State Key Laboratory of Coal Combustion

The effects of initial conditions on interaction between a boundary layer over a flat plate and flow around a wall-mounted finite-length cylinder were experimentally investigated. A square cylinder with a characteristic width (d) of 20mm and a length of H=5d was vertically mounted on a horizontal flat plate. Three different boundary layers were investigated, their momentum thickness being 0.07d, 0.13d, and 0.245d, respectively, measured at the cylinder axis in the absence of the cylinder. All the experiments were carried out in a closed-loop water tunnel at a Reynolds numbers of 11 500 based on d and the free-stream velocity U∞. It is found that initial boundary layer conditions have a profound effect on the near wake, including the flow near the cylinder free end that is well beyond the boundary layer. With increasing boundary layer thickness, the base vortex is enhanced, inducing a stronger upwash flow from the cylinder base, which acts to weaken the downwash free-end shear layer and the tip vortex. Consequently, spanwise vortices gain strength near the free end but impair near the wall, causing the ratio of symmetrically to antisymmetrically arranged vortices to vary and subsequently the Reynolds stresses to increase significantly in magnitude near the free end but to decrease near the wall.

A comprehensive review of the recent advances in MgO-based sorbents for CO₂capture is provided.

FeS₂-anchored transition metal single-atom catalysts show excellent catalytic activity towards the hydrogen evolution reaction.

10 CaO-based sorbents were synthesized by a sol–gel process supported with various materials, and their cyclic behavior was investigated under the same reaction conditions.

More than half of the waste heat rejected into the environment has temperatures lower than 100 °C, which accounts for nearly 85 PWh/year worldwide. Efficiently harvesting low-grade heat could be a promising step toward carbon neutrality. Recent developments of ionic thermoelectrics (i-TE) with giant thermopower have provoked intensive interest in using ions as energy and charge carriers for efficient thermal energy harvesting. However, current literature primarily focuses on improving thermopower only, while the ion transport and thermodynamics affecting the efficiencies have been largely neglected. This Review clarifies the fundamentals of electrochemistry and thermodynamics for developing highly efficient i-TE devices. Two major types of i-TE devices, thermo-ionic capacitors (TICs) and thermogalvanic cells (TGCs), are discussed in detail. The Review analyzes the methods of enhancing ionic thermopower in the literature by taking an entropic point of view. We also derived modified thermoelectric factor Z for both TICs and TGCs that fully incorporate the dynamics of ion transport and electrochemical reactions. Recent developments of hybrid devices showing improved efficiencies, power density, and multifunctionality are reviewed. Finally, we comment on the remaining challenges and provide an outlook on future directions.

It is known that the combination of TiO2 and graphene and the control of TiO2 crystal facets are both effective routes to improve the photocatalytic performance of TiO2. Here, we report the synthesis and the photocatalytic CO2 reduction performance of graphene supported TiO2 nanocrystals with coexposed {001} and {101} facets (G/TiO2-001/101). The combination of TiO2 and graphene enhanced the crystallinity of TiO2 single nanocrystals and obviously improved their dispersion on graphene. The "surface heterojunction" formed by the coexposed {001} and {101} facets can promote the spatial separation of photogenerated electrons and holes toward different facets and the supports of graphene can further enhance the separation through accelerated electron migration from TiO2 to graphene. The G/TiO2-001/101 exhibited high photocatalytic CO2-reduction activity with a maximum CO yield reaching 70.8 μmol g(-1) h(-1). The enhanced photocatalytic activity of the composites can be attributed to their high surface area, good dispersion of TiO2 nanoparticles, and effective separation of excited charges due to the synergy of graphene supports and the co-exposure of {001} and {101} facets.

Highly selective conversion of xylose into levulinic acid/ester was achieved over the Zr-beta catalyst with balanced distribution of acidic sites.

Nitrogen-rich agricultural waste, soybean straw, was used as a raw material to prepare high efficiency CO₂ adsorbents (nitrogen-doped porous modified biochars).

Naturally abundant pomelo peels were explored for the preparation of the metal-free carbon-based microspheres with high electrocatalytic activity and long-term durability toward ORR, holding potential for replacing noble metal-based catalysts.

This paper discusses the impact of catalyst contact time on the catalytic fast pyrolysis yield.

Transition-metal phosphides (TMPs) are considered as promising non-noble electrochemical catalysts for hydrogen evolution reaction (HER). Their highly active sites are located on certain facets, and single crystalline two-dimensional (2D) structures enable them to expose the most active facets for HER. However, the synthesis of single crystalline 2D TMPs is still a challenge owing to their intrinsically non-layered structures. Herein, we demonstrate the synthesis of various single crystalline 2D TMPs (Co2P, MoP2, Ni12P5 and WP2) by a salt-templating method. The as-synthesized 2D Co2P exhibited efficient electrocatalytic ability for HER with an overpotential of 41 mV at 10 mA cm-2 and a Tafel slope of 35 mV dec-1 in 0.5 M H2SO4 solution. We expect that the synthesis of 2D TMPs reported here will open the way to expand the family of 2D materials for electrocatalysis and beyond.

To understand the formation mechanism of high-calcium fly ashes, the mineralogical, physical, and chemical properties of several high calcium fly ashes and their different density fractions (<1.0, 1.0−2.5, 2.5−2.89, and >2.89 g/cm3) from a coal-fired power plant were characterized by X-ray diffractometry (XRD), field scanning electron microscopy equipped with energy dispersive X-ray analysis (FSEM-EDX), and X-ray fluorescence spectroscopy (XRF). The occurrence of calcium in coal was determined using sequential extraction tests. The results show that the carbonate-bonded calcium is the dominant species in Xiaolongtan coal, and the ion-exchangeable calcium only occupies 19.2% of total calcium. The major calcium-bearing minerals in low temperature ash (LTA) of the feed coal, lignite from the Yunnan province, include calcite, bassanite, and dolomite. The fly ashes examined contained aluminosilicates with a high concentration of calcium oxide. The major minerals include mullite, quartz, lime, anhydrite, and gehlenite, and the minor minerals are comprised of hematite, magnetite, akermanite, portlandite, and larnite. Minerals in the density faction less than 1.0 g/cm3 consist of lime, calcite, anhydrite, and clay; between 1.0−2.5 g/cm3, quartz, mullite, anhydrite, and gehlenite; between 2.5−2.89 g/cm3, anhydrite, lime, gehlenite, hematite, and quartz; and greater than 2.89 g/cm3, larnite, gehlenite, anhydrite, brownmillerite, and some heavy minerals. In accordance with the microstructural characteristics of the fly ash particles, high-calcium fly ash can be classified into several groups, namely hollowed smooth particles, dense particles, agglomerate particles, porous particles, plerosphere, and other particles with complex surface characteristics. On the basis of chemical composition, high-calcium fly ashes can be classified into four groups namely: calcium oxide, calcium sulfates, Ca−Al−Si compounds, and Ca−S−X (X: Fe, Al, Si, Mg, etc.) compounds. Calcium oxide and calcium sulfates are mainly derived from the original calcium-bearing minerals in coal, whereas Ca−Al−Si and Ca−S−X compounds are formed by the secondary reaction of CaO and CaSO4.

Adsorption-driven heat pumps (AHPs) based on metal–organic frameworks (MOFs) have been garnering rapidly growing research interests due to their outstanding adsorption performance.

This paper demonstrates the effect of ammonia addition on soot formation co-firing with ethylene combined with reactive force field molecular dynamics simulations and experimental study. The effects of ammonia addition on soot propensity and polycyclic aromatic hydrocarbons (PAHS) evaluated from simulation results were consistent with the laser-induced incandescence/laser-induced fluorescence (LII/LIF) findings. By tracing the evolution of species and the visualization of reactions, the inhibitory mechanisms that occurred with the increased proportion of ammonia were revealed and embodied in the fuel decomposition stage and growth stage of PAHs and soot. In the fuel decomposition stage, the pools of aromatic hydrocarbon precursors weakened with the increase in the proportion of NH3 and generated more nitrogen–carbon species, which continuously showed rising trends until the end of simulations. The overlap between the consumption of acetylene and the incipience of C13+ and C16+ species indicated that the strong inhibition on the growth of heavy PAHs was due in part to less acetylene generated. The snapshots of acetylene addition reactions with the PAH molecules in simulations provided further evidence for this result. The morphology of nanoparticles formed at 3 ns of simulations for 15 and 30% ammonia blending ratios was presented. The nitrogen atoms were mostly distributed at the edge sites of particles. The nitrogen–carbon molecules reacted with PAH-like molecules and mainly formed the edge sites of nanoparticles rather than becoming involved in establishing the internal skeleton of nanoparticles. In addition, with the increased proportion of ammonia, the nitrogen atom sites grabbed more active sites originally meant for hydrogen atoms, thus further inhibiting the growth of PAHs and soot.

Vapor generation is of prime importance for a broad range of applications: domestic water heating, desalination and wastewater treatment, etc. However, slow and inefficient evaporation limits its development. In this study, a nano-ratchet, a multilayer graphene with cone-shaped nanopores (MGCN), to accelerate vapor generation has been proposed. By performing molecular dynamics simulation, we found that air molecules were spontaneously transported across MGCN and resulted in a remarkable pressure difference, 21 kPa, between the two sides of MGCN. We studied the dependence of the pressure difference on the ambient temperature and geometry of MGCN in detail. Through further analysis of the diffusive transport, we found that pressure difference depended on the competition between ratchet transport and Knudsen diffusion and it was further found that ratchet transport is dominant. The significant pressure difference could lead to a 15-fold or greater enhancement of vapor generation, which shows the wide applications of this nano-ratchet.

Nickel phosphide species can tailor the selectivity of hydrogenation sites. The yields of CPO and CPL reached 93.5% over 15%Ni–25%P/Al₂O₃. The balanced distribution of hydrogenation/acid sites maximizes the yield of CPO.

A chainmail catalyst of Ni₂P core encapsulated by ultrathin P-doped carbon shell anchored on graphene network demonstrates efficient and robust activity towards hydrogen evolution.

A strategy to increase the efficiency of layered organic thermoelectric material is proposed by utilizing the overlap of p<italic>z</italic> orbitals.

Small carbon pores below 1 nm become increasingly ionophobic which enables the more and more permselective charge storage and perspectives for capacitive deionization with porous carbons even at high molar strength.

Novel nanocomposites of graphene oxide, Ag nanoparticles, and magnetic ferrite nanoparticles for elemental mercury (Hg⁰) removal from combustion gases.