Qihua Yang

Hierarchical mesoporous organic polymer with an intercalated metal complex for the efficient synthesis of cyclic carbonates from flue gas

CO2 capture and utilization is one of the most attractive and challenging topics of the twenty-first century. The direct conversion of CO2 using flue gas as a feedstock is an energy saving process, but it has been rarely reported. Herein, we report an efficient CO2 cycloaddition reaction using diluted gas (20% CO2 and 80% N2, simulating flue gas) as a feedstock, catalyzed by a 2,2′-bipyridine zinc(II) based hierarchical meso/microporous polymer, Bp-Zn@MA. Bp-Zn@MA, constructed via a template-free polycondensation reaction without using any catalyst, can efficiently catalyze the cycloaddition of propylene oxide with a TOF of up to 1580 h−1 (100 °C) and 8041 h−1 (150 °C), using diluted gas and pure CO2, respectively. This is among the best performing solid catalysts ever reported for the CO2 cycloaddition reaction. The high catalytic activity of the polymer, especially when diluted CO2 was employed, can be mainly attributed to its hierarchical meso/microporous structure, which contains mesopores for facilitating the diffusion of reactants and micropores for CO2 enrichment. The construction of this hierarchical structured porous material provides an efficient approach for realizing CO2 conversion using flue gas as a feedstock.

Highly active water oxidation on nanostructured biomimetic calcium manganese oxide catalysts

Water oxidation is a crucial reaction step in solar-to-chemical energy conversion processes such as photocatalytic water splitting and carbon dioxide reduction. In natural photosynthesis, the water oxidation reaction is catalyzed by μ-oxido-Mn4Ca clusters in photosystem II (PSII). Herein, we report the fabrication of nanostructured biomimetic calcium manganese oxides (CaxMnOy) via a simple process under mild conditions utilizing H2O2 as an oxidant and TMAOH (tetramethylammonium hydroxide) as an alkaline source. CaxMnOy materials with x higher than 0.26 are composed of nanoparticles with particle sizes ranging from 15 to 30 nm according to the result of HRTEM. The results of X-ray absorption fine structure (XAFS) indicate that calcium manganese oxides have similar structural motifs to the catalytically active site for water oxidation in PSII. It was also found that the content of Ca and the concentration of H2O2 in the initial mixture could affect the crystallinity and the average Mn valence state of calcium manganese oxides. Water oxidation experiments for both chemical and photocatalytic systems suggest that the disordered structure of calcium manganese oxides and a modest valence state of Mn (+3.7 to +3.8) are necessary for achieving high activity. Our method provides a strategy for synthesis and modulation of nanostructured biomimetic water oxidation catalysts.

Improved catalytic performance of encapsulated Ru nanowires for aqueous-phase Fischer–Tropsch synthesis

Fischer–Tropsch (F–T) synthesis at low temperature has attracted a lot of research attention due to its thermodynamically favorable nature at low temperature. Herein, we report a highly efficient solid nanoreactor for low temperature liquid-phase F–T synthesis. The solid nanoreactor was fabricated by encapsulation of Ru–PVP nanowires in ethane–silica hollow nanospheres via a one-pot co-condensation method. Under similar reaction conditions, the solid nanoreactor shows higher activity (activity: 6.35 versus 5.96 molCO mol−1Ru h−1) and selectivity towards oxygenate products (41.3 versus 21.6%) than free Ru–PVP in aqueous F–T synthesis. The high activity and selectivity of the encapsulated Ru–PVP is mainly attributed to the low PVP/Ru ratio and the unique yolk–shell nanostructure in increasing the degree of exposure of the active sites. It was also observed that the selectivity towards C5–12 products could be increased to 63.8% in a water/cyclohexane biphasic system. Encapsulation not only gave rise to the quasi-homogeneous Ru–PVP with facile recycling ability, but also enhanced its activity and selectivity towards oxygenates.

Nanostructured hybrid NiFeOOH/CNT electrocatalysts for oxygen evolution reaction with low overpotential

Oxygen evolution reaction (OER) has been recognized as a crucial half-reaction in water splitting for the production of hydrogen, one of the most important clean energies. In this article, we report the synthesis of a series of Ni-based NiMOOH layered double hydroxide (LDH, M = Cr, Fe, Co) nanosheets with sizes of about 20 nm with tetramethylammonium hydroxide (TMAOH) as a base source under mild reaction conditions. NiFeOOH shows much lower onset potential than NiCoOOH, NiCrOOH and Ni(OH)2 in alkaline solution. To further improve the OER activity, NiMOOH/CNT hybrid composites was prepared by in situ addition of carbon nanotubes (CNT) during the synthesis process of NiMOOH. The hybrid composites afford much higher activity than NiMOOH alone, especially for NiFeOOH/CNT with the overpotential of 278 mV at 10 mA cm−2 in alkaline solution. The significantly improved OER activity of NiMOOH/CNT hybrid composites is mainly attributed to the synergetic effect of CNT and nanostructured NiMOOH by improving the electric conductivity and increasing the exposure degree of active sites for OER. Moreover, the hybrid composites also possess high stability for a prolonged testing time.

Enhancing the catalytic activity of Ru NPs deposited with carbon species in yolk–shell nanostructures

The synthesis of metal NPs with a well-defined size, shape and composition provides opportunities for tuning the catalytic performance of metal NPs. However, the presence of a stabilizer on the metal surface always blocks the active sites of metal NPs. Herein, we report an efficient method to remove the stabilizer on the metal surface via H2 pyrolysis with Ru–poly(amindoamine) encapsulated in silica-based yolk–shell nanostructures as an example. The CO uptake amount of Ru NPs increases sharply after H2 pyrolysis, indicating that the exposure degree of Ru NPs is increased. No aggregation of the colloidal Ru NPs occurs after H2 pyrolysis, which could be mainly assigned to the protection effect of C and N species formed on Ru NPs. The overall activity of Ru NPs in the yolk–shell nanostructure after the pyrolysis could reach as high as 20u2006300 mmol per mmol Ru per h in the hydrogenation of toluene, which is much higher than that of most reported Ru-based solid catalysts. It was found that the yolk–shell nanostructure could efficiently prevent the leaching of Ru NPs during the catalytic process. Ru NPs in the yolk–shell nanostructure could also catalyze the hydrogenation of benzoic acid and Levulinic acid with high activity and selectivity.

A highly active non-precious metal catalyst based on Fe–N–C@CNTs for nitroarene reduction

Research on transition metal–nitrogen–carbon (M–N–C) materials revealed their potential as catalysts in several important traditional reactions. However, the activity of M–N–C still needs to be further improved and the real active center of M–N–C catalysts is still under debate. In this work, an efficient Fe–N–C@CNTs for the hydrogenation of nitroarenes was prepared by pyrolysis of FeCl3, phenanthroline and CNTs. Fe–N–C supported on CNTs is much more active than that supported on activated carbon, showing the promotion effect of CNTs. The characterization results suggest that the high activity of Fe–N–C is mainly attributed to the formation of e-Fe3N, which is the active site for the hydrogenation reaction. Nitrogen/carbon atoms contacted to the active centers could serve as bridges to transport the dissociated hydrogen atoms via spillover effect. The catalytic performance of Fe–N–C was also tested on fixed bed reactor under continuous flow condition for the first time and could smoothly catalyze the reaction for over 300 hours.