Study On The Preparation And Catalytic Properties Of Solid Char-based Acid/basic Catalytic Materials

As environmental friendly catalytic material,solid catalysts have the advantages of high selectivity,good catalytic performance,easily being recycled,and good recyclability in catalyzing various types of reactions.Biomass resources are mainly derived from the photosynthesis of plant materials,and have the advantages of renewable and abundant reserves,so they are received more and more attentions.The use of biomass resources as raw materials for the preparation of solid catalyst materials is conducive to the rational use of biomass resources,reducing environmental pollution and is accorded with the requirements of green chemistry,which has been attracted more and more attentions by researchers.In this paper,a series of preparing methods for carbon-based solid acid/base catalysts were explored by using activated carbon and bamboo powders as raw materials,and their structure and catalytic properties were studied,which was mainly included the followings.(1)By using activated carbon as a raw material after oxidation with nitric acid,an oxidized activated carbon with a surface carboxylic acid functional group content of 0.78 mmol/g was prepared.The carboxyl group on the surface of the oxidized activated carbon was reacted with ethylenediamine,then a novel imidazole-based activated carbon solid base AC-N was successfully prepared.When the concentration of HNO₃was 12 mol/L,the oxidation temperature was 100^oC,the oxidation time was 8 h,and the amination temperature was 120^oC,the content of the basic functional group on the surface of the imidazole-based activated carbon was 0.96 mmol/g.It was proved by FT-IR,XPS and other characterization methods that the basic group was mainly imidazole structure.The specific surface area of the imidazole-based activated carbon was 418 m²/g,and the hydrophilicity was superior to that of activated carbon.The catalytic performance of AC-N in Michael addition was investigated by the reaction of furfural Micheal as a probe.The conversion of furfural was 87.1%and the selectivity was 99.0%when the catalyst was used at 2%under 120°C for 7 h.The catalytic performance was better than the common alkali like KOH,Ca O,Ce CO₃and methyl imidazole and it was showed good reusability and substrate suitability.(2)With the prepared imidazole-based activated carbon as raw material,a novel imidazole-based activated carbon solid acid material AC-N-HSO₄ with surface acidic functional group was prepared after being impregnated with sulfuric acid.When the concentration of HNO₃was 12 mol/L,the amination temperature was 120°C,the concentration of dilute sulfuric acid was 4 mol/L,and the leaching time of sulfuric acid was 4 h,the surface acid content of prepared AC-N-HSO₄ was 0.85mmol/g,and the specific surface area was 384 m²/g.Catalytic performance of AC-N-HSO₄ in acetal(ketone)was investigated by using benzaldehyde condensed ethylene glycol as probe.When the reaction temperature was 80°C,the reaction time was 5 h,the catalyst dosage was accounted for 5%of benzaldehyde,and the molar ratio aldol to benzaldehyde was 1.75,the conversion of benzaldehyde was 99.4%.After 10 times of use,the conversion of benzaldehyde remained above99%,and it was suitable for different substrates in the aldehyde(ketone)reaction.AC-N-HSO₄ was showed good catalytic performance in both ethanoloyl etherolysis and n-butyl acetate esterification.(3)With bamboo powders as raw material,after carbonization,ammonium persulfate oxidation,and ethylenediamine amination,BC-N-SO₃H was prepared after sulfonation with chlorosulfonic acid as sulfonating agent.When the concentration of chlorosulfonic acid/dichloromethane was 15%and sulfonated at room temperature for 8h,the sulfonic acid group of prepared BC-N-SO₃H was 1.23 mmol/g.After modification,the hydrophilicity of BC-N-SO₃H was obviously enhanced,and the stability of the carbon skeleton was also improved to some extent.The catalytic performance of BC-N-SO₃H in the esterification reaction was studied by esterification of n-butanol acetate as a probe reaction.The results showed that when the molar ratio of acid to alcohol was 1:2,the amount of acid in the catalyst was 0.3%of the acetic acid molar,the reaction temperature was 117°C,and the reaction time was 5 h,the conversion of acetic acid was 95.11%.After being repeated use for 5 times,the conversion of acetic acid was still 87.4%.BC-N-SO₃H was also showed good catalytic performance and catalytic stability in the reaction of acetal(ketone)and epoxycyclohexane alcoholysis.(4)With activated carbon or bamboo char as raw materials,modified activated carbon AC-Ph and modified bamboo char BC-Ph with sulfonable site were prepared after oxidizing with nitric acid and modified with bromobenzene.Then novel carbon-based solid sulfonic acid AC-Ph-SO₃H and BC-Ph-SO₃H were prepared by sulfonation with concentrated sulfuric acid.When the mass fraction of bromobenzene was 10%,the modification time was 5 h,and the sulfonation temperature was 150°C,the surface sulfonic acid content of prepared AC-Ph-SO₃H and BC-Ph-SO₃H were 0.64 mmol/g and 1.45 mmol/g,respectively.The stability of the prepared carbon sulfonic acid in the solvent was found to be gradually reduced with the polarity of the solvent increased.The catalytic effect of AC-Ph-SO₃H in the biodiesel production of methyl palmitate was investigated.When the reaction time was 6 h,the acidity of the catalyst was 2.5 mol%of the palmitic acid and the methanol/palmitic acid molar ratio was 40,the conversion of palmitic acid was 95.2%,while the conversion of palmitic acidification of its precursors AC,AC-O and AC-Ph was only about 4.5%.(5)With bamboo powders as raw material,oxidized bamboo charcoal BC-O with surface carboxylic acid functional group content of1.32 mmol/g was prepared after carbonization and ammonium persulfate oxidation.Bamboo charcoal material with sulfonated benzene ring on the surface was prepared with the carboxy group on BC-O surface decarboxylated with benzoic acid under electrochemical treatment,and bamboo charcoal solid sulfonic acid BC-Ph-SO₃H was prepared by sulfonation with concentrated sulfuric acid.When the electrolysis voltage was 5.0 V,the benzoic acid/methanol concentration was 0.3mmol/g,and the electrolysis time was 4 h,the surface sulfonate functional group of BC-Ph-SO₃H was 1.28 mmol/g.By studying the stability of BC-Ph-SO₃H in cyclohexane,ethanol,water,toluene,acetic acid and other solutions refluxed for 20 h,it was found that the sulfonic acid group of BC-Ph-SO₃H was stable in the less polar solvent,while the lost in higher polar solvent acetic acid was 60.2%.BC-Ph-SO₃H was showed good catalytic performance and reusability in the reaction of benzaldehyde condensed ethylene glycol,n-butanol acetate esterification and epoxycyclohexane alcoholysis.