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covalency triggers high catalytic activity of amorphous molybdenum oxides for oxidative desulfurization

中国科学：化学英文版 2023年第4期66卷 1211-1220页

作者： Juncong Zou Yan Lin Chunping Yang College of Environmental Science and Engineering Hunan University and Key Laboratory of Environmental Biology and Pollution Control(Hunan University)Ministry of EducationHunan UniversityChangsha 410082China Guangdong Provincial Key Laboratory of Petrochemcial Pollution Processes and Control and School of Environmental Science and EngineeringGuangdong University of Petrochemical TechnologyNaoming 525000China School of Environmental and Chemical Engineering Nanchang Hangkong UniversityNanchang 330063China

Oxidative desulfurization(ODS)is a promising technology to produce clean fuel with requiring superior catalysts to lower kinetic barriers.Although most ODS catalysts are based on crystalline transition-metal oxides(TMOs),extraordinary activity also can be achieved with amorphous TMOs.However,the origin of the remarkable catalytic activity of the amorphous TMOs remains greatly ambiguous.Here,we found the crucial role of Mo–O covalency in ruling the intrinsic catalytic activity of amorphous molybdenum oxides(MoO_(x)).Experimental and theoretical analysis indicated that the nonequivalent connectivity in the amorphous structure strongly enhanced Mo–O covalency,thereby increasing the content of electrophilic oxygen and nucleophilic molybdenum to favor the MoO_(x)–H_(2)O_(2) interaction.With the boosted Mo–O covalency to improve the flexibility of the charge state,the amorphous MoO_(x)-based composite catalyst(PE-MoO_(x)/S-0.05)exhibited outstanding catalytic activity for ODS of fuel oil.The turnover frequency(TOF)value of the catalyst(18.63 h^(-1))was almost an order of magnitude higher than that of most reported crystalline MoO_(x)/molecular sieve composite catalysts.The in-depth understanding of the origin of the amorphous TMOs activity for ODS provides a valuable reference for developing ODS catalysts.

关键词： amorphous molybdenum oxide oxidative desulfurization covalency

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Low-temperature dielectric relaxation associated with NbO_6 octahedron distortion in antimony modified potassium sodium niobate ceramics

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Journal of Materials Science & Technology 2022年第20期115卷 189-198页

作者： Nan Zhang Xiang Lv Xi-xiang Zhang Jing Lyu Shuo-Wang Yang Jiagang Wu Department of Materials Science Sichuan UniversityChengdu 610065China Division of Physical Science and Engineering King Abdullah University of Science and TechnologyThuwal 23955-6900Saudi Arabia Department of Chemistry National University of Singapore3 Science Drive 3117543Singapore Institute of High Performance Computing Agency for ScienceTechnology and Research1 Fusionopolis Way#16-16 Connexis138632Singapore

Although the antimony(Sb) has been widely used to modify potassium sodium niobate(KNN) ceramics for tailoring the phase structure and performance, the role of Sb still remains insufficiently understood,consequently hindering the understanding of the physical origin of high-performance KNN-based ceramics. Here, we combine the experiments and first-principles calculations to deeply reveal the effects of Sb on KNN ceramics. Our results reveal a re-entrant-like relaxation behavior near the rhombohedralorthorhombic(R-O) phase transition at the low content of Sb, which transforms into a canonical one at higher content of Sb. First-principles calculations show a significantly decreased difference in the bond length of six B-O bonds of Nb O6 octahedral in Sb-modified KNN ceramics compared to pristine KNN ceramics, responsible for the low-temperature re-entrant-like dielectric relaxation. Furthermore, the addition of Sb would soften the B-O repulsion and gradually break the long-range ferroelectric ordering,resulting in the occurrence of nanoscale domains and enhanced local heterogeneity. Finally, we find that the optimized piezoelectric properties are the trade-off between the long-range ferroelectric ordering and the local heterogeneity. Therefore, this work not only deeply reveals the effects of Sb on KNN ceramics from multi-scale perspectives but also helps the future composition design for achieving high piezoelectricity.

关键词： KNN-based ceramics Re-entrant-like relaxation covalency Multiphase coexistence Local heterogeneity

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Rapid Evaluation of Individual Hydrogen Bonding Energies in Linear Water Chains

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Chemical Research in Chinese Universities 2014年第3期30卷 447-454页

作者： HAO Jiaojiao LI Shushi JIANG Xiaonan HUANG Cuiying WANG Changsheng School of Chemistry and Chemical Engineering Liaoning Normal University Dalian 116029 P. R. China

A model is proposed to rapidly evaluate the individual hydrogen bonding energies in linear water chains. We regarded the two O--H bonds of a water molecule as two dipoles. The magnitude of the O--H bond dipole mo- ment can be varied due to the other water molecules＇ presence. An analytic potential energy function, which explicitly contains the permanent dipole-dipole interactions, the polarization interactions, the van der Waals interactions and the covalent interactions, was therefore established. The individual hydrogen bonding energies in a series of linear water chains were evaluated via the analytic potential energy function and compared with those obtained from the CP-corrected MP2/aug-cc-pVTZ calculations. The results show that the analytic potential energy function not only can produce the individual hydrogen bonding energies as accurately as the CP-corrected MP2/aug-cc-pVTZ method, but is very efficient as well, demonstrating the model proposed is reasonable and useful. Based on the individual hy- drogen bonding energies obtained, the hydrogen bonding cooperativity in the linear water chains was explored and the natures of the hydrogen bonding in these water chains were discussed.

关键词： Hydrogen bond Dipole-dipole interaction Polarization covalency Water chain Cooperativity

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