Gai Miao

One-pot catalytic conversion of microalgae (Chlorococcum sp.) into 5-hydroxymethylfurfural over the commercial H-ZSM-5 zeolite

Herein, we report a one-pot approach to produce HMF from aquatic microalgae (Chlorococcum sp.) with a yield up to 48.0% under mild reaction conditions (200 °C, 2 h) over the commercial cheap H-ZSM-5 catalyst. Conversion of microalgae to HMF involved three steps: (1) degradation of microalgae to carbohydrates; (2) hydrolysis of polysaccharides to glucose and mannose; (3) their isomerization to fructose on Lewis acid sites and its further dehydration to HMF over Bronsted acid sites. Proteins and lipids in microalgal cells play an important role in stabilizing HMF in water. Ball-milling pretreatment or addition of another organic solvent enhanced the productivity of HMF from microalgae. Besides, this cheap H-ZSM-5 catalyst also demonstrated excellent stability, and a slight loss of its activity can be easily recovered by simple calcination treatment.

Efficient one-pot production of 1,2-propanediol and ethylene glycol from microalgae (Chlorococcum sp.) in water

The catalytic valorization of microalgae, a sustainable feedstock to alleviate dependence on fossil fuel and offset greenhouse gases emissions, is of great significance for production of biofuels and value-added chemicals from aquatic plants. Here, an interesting catalytic process is reported to convert microalgae (Chlorococcum sp.) into 1,2-propanediol (1,2-PDO) and ethylene glycol (EG) in water over nickel-based catalysts. The influences of reaction temperature, initial H2 pressure and reaction time on the product distribution were systematically investigated by using a batch reactor. Under optimal reaction conditions (at 250 °C for 3 h with 6.0 MPa of H2 pressure), microalgae were directly and efficiently converted over a Ni–MgO–ZnO catalyst and the total yield of polyols was up to 41.5%. The excellent catalytic activity was attributed to the smaller size and better dispersion of Ni particles on the MgO–ZnO supporter based on the characterization results as well as its tolerance to nitrogen-containing compounds. Besides, the reaction pathway was proposed based on the formation of reaction intermediates and the results of model compound conversion.

Preparation of N-doped activated carbons with high CO2 capture performance from microalgae (Chlorococcum sp.)

N-Doped activated carbons with high CO2 adsorption capacity have been prepared from sugar-rich microalgae (Chlorococcum sp.) feedstock via simple hydrothermal carbonization coupled with KOH activation or NH3 modification. The KOH activated carbons exhibit higher CO2 capture performance compared with the ones treated by NH3. The nitrogen-enriched hydro-char derived from microalgae was activated with KOH at 700 °C to improve the textural characteristics (surface area, pores size, and total pore volume), and the resulting carbon showed a highly ordered structure with a surface area of 1745 m2 g−1, and narrow pore size distribution with the maxima peak located in the micropore range (<1.0 nm). The activated carbon exhibited CO2 uptakes of 4.03 and 6.68 mmol g−1 at 25 °C and 0 °C, respectively. Further XPS analysis revealed the effective pyridonic-nitrogen species (up to 58.32%) on the carbon surface favored a higher CO2 capture capacity. The N-doped activated carbons displayed rapid adsorption kinetics with ultrahigh selectivity for CO2 over N2 (up to 11 at 25 °C), and no obvious decrease in the CO2 uptake capacity was observed even after seven cycles, which may be due to the dominant physisorption between CO2 and the surface of carbon.

Field emission performance of hierarchical ZnO nanocombs

Hierarchical ZnO nanocombs (ZnO NCs) with a high field enhancement factor were synthesized on Si substrates by the chemical vapor deposition method. The X-ray diffraction (XRD) pattern indicates that ZnO NCs have a hexagonal wurtzite structure. Electric field emission (FE) from hierarchical ZnO NCs was realized. The turn-on field was measured to be 3.6 V mu m(-1), and the field enhancement factor of the hierarchical ZnO NCs was estimated to be 3490. The high field enhancement factor is derived from the special morphology of the product. This kind of hierarchical ZnO NCs has a great potential for field emission displays.

Catalytic conversion of glucose into alkanediols over nickel-based catalysts: a mechanism study

The conversion of isotope-labeled glucose (D-1-13C-glucose) into alkanediols was carried out in a batch reactor over a Ni–MgO–ZnO catalyst to reveal the C–C cleavage mechanisms. The unique role of the MgO–ZnO support was highlighted by 13C NMR and GC-MS analysis qualitatively and the MgO–ZnO favored isomerization of glucose to fructose. 13C NMR, GC-MS and HPLC analysis demonstrated that the C1 position of ethylene glycol, the C1 and C3 positions of 1,2-propanediol and the C1 position of glycerin were labeled with 13C, which is attributed to a C–C cleavage at D-1-13C-glucoses corresponding positions through retro-aldol condensation. A hydrogenolysis followed by hydrogenation pathway was proposed for glucose converted into alkanediols at 493 K with 6.0 MPa of H2 pressure over Ni based catalysts.

Formic Acid-Induced Controlled-Release Hydrolysis of Microalgae (Scenedesmus) to Lactic Acid over Sn-Beta Catalyst

Formic acid-induced controlled-release hydrolysis of sugar-rich microalgae (Scenedesmus) over the Sn-Beta catalyst was found to be a highly efficient process for producing lactic acid as a platform chemical. One-pot reaction with a very high lactic acid yield of 83.0 % was realized in a batch reactor using water as the solvent. Under the attack of formic acid, the cell wall of Scenedesmus was disintegrated, and hydrolysis of the starch inside the cell was strengthened in a controlled-release mode, resulting in a stable and relatively low glucose concentration. Subsequently, the Sn-Beta catalyst was employed for the efficient conversion of glucose into lactic acid with stable catalytic performance through isomerization, retro-aldol and de-/rehydration reactions. Thus, the hydrolysis of polysaccharides and the catalytic conversion of the monosaccharide into lactic acid was realized by the combination of an organic Brønsted acid and a heterogeneous Lewis acid catalyst.