSD (T)] calculations were used to study the niobium-mixed di-nuclear molybdenum sulfide clusters NbMoSn-/0(n=3~7). In our calculations, their ground-state structures were determined and the effects of doping metal, adjusting the sulfur content (n) and changing the charge states of clusters were discussed on the geometries, electronic structures and chemical bonding of NbMoSn-/0(n=3~7). NbMoSn-/0(n=3~7) clusters can be viewed as linking different sulfur ligands to the NbMoS2 four-membered rings. Among them, diverse poly-sulfur ligands, such as bridging S2, terminal S2 and terminal S3 groups, emerged in the sulfur-rich clusters. Generalized Koopmans' Theorem was employed to predict the vertical detachment energies (VDEs), and simulate the corresponding anionic photoelectron spectra (PES). The first VDEs (VDE1st) of NbMoSn-(n=3~6) increased gradually as a function of n, and then decreased suddenly when the sulfur content (n) reached 7. The VDE1st reached the maximum by 4.69 eV when the sulfur content equaled to 6. The driving forces (-ΔG) of the reduction reactions between NbMoSn-/0(n=3~7) and H2 were evaluated. The NbMoS7- anion with the terminal S22- group yielded the negative value of ΔG, which indicated that the reaction is thermodynamically favored even at the room temperature. We predicted that doping niobium into the molybdenum sulfides may improve the emergence of S2 group which may be helpful in producing the coordinatively unsaturated sites (CUS) under the H2/H2S atmosphere. Molecular orbital analyses are performed to improve our understanding on the structural evolution and the chemical bonding of NbMoSn-/0(n=3~7) clusters.
Recently, transition metal sulfides (TMS) have played an important role in many catalytic reactions. In particular, they are widely used in the petrochemical industry, such as the hydrodesulfurization (HDS) and the hydrodenitrogenation (HDN) processes. In this work, density functional theory (DFT) and coupled cluster theory[CCSD (T)] calculations were used to study the niobium-mixed di-nuclear molybdenum sulfide clusters NbMoSn-/0(n=3~7). In our calculations, their ground-state structures were determined and the effects of doping metal, adjusting the sulfur content (n) and changing the charge states of clusters were discussed on the geometries, electronic structures and chemical bonding of NbMoSn-/0(n=3~7). NbMoSn-/0(n=3~7) clusters can be viewed as linking different sulfur ligands to the NbMoS2 four-membered rings. Among them, diverse poly-sulfur ligands, such as bridging S2, terminal S2 and terminal S3 groups, emerged in the sulfur-rich clusters. Generalized Koopmans' Theorem was employed to predict the vertical detachment energies (VDEs), and simulate the corresponding anionic photoelectron spectra (PES). The first VDEs (VDE1st) of NbMoSn-(n=3~6) increased gradually as a function of n, and then decreased suddenly when the sulfur content (n) reached 7. The VDE1st reached the maximum by 4.69 eV when the sulfur content equaled to 6. The driving forces (-ΔG) of the reduction reactions between NbMoSn-/0(n=3~7) and H2 were evaluated. The NbMoS7- anion with the terminal S22- group yielded the negative value of ΔG, which indicated that the reaction is thermodynamically favored even at the room temperature. We predicted that doping niobium into the molybdenum sulfides may improve the emergence of S2 group which may be helpful in producing the coordinatively unsaturated sites (CUS) under the H2/H2S atmosphere. Molecular orbital analyses are performed to improve our understanding on the structural evolution and the chemical bonding of NbMoSn-/0(n=3~7) clusters.
2017, 75(3): 321-328
doi: 10.6023/A16100569
Abstract:
Partial hydrogenation of benzene to cyclohexene is an important industrial process and features exceptional superiority to processes such as dehydration of cyclohexanol, dehydrogenation of cyclohexane, and the Birch reduction in terms of inexpensive feedstock, succinct reaction route and consequently, improved operational simplicity. In this work, the pore size effect on the partial hydrogenation of benzene to cyclohexene over the Ru-Zn/ZrO2 catalysts was studied for the first time. Three ZrO2 supports with the same tetragonal crystallographic form (t-ZrO2) but different pore sizes were synthesized by the precipitation and the solvothermal methods. Using these ZrO2 samples, the Ru-Zn/ZrO2 catalysts were prepared by the deposition-precipitation method followed by reduction in ZnSO4·7H2O aqueous solution. The supports and catalysts were characterized by powder X-ray diffraction (XRD), N2 physisorption, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), CO chemisorption, X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge structure (XANES), temperature-programmed reduction of H2 (H2-TPR), and transmission electron microscopy (TEM). It is identified that the Ru nanoparticles (NPs) on these catalysts had similar size and chemical state. In the partial hydrogenation of benzene to cyclohexene, a pronounced pore size effect of the catalyst was identified. With the increase in the pore size, while the turnover frequency (TOF) of benzene was essentially unchanged, the initial selectivity (S0) to cyclohexene increased steadily. The Ru-Zn/ZrO2(11.7) catalyst with the ZrO2 support having the pore size of 11.7 nm exhibited the highest S0 (88%) and yield (54%) of cyclohexene. On the basis of the characterization results, the similarity in the TOFs of benzene on the Ru-Zn/ZrO2 catalysts with different pore sizes is associated with the identical sizes of the Ru NPs. On the other hand, we tentatively propose that the ZrO2 support with large pore size is beneficial for the out-diffusion of the cyclohexene nano-droplets formed in the pore channels, thus avoiding consecutive hydrogenation to cyclohexane and improving the S0.
Partial hydrogenation of benzene to cyclohexene is an important industrial process and features exceptional superiority to processes such as dehydration of cyclohexanol, dehydrogenation of cyclohexane, and the Birch reduction in terms of inexpensive feedstock, succinct reaction route and consequently, improved operational simplicity. In this work, the pore size effect on the partial hydrogenation of benzene to cyclohexene over the Ru-Zn/ZrO2 catalysts was studied for the first time. Three ZrO2 supports with the same tetragonal crystallographic form (t-ZrO2) but different pore sizes were synthesized by the precipitation and the solvothermal methods. Using these ZrO2 samples, the Ru-Zn/ZrO2 catalysts were prepared by the deposition-precipitation method followed by reduction in ZnSO4·7H2O aqueous solution. The supports and catalysts were characterized by powder X-ray diffraction (XRD), N2 physisorption, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), CO chemisorption, X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge structure (XANES), temperature-programmed reduction of H2 (H2-TPR), and transmission electron microscopy (TEM). It is identified that the Ru nanoparticles (NPs) on these catalysts had similar size and chemical state. In the partial hydrogenation of benzene to cyclohexene, a pronounced pore size effect of the catalyst was identified. With the increase in the pore size, while the turnover frequency (TOF) of benzene was essentially unchanged, the initial selectivity (S0) to cyclohexene increased steadily. The Ru-Zn/ZrO2(11.7) catalyst with the ZrO2 support having the pore size of 11.7 nm exhibited the highest S0 (88%) and yield (54%) of cyclohexene. On the basis of the characterization results, the similarity in the TOFs of benzene on the Ru-Zn/ZrO2 catalysts with different pore sizes is associated with the identical sizes of the Ru NPs. On the other hand, we tentatively propose that the ZrO2 support with large pore size is beneficial for the out-diffusion of the cyclohexene nano-droplets formed in the pore channels, thus avoiding consecutive hydrogenation to cyclohexane and improving the S0.
