Qiong Xu

Microwave-assisted hydrolysis of crystalline cellulose catalyzed by biomass char sulfonic acids

The development of an environmentally benign process for the hydrolysis of cellulose into reducing sugars can be one of the key technologies for making full use of cellulosic biomass in the future. Here, a biomass char sulfonic acid (BC-SO3H)-catalyzed hydrolysis of cellulose in water was achieved under microwave irradiation. The BC-SO3H catalysts prepared cheaply from natural bamboo, cotton and starch, showed a much higher turnover number (TON, 1.33-1.73) for this reaction compared to a dilute H2SO4 solution (TON, 0.02), which was likely due to their strong affinity to β-1,4-glycosidic bonds of cellulose. In addition, microwave irradiation played key roles in activating cellulose molecules and strengthening particle collision, which can lead to a remarkable acceleration effect on this heterogeneously catalytic process.

Ionic liquid-functionalized biochar sulfonic acid as a biomimetic catalyst for hydrolysis of cellulose and bamboo under microwave irradiation

The development of a highly efficient and environmentally friendly process for the hydrolysis of cellulose into reducing sugars could be one of the key technologies for large-scale use of cellulosic biomass in the future. In order to pursue this goal, an ionic liquid (IL)-grafting biochar sulfonic acid catalyst (BC-SO3H-IL) was proposed and conveniently prepared with bamboo powder as a carbon resource and 1-(trimethoxy propyl silane)-3-methyl imidazolium chloride as the IL. Its catalytic performance for the heterogeneous hydrolysis of cellulose and bamboo was checked under microwave irradiation. The designed BC-SO3H-IL catalyst was found to show much higher turnover number (TON, 3.22–6.23 for cellulose and 0.26–2.53 for bamboo) and excellent repeatability for this hydrolysis compared to the corresponding biochar sulfonic acid (BC-SO3H, TON, 1.51–1.81 for cellulose and 0.14–1.33 for bamboo). This is likely to be because the IL groups flexibly joined to biochar sulfonic acid, like cellulose binding domain (CBD) of cellulase, efficiently breaks in the hydrogen bonding network of cellulose molecules. On the other hand, they probably play a harmonious role in the SO3H groups (as a catalysis domain (CD) of cellulase) catalyzing cleavage of the β-1,4 glycosidic bonds of cellulose, as supported by TGA characterization and catalytic reaction results.

Biochar sulfonic acid immobilized chlorozincate ionic liquid: an efficiently biomimetic and reusable catalyst for hydrolysis of cellulose and bamboo under microwave irradiation

A chlorozincate ionic liquid-functionalized biochar sulfonic acid (BC-SO3H-IL-Zn) was designed and conveniently prepared via multistep processes, involving the syntheses of biochar sulfonic acid (BC-SO3H) and 1-trimethoxysilylpropyl-3-methylimidazolium chloride (IL)-ZnCl2 (IL-Zn), followed by grafting the IL-Zn onto BC-SO3H. The proposed catalyst was found to show a much higher turnover number (TON, 5.91 for cellulose and 1.78 for bamboo) for the microwave-assisted hydrolysis of cellulose and bamboo to reducing sugars (RSs) in water compared to the corresponding IL-functionalized BC-SO3H (BC-SO3H-IL, TON, 3.23 for cellulose and 0.46 for bamboo) and BC-SO3H (TON, 1.51 for cellulose and 0.15 for bamboo). Furthermore, it, like BC-SO3H-IL, possessed an excellent repeatability for cellulose hydrolysis. The excellent catalytic performance of BC-SO3H-IL-Zn is likely due to the following reasons: Firstly, the introduction of ZnCl2 bestows the catalyst with a delignification function. Secondly, in comparison with the OH groups of BC-SO3H, the IL and especially IL-Zn groups flexibly bound to BC-SO3H, like cellulose binding domain of cellulose, show an stronger affinity for cellulose molecules, on the other hand, they play a better synergistic role and improved acidity in the SO3H groups (as a catalysis domain of cellulase) catalyzing cleavage of the β-1,4-glycosidic bonds of cellulose, as supported by the adsorption experiments of catalysts to oligosaccharides, their thermogravimetric analysis and catalytic reaction results.Graphical AbstractChlorozincate ionic liquid functionalized biochar sulfonic acid (BC-SO3H-IL-Zn) proposed by us was found to be an efficiently biomimetic catalyst for the heterogeneous hydrolysis of cellulose and lignocelluloses to RSs and 5-hydroxymethyl furfural (5-HMF) under microwave irradiation.

A non-nitric acid method of adipic acid synthesis: organic solvent- and promoter-free oxidation of cyclohexanone with oxygen over hollow-structured Mn/TS-1 catalysts

A novel hollow-structured Mn/TS-1 catalyst has been reported as a non-nitric acid route for adipic acid production from oxidative cleavage of cyclohexanone. The method generates adipic acid in high yields with molecular oxygen under organic solvent- and promoter-free conditions. The hollow nature of the catalyst with large intra-particle voids facilitates the diffusion of bulky molecules to the internal catalytic site and increases the catalyst activity. The advantage of this catalyst is its reusability with almost consistent reactivity, thereby making it viable for industrial applications.

A novel route for preparation of Mn-containing hollow framework TS-1, and its selective allylic oxidation of cyclohexene

A new manganese-containing hollow framework TS-1 (MTS-1) was prepared via simple recrystallization of traditional TS-1 in the presence of tetrapropylammonium hydroxide (TPAOH) and manganese(III)–acetylacetonate, and its catalytic performance was tested for aerobic oxidation of cyclohexene without any solvents. This hollow bimetal TS-1 catalyst is more active than catalysts containing Mn or Ti solely; the formation of metal framework sites may be responsible for increased activity. The characterization techniques such as UV-vis, FT-IR, Raman, XRD, N2-adsorption, TEM, and XPS confirm the incorporation of Mn and Ti in the zeolite framework sites. This hollow catalyst shows high catalytic activity and stability (ten cycles) in the oxidation of cyclohexene, and demonstrates the potential of TS-1 catalysts for use in aerobic oxidations.

Consideration of roles of commercial TiO2 pigments in aromatic polyurethane coating via the photodegradation of dimethyl toluene-2,4-dicarbamate in non-aqueous solution

Dimethyl toluene-2,4-dicarbamate (2,4-TDC) was selected as a model compound for aromatic polyurethane to investigate the photo-chemical behavior of commercial TiO2 pigments in non-aqueous solution. The UV–Visible spectrometry analysis results showed that the UV-shielding ability of the rutile TiO2 pigment was better than that of the anatase TiO2 pigment. Photodegradation experiments suggested that the photodegradation of 2,4-TDC was retarded by rutile TiO2 pigment, while accelerated by anatase TiO2 pigment. With the help of the degradation intermediates during the photodegradation process and calculated data, such as point charges and bond length, the preliminary photodegradation mechanism of 2,4-TDC was also briefly elucidated, including the addition of hydroxyl radicals and the cleavage of the carbamate side chain. Additionally, the photodegradation of 2,4-TDC was used to evaluate the photoreactivity of TiO2 pigments, this is proved to an efficient approach with potential application in industry.

Highly efficient and recyclable alkylammonium hydrosulfate catalyst for formation of bisphenol F by condensation of phenol with formaldehyde

Several C1–C4 alkylammonium hydrosulfates [R3NH][HSO4] have been conveniently prepared from the cheap raw materials sulfuric acid and alkylamines. Their acidities were measured by chemical titration and determined using UV-vis spectroscopy with a basic indicator 4-nitroaniline. The catalytic performance of these hydrosulfates for the condensation of phenol with formaldehyde to bisphenol F (BPF) was evaluated in detail on a batch reactor. The results indicated that the proposed catalysts are very active for such condensation due to its homogeneous catalysis characteristics in reaction conditions. Among the catalysts examined, [H3NCH2CH2NH3][HSO4]2 shows the best catalytic performance and it can achieve a complete conversion of formaldehyde, providing a higher than 90% selectivity for BPF under the optimal conditions. Furthermore, the catalyst can be recovered from the reaction mixture via an azeotropic distillation with cyclohexane to remove water and then filtration and used repeatedly six times almost without loss of activity, showing an excellent reusability. It is suggested that the present catalytic process combines the characteristics of a homogenized reaction and heterogenized recovery so might provide a highly-efficient, environmentally-friendly and low-cost route for synthesis of bisphenol F.