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2016 Volume 37 Issue 5
2016, 37(5): 637-643
doi: 10.1016/S1872-2067(15)61087-7
Abstract:
2016, 37(5): 644-670
doi: 10.1016/S1872-2067(15)61065-8
Abstract:
The catalytic performance of solid catalysts depends on the properties of the catalytically active sites and their accessibility to reactants, which are significantly affected by the microstructure (morphology, shape, size, texture, and surface structure) and surface chemistry (elemental components and chemical states). The development of facile and efficient methods for tailoring the microstructure and surface chemistry is a hot topic in catalysis. This contribution reviews the state of the art in modulating the microstructure and surface chemistry of carbocatalysts by both bottom-up and top-down strategies and their use in the oxidative dehydrogenation (ODH) and direct dehydrogenation (DDH) of hydrocarbons including light alkanes and ethylbenzene to their corresponding olefins, important building blocks and chemicals like oxygenates. A concept of microstructure and surface chemistry tuning of the carbocatalyst for optimized catalytic performance and also for the fundamental understanding of the structure-performance relationship is discussed. We also highlight the importance and challenges in modulating the microstructure and surface chemistry of carbocatalysts in ODH and DDH reactions of hydrocarbons for the highly-efficient, energy-saving, and clean production of their corresponding olefins.
The catalytic performance of solid catalysts depends on the properties of the catalytically active sites and their accessibility to reactants, which are significantly affected by the microstructure (morphology, shape, size, texture, and surface structure) and surface chemistry (elemental components and chemical states). The development of facile and efficient methods for tailoring the microstructure and surface chemistry is a hot topic in catalysis. This contribution reviews the state of the art in modulating the microstructure and surface chemistry of carbocatalysts by both bottom-up and top-down strategies and their use in the oxidative dehydrogenation (ODH) and direct dehydrogenation (DDH) of hydrocarbons including light alkanes and ethylbenzene to their corresponding olefins, important building blocks and chemicals like oxygenates. A concept of microstructure and surface chemistry tuning of the carbocatalyst for optimized catalytic performance and also for the fundamental understanding of the structure-performance relationship is discussed. We also highlight the importance and challenges in modulating the microstructure and surface chemistry of carbocatalysts in ODH and DDH reactions of hydrocarbons for the highly-efficient, energy-saving, and clean production of their corresponding olefins.
2016, 37(5): 671-680
doi: 10.1016/S1872-2067(15)61091-9
Abstract:
This review discussed the use of nano ZSM-5 in naphtha catalytic cracking. The impact of nano ZSM-5 on product selectivity, reaction conversion and catalyst lifetime were compared with micro-sized ZSM-5. The application of nano ZSM-5 not only increased the catalyst lifetime, but also gave more stability for light olefins selectivity. The effects of the reaction parameters of temperature and feedstock on the performance of nano ZSM-5 were investigated, and showed that high temperature and linear alkanes as feedstock improved light olefin selectivity and conversion.
This review discussed the use of nano ZSM-5 in naphtha catalytic cracking. The impact of nano ZSM-5 on product selectivity, reaction conversion and catalyst lifetime were compared with micro-sized ZSM-5. The application of nano ZSM-5 not only increased the catalyst lifetime, but also gave more stability for light olefins selectivity. The effects of the reaction parameters of temperature and feedstock on the performance of nano ZSM-5 were investigated, and showed that high temperature and linear alkanes as feedstock improved light olefin selectivity and conversion.
2016, 37(5): 681-691
doi: 10.1016/S1872-2067(15)61069-5
Abstract:
This paper reviews several important factors that influence the synthesis of dumbbell-like nanoparticles, which can significantly enhance the catalyst activity in catalytic combustion. The dumbbell-like nanoparticles discussed in this article refer to a hetero-structure with two nanoparticles of different materials in contact with each other. This nanostructure can be considered as a special intermediate between individual spherical nanoparticles and a core-shell nanostructure. Therefore, the synthesis of dumbbell-like nanoparticles is more difficult than other structures. The controllability of the synthesis process, the nanoparticle size and size distribution, and the morphology of the final products depend on many factors: the seed size and size ratio could be used to influence the controllability of epitaxial growth. The component sizes and size distribution could be varied by carefully controlling the reaction temperature and reaction time. The morphology of the dumbbell-like nanoparticles is closely related to the solvent polarity, the precursor ratio, the lattice mismatch between the two components, and the surfactant concentration. Some related synthesis methods are also briefly introduced in each section to facilitate understanding. This summary will benefit the development of new dumbbell-like nanoparticles with various components, which have great potential in catalytic combustion of more dysoxidizable gases.
This paper reviews several important factors that influence the synthesis of dumbbell-like nanoparticles, which can significantly enhance the catalyst activity in catalytic combustion. The dumbbell-like nanoparticles discussed in this article refer to a hetero-structure with two nanoparticles of different materials in contact with each other. This nanostructure can be considered as a special intermediate between individual spherical nanoparticles and a core-shell nanostructure. Therefore, the synthesis of dumbbell-like nanoparticles is more difficult than other structures. The controllability of the synthesis process, the nanoparticle size and size distribution, and the morphology of the final products depend on many factors: the seed size and size ratio could be used to influence the controllability of epitaxial growth. The component sizes and size distribution could be varied by carefully controlling the reaction temperature and reaction time. The morphology of the dumbbell-like nanoparticles is closely related to the solvent polarity, the precursor ratio, the lattice mismatch between the two components, and the surfactant concentration. Some related synthesis methods are also briefly introduced in each section to facilitate understanding. This summary will benefit the development of new dumbbell-like nanoparticles with various components, which have great potential in catalytic combustion of more dysoxidizable gases.
2016, 37(5): 692-699
doi: 10.1016/S1872-2067(15)61090-7
Abstract:
The heterogeneity of active sites is the main obstacle for selectivity control in heterogeneous catalysis. Single atom catalysts (SACs) with homogeneous isolated active sites are highly desired in chemoselective transformations. In this work, a Pd1/ZnO catalyst with single-atom dispersion of Pd active sites was achieved by decreasing the Pd loading and reducing the sample at a relatively low temperature. The Pd1/ZnO SAC exhibited excellent catalytic performance in the chemoselective hydrogenation of acetylene with comparable chemoselectivity to that of PdZn intermetallic catalysts and a greatly enhanced utilization of Pd metal. Such unusual behaviors of the Pd1/ZnO SAC in acetylene semi-hydrogenation were ascribed to the high-valent single Pd active sites, which could promote electrostatic interactions with acetylene but restrain undesired ethylene hydrogenation via the spatial restrictions of σ-chemical bonding toward ethylene.
The heterogeneity of active sites is the main obstacle for selectivity control in heterogeneous catalysis. Single atom catalysts (SACs) with homogeneous isolated active sites are highly desired in chemoselective transformations. In this work, a Pd1/ZnO catalyst with single-atom dispersion of Pd active sites was achieved by decreasing the Pd loading and reducing the sample at a relatively low temperature. The Pd1/ZnO SAC exhibited excellent catalytic performance in the chemoselective hydrogenation of acetylene with comparable chemoselectivity to that of PdZn intermetallic catalysts and a greatly enhanced utilization of Pd metal. Such unusual behaviors of the Pd1/ZnO SAC in acetylene semi-hydrogenation were ascribed to the high-valent single Pd active sites, which could promote electrostatic interactions with acetylene but restrain undesired ethylene hydrogenation via the spatial restrictions of σ-chemical bonding toward ethylene.
2016, 37(5): 700-710
doi: 10.1016/S1872-2067(15)61080-4
Abstract:
Cu nanoparticles supported on a variety of oxide supports, including SiO2, TiO2, ZrO2, Al2O3, MgO and ZnO, were investigated for the hydrogenolysis of biomass-derived furfuryl alcohol to 1,2-pentanediol and 1,5-pentanediol. A Cu-Al2O3 catalyst with 10 wt% Cu loading prepared by a co-precipitation method exhibited the best performance in terms of producing pentanediols compared with the other materials. This catalyst generated an 85.8% conversion and a 70.3% combined selectivity for the target pentanediols at 413 K and 8 MPa H2 over an 8-h reaction. The catalyst could also be recycled over repeated reaction trials without any significant decrease in productivity. Characterizations with X-ray diffraction, NH3/CO2-temperature programmed desorption, N2 adsorption, transmission electron microscopy and N2O chemisorption demonstrated that intimate and effective interactions between Cu particles and the acidic Al2O3 support in this material greatly enhanced its activity and selectivity. The promotion of the hydrogenolysis reaction was found to be especially sensitive to the Cu particle size, and the catalyst with Cu particles 1.9 to 2.4 nm in size showed the highest turnover frequency during the synthesis of pentanediols.
Cu nanoparticles supported on a variety of oxide supports, including SiO2, TiO2, ZrO2, Al2O3, MgO and ZnO, were investigated for the hydrogenolysis of biomass-derived furfuryl alcohol to 1,2-pentanediol and 1,5-pentanediol. A Cu-Al2O3 catalyst with 10 wt% Cu loading prepared by a co-precipitation method exhibited the best performance in terms of producing pentanediols compared with the other materials. This catalyst generated an 85.8% conversion and a 70.3% combined selectivity for the target pentanediols at 413 K and 8 MPa H2 over an 8-h reaction. The catalyst could also be recycled over repeated reaction trials without any significant decrease in productivity. Characterizations with X-ray diffraction, NH3/CO2-temperature programmed desorption, N2 adsorption, transmission electron microscopy and N2O chemisorption demonstrated that intimate and effective interactions between Cu particles and the acidic Al2O3 support in this material greatly enhanced its activity and selectivity. The promotion of the hydrogenolysis reaction was found to be especially sensitive to the Cu particle size, and the catalyst with Cu particles 1.9 to 2.4 nm in size showed the highest turnover frequency during the synthesis of pentanediols.
2016, 37(5): 711-719
doi: 10.1016/S1872-2067(15)61078-6
Abstract:
Ag3PO4 powders were prepared through a precipitation reaction between AgNO3 and precipitating agent solutions that were prepared by adjusting the amount of H3PO4 in the Na3PO4solutions. The Ag3PO4 powders prepared from the precipitation solution with a pH of 6 showed the highest photocatalytic activity for decolorizing the methylene blue and rhodamine B dyes. These Ag3PO4 powders were further modified by the addition of KBr solutions to obtain AgBr/Ag3PO4 powders and these photocatalysts can decolorize the anionic dyes as reactive orange and methyl orange. The reactive species involved in the photocatalytic degradation process were evaluated for their inhibitory activity using the appropriate scavengers. After photocatalysis, mass spectrometry confirmed that the dyes were degraded to smaller molecules. The ecotoxicities of the dye solutions before and after treatment were evaluated by studying their ability to inhibit the growth of the bioindicator Chlorella vulgaris.
Ag3PO4 powders were prepared through a precipitation reaction between AgNO3 and precipitating agent solutions that were prepared by adjusting the amount of H3PO4 in the Na3PO4solutions. The Ag3PO4 powders prepared from the precipitation solution with a pH of 6 showed the highest photocatalytic activity for decolorizing the methylene blue and rhodamine B dyes. These Ag3PO4 powders were further modified by the addition of KBr solutions to obtain AgBr/Ag3PO4 powders and these photocatalysts can decolorize the anionic dyes as reactive orange and methyl orange. The reactive species involved in the photocatalytic degradation process were evaluated for their inhibitory activity using the appropriate scavengers. After photocatalysis, mass spectrometry confirmed that the dyes were degraded to smaller molecules. The ecotoxicities of the dye solutions before and after treatment were evaluated by studying their ability to inhibit the growth of the bioindicator Chlorella vulgaris.
2016, 37(5): 720-726
doi: 10.1016/S1872-2067(15)61074-9
Abstract:
The synthesis of anisole by vapor phase methylation of phenol with methanol over activated alumina (AA) supported catalysts was investigated in a fixed bed reactor. KH2PO4/AA gave the best performance among the eight tested catalysts. The catalyst was prepared by loading KH2PO4 on AA and then calcining at the optimized temperature of 700 ℃ for 8 h. In the vapor phase reaction, the level of anisole yield (LAY) has a maximum at 400-450 ℃ when the temperature varied from 300 to 500 ℃, which decreased slightly with increasing WHSV and increased distinctly with increasing mole fraction of methanol. On comparing O-methylation and C-methylation of phenol, a low temperature, high WHSV (short residence time), and a low methanol concentration over the KH2PO4/AA catalyst with higher K contents were found to increase anisole selectivity by O-methylation of phenol. The reaction routes to the major products and the catalytic mechanism were suggested, and a ‘K-acid' bifunctional process may be a critical factor to the formation of anisole.
The synthesis of anisole by vapor phase methylation of phenol with methanol over activated alumina (AA) supported catalysts was investigated in a fixed bed reactor. KH2PO4/AA gave the best performance among the eight tested catalysts. The catalyst was prepared by loading KH2PO4 on AA and then calcining at the optimized temperature of 700 ℃ for 8 h. In the vapor phase reaction, the level of anisole yield (LAY) has a maximum at 400-450 ℃ when the temperature varied from 300 to 500 ℃, which decreased slightly with increasing WHSV and increased distinctly with increasing mole fraction of methanol. On comparing O-methylation and C-methylation of phenol, a low temperature, high WHSV (short residence time), and a low methanol concentration over the KH2PO4/AA catalyst with higher K contents were found to increase anisole selectivity by O-methylation of phenol. The reaction routes to the major products and the catalytic mechanism were suggested, and a ‘K-acid' bifunctional process may be a critical factor to the formation of anisole.
2016, 37(5): 727-734
doi: 10.1016/S1872-2067(15)61068-3
Abstract:
Sulfur in transportation fuels is a major source of air pollution. New strategies for the desulfurization of fuels have been explored to meet the urgent need to produce cleaner gasoline. Adsorptive desulfurization (ADS) is one of the most promising complementary and alternative methods. Herein, nanocrystalline ferrite adsorbents were synthesized from metal nitrates and urea using a microwave assisted combustion method. A series of ADS experiments were performed using a fixed-bed reactor to evaluate the ADS reactivity over the ferrites, which was found to have the order MgFe2O4 > NiFe2O4 > CuZnFe2O4 > ZnFe2O4 > CoFe2O4. This effect is explained by the fact that the low degree of alloying of Mg-Fe and the doped Mg increased the interaction between Fe and S compounds, leading to a significant improvement in the desulfurization capability of the adsorbent. Additionally, Mg can dramatically promote the decomposition of thiophene. X-ray diffraction and Mössbauer spectroscopy were used to characterize the fresh, regenerated, and sulfided adsorbents. Although the ferrite adsorbents were partially sulfided to bimetallic sulfides during the adsorption process, they were successfully regenerated after calcining at 500 ℃ in air.
Sulfur in transportation fuels is a major source of air pollution. New strategies for the desulfurization of fuels have been explored to meet the urgent need to produce cleaner gasoline. Adsorptive desulfurization (ADS) is one of the most promising complementary and alternative methods. Herein, nanocrystalline ferrite adsorbents were synthesized from metal nitrates and urea using a microwave assisted combustion method. A series of ADS experiments were performed using a fixed-bed reactor to evaluate the ADS reactivity over the ferrites, which was found to have the order MgFe2O4 > NiFe2O4 > CuZnFe2O4 > ZnFe2O4 > CoFe2O4. This effect is explained by the fact that the low degree of alloying of Mg-Fe and the doped Mg increased the interaction between Fe and S compounds, leading to a significant improvement in the desulfurization capability of the adsorbent. Additionally, Mg can dramatically promote the decomposition of thiophene. X-ray diffraction and Mössbauer spectroscopy were used to characterize the fresh, regenerated, and sulfided adsorbents. Although the ferrite adsorbents were partially sulfided to bimetallic sulfides during the adsorption process, they were successfully regenerated after calcining at 500 ℃ in air.
2016, 37(5): 735-742
doi: 10.1016/S1872-2067(15)61066-X
Abstract:
The anaerobic digestion of sludge has recently received increased interest because of the potential to transform organic matter into methane-rich biogas. However, digested sludge, the residue produced in that process, still contains high levels of heavy metals and other harmful substances that might make traditional disposal difficult. We have devised a facile method of converting digested sludge into a mesoporous material that acts as an effective and stable heterogeneous catalyst for the photo-Fenton reaction. A comparison of the removal of rhodamine B under different conditions showed that FAS-1-350, which was synthesized by mixing the digested sludge with a 1 mol/L (NH4)2Fe(SO4)2 solution followed by calcination at 350 ℃, exhibited the best catalytic activity owing to its faster reaction rate and lower degree of Fe leaching. The results indicate that Fe2+-loaded catalysts have significant potential to act as stable and efficient heterogeneous promoters for the photo-Fenton reaction, with better performance than Fe3+-loaded catalysts because the Fe(II)/Fe(III) compounds formed in the calcination process are necessary to sustain the Fenton reaction. This protocol provides an alternative, environmentally friendly method of reusing digested sludge and demonstrates an easily synthesized mesoporous material that effectively degrades azo dyes.
The anaerobic digestion of sludge has recently received increased interest because of the potential to transform organic matter into methane-rich biogas. However, digested sludge, the residue produced in that process, still contains high levels of heavy metals and other harmful substances that might make traditional disposal difficult. We have devised a facile method of converting digested sludge into a mesoporous material that acts as an effective and stable heterogeneous catalyst for the photo-Fenton reaction. A comparison of the removal of rhodamine B under different conditions showed that FAS-1-350, which was synthesized by mixing the digested sludge with a 1 mol/L (NH4)2Fe(SO4)2 solution followed by calcination at 350 ℃, exhibited the best catalytic activity owing to its faster reaction rate and lower degree of Fe leaching. The results indicate that Fe2+-loaded catalysts have significant potential to act as stable and efficient heterogeneous promoters for the photo-Fenton reaction, with better performance than Fe3+-loaded catalysts because the Fe(II)/Fe(III) compounds formed in the calcination process are necessary to sustain the Fenton reaction. This protocol provides an alternative, environmentally friendly method of reusing digested sludge and demonstrates an easily synthesized mesoporous material that effectively degrades azo dyes.
2016, 37(5): 743-749
doi: 10.1016/S1872-2067(15)61071-3
Abstract:
Ni-CeO2 catalysts with a nickel content of 50 mol% were prepared using RF thermal plasma, and their catalytic activities for methane partial oxidation were characterized. For the synthesis of Ni-CeO2 catalysts, a precursor containing Ni (~5-μm diameter) and CeO2 (~200-nm diameter) powders were heated simultaneously using an RF plasma at a power level of ~52 kVA and a powder feeding rate of ~120 g/h. From the X-ray diffraction data and transmission electron microscopy images, the precursor formed into high crystalline CeO2 supports with nanosized Ni particles (< 50-nm diameter) on their surfaces. The catalytic performance was evaluated under atmospheric pressure at > 500 ℃ and a CH4:O2 molar ratio of 2:1 with Ar diluent. Although the Ni content was high (~50 mol%), the experimental results reveal a methane conversion rate of > 70%, selectivities of CO and H2 greater than 90% and slight carbon coking during an on-stream test at 550 ℃ for 24 h. However, at 750 ℃, the on-stream test revealed the formation of filament-like carbons with an increased methane conversion rate over 90%.
Ni-CeO2 catalysts with a nickel content of 50 mol% were prepared using RF thermal plasma, and their catalytic activities for methane partial oxidation were characterized. For the synthesis of Ni-CeO2 catalysts, a precursor containing Ni (~5-μm diameter) and CeO2 (~200-nm diameter) powders were heated simultaneously using an RF plasma at a power level of ~52 kVA and a powder feeding rate of ~120 g/h. From the X-ray diffraction data and transmission electron microscopy images, the precursor formed into high crystalline CeO2 supports with nanosized Ni particles (< 50-nm diameter) on their surfaces. The catalytic performance was evaluated under atmospheric pressure at > 500 ℃ and a CH4:O2 molar ratio of 2:1 with Ar diluent. Although the Ni content was high (~50 mol%), the experimental results reveal a methane conversion rate of > 70%, selectivities of CO and H2 greater than 90% and slight carbon coking during an on-stream test at 550 ℃ for 24 h. However, at 750 ℃, the on-stream test revealed the formation of filament-like carbons with an increased methane conversion rate over 90%.
2016, 37(5): 750-759
doi: 10.1016/S1872-2067(15)61072-5
Abstract:
A series of meso-microporous copper-supporting chabazite molecular sieve (Cu-SAPO-34) catalysts with excellent performance in low-temperature ammonia selective catalytic reduction (NH3-SCR) have been synthesized via a one-pot hydrothermal crystallization method. The physicochemical properties of the catalysts were characterized by scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption measurements, X-ray diffraction, 27Al magic angle spinning nuclear magnetic resonance, diffuse reflectance ultraviolet-visible spectroscopy, inductively coupled plasma-atomic emission spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction measurements, and electron paramagnetic resonance analysis. The formation of micro-mesopores in the Cu-SAPO-34 catalysts decreases diffusion resistance and greatly improves the accessibility of reactants to catalytic active sites. The main active sites for NH3-SCR reaction are the isolated Cu2+ species displaced into the ellipsoidal cavity of the Cu-SAPO-34 catalysts.
A series of meso-microporous copper-supporting chabazite molecular sieve (Cu-SAPO-34) catalysts with excellent performance in low-temperature ammonia selective catalytic reduction (NH3-SCR) have been synthesized via a one-pot hydrothermal crystallization method. The physicochemical properties of the catalysts were characterized by scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption measurements, X-ray diffraction, 27Al magic angle spinning nuclear magnetic resonance, diffuse reflectance ultraviolet-visible spectroscopy, inductively coupled plasma-atomic emission spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction measurements, and electron paramagnetic resonance analysis. The formation of micro-mesopores in the Cu-SAPO-34 catalysts decreases diffusion resistance and greatly improves the accessibility of reactants to catalytic active sites. The main active sites for NH3-SCR reaction are the isolated Cu2+ species displaced into the ellipsoidal cavity of the Cu-SAPO-34 catalysts.
2016, 37(5): 760-768
doi: 10.1016/S1872-2067(15)61079-8
Abstract:
Hierarchical microspheres of a graphene oxide (GO) coupled to N-doped (BiO)2CO3 composite (N-BOC-GO) was synthesized by a simple hydrothermal approach. The N-BOC-GO composite gave enhancement in photocatalytic activity compared to the pure BOC and N-BOC samples. With 1.0 wt% GO, 62% NO removal was obtained with N-BOC-GO. The factors enhancing the photocatalytic performance were the high electron-withdrawing ability and high conductivity of GO and improved visible light-harvesting ability of N-BOC-GO with a 3D hierarchical architecture due to the surface scattering and reflecting (SSR) effect. An effective charge transfer from N-BOC to GO was demonstrated by the much weakened photoluminescene intensity of the N-BOC-GO composite. This work highlights the potential application of GO-based photocatalysts in air purification.
Hierarchical microspheres of a graphene oxide (GO) coupled to N-doped (BiO)2CO3 composite (N-BOC-GO) was synthesized by a simple hydrothermal approach. The N-BOC-GO composite gave enhancement in photocatalytic activity compared to the pure BOC and N-BOC samples. With 1.0 wt% GO, 62% NO removal was obtained with N-BOC-GO. The factors enhancing the photocatalytic performance were the high electron-withdrawing ability and high conductivity of GO and improved visible light-harvesting ability of N-BOC-GO with a 3D hierarchical architecture due to the surface scattering and reflecting (SSR) effect. An effective charge transfer from N-BOC to GO was demonstrated by the much weakened photoluminescene intensity of the N-BOC-GO composite. This work highlights the potential application of GO-based photocatalysts in air purification.
2016, 37(5): 769-777
doi: 10.1016/S1872-2067(15)61076-2
Abstract:
A carbon solid acid catalyst was prepared by the sulfonation of partially carbonized peanut shell with concentrated H2SO4. The structure and acidity of the catalyst were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, and elemental analysis, which showed that it was an amorphous carbon material composed of aromatic carbon sheets in random orientations. Sulfonic acid groups were present on the surface at a density of 0.81 mmol/g. The carbon solid acid catalyst showed better performance than HZSM-5 for the esterification of cyclohexene with formic acid. At a 3:1 molar ratio of formic acid to cyclohexene, catalyst loading of 0.07 g/mL of cyclohexene, and reaction time of 1 h at 413 K, the cyclohexene conversion was 88.4% with 97.3% selectivity to cyclohexyl formate. The carbon solid acid catalyst showed better reusability than HZSM-5 because its large pores were minimally affected by the accumulation of oligomerized cyclohexene, which deactivated HZSM-5. The activity of the carbon solid acid catalyst decreased somewhat in the first two recycles due to the leaching of polycyclic aromatic hydrocarbon containing -SO3H groups and then it remained constant in the following reuse.
A carbon solid acid catalyst was prepared by the sulfonation of partially carbonized peanut shell with concentrated H2SO4. The structure and acidity of the catalyst were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, and elemental analysis, which showed that it was an amorphous carbon material composed of aromatic carbon sheets in random orientations. Sulfonic acid groups were present on the surface at a density of 0.81 mmol/g. The carbon solid acid catalyst showed better performance than HZSM-5 for the esterification of cyclohexene with formic acid. At a 3:1 molar ratio of formic acid to cyclohexene, catalyst loading of 0.07 g/mL of cyclohexene, and reaction time of 1 h at 413 K, the cyclohexene conversion was 88.4% with 97.3% selectivity to cyclohexyl formate. The carbon solid acid catalyst showed better reusability than HZSM-5 because its large pores were minimally affected by the accumulation of oligomerized cyclohexene, which deactivated HZSM-5. The activity of the carbon solid acid catalyst decreased somewhat in the first two recycles due to the leaching of polycyclic aromatic hydrocarbon containing -SO3H groups and then it remained constant in the following reuse.
