1、申 文 杰,中国科学院大连化学物理研究所催化基础国家重点实验室,2004 年 12 月 8 日,Catalytic Reaction Mechanism & Kinetics,OUTLINES,What is CatalysisCatalytic Reaction KineticsReactivity of Nanoparticles,In 1836 Jakob J. Berzelius introduced the word catalysis.,Jens Rostrup-Nielsen: XVII Sympsio Iberoamericano de Catlisis, July 16-21
2、, 2000,Dream reactions waiting for a catalyst,CH4 + 0.5 O2 CH3OH CH4 + 0.5 O2 CO + 2H2 2CH4 + O2 C2H4 + 2H2O nCH4 CnH2n+2 + (2n-2)H2,2NO N2 + O2 2N2 + 2H2O + 5O2 4HNO3,H2 + O2 H2O2,DME CH3CH2OH,Scientific challenges in Catalysts preparation,Theory modeling and simulation- Predict structure/activity
3、relationships- Electronic properties of nano-particles,Synthetic control of particle size, pore size, support structure,Structure/reactivity relationships,Integrate nano-structures to form catalytic assembly,In situ characterization of catalytic reactions,Grand Challenges of Nano-structured Material
4、s for Highly Selective Catalysis,How can we achieve complete control of selectivity, activity, and stability through tailoring of catalyst and support at all length scales?,The potential energy picture The kinetic picture The chemical bonding picture,What is catalysis?,Catalytic Reaction,Consequence
5、s for orders of reaction temperature dependence,The Langmuir Adsorption Isotherm,Molecular Adsorption on a d-metal,This picture is the key to understanding catalysis in terms of orbital theory,The CO molecule dissociates in the transition state: optimal overlap between d- and 2*-orbitals,CO Dissocia
6、tion,Trends in chemisorption,Dissociation on Different Metals e.g. Rh and Fe,NO + CO 1/2N2 + CO2,Elementary surface reactions,The potential energy picture The kinetic picture The chemical bonding picture If you can explain catalysis along these three lines you have a pretty good understanding of wha
7、t catalysis on metals means.,What is catalysis?,Surface Reactions,Kinetics and Reaction Rate Theory,Temperature Dependence of the Rate,Molecules collide, but only a small fraction of the collisions is reactive collision theory transition state theory,Reaction Rate Theory,Reaction Rate Theory,reactio
8、n parameter,E,Collision Theory of Reaction Rates, reaction if collision energy barrier energy incidentally successful usually predicts prefactors that are too high major problem: disagrees with vant Hoff equation for the equilibrium constant,Collision Theory,Transition State Theory,Collision Theory
9、hard spheres scatter or react upon collision Transition State Theory molecules possess internal degrees of freedom translation vibration rotation described by statistical thermodynamics (partition functions),Reaction Rate Theory,Boltzmann Statistics: The basis of statistical thermodynamics,Ludwig Bo
10、ltzmann (1844- 1906),Partition Function,Thermodynamical function of state Contains information on energy and entropy,All Molecules,Transition State Theory,Henry Eyring 1901 - 1981,reaction coordinate,Transition State Theory: The Assumptions, passage over barrier only in forward direction equilibrium
11、 between reactants and products for all degrees of freedom, except for reaction coordinate passage over barrier is classical event, described by one reaction coordinate only,How to Compare Transition State Theory Expressions with the Arrhenius Equation?,Key:,in transition state theory the activation
12、 energy is not precisely equal to the barrier energy,m: number of times T appears in the rate expression,How to Compare Transition State Theory Expressions with the Arrhenius Equation?,The Meaning of Preexponential Factors,Application to Surface Reactions Adsorption,Application to Surface Reactions
13、Desorption,Desorption of Atoms and Molecules,Temperature Programmed Desorption,Thermal desorption of CO,Preexponential Factors for Desorption at Low Coverages,from V.P. Zhdanov, Elementary Physicochemical Processes at Surfaces, Plenum, New York, 1991,Ammonia on Rh(111),Peculiar TPD patterns,Lateral
14、Interactions? Preexponential Factor?,R. M. van Hardeveld, R.A. van Santen and J.W. Niemantsverdriet Surface Sci. 369 (1996) 23,Dissociation of Adsorbed Molecules,C T Campbell, Y K Sun and W H Weinberg, Chem. Phys. Lett. 179 (1991) 53,Dissociation proceeds through tight transition states with prefact
15、ors smaller than for desorption.,CO oxidation (surface-mediated),reaction coordinate,Eley - Rideal Mechanism,in the most favorable case for ER (Eact = 0): kER / kLH = 7 x 10-6,更刺激，更清爽 生活像一杯水，有的时候需要加点冰,From the century of the rate equation to the century of the rate constant: a revolution in catalyti
16、c kinetic and assisted catalyst design -M. Boudart, Catal. Letter, 65 (2000) 1-3,1910s,1940s,1990s,Michaelis-Menten,Langmuir-Hinshelwood,Hougen-Watson,Dumesic-Rudd; Froment,Extracted ki,Calculated or measured ki,Strategy of Microkinetic Modeling,Microkinetic modeling,ReactionMechanism,Rate constants
17、 ki=A0exp(-Ei/RT),Calibration,Steam reforming dry reforming methane decomposition CO hydrogenation CO2 methanation,A0: transition state collision Ei: Bond order conservation,Bond strength: M-C,M-H,M-O,X,W/F0,R(T,Ci, catalyst) Suggestion for catalyst improvement Connection to other experiments,Reacti
18、on Mechanism,Reaction Rate constant Rate constant Forward reaction Reverse reactionr1 CH4 + 2* *CH3 + *H 6.5107e-57500/RT 1.51010e-80900/RT r2 *CH3 + * *CH2 + *H 1.01013e-99900/RT 2.01012e-49600/RT r3 *CH2 + * *CH + *H 1.01013e-97000/RT 1.01013e-73700/RT r4 *CH + 2* *C + *H 1.01013e-189700/RT 1.0101
19、3e-173000/RT r5 H2O + * *H2O 2.4106 1.01013e-68900/RT r6 *H2O + * *OH+*H 1.01016e-86700/RT 1.01013e-42700/RT r7 *C + *OH *CHO + * 1.01013e-86800/RT 6.731011T-3.03e-103600/RT r8 *COOH+*H *CHO+*OH 3.381018T-0.968e-108900/RT 1.01015e-24900/RT r9 *CHO + * *CO + *H 1.01011e-16800/RT 1.01011e-66700/RT r10
20、 *CO CO + 2* 3.21012e-122400/RT 1108 r11 2*H H2 + 2* 11013e-97600/RT 3.2108e-5600/RT r12 CO2 + 2* *CO2 1.0106 1.01013e-27300/RT r13 *CO2 + *H *COOH + * 1.01013 1.01013e-18400/RT,Estimation of rate constants,For a elemental reaction step:A*+B*AB* r=k0exp(-E/RT)AB k0: Preexponential factor:transition-
21、state theorycollision theory E: Activation energy:ab initio: bond prepared cluster model Bond order conservation (BOC)Evans-Polanyi correlation,ABConsidering both M-A and A-B interactions to be Morse type and additive The maximal bond energy can be identified to the molecular heat of chemisorption (
22、Q),Bond Order Conservation-Morse Potential (BOC-MP),Activation Energy,Dissociation:ABg A* +B*Dissociation: AB* A* +B*Recombination: A* +B* AB,Bond strength of QC-Ni , QH-Ni, QO-Ni are the model inputs,Microkinetic Model of MR,Reaction Rate constant Rate constant Forward reaction Reverse reactionr1 C
23、H4 + 2* *CH3 + *H 6.5107e-57500/RT 1.51010e-80900/RT r2 *CH3 + * *CH2 + *H 1.01013e-99900/RT 2.01012e-49600/RT r3 *CH2 + * *CH + *H 1.01013e-97000/RT 1.01013e-73700/RT r4 *CH + 2* *C + *H 1.01013e-189700/RT 1.01013e-173000/RT r5 H2O + * *H2O 2.4106 1.01013e-68900/RT r6 *H2O + * *OH+*H 1.01016e-86700
24、/RT 1.01013e-42700/RT r7 *C + *OH *CHO + * 1.01013e-86800/RT 6.731011T-3.03e-103600/RT r8 *COOH+*H *CHO+*OH 3.381018T-0.968e-108900/RT 1.01015e-24900/RT r9 *CHO + * *CO + *H 1.01011e-16800/RT 1.01011e-66700/RT r10 *CO CO + 2* 3.21012e-122400/RT 1108 r11 2*H H2 + 2* 11013e-97600/RT 3.2108e-5600/RT r1
25、2 CO2 + 2* *CO2 1.0106 1.01013e-27300/RT r13 *CO2 + *H *COOH + * 1.01013 1.01013e-18400/RT,Simulation of Methane Steam Reforming on Ni/MgO-MgAlO Results from Xu and Froment AIChEJ 35 (1989) 88,Reaction conditions:P=15 bar, S/C=3, H2/C=1.25,T=500,525,550,575 C,Simulation of steam reforming on Ni cata
26、lyst in the presence of steam,The external temperature gradients have been taken into account by Excel sheet developed in EuroKin . No change in microkinetic model was made,Reaction conditions. T= 650 C, P=20 bar, PCH4=4 bar and S/C=2 =35 K,Mechanism of Carbon Formation,Dissolution/segregationC* C N
27、i,f + *Diffusion of carbon trough NiC Ni,f C Ni,rPrecipitation/dissolution of carbonC Ni,r Cw Encapsulating carbon formationnC* n C,Microkinetic model for carbon formation,Segregation is described by a Langmuir equation,Carbon diffusion through Ni:,Encapsulating carbon formation:,3*C3Cp,r=kC3,Coking
28、 Rates and Coking Thresholds,650 C,600 C,550 C,630 C,Reaction conditions.T= 650 C, P=20 bar, PCH4=4 bar and S/C=2,Experimental Coking Threshold and Estimated Saturation Concentration of Carbon Filaments in Ni,Catalyst Design,New Catalyst,Microkinetic Modeling,BOC,Experiments,Ensemble Size Effects Cr
29、ystal Size Effects,Bond Strength,Support,Promoter,Alloy,Coke,crystal,Catalytic Reactivity of Nanoparticles,1. Nanoparticles and how to make them 2. Particle-size effects in catalysis.Ensemble theory.Specifc sites on small particles. Electronic effects 3. Nanoparticles on planar substrates as model c
30、atalysts,Reactivity of Nanoparticles,length and time scales in catalytic processes,Catalyst Particles: Dispersion and Specific Area,Catalyst Preparation: Pore Volume Impregnation,Anchoring of catalyst precursors to the support,XPS: Dispersion,A.C.Q.M. Meijers ertal. Appl. Catal. 70(1991) 53,Nanopart
31、icles on Planner Substrates,Activation: Calcination, Reduction or Sulfidation,Guaranteed: nanoparticles of 3 -15 nm,AFM,Particle Size Effect on Catalytic Activity,S.H. Oh and C.C. Eickel, J. Catal. 128 (1991) 526,CO Oxidation on Au Particles at 0 C,M. Haruta, Catalysis Today 36 (1997),Turn over freq
32、uencies and band-gap measured by STM as a function of the diameter of Au islands deposited on TiO2.,M.Valden, X. Lai and D.W. Goodman. Science281(1998), p. 1647.,Catalytic Activity of Au/Al2O3catalyst,Ensembles on particles of different size,Dissociation on small Particles: Ensembles +Specific Sites
33、 with Higher Reactivity,H.-J. Freund, M. Baumer and H. Kuhlenbeck, Advances in Catalysis, 45 (2000) 333,Specific sites on small particles,Statistics ( for static particles.),However, morphology depends on environment,Cu/ZnO,P.L. Hansen, J.B. Wagner, S. Helveg, J. Rostrup-Nielsen, B.S.Clausen, and H.
34、 Topsoe, Science, 295 (2002) 2053,Particle Morphology Depends on Environment,What do we need in the field of nanoparticles?,谢 谢 大 家 !,Fundamental Aspects and Common Principles,Surface Sensitivity,Intensity Factors,Catalyst Characterization,Characterization Techniques I,Characterization Techniques II
35、,Characterization Techniques III,In-situ Techniques,Methods of catalyst characterization generated by the combination of photon, electron and ion,Methods of catalyst characterization generated by the combination of photon, electron and ion,Methods of catalyst characterization generated by the combin
36、ation of photon, electron and ion,X-Ray Photoelectron Spectroscopy (XPS) - Principle,X-Ray Photoelectron Spectroscopy (XPS) - Principle,X-Ray Photoelectron Spectroscopy (XPS) - Chemical Shift,XPS Application - Angular Dependence of Intensities: Surface Carbonate on Ni(100),R.J. Behm and C.R. Brundle
37、, Surf. Sci. 255 (1991) 327,XPS Application - Surface Carbonate on Ni(100),R.J. Behm and C.R. Brundle, Surf. Sci. 255 (1991) 327,XPS Application - Surface Carbonate Decomposition on Ni(100),R.J. Behm and C.R. Brundle, Surf. Sci. 255 (1991) 327,X-Ray Photoelectron Spectroscopy (XPS) - Charging,Chargi
38、ng on a MoO3/SiO2 Catalyst,Energy Scheme,Ion Scattering Spectroscopy (ISS) - Principle,ISS Application - Calcination of La2O3/Al2O3 Catalyst,G.C. van Leedam et al, Appl. Surf. Sci. 55 (1992) 11,ISS Application - Sputtering of a Rh/Al2O3 Model Catalyst,Ch. Linsmeier et al., Surf. Sci. 275 (1992) 101,
39、Secondary Ion Mass Spectrometry (SIMS) - Principle,SIMS Application - Calcination of ZrO2/SiO2 Catalyst,A.C.Q.M. Meijers et al, Appl. Catal. 70 (1991) 53,SIMS Application - Characterization of a Promoted Fe-Sb Oxide Catalyst,J.W. Niemantsverdriet, “Spectroscopy in Catalysis” (VCH, Weinheim, 1993),X-
40、Ray Absorption Spectroscopy: EXAFS and XANES,X-Ray Absorption Spectroscopy: EXAFS and XANES,S.M.A.M. Bouwens et al.,J.Phys.Chem. 94 (190) 3711,Vibrational Spectroscopy - Principle,Diffuse Reflectance FT- Infrared Spectroscopy (DRIFTS),IR Application - CO Adsorption on PdAg-Catalyst,Y. Soma-Nato et a
41、l. , J. Catal. 32 (1974) 315,DRIFTS Application - Vibrations in a Silica Support,J.W. Niemantsverdriet, “Spectroscopy in Catalysis” (VCH, Weinheim, 1993),Atomic Force Microscopy (AFM) - Principle,Transmission Electron Microscopy - Schematics,L. Reimer,“ Transmiss. Electron Spectroscopy”(Springer, Be
42、rlin, 1989),Transmission Electron Microscopy: Dark Field - Bright Field Operation,Conditioning Procedure,Catalyst Conditioning - XPS,Particle Size Sintering,Mean Free Path of Slow Electrons,G.A. Somorjai, “Introduction to Surface Chemistry and Catalysis” (Wiley, New York, 1994), p.383,Energy Distribution of Scattered Electrons,
