Preparation Of Sulfonated Mesoporous Carbon Materials And Their Applications

Mesoporous carbon materials have various potential applications in the fields of adsorption, separation, catalysis, electronic devices, energy storage, etc, owing to their benign characteristics such as the high surface area, large pore volume, uniform mesoporous structures and good thermal stability. However, the widely applications of mesoporous carbons were restricted especially in catalysis because of their hydrophobic and inert nature. It is reported that the introduction of active functional groups on the surface of mesoporous materials can change the hydrophilic and hydrophobic of materials. Consequently, the modified materials possess more specific functions and play a greater role in multiple areas.Significant efforts have been devoted to the sulfonation of mesoporous carbons, and their extensive applications in catalysis have been reported. This thesis is about the preparation of sulfonated carbon nanocage material and its application research as a carbon-based solid acid catalyst in the esterification and cross-Aldol condensation. Specific content is divided into following three parts:1. A series of three-dimensional cage type mesoporous carbons (CKTs) with well ordered pore structure, high specific pore volume, specific surface area and tunable pore diameter have been used in adsorption and separation. The three-dimensional carbon nanocages, as new mesoporous carbon materials, are made up of connected cage of each other. The connected structure of pore is benefit to mass transport in chemical reaction, and each cage is like a micro-reactor to help the reaction to proceed in a short time. However, the hydrophobic and inert nature of mesoporous carbons can be unfavorable for direct applications.In this paper, the novel sulfonated carbon nanocages are successfully prepared through the reaction of sulfophenyl radical in-situ generated from 4-aminobenzenesulfonic acid and isoamyl nitrite. The sulfonated carbon nanocage material (S-CKT) was characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, small-angle X-ray powder diffraction and nitrogen sorption measurements. The results showed that the S-CKT still possess high specific surface area (787 m2/g) and uniform mesoporous (pore diameter 4.7 nm) structures, although the structure of S-CKT is slightly disorder, compared with its unsulfonated precursor. In addition, S-CKT has higher density of the SO3H group (1.53 mmol/g) and presents good suspension in water and some highly polar solvents. The results indicated that surface sulfonation of carbon nanocage materials have changed its character from hydrophobicity to hydrophilicity, and enable them to be available as a good solid acid catalyst.2. Esterification is an important reaction in synthesizing fine organic chemical products, such as solvents, resins, coatings, flavors, fragrances, cosmetics, Pharmaceuticals, surfactants, etc. Currently, the liquid acid catalysts are still used in esterification reaction in industry. These techniques bring about not only environmental contamination, but also insuperable shortcomings such as corrosion of equipments, lower selectivity of target products and so on. Instead of liquid acid with solid acid catalysts not only overcomes the above shortcomings, but also consists with the principles of green chemistry and the zero environmental pollution. Recently, there are already many reports about solid acid catalysts for esterification reaction. However, some of the solid acid catalysts reported still present various drawbacks such as low catalytic activity or poor recycling.S-CKT is used as the carbon-based solid acid catalyst to study its catalytic properties in the esterification in this thesis. Firstly, the catalytic activities of S-CKT were examined for the esterification of acetic acid with ethanol as the model reaction. Compared with other acid catalysts (acid resin and sulfuric acid), the S-CKT has better catalytic activity with high conversion and good recycling at 75℃. The investigation to the cycle number of S-CKT showed that the catalyst still has certain catalytic activity after being recycled for four runs. Finally, the adaptability of catalyst was tested through the esterification of various organic acids with alcohols at optimal reaction conditions. The result from the determination of gas chromatography to the reaction mixture indicated high selectivity and good yields (70-95%) to various esters were obtained. In this reaction, the S-CKT presented several advantages including simple experimental procedures, higher selectivity and reuse.3. The Aldol condensation reaction is recognized to be one of the most important carbon-carbon bond-forming processes in organic synthesis. It is well known that the catalyst of Aldol condensation can be either base or acid. In last section of this thesis, S-CKT, as a carbon-based solid acid catalyst, was used in the cross-Aldol condensation reactions of ketones with aromatic aldehydes under solvent-free condition. In here, the cross-Aldol condensation of cyclohexanone and benzaldehyde was used as a model reaction to optimize reaction conditions. Comparing with other solid acid catalysts (acid resin and p-tolenesulfonic acid), the experiment result suggested that S-CKT possess a better catalytic activity to the cross-Aldol condensation. The investigation of the reuse of S-CKT showed that the catalyst could be recycled at least six runs without obviously decrease in catalytic activity. Finally, the adaptability of catalyst was tested through expanding reaction substrates at optimal reaction conditions. The results indicated that all condensation reactions can be completed within short reaction time (30-120 min) and in high yield (72-92%). In this catalysis reaction, the S-CKT presented several advantages including shorter reaction time, simple experimental procedures, reusing of the catalyst and environmental friendly.