环境催化技术1.ppt

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 Froment,Extracted ki,Calculated or measured ki,Strategy of Microkinetic Modeling,Microkinetic modeling,Reaction Mechanism,Rate constants ki=A0exp(-Ei/RT),Calibration,Steam reforming dry reforming methane decomposition CO h

2、ydrogenation 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,Reaction Mechanism,Reaction Rate constant Rate constant Forward reaction Reverse reaction r1

3、 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 1.01013e-173000/RT r5 H2O + * *H2O 2.4106 1.01013e-68900/RT r6 *H2O + * *OH+*H 1.01016e-867

4、00/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

5、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-state theory collision theory E: Activation energy: ab initio: bond prepared cluste

6、r model Bond order conservation (BOC) Evans-Polanyi correlation,AB Considering 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 (Q),Bond Order Conservation-Morse Potential (BOC-MP),Activation Energy,Dissociat

7、ion: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 reaction r1 CH4 + 2* *CH3 + *H 6.5107e-57500/RT 1.51010e-80900/RT r2 *CH3 + * *CH2 + *H 1

8、.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/RT 1.01013e-42700/RT r7 *C + *OH *CHO + * 1.01013e-86800/RT 6.731011T-3.03e

9、-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 r12 CO2 + 2* *CO2 1.0106 1.01013e-27300/RT r13 *CO2 + *H *COOH + * 1.01013 1.0

10、1013e-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 catalyst in the presence of steam,The external temperature gradients have been t

11、aken 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/segregation C* C Ni,f + * Diffusion of carbon trough Ni C Ni,f C Ni,r Precipitation/dissoluti

12、on of carbon C Ni,r Cw Encapsulating carbon formation nC* 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 Rates and Coking Thresholds,650 C,600 C,550 C,630 C,Reaction conditio

13、ns.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 Crystal Size Effects,Bond Strength,Support,Promoter,Alloy,Coke,crystal,

14、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 catalysts,Reactivity of Nanoparticles,length and time scales in cata

15、lytic 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,Nanoparticles on Planner Substrates,Activation: Calcination, Reduction or S

16、ulfidation,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 frequencies and band-gap measured by STM as a function of the diameter

17、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 with Higher Reactivity,H.-J. Freund, M. Baumer and H. Kuhlenbeck,

18、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. Topsoe, Science, 295 (2002) 2053,Particle Morphology Depends on En

19、vironment,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,Characterization Techniques III,In-situ Techniques,Methods of cata

20、lyst 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 combination of photon, electron and ion,X-Ray Photoelectron Spectroscopy

21、(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, Surf. Sci. 255 (1991) 327,XPS Application - Surface Carbonate on

22、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,Charging on a MoO3/SiO2 Catalyst,Energy Scheme,Ion Scattering Spectroscop

23、y (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,Secondary Ion Mass Spectrometry (SIMS) - Principle,SIMS Application

24、 - 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-Ray Absorption Spectroscopy: EXAFS and XANES,X-Ray Absorption Spectroscopy: EXAFS and XANES,S.M.A.M. Bouwens et al.,J.Phys.