Keke Hou

Efficient synthesis and sulfonation of ordered mesoporous carbon materials

Ordered mesoporous carbons (OMCs) with hexagonal structure were efficiently synthesized via cooperative self-assembly of phenol/formaldehyde resol and surfactant F127 under acidic aqueous conditions. Induced by HCl, a gel phase mainly containing phenol/formaldehyde resol and F127 was obtained within several hours. X-ray diffraction (XRD), transmission electron microscope (TEM) and nitrogen adsorption isotherms indicated that the synthesized samples possess 2-D hexagonal mesostructure. The influence of the synthesis conditions, including acid concentration and mass ratio of resol to F127, was investigated. When the acid concentration was fixed in the range of 0.6-2.0 M and the mass ratio of resol to F127 in the range of 3.5-4.0, highly ordered mesoporous carbon could be synthesized. The synthesized OMCs could be easily sulfonated in concentrated sulfuric acid at elevated temperature. The results indicate that the mesostructural stability and the content of the surface sulfonic acid (SO(3)H) groups depend mainly on the pyrolysis temperature of the OMCs and the sulfonation temperature, suggesting that the combination of pyrolysis and sulfonation temperature is essential for developing OMCs with high densities of SO(3)H groups.

Mesostructure-tunable and size-controllable hierarchical porous silica nanospheres synthesized by aldehyde-modified Stöber method

Mesostructure-fine-tuned and size-controlled hierarchical porous silica nanospheres were synthesized by aldehyde-modified Stober method in the TEOS–CTAB–NH3·H2O–aldehyde system. The samples were characterized by XRD, N2 adsorption–desorption isotherms, SEM, TEM and TG analysis. The results indicate that the particle size of the micro/mesoporous silica nanospheres synthesized with acetaldehyde as a co-solvent can be controlled from 40 to 850 nm by regulating the molar ratio of acetaldehyde to water and the initial pH of the synthesis solution. When propionaldehyde or butyraldehyde was used as a co-solvent, hierarchical porous silica nanospheres with large cone-like cavities and small mesopores in the cavity wall were synthesized; the diameter of the flower-like nanospheres is less than 130 nm. The hierarchical pore structure of the flower-like silica nanospheres can be fine-tuned by controlling the polymerization of butyraldehyde by the synthesis temperature from 27 to 100 °C, both the depth and opening diameter of the cone-like cavities can be fine-tuned from 40 to 2 nm; simultaneously, the small mesopores templated by CTAB become more ordered.

Effect of ZSM-5 zeolite morphology on the catalytic performance of the alkylation of toluene with methanol

Abstract A series of ZSM-5 zeolites, with the morphologies of sphere, sphere with cubic particles on the surface, and cubic particles, were synthesized by hydrothermal method using n-butylamine as the template, assisted by the addition of NaCl and crystal seed. X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray fluorescence (XRF) and temperature-programmed desorption of ammonia (NH3-TPD) were used to characterize these samples. The samples were tested with toluene methylation reaction. The modified sample composed of spherical particles with 3 μm crystal particles on the surface had a para-xylene selectivity of 95% and maintained 79% of the initial conversion after running the reaction for 50 h. This modified sample showed the best stability among the tested three modified samples.

The influence of the acid source on the structural and anti-oxidation properties of ordered mesoporous carbons

The synthesis of ordered mesoporous carbons (OMCs) was carried out under acidic aqueous conditions, by cooperative self-assembly of phenol–formaldehyde resol and surfactant F127. The influence of the acid source on the structural and anti-oxidation properties of the OMCs was investigated. The acids (HCl, HNO3, H3PO4 and H2SO4) used in the synthesis are sufficient to induce the self-assembly of resol and F127 to form the mesophase, while the final products carbonized at 600 °C show different structural properties. This was mainly due to the different decomposition behaviors of the surfactant during the carbonization process, which depends on the nature of the anions from the acids. After oxidization in acidic (NH4)2S2O8 solution, the H3PO4 catalyzed sample undergoes a minimum reduction in surface area and pore volume, and exhibits a larger adsorptive capacity for Co2+, compared with those using HCl and HNO3 as catalyst. This was related to the incorporation of the phosphorus atoms in the sample with H3PO4 as catalyst, which is in favour of increasing the carbonization degree of the sample, and they can also act as adsorptive sites for Co2+.

Zirconium-promoted hydrothermal synthesis of hierarchical porous carbons with ordered cubic mesostructures under acidic aqueous conditions

The zirconium-promoted hydrothermal synthesis of hierarchical porous carbons with ordered cubic mesostructures (Im3m) under acidic aqueous conditions was first presented using F127 as a template, pre-synthesized resol as carbon precursor, hydrochloric acid as catalyst and zirconium oxychloride as an assistant agent. The effects of the zirconium oxychloride assistant, acid concentration, hydrothermal treatment time and treatment conditions on the structural properties of the hierarchical porous carbons were investigated. The results indicate that the zirconium polyoxo oligomers in the acid synthesis solution can suppress the condensation of the resols at a moderate rate around the micelles of F127 to form mesosporous carbon. Under hydrothermal conditions, zirconium polyoxo oligomers could interact with the polyethylene (PEO) chains of F127 through hydrogen bonding, increasing the hydrophilic/hydrophobic volume ratio and the interfacial curvature to promote the phase transformation of the mesostructure from 2-D hexagonal to 3-D body-centered cubic. With suitable acid concentration (1.0–3.0 M), hierarchical porous carbons with ordered cubic mesostructures can be synthesized in 8 h on a large scale. After activation with KOH, the equilibrium CO2 adsorption capacities of the resulting materials at 1 atm were in the range of 3.3–4.1 mmol g−1 at 25 °C and 4.8–6.6 mmol g−1 at 0 °C.