| Carbon-based non-metallic catalysts have emerged as promising alternatives of metal-based catalyst for solving pollution problems and contributing to the sustainable development of green chemical engineering.Carbon nanomaterials possess rich surface chemical groups and defective structures which can act as active centres for catalysis,adsorbing and activating substrate molecules.However,carbon catalytic materials in the form of ultrafine powders tend to not only cause mass transfer problems in the reactor but also increase the subsequent separation costs.Therefore,it is necessary to prepare monolithic carbon-based catalysts that are more suitable for the reactor.In this work,carbon cloth with three-dimensional structure,thermal stability,acid and alkali resistance and mechanical stability was selected as the substrate,and the surface modification of carbon cloth was carried out by a one-step hydrothermal method coupled with an assisted rapid cooling microwave treatment to prepare highly stable structured non-metallic carbon-based catalysts,which were applied to the liquid phase oxidation reaction of benzyl alcohol.The reaction process was investigated in a high-gravity environment.The main studies of this paper are as follows:(1)The oxygen modification of the carbon cloth was effectively achieved by a microwave treatment assisted by rapid cooling under air atmosphere in order to graft oxygen-containing functional groups on the surface of the carbon cloth,and to increase surface defects and change its hydrophobicity.The effect of different conditions on the doping results was investigated using thiourea as the source of sulphur and nitrogen and boric acid as the source of boron to determine the optimal doping conditions.The elemental ratios of carbon,oxygen,sulphur and nitrogen in the nitrogen double-doped materials synthesised under these conditions were 77.85%,11.14%,4.28%and 6.73%,respectively.The elemental content of carbon,oxygen and boron of the synthesized boron-doped materials were 76.24%,20.02%and 3.74%,respectively.(2)The catalytic performance of the heteroatom-doped oxygen-modified carbon cloth was evaluated using the liquid-phase oxidation of benzyl alcohol(BzOH)to benzaldehyde(BzH)as the target reaction,and the optimal reaction conditions were determined.Under these conditions,the BzOH conversion was 19.01%and the BzH selectivity was 95.59%for the experimental group with the addition of sulfur and nitrogen double-doped oxygen-modified carbon cloth;the BzOH conversion was 17.20%and the BzH selectivity was 93.60%for the experimental group with the addition of boron-doped oxygen-modified carbon cloth.(3)The adsorption structure,charge density difference and difference in adsorption energy of benzyl alcohol and hydrogen peroxide(H2O2)on the carbon cloth model doped with sulfur and nitrogen species and undoped carbon cloth model were calculated by density functional theory.The results showed that the adsorption energy of BzOH and H2O2 molecules on the doped carbon cloth was higher than that on the undoped carbon cloth.The kinetic study of the H2O2 activation decomposition process on the surface of both carbon cloths showed that H2O2 decomposed into O*actives on the surface of the doped carbon cloths with a lower energy barrier(0.46 eV→0.31 eV),which made the reaction easier,confirming that the synergistic effect of the double doping of sulfur and nitrogen had a great effect on the adsorption and activation of the reactants and oxide molecules.(4)A study on the catalytic liquid-phase oxidation of benzyl alcohol to benzaldehyde based on a high-gravity rotating packed bed(RPB)was carried out.Optimal process conditions in RPB were obtained,under which the conversion of BzOH was 29.30%for the experimental group with the addition of sulfur and nitrogen double-doped oxygen modified carbon cloth and 28.11%for the experimental group with the addition of boron doped oxygen modified carbon cloth. |
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