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Kinetics and mechanistic insights into the active sites of Au catalysts for selective propylene oxidation

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Nano Research 2023年第5期16卷 6220-6227页

作者： Qianhong Wang Zhihua Zhang Keng Sang Wenyao Chen Gang Qian Jing Zhang xinggui zhou Xuezhi Duan State Key Laboratory of Chemical Engineering School of Chemical EngineeringEast China University of Science and TechnologyShanghai 200237China

Identification of the catalytically active sites emerges as the prerequisite for an atomic-level comprehensive understanding and further rational design of highly efficient catalysts.Here,we demonstrate a kinetics strategy to identify the active sites of Au catalyst for the disentanglement of geometric and electronic effects on the selective oxidation of propylene to acrolein.Both the Ti-containing titanium-silicalite-1(TS-1)and Ti-free silicalite-1(S-1)were employed as supports to immobilize Au catalysts,which were investigated by a combination of multiple characterization,kinetics analysis,crystal structure modelling.The Au(111)sites are identified as the main active site for acrolein formation,while their electronic effects are highly relevant to the presence or absence of Ti.Moreover,propylene epoxide(PO)formation mainly involves the co-participation of Au and Ti sites,the proximity between Au and Ti sites is found to have less influences on PO formation in a certain distance.In comparison,acrolein is very likely to generate over Au(111)sites via the hydrogen-assisted O_(2) activation to oxygenated species for its oxidizing propylene.The insights gained here could guide the design and preparation of Au catalysts for selective propylene oxidation.

关键词： propylene oxidation Au catalysts active site geometric and electronic effects Au-Ti proximity

Effects of particle shape and packing style on ethylene oxidation reaction using particle-resolved CFD simulation

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Particuology 2023年第11期82卷 87-97页

作者： Yao Shi Hao Chen Wenyao Chen Guanghua Ye Jin Qu Jinbing Li xinggui zhou Xuezhi Duan State Key Laboratory of Chemical Engineering School of Chemical EngineeringEast China University of Science and TechnologyShanghai200237China Yanshan Branch of Beijing Research Institute of Chemical Industry China Petroleum&Chemical Company(Sinopec Corp.)Beijing102500China

Gaining in-depth insights into the effects of particle shapes and packing style on ethylene oxidation reaction is of paramount industrial importance.In this work,reactor models of five packing structures with different particle shapes and three packing structures with different packing styles are established by employing software Blender and COMSOL Multiphysics to explore how the reaction-diffusion behaviors affect ethylene oxidation process.The reliabilities of rigid body dynamics model and particle-resolved reactor model are verified by comparing simulated and experimental pressure drops and ethylene conversions.In all the five packing structures with laminar flow conditions,the high bed porosity and low total particle surface area for the trilobe packing structure give rise to the lowest pressure drop of 27.8 Pa/m,while the internal voids cutting mode provides the excellent heat transfer capacity for the Raschig ring packing structure and the highest ethylene conversion and thereby the highest bed temperature rise of 25.1 K for the four-hole cylinder packing structure.Based on these analyses,changing the packing style to the bottom-up Raschig ring-four hole cylinder packing structure would be a good strategy for the effectively lowered reactor temperature rise by 4.8 K together with the slightly reduced ethylene conversion.

关键词： Ethylene oxidation Particle shape Packing style Heat transfer

Residence time distribution and heat/mass transfer performance of a millimeter scale butterfly-shaped reactor

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Chinese Chemical Letters 2023年第4期34卷 332-337页

作者： Haicheng Lv Jundi Wang Zhongming Shu Gang Qian Xuezhi Duan Zhirong Yang xinggui zhou Jing Zhang State Key Laboratory of Chemical Engineering East China University of Science and TechnologyShanghai 200237China

A millimeter scale butterfly-shaped reactor was proposed based on sizing-up strategy and fabricated via femtosecond laser engraving. An improvement of mixing performance and residence time distribution was realized by means of contraction and expansion of the reaction channel. The liquid holdup was greatly increased through connection of multiple mixing units. Structure optimization of the reactor was carried out by computational fluid dynamics simulation, from which the effect of reactor internals on mixing and the influence of parallel branching structure on heat transfer were discussed. The UV–vis absorption spectroscopy was used to determine the residence time distribution in the reactor, and characteristic parameters such as skewness and dimensionless variance were obtained. Further, a chained stagnant flow model was proposed to precisely describe the trailing phenomenon caused by fluid stagnation and laminar flow in small scale reactors, which enables a better fit for the experimental results of the asymmetric residence time distribution. In addition, the heat transfer performance of the reactor was investigated, and the overall heat transfer coefficient was 110–600 W m^(-2)K-1in the flow rate range of 10–40 m L/min.

关键词： Millimeter scale reactor Computational fluid dynamics Residence time distribution Chained stagnant flow model Overall heat transfer coefficient

Mechanistic insights into the active intermediates of 2,6-diaminopyridine dinitration

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Chinese Journal of Chemical Engineering 2023年第4期56卷 160-168页

作者： Junao Zhu Zhirong Yang Yuanhan Chen Mingming Chen Zhen Liu Yueqiang Cao Jing Zhang Gang Qian xinggui zhou Xuezhi Duan State Key Laboratory of Chemical Engineering School of Chemical EngineeringEast China University of Science and TechnologyShanghai 200237China

Mechanistic understanding of the active intermediates of 2,6-diaminopyridine(DAP) dinitration in the concentrated nitric-sulfuric acid system is of crucial importance for the selectivity control of target product, i.e., 2,6-diamino-3,5-dinitropyridine(DADNP). The active intermediates determining the product selectivity are theoretically studied. The HSO_(4)^(-)-NO_(2)^(+) complex is proposed as the dominant active nitrating intermediate for the first time, which shows low energy barrier(i.e., 10.19 kcal·mol^(-1),1 kcal = 4.186 k J) for direct dinitration of DAP to DADNP. The formed water during the reaction results in not only the formation of less active SO_(4)^(2-)-NO_(2)^(+) complex, but also the occurance of DAP sulfonation(DAP-SO_(3)H intermediate)to facilitate the formation of mononitration byproduct. Meanwhile, the accompanied thermal effects cause the generation of undesirable pyridine-NHNO_(2) intermediate, which is difficult to be rearranged to yield DADNP, inhibiting the reaction and thus giving low DAP conversion. The insights reported here elucidates the importance of thermal effects elimination and water content control, confirmed experimentally in the batch-and micro-reaction systems.

关键词： 2,6-Diaminopyridine Nitration mechanism Active intermediates Thermal effects Negative water effects

Mechanistic aspects of facet-dependent CH_(4)/C_(2+)selectivity over aχ-Fe_(5)C_(2)Fischer-Tropsch catalyst

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Green Energy & Environment 2022年第3期7卷 449-456页

作者： Thanh Hai Pham Junbo Cao Nan Song Yueqiang Cao Bingxu Chen Gang Qian xinggui zhou De Chen Xuezhi Duan State Key Laboratory of Chemical Engineering East China University of Science and Technology130 Meilong RoadShanghai200237China Vietnam Institute for Tropical Technology and Environmental Protection 57A Truong Quoc DungHo Chi MinhViet Nam Department of Chemical Engineering Norwegian University of Science and TechnologyN-7491TrondheimNorway

Structure-performance relationship is a complex issue in iron-catalyzed Fischer-Tropsch synthesis,and it is not easy to elucidate it by experimental investigations.First-principle calculation is a powerful method for explaining experimental results and guiding catalyst design.In this study,we investigated the reaction mechanisms of CH_(4)formation and C-C coupling on fourχ-Fe_(5)C_(2)surfaces and established the kinetic equations to compare the rates of CH_(4)formation and C_(1)+C_(1)coupling reactions and determine the CH_(4)/C_(2+)selectivity.The results show that the geometry of theχ-Fe_(5)C_(2)surfaces has little effect on the formation rate of CH_(4);however,the C_(1)+C_(1)coupling reactions are significantly affected by the surface geometry.The C_(1)+C_(1)coupling reaction rates on the terraced-like(510)and(021)surfaces are much higher than those on the stepped-like(001)and(100)surfaces.Based on these results,we established a Brùnsted-Evans-Polanyi(BEP)relationship between the effective barrier difference for CH_(4)formation and C_(1)+C_(1)coupling(ΔE_(eff))and the adsorption energy of C+4H(ΔE_(C+4H))onχ-Fe_(5)C_(2)surfaces.ΔE_(C+4H)can be used as a descriptor for CH_(4)/C_(2+)selectivity on different surfaces ofχ-Fe_(5)C_(2).

关键词： selectivity catalyst coupling

Catalyst particle shapes and pore structure engineering for hydrodesulfurization and hydrodenitrogenation reactions

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Frontiers of Chemical Science and Engineering 2022年第6期16卷 897-908页

作者： Yao Shi Zhao Li Changfeng Yang Zhanlin Yang Zhenhui Lv Chong Peng Bao-Lian Su Weikang Yuan xinggui zhou Xuezhi Duan State Key Laboratory of Chemical Engineering East China University of Science and TechnologyShanghai 200237China Dalian Research Institute of Petroleum and Petrochemicals SINOPECDalian 116045China Laboratory of Inorganic Materials Chemistry University of NamurB-5000 NamurBelgium

Catalyst particle shapes and pore structure engineering are crucial for alleviating internal diffusion limitations in the hydrodesulfiirization(HDS)/hydrodeni-trogenation(HDN)of gas oil.The effects of catalyst particle shapes(sphere,cylinder,trilobe,and tetralobe)and pore structures(pore diameter and porosity)on HDS/HDN performance at the particle scale are investigated via mathematical modeling.The relationship between particle shape and effectiveness factor is first established,and the specific surface areas of different catalyst particles show a positive correlation with the average HDS/HDN reaction rates.The catalyst particle shapes primarily alter the average HDS/HDN reaction rate to adjust the HDS/HDN effectiveness factor.An optimal average HDS/HDN reaction rate exists as the catalyst pore diameter and porosity increase,and this optimum value indicates a tradeoff between diffusion and reaction.In contrast to catalyst particle shapes,the catalyst pore diameter and the porosity of catalyst particles primarily alter the surface HDS/HDN reaction rate to adjust the HDS/HDN effectiveness factor.This study provides insights into the engineering of catalyst particle shapes and pore structures for improving HDS/HDN catalyst particle efficiency.

关键词： hydrodesulfiirization hydrodenitrogenation particle shape pore structure

Taming Electrons in Pt/C Catalysts to Boost the Mesokinetics of Hydrogen Production

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Engineering 2022年第7期8卷 124-133页

作者： Wenyao Chen Wenzhao Fu Xuezhi Duan Bingxu Chen Gang Qian Rui Si xinggui zhou Weikang Yuan De Chen State Key Laboratory of Chemical Engineering East China University of Science and TechnologyShanghai 200237China Shanghai Synchrotron Radiation Facility Shanghai Institute of Applied PhysicsChinese Academy of SciencesShanghai 201204China Department of Chemical Engineering Norwegian University of Science and TechnologyTrondheim N-7491Norway

Taming the electron transfer across metal–support interfaces appears to be an attractive yet challenging methodology to boost catalytic properties.Herein,we demonstrate a precise engineering strategy for the carbon surface chemistry of Pt/C catalysts—that is,for the electron-withdrawing/donating oxygencontaining groups on the carbon surface—to fine-tune the electrons of the supported metal nanoparticles.Taking the ammonia borane hydrolysis as an example,a combination of density functional theory(DFT)calculations,advanced characterizations,and kinetics and isotopic analyses reveals quantifiable relationships among the carbon surface chemistry,Pt charge state and binding energy,activation entropy/enthalpy,and resultant catalytic activity.After decoupling the influences of other factors,the Pt charge is unprecedentedly identified as an experimentally measurable descriptor of the Pt active site,contributing to a 15-fold increment in the hydrogen generation rate.Further incorporating the Pt charge with the number of Pt active sites,a mesokinetics model is proposed for the first time that can individually quantify the contributions of the electronic and geometric properties to precisely predict the catalytic performance.Our results demonstrate a potentially groundbreaking methodology to design and manipulate metal–carbon catalysts with desirable properties.

关键词： Mesokinetics model Catalyst descriptor Pt charge state Carbon surface chemistry Hydrogen generation activity

Bi_(2)S_(3) Nanostructures: A New Photocatalyst

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Nano Research 2010年第5期3卷 379-386页

作者： Tong Wu xinggui zhou Hua Zhang Xinhua Zhong State Key Laboratory of Chemical Engineering Department of ChemistryEast China University of Science and TechnologyShanghai 200237China

Uniform colloidal Bi_(2)S_(3) nanodots and nanorods with different sizes have been prepared in a controllable manner via a hot injection method. X-ray diffraction (XRD) results show that the resulting nanocrystals have an orthorhombic structure. Both the diameter and length of the nanorods increase with increasing concentration of the precursors. All of the prepared Bi_(2)S_(3) nanostructures show high efficiency in the photodegradation of rhodamine B, especially in the case of small sized nanodots-which is possibly due to their high surface area. The dynamics of the photocatalysis is also discussed.

关键词： Bi_(2)S_(3) nanostructures hot injection photocatalyst

Iron-based Fischer–Tropsch synthesis of lower olefins: The nature of χ-Fe_5C_2 catalyst and why and how to introduce promoters

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Journal of Energy Chemistry 2016年第6期25卷 911-916页

作者： Di Wang Bingxu Chen Xuezhi Duan De Chen xinggui zhou State Key Laboratory of Chemical Engineering East China University of Science and Technology Department of Chemical Engineering Norwegian University of Science and Technology

As a sustainable and short-flow process, iron-catalyzed direct conversion of CO-rich syngas to lower olefins without intermediate steps, i.e., Fischer–Tropsch-to-Olefins (FTO), has received increasing attention. However, its fundamental understanding is usually limited by the complex crystal phase composition in addition to the interferences of the promoter effects and inevitable catalyst deactivation. Until recently, the combination of multiple in-situ/ex-situ characterizations and theoretical studies has evidenced H?gg iron carbide (χ-Fe5C2) as the dominant active phase of iron-based Fischer–Tropsch catalysts. This perspective attempts to review and discuss some recent progresses on the nature of χ-Fe5C2catalyst and the crucial effects of promoters on the FTO performance from theoretical and experimental viewpoints, aiming to provide new insights into the rational design of iron-based FTO catalysts. ? 2016 Science Press

关键词： Carbides Catalyst deactivation Catalysts Iron Olefins Phase composition