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Isolating Single Sn Atoms in CuO Mesocrystal to Form Ordered Atomic Interfaces: An Effective Strategy for Designing Highly Efficient Mesocrystal Catalysts
No full textTuning the electronic structures of mesocrystals at the atomic level is an effective approach to obtaining unprecedented properties. Here, a lattice-confined strategy to obtain isolated single-site Sn atoms in CuO mesocrystals to improve catalytic performance is reported. The Sn/CuO mesocrystal composite (Sn/CuO MC) has ordered Sn-O-Cu atomic interfaces originated from the long-range ordering of the CuO mesocrystal itself. X-ray absorption fine structure measurements confirm that the positively charged Sn atoms can tune the electronic structure of the Cu atoms to some extent in Sn/CuO MC, quite different from that in the conventional single-atom Sn-modified CuO nanoparticles and nanoparticulate SnO2-modified CuO mesocrystal catalysts. When tested for the Si hydrochlorination reaction to produce trichlorosilane, Sn/CuO MC exhibits significantly better performances than the above two catalysts. Theoretical calculations further reveal the electronic modification to the active Cu component and the induced improvement in HCl adsorption, and thus enhance the catalytic performance. This work demonstrates how to design efficient metal oxide mesocrystal catalysts through an electronic structure modification approach
Different roles of Fe atoms and nanoparticles on g-C3N4 in regulating the reductive activation of ozone under visible light (vol 296, 120362, 2021)
No full textDetermination of the oxygen removal limits from Ti and Ti-6Al-4V by the hydrogen-assisted Mg deoxygenation method
No full textDeoxygenation is in high demand in the titanium industry. This research was carried out to experimentally determine the oxygen removal limits by the novel hydrogen-assisted Mg deoxygenation method. Spherical Ti and Ti-6Al-4V (or TC4, Ti64) powders with around 2.2 wt% oxygen were prepared for the deoxygenation research. The deoxygenation kinetics were modeled based on a non-steady-state radial diffusion. There-sults show that in the beta phase region, the time to reach the equilibrium is slightly affected by the initial oxygen content in titanium, but is strongly influenced by the particle size. The reliance of the equilibrium duration on the diffusion coefficient is stronger when the particle size is larger. Guided by the kinetic prediction, deoxygenation experiments were carried out. Under a 1 atm pure H2 atmosphere, the deoxygenation limits by Mg for pure Ti are 252 ppm at 700 & DEG;C, 289 ppm at 750 & DEG;C, and 554 ppm at 800 & DEG;C, and for TC4 are 296 ppm at 750 & DEG;C, 371 ppm at 800 & DEG;C, and 743 ppm at 850 & DEG;C, consistent with the thermodynamics that a lower temperature possesses a more potent driving force for deoxygenation. These data have clearly demonstrated the strong deoxygenation capability of the hydrogen-assisted Mg deoxygenation method.(C) 2022 Elsevier B.V. All rights reserved
Recycling of blast furnace slag to prepare calcium silicate hydrate by mechanical-chemical co-activation and its application to calcium silicate fireproof board
No full textThe high-value utilization of water quenched slag (WQS), one of the bulk byproducts originating from the iron manufacturing industry, remains an important subject in the environment. Through a mechano-chemical coactivation strategy, WQS can be used to prepare porous calcium silicate hydrate (C-S-H), which was applied as gelling filler to prepare fiber-reinforced calcium silicate fireproof board (FCSFB) and extremely improved its high-temperature performance and non-combustibility. The optimal activation conditions for WQS are ball milling time of 30 min, reaction temperature of 90 degrees C, reaction time of 5 h, and Ca/Si molar ratio of 1.5:1. The thermal conductivity for FCSFB prepared by the optimal A-WQS is 0.17 W/(m center dot K), and its overheating time of the applied temperature at 803.7 degrees C is 1335.5 s. The improvement mechanism of the performance of FCSFB can be attributed to the transformation of C-S-H toward more high crystallinity flaky tobermorite, which uniformly and closely combined with pulp fiber to form a micro-porous cavity structure to delay flame penetration period. The application of WQS in FCSFB can provide essential guidance for the utilization of other similar solid wastes
Perovskite Micro-Nano Cage SrTiO3: Formation Mechanism, Vacancy Analysis, and Exciton Dynamics
No full textIn the former research, we produced the regular polyhedron single-crystalline SrTiO3 particles with multiple crystal facets exposed by a one-step hydrothermal method. In this work, the dissolution process mechanism of SrTiO3 has been analyzed based on the evidence of the crystal structure and particle morphology with a completely new point of view. The anisotropic formation process of perovskite micro-nano cage SrTiO3 was primarily summarized, and the defective vacancy composition was analyzed. Simultaneously, based on femtosecond transient absorption spectroscopy, the exciton dynamic of SrTiO3 was deduced, and it will play a key role in improving the photoelectric properties of SrTiO3. Furthermore, the abundant defective vacancies promote the ability of SrTiO3 to oxidize Co species, which has a great advantage in the wastewater treatment processes
Kinetic modelling and experimental validation of single large particle combustion of coal char
No full textUnderstanding apparent kinetics of single large fuel particle combustion is of significance to the design and optimization of grate-firing and circulating fluidized bed boilers. Based on the concept of finite reaction zone approximation, a simple heterogeneous single particle model was formulated to consider the effects of external gas film, ash layer and chemical reaction simultaneously. To validate the proposed model and gain insight into the prevailing rate-controlling mechanism during the single particle combustion process at different combustion temperatures and particle sizes, the experiments on the combustion of coal char powder and single large char particles were carried out in a thermal gravimetric analyzer and a bench scale fixed-bed reactor, respectively. The intrinsic and apparent kinetics as well as the effective reacting zone thickness of single large particle combustion were quantified by combining theoretical analyses and experimental data. Both the bulk flow temperature and particle size have a remarkable influence on the global reactivity. The rate-controlling process was found to shift from the intrinsic chemical reaction to ash layer diffusion and return again to the intrinsic kinetics at the burnout stage. Particularly, an external effectiveness factor was defined as a function of conversion degree to better describe the ash diffusion effect on the apparent reactivity of large particles. The proposed model is physically general but simple enough to be incorporated into the computational fluid dynamic simulation of large-scale grate-firing and fluidized bed boilers
Center for Mesoscience, Institute of Process Engineering, Chinese Academy of Sciences, State Key Laboratory of Multiphase Complex Systems[MPCS- 2019-A-09]
No full textThe Behavior of CO2 Supersonic Jets in the Converter Slag-Splashing Process
No full textA numerical model was developed to investigate the possibility of using CO2 to replace conventional N-2 for the converter slag-splashing process and, thus, promote the recycling of CO2 in the steel industry. The validity of the numerical model was demonstrated using one-dimensional isentropic flow theory and experimental data. By comparing with N-2 and O-2, it was found that CO2 has a lower velocity and dynamic pressure, higher temperature at the exit of the oxygen lance, and the difference between the three gases decreases gradually with the increasing of axial distance. The oxygen lance is required to have excellent stirring and splashing performance simultaneously for the CO2 slag-splashing process. The five-hole oxygen lance with a central nozzle combines the advantages of single-hole and four-hole oxygen lances, with higher impact force, slower decay of dynamic pressure, higher impact area, and more tremendous average turbulent kinetic energy at a low lance position, providing a better choice for slag splashing. Decreasing the axial distance, increasing the CO2 stagnation pressure, and raising the CO2 preheating temperature could improve the CO(2 )jet performance by different degrees. This work provides a theoretical basis for the application of CO2 in the converter slag-splashing process.
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