We think you have liked this presentation. If you wish to download it, please recommend it to your friends in any social system. Share buttons are a little bit lower. Thank you!
Presentation is loading. Please wait.
Published byAngie Willets
Modified over 2 years ago
© 2004 Quantachrome Instruments This presentation is the property of Quantachrome Corporation and has been provided to Johnson-Matthey for its internal use by its bona-fide employees only. Under no circumstances shall the presentation, or any part of it, be provided to an external or third party without the express prior written permission of Quantachrome Corporation. The material contained within is, to the best of Quantachromes knowledge, accurate as of the date shown. Nevertheless, it shall be used at your own risk. Under no circumstances will Quantachrome be responsible for damages or losses arising out of its use. Unless otherwise stated, all material is Copyright © 2004 Quantachrome Corporation. Copyright notices shall neither be removed nor modified. By viewing this presentation in part or entirety you agree to the above terms. Quantachrome I N S T R U M E N T S
© 2004 Quantachrome Instruments Chemisorption Quantachrome I N S T R U M E N T S 3
© 2004 Quantachrome Instruments 3. Chemisorption Techniques 3.1 Introduction: Physisorption/Chemisorption 3.2Classical Models 3.3Active Metal Area Measurement 3.4Adsorption Thermodynamics 3.5Pulse vs. Static 3.6Temperature Programmed Analyses
© 2004 Quantachrome Instruments Introduction Quantachrome I N S T R U M E N T S 3.1
© 2004 Quantachrome Instruments 3.1 Introduction 3.1 Introduction: Physisorption/Chemisorption 3.2Classical Models 3.3Active Metal Area Measurement 3.4Adsorption Thermodynamics 3.5Pulse vs. Static 3.6Temperature Programmed Analyses
© 2004 Quantachrome Instruments The Nature of Gas Sorption at a Surface When the interaction between a surface and an adsorbate is relatively weak only physisorption takes place. However, surface atoms often possess electrons or electron pairs which are available for chemical bond formation. This irreversible adsorption, or chemisorption, is characterized by large interaction potentials which lead to high heats of adsorption.
© 2004 Quantachrome Instruments Physisorption vs Chemisorption
© 2004 Quantachrome Instruments On The Nature of Chemisorption Chemisorption is often found to occur at temperatures far above the critical temperature of the adsorbate. As is true for most chemical reactions, chemisorption is usually associated with an activation energy, which means that adsorbate molecules attracted to a surface must go through an energy barrier before they become strongly bonded to the surface.
© 2004 Quantachrome Instruments Adsorption Potentials A Potential energy curves for molecular (non-dissociative) adsorption
© 2004 Quantachrome Instruments Adsorption Potentials Potential energy curves for activated adsorption
© 2004 Quantachrome Instruments Adsorption Potentials Potential energy curves for non-activated adsorption
© 2004 Quantachrome Instruments Isobars Isobaric variation in quantity adsorbed with temperature. Physisorption isobar (a) represents lower heat of adsorption than chemisorption isobar (b). Temperature Quantity adsorbed (a) (b) (c)
© 2004 Quantachrome Instruments On The Nature of Chemisorption Because chemisorption involves a chemical bond between adsorbate and adsorbent, unlike physisorption, only a single layer of chemisorbed species can be realized on localized active sites such as those found in heterogeneous catalysts. However, further physical adsorption on top of the chemisorbed layer and diffusion of the chemisorbed species into the bulk solid can obscure the fact that chemisorbed material can be only one layer in depth
© 2004 Quantachrome Instruments Classical Models Quantachrome I N S T R U M E N T S 3.2
© 2004 Quantachrome Instruments 3.2 Classical Models Langmuir Freundlich Temkin
© 2004 Quantachrome Instruments Adsorption Process Active Sites (Adsorbent) Adsorbate Adsorptive
© 2004 Quantachrome Instruments Graduated as a metallurgical engineer from the School of Mines at Columbia University in M.A. and Ph.D. in 1906 from Göttingen Instructor in Chemistry at Stevens Institute of Technology, Hoboken, New Jersey –1950 General Electric Company at Schenectady where he eventually became Associate Director Invented the gas filled, coiled tungsten filament incandescent lamp to 1921, his interest turned to an examination of atomic theory, and he published his "concentric theory of atomic structure". In it he proposed that all atoms try to complete an outer electron shell of eight electrons Irving Langmuir ( )
© 2004 Quantachrome Instruments 1927 Coined the use of the term "plasma" for an ionized gas The Nobel Prize in Chemistry "for his discoveries and investigations in surface chemistry" With Katherine Blodgett studied thin films With Vincent Schaefer discovered that the introduction of dry ice and iodide into a sufficiently moist cloud of low temperature could induce precipitation. Irving Langmuir ( )
© 2004 Quantachrome Instruments Langmuirs Kinetic Approach rate of adsorption = k a P(1- ) where is the fraction of the surface already covered with adsorbate, i.e., = V/Vm rate of desorption = k d Suggests a dynamic equilibrium. Is it?
© 2004 Quantachrome Instruments Langmuir (continued…) At equilibrium (any pressure) k a P(1- ) = k d from which = V/Vm = KP/(1+KP) where K = k a / k d. In its linear form, the above equation can be expressed as: 1/V = 1/Vm + 1/(VmKP)
© 2004 Quantachrome Instruments Confining adsorption to a monolayer, the Langmuir equation can be written where V is the volume of gas adsorbed at pressure P, V m is the monolayer capacity (i.e. θ=1) expressed as the volume of gas at STP and K is a constant for any given gas-solid pair. Rearranging in the form of a straight line (y=ab+x) gives Or, if you prefer…
© 2004 Quantachrome Instruments Langmuir Plot 1/P 1/V Slope = 1/(VmK) Intercept = 1/Vm 1/V = 1/Vm + 1/(VmK c P 1/s )
© 2004 Quantachrome Instruments Temperature Dependent Models generally K = Ko exp(q/RT) where Ko is a constant, R is the universal gas constant, T is the adsorption temperature and q is the heat of adsorption Langmuir:K is constant;q is constant at all Temkin: assumed that q decreases linearly with increasing coverage Freundlich: assumed that q decreases exponentially with increasing coverage
© 2004 Quantachrome Instruments Temkin Temkin assumed that q decreases linearly with increasing coverage, that is, Q=q o (1- ) Where q o is a constant equal to the heat of adsorption at zero coverage ( = 0) and is a proportionality constant.
© 2004 Quantachrome Instruments Temkin = A ln P + B or, since = V/Vm V = Vm A lnP + VmB Where A = RT/qo and B = A ln Ko + 1/
© 2004 Quantachrome Instruments Temkin Plot Ln(P) V Slope = VmA Intercept = VmB V = Vm A lnP + VmB
© 2004 Quantachrome Instruments Multiple Temkin Plots to find Ln(P) V Temp HTemp MTemp L * denotes temperature invariant or thermally irreversible quantity experimentalextrapolated
© 2004 Quantachrome Instruments Freundlich Temkin assumed that q decreases exponentially with increasing coverage, that is, Q = -q m ln Where q m is a constant equal to the heat of adsorption at =
© 2004 Quantachrome Instruments Freundlich ln = C lnP + D or, since = V/Vm ln(V/Vm) = C lnP + D Where C=RT/ q m and D = C lnKo
© 2004 Quantachrome Instruments Freundlich (continued…) Ln(P) Ln(V) Slope = C Intercept = D + ln(Vm) Ln( V/Vm) = C lnP + D
© 2004 Quantachrome Instruments Multiple Temkin Plots to find Ln(P) Ln(V) Temp HTemp MTemp L * denotes temperature invariant or thermally irreversible quantity experimentalextrapolated
© 2004 Quantachrome Instruments Active Metal Area Quantachrome I N S T R U M E N T S 3.3
© 2004 Quantachrome Instruments 3.3 Active Metal Area Principles of Calculation 3.3.2Choice of Adsorbate 3.3.3Active Site Size Calculation 3.3.4Metal Dispersion 3.3.5Accessible vs non-accessible sites
© 2004 Quantachrome Instruments Active Site Quantification Because the formation of a chemical bond takes place between an adsorbate molecule and a localized, or specific, site on the surface of the adsorbent, the number of active sites on catalysts can be determined simply by measuring the quantity of chemisorbed gas
© 2004 Quantachrome Instruments Active Site on a Catalyst Metal on support. Island-like crystallites Not all metal atoms exposed. Adsorption technique perfectly suited. (cf Chemical analysis of entire metal content )
© 2004 Quantachrome Instruments Principles of Calculation Monolayer Volume, Vm = volume of gas chemisorbed in a monomolecular layer
© 2004 Quantachrome Instruments Methods to Determine V m Extrapolation Bracketing Langmuir Temkin Freundlich = volume of gas chemisorbed in a monomolecular layer
© 2004 Quantachrome Instruments Vm Volume Adsorbed Pressure (mm Hg) Extrapolation method First (only?)isotherm
© 2004 Quantachrome Instruments Volume Adsorbed Pressure (mm Hg) The second isotherm combined Weak only
© 2004 Quantachrome Instruments Volume Adsorbed Pressure (mm Hg) The difference isotherm combined Weak only Strong
© 2004 Quantachrome Instruments V m from Pulse Titration … will be covered in 3.5.2
© 2004 Quantachrome Instruments Metal Area Calculation To Calculate Metal Surface Area: A = (V m ) x (MXSA) x (S) x 6.03 x 10-3 (units m 2 /g) where MXSA = metal cross sectional area (Å 2 ) and S = stoichiometry = metal atoms per gas molecule To calculate metal area per gram of metal, A m : A m = A x l00/L where L = metal loading (%) = known value from chemical analysis
© 2004 Quantachrome Instruments Stoichiometry The gas-sorption stoichiometry is defined as the number of metal atoms with which each gas molecule reacts. Since, in the gas adsorption experiment to determine the quantity of active sites in a catalyst sample, it is the quantity of adsorbed gas which is actually measured, the knowledge of (or at least a reasonably sound assumption of) the stoichiometry involved is essential in meaningful active site determinations (area, size, dispersion).
© 2004 Quantachrome Instruments Choice of Adsorbate Chemisorption CO or H 2 on Pt, Pd at 40 o C CO or H 2 on Ni For metal-only area (& dispersion etc) Physisorption N 2 at 77K Ar at 87K Kr at 77K CO 2 at 273K For total surface area and pore size
© 2004 Quantachrome Instruments Active Site Size Calculation To calculate average crystallite size: d = (L x 100 x f )/AD (units Å) where f = shape factor = 6 ρ = density of metal (g/ml)
© 2004 Quantachrome Instruments Shape Factor & Crystallite Size The default shape factor of 6 is for assumed cubic geometry. Consider a cube of six sides (faces) each of length l. then the total surface area, A = 6l 2. The volume of the cube is given by l 3 or, in terms of total area, substitute A /6 for l 2 to give V= l A/6 For a cube whose mass is unit mass, its volume is given by 1/ (where is the density of the material). V=1/
© 2004 Quantachrome Instruments Shape Factor & Crystallite Size For the same cube of unit mass, the area is then the area per unit mass A and l is rewritten d (crystallite size), the length required to give a cube whose mass is unity. Equating both terms for volume: dA/6=1/ or d=6/A For a supported metal, the loading, L, must be taken into consideration. d=L6/A Other geometries can be treated in a similar fashion. For example, a rectangular particle whose length is three times its width has a shape factor of 14/3.
© 2004 Quantachrome Instruments Supported metals It is most likely that the catalyst exists as a collection of metal atoms distributed over an inert, often refractory, support material such as alumina. At the atomic level it is normal that these atoms are assembled into island-like crystallites on the surface of the support. 3.3 Metal Dispersion
© 2004 Quantachrome Instruments 3.3 Metal Dispersion In the case of supported metal catalysts, it is important to know what fraction of the active metal atoms is exposed and available to catalyze a surface reaction. Those atoms that are located inside metal particles do not participate in surface reactions, and are therefore wasted.
© 2004 Quantachrome Instruments Exposed metal atoms Since these islands vary in size due to both the intrinsic nature of the metal and the support beneath, plus the method of manufacture more or less of the metal atoms in the whole sample are actually exposed at the surface. It is evident therefore that the method of gas adsorption is perfectly suited to the determination of exposed active sites. support Exposed active sites Adsorbed gas
© 2004 Quantachrome Instruments Metal Dispersion Dispersion is defined as the percentage of all metal atoms in the sample that are exposed. The total amount of metal in the sample is termed the loading, χ, as a percentage of the total sample mass, and is known from chemical analysis of the sample.
© 2004 Quantachrome Instruments Metal Dispersion The dispersion, δ, is calculated from: Where M is the molecular weight of the metal, N a is the number of exposed metal atoms found by adsorption and W S is the mass of the sample.
© 2004 Quantachrome Instruments Accessible vs. Non-accessible Sites 1.Adventitious moisture 2.Reducing gas accessibility 3.Diffusion 4.Purge 5.Physisorption blocks 6.Bulk hydride 7.Spillover 8.Stoichiometry 9.Characterization gas vs. Process gas
© 2004 Quantachrome Instruments Spatial Ordering There may exist a number of different adsorption sites that involve different numbers of metal atoms per adsorbate molecule.
© 2004 Quantachrome Instruments Adsorption Thermodynamics Quantachrome I N S T R U M E N T S 3.4
© 2004 Quantachrome Instruments 3.4 Adsorption Thermodynamics Isosteric Heats from Isotherms See also activation energy under 3.6.1
© 2004 Quantachrome Instruments Heats of Adsorption Whenever a gas molecule adsorbs on a surface, heat is (generally) released, i.e. the process of adsorption is exothermic. This heat comes mostly from the loss of molecular motion associated with the change from a 3- dimensional gas phase to a 2-dimensional adsorbed phase. Heats of adsorption provide information about the chemical affinity and the heterogeneity of a surface, with larger amounts of heat denoting stronger adsorbate-adsorbent bonds. There are at least two ways to quantify the amount of heat released upon adsorption: in terms of (i) differential heats, q, and (ii) integral heat, Q.
© 2004 Quantachrome Instruments Differential Heats of Adsorption q, is defined as the heat released upon adding a small increment of adsorbate to the surface. Its value depends on (i) the strength of the bonds formed and (ii) the degree to which surface is already covered. i.e a plot of q vs. θ provides a curve illustrating the energetic heterogeneity of the surface. Use it to fingerprint surface energetics and to test of the validity of any Vm evaluation method used (see earlier) since each method assumes a different relationship between q and θ.
© 2004 Quantachrome Instruments Differential Heats of Adsorption Since q can, and most often does, vary with θ, it is convenient to express it as an isosteric heat of adsorption, that is, at equal surface coverage for different temperatures. Thus, obtain two or more isotherms at different temperatures. Determine pressures corresponding to equal coverage at different temperatures. Construct an Arrhenius plot of (lnP) versus (1/T). Values for q at any given coverage, θ, can be calculated from the Arrhenius slopes, m.
© 2004 Quantachrome Instruments Slopes of (lnP) vs. (1/T). where m = d lnP/d(1/T) and R is the universal gas constant.
© 2004 Quantachrome Instruments Integral Heat of Adsorption This is simply defined as the total amount of heat released, Q, when one gram of adsorbent takes up X grams of adsorbate. It is equivalent to the sum, or integral, of q over the adsorption range considered, that is: where Vm is expressed in mL at STP, and θ ideally ranges from θ min = 0 to θ max = maximum coverage attained experimentally.
© 2004 Quantachrome Instruments Experimental Approaches Quantachrome I N S T R U M E N T S 3.5
© 2004 Quantachrome Instruments 3.5 Experimental Approaches Pulse Static
© 2004 Quantachrome Instruments Preparation Techniques Sample is heated under inert flow to remove adsorbed moisture. Whilst reduction step creates moisture, we dont ant the reducing gas to compete for diffusion to surface. Reduce with H 2 : can be pure hydrogen or diluted with nitrogen or argon. Higher concentrations give higher space velocities for the same volumetric flow rate.
© 2004 Quantachrome Instruments Preparation Techniques (continued…) Purging with inert gas (normally helium) strips excess reducing gas quickly. Can shorten prep time and/or give more reproducible data since hydrogen is difficult to pump. Cooling is done under vacuum/flow to ensure continued removal of residual reducing gas… though it is the hot removal step (above) which is critical. That is, dont cool before removing as much reducing gas as possible.
© 2004 Quantachrome Instruments Chemisorption Techniques Vacuum method Flow methods
© 2004 Quantachrome Instruments Vacuum Technique Sample is heated under inert flow Reduced with H 2 Purged with inert, cooled under vacuum/flow Adsorbate dosed to obtain isotherm Calculate the amount adsorbed
© 2004 Quantachrome Instruments Static (volumetric) Setup furnace manifold adsorptives vent diaphragm pump Turbo- molecular (drag) pump Flow U cell
© 2004 Quantachrome Instruments Setup Filler rod goes here Quartz wool samplecapillary
© 2004 Quantachrome Instruments Flow (Pulse) Chemisorption
© 2004 Quantachrome Instruments Flow Types of Analysis TPR TPO TPD Monolayer by Titration BET support active sites A flow system permits multi- functional catalyst characterization :
© 2004 Quantachrome Instruments Overview Analysis is done by detecting changes in gas composition downstream of sample. Detector senses –abstraction of reactive species during adsorption –evolution of previously adsorbed species during desorption –decomposition products Signal detection –Standard: thermal conductivity detector –Optional: mass spectrometer
© 2004 Quantachrome Instruments ChemBET 3000 TPR
© 2004 Quantachrome Instruments Flow Diagram AB A IN OUT CLICK FOR BYPASS & LONGPATH
© 2004 Quantachrome Instruments Flow/Static (FloStat ) Flow Diagram to mass spec (optional) to vent B A oil-free high vacuum vapor source (optional) heater Schematic representation only. Some vacuum volumetric components omitted for clarity. heated zone (vapor option)
© 2004 Quantachrome Instruments TPRWin Software Data Acquisition
© 2004 Quantachrome Instruments Overview Quartz flow-through cell allows –high-temperature (up to 1100 degC) –in-cell temperature monitoring –Two t/cs if necessary, one to DAQ, one to MassSpec. –mass spectrometer sampling port. T/C #1 T/C #2 Modified cell holder Capillary to mass spec. Gas flow
© 2004 Quantachrome Instruments Pulse Titration Metal area, dispersion and crystallite size are calculated from the amount of analysis (reactive) gas adsorbed. Variable volumes of analysis gas are injected into the inert carrier gas stream, which continuously flows over the sample. Detector measures the volume of gas that remains unadsorbed by the sample. Subtraction from the total amount injected gives the total amount adsorbed to within 1uL accuracy.
© 2004 Quantachrome Instruments Titration Pulse Titration of Active Sites H 2 or CO titration N 2 and He carrier respectively Constant temperature (room temp?) Multiple injections until saturation M M M M H H H H H H2H2 CO N2N2 He
© 2004 Quantachrome Instruments Titration Data Acquisition
© 2004 Quantachrome Instruments Titration injections signal LOADINJECT
© 2004 Quantachrome Instruments Titration Calculations 1. Calculate total nominal volume of reactive gas adsorbed by comparison with calibration injection or average of last n (three) peaks (note: peak area represents gas not adsorbed!) Total vol adsorbed = (Peak Avg - Peak1) + (Peak Avg - Peak2) + (Peak Avg - Peak3) etc x nominal injection volume = V nom (units l)
© 2004 Quantachrome Instruments Titration Calculations 2. Convert to STP: (V nom ) x (273/rt) x (P amb /760) = V stp (units l) 3. Convert to specific volume adsorbed: V stp /sample wt = V sv (units l/g) 4. Convert to micromoles per gram (weight as supplied ): V sv / 22.4 = V m (units mole/g)
© 2004 Quantachrome Instruments Requirements for Different Analysis Types Long cell Short cell Std. cell 5% H2 100% H2 5% O2 100% N2 100 % He 30% N2 Inj. Furnac e MantleDewarLong path TPR ( ) TPO TPD Metal Area * ( ) ( ) * * BET ( ) * Using H2 active gas. If using CO, substitute 100% CO for 100% H2 & 100% He for 100% N2. L
© 2004 Quantachrome Instruments Temperature Programmed (TP) Experiments Quantachrome I N S T R U M E N T S 3.5
© 2004 Quantachrome Instruments 3.6 Temperature Programmed (TP) Experiments TP-Reduction TP-Oxidation TP-Desorption TP-Reaction
© 2004 Quantachrome Instruments TP-Reduction Metal oxides are readily characterized by their ease of reduction. CeO 2 CeO 2-x + x / 2 O 2 TPR profiles represent that ease of reduction as reduction rate as a function of increasing temperature. 2CeO 2 + H 2 Ce 2 O 3 + H 2 O
© 2004 Quantachrome Instruments Temperature Programmed Reduction A low concentration of pre-mixed hydrogen (e.g.5%) in nitrogen or argon (or other reducing gas for custom research applications) flows over the sample as it is heated during a linear increase (ramp) in temperature. Peak reduction temperature is also a function of heating rate and may be used to calculate activation energy for the reduction process.
© 2004 Quantachrome Instruments TPR Temperature Programmed Reduction Metal oxide to metal 5% hydrogen reactive gas Balance N 2 or Ar (not He !...unless MS) Ramp rate Activation Energy H2H2 MO H2OH2O M M M M
© 2004 Quantachrome Instruments TPR temperature signal t max
© 2004 Quantachrome Instruments TPR Linearly ramped furnace is essential for standard TP profiles
© 2004 Quantachrome Instruments time signal t max temperature TPR Profiles for Different Heating Rates 1 2 3
© 2004 Quantachrome Instruments TPR Profiles for Different Heating Rates
© 2004 Quantachrome Instruments TPR Profile Heating Rate (K -1 ) Peak Temperature (T max ) Heating Rate & Peak Temperature
© 2004 Quantachrome Instruments Kissinger (Redhead) Equation
© 2004 Quantachrome Instruments TP-Oxidation Temperature programmed oxidation (using 2%-5% O 2 in He for example) is performed in a manner analogous to TPR. TPO can be particularly useful for looking at carbons: –Carbon supports (graphite vs. amorphous) –Carbon deposits from coking –Carbides
© 2004 Quantachrome Instruments TPO Temperature Programmed Oxidation Metals and carbon to oxides 2-5% oxygen reactive gas balance He (not N 2 !) Ramp rate Activation Energy O2O2 C C C C CO + CO 2 M M M M carbon
© 2004 Quantachrome Instruments TPO: Signal vs. Temperature
© 2004 Quantachrome Instruments TPO: Signal & Temp. vs. Time
© 2004 Quantachrome Instruments Temperature Programmed Oxidation Zhang and Verykios reported that three types of carbonaceous species designated as C, C, and C were found over Ni/Al 2 O 3 and Ni/CaO±Al 2 O 3 catalysts in the TPO experiments. Zhang ZL and Verykios XE,. Catal. Today (1994). Goula et al identified two kinds of carbon species on Ni/CaO Al2O3 catalysts from TPO experiments. The high-temperature peak was assigned to amorphous and/or graphite forms of carbon. The lower temperature peak suggested a filamentous form. Goula MA, Lemonidou AA and Efstathiou AM, J Catal (1996).
© 2004 Quantachrome Instruments Temperature Programmed Desorption The monitoring of desorption processes is equally easy. A pure unreactive carrier gas carries evolved species from the sample to the detector as the user-programmable furnace heats the sample. This technique is commonly employed to determine the relative-strength distribution of acidic sites by means of ammonia desorption.
© 2004 Quantachrome Instruments TPD Temperature Programmed Desorption Remove previously adsorbed species Helium/Nitrogen purge Ramp rate Activation Energy NH 3 MO NH 3
© 2004 Quantachrome Instruments Ammonia TPD
© 2004 Quantachrome Instruments Pyridine TPD Physisorbed pyridine is clearly evident in the first sample (low temp.), but absent in the second. Multiple acid sites revealed by peak deconvolution
© 2004 Quantachrome Instruments TPD temperature signal t max Increasing mass
© 2004 Quantachrome Instruments Overview Quartz flow-through cell allows –high-temperature (up to 1100 degC) –in-cell temperature monitoring –Two t/cs if necessary, one to DAQ, one to MassSpec. –mass spectrometer sampling port. T/C #1 T/C #2 Modified cell holder Capillary to mass spec. Gas flow
© 2004 Quantachrome Instruments With Mass Spectrometer Capillary or capillary connector to mass spectrometer Tube ends just below port connection In-situ thermocouple ¼ swagelok ® compression fitting T/C #1 T/C #2 Modified cell holder Capillary to mass spec. Gas flow
© 2004 Quantachrome Instruments TP-Reaction Essentially everything that is not standard TPR or TPO!! Can be a single reactive gas, or a mixture of reactants… akin to microreactor work. Need not be done over a bare metal surface… might have one reactive species preadsorbed on the surface e.g.
Gas Properties and Gas Laws Chapters Kinetic Molecular Theory of Gases An ideal gas is one that fits all the assumptions of this theory: 1) Gases.
Metal surface area What do we mean by metal surface area ? How it is related to catalytic activity? How do we measure metal surface area?
Heterogeneous catalysis LEC.8. Individual Steps in Heterogeneous Catalysis Heterogeneously catalyzed reactions are composed of purely chemical and purely.
Chemistry. Surface Chemistry - 1 Session Session Objectives Adsorption versus absorption Types of adsorption: physisorption and chemisorption Desorption.
Adsorption and Catalysis Dr. King Lun Yeung Department of Chemical Engineering Hong Kong University of Science and Technology CENG 511 Lecture 3.
KINETICS. What is Kinetics? Kinetics is the study of the speed of reactions and is largely an experimental science. Some general qualitative ideas about.
Chemical Equilibrium Reference: Chapter 9 Reactions Rates and Equilibrium.
Adsorption Calorimetry Modern Methods in Heterogeneous Catalysis F.C. Jentoft, November 22, 2002.
Lecture 2—Adsorption at Surfaces 1.Adsorption/Desorption 2.Overlayers, lifting reconstruction 3.Dissociative and Associative adsorption 4.1 st and 2 nd.
Lecture 20. Adsorption Phenomena. Adsorption is the accumulation of atoms or molecules on the surface of a material. This process creates a film of the.
Lecture 3. Adsorption on the interphase of liquid-gas Prepared by PhD Falfushynska Halina.
Heterogeneous catalysis Lec 9 week 12. Comparison of homogeneous and heterogeneous catalysts.
Temperature Programmed Desorption March 31, 2015.
Pressure – Volume – Temperature Relationship of Pure Fluids.
Chemical Kinetics Chapter 12. Chemical Kinetics The area of chemistry that concerns reaction rates.
1111 Chemistry 132 NT I never let my schooling get in the way of my education. Mark Twain.
Lecture 4 CHEMICAL AND PHASE EQUILIBRIUM (1). Objectives 1.Develop the equilibrium criterion for reacting systems based on the second law of thermodynamics.
Chapter 10; Gases. Elements that exist as gases at 25 0 C and 1 atmosphere.
Gas-Solid Interactions Light bulbs, Three way catalysts, Cracking, Corrosion, Electronic Devices etc.
Kinetic analysis of Temperature Programmed Reduction R. Jude vimal Michael National Centre for Catalysis Research 31 January 2009.
Partial Molar Quantities and the Chemical Potential Lecture 6.
Chemical Equilibrium unit 4 Lecture 2. Chemical Change Recap Chemical change occurs when the atoms that make up one or more substances rearrange themselves.
Chemical Reactions in Ideal Gases. Non-reacting ideal gas mixture Consider a binary mixture of molecules of types A and B. The canonical partition function.
CHAPTER 13 – States of Matter THE KINETIC THEORY 1.All matter is composed of very small particles 2.These particles are in constant, random motion.
Prentice Hall © 2003Chapter 15 Chapter 15 Chemical Equilibrium CHEMISTRY The Central Science 9th Edition David P. White.
States Of Matter!. Gases – Kinetic Molecular Theory Explains the forces between molecules and the energy the molecules possess.
Review of Chemical Thermodynamics Combustion MECH 6191 Department of Mechanical and Industrial Engineering Concordia University Lecture #1 Textbook: Introduction.
Chapter 21 The Kinetic Theory of Gases. Macroscopic vs. Microscopic Descriptions So far we have dealt with macroscopic variables: Pressure Volume Temperature.
1 Chemical Equilibrium You learned when we studied mechanisms that some rxns are reversible or equilibrium rxns The double arrow is used to show this.
A.P. Chemistry Chapter 10 Liquids & Solids Intermolecular Forces Intramolecular Bonding- when atoms form stable units called molecules by sharing.
SOME IMPORTANT ASPECTS OF PHYSISORPTION EXPERIMENT TO STUDY MESO- AND MICRO-POROUS MATERIALS BY D.K. SHARMA KUNASH INSTRUMENTS.
IC-1/38 Lecture Kinetics IC-2/38 Lecture What is Kinetics ? Analysis of reaction mechanisms on the molecular scale Derivation.
Lecture 18 (Ch 18) HW: Ch 18: 1, 3, 15, 41 Kinetics pt 2: Temperature Dependence of Rate Constants.
Collision Theory Collision theory is a theory proposed independently by Max Trautz in 1916 and William Lewis in 1918, that qualitatively explains how.
Heterogeneous Catalysis: Kinetics in Porous Catalyst Particles Assoc. Prof. Dr. Nesrin E. Machin Ref: S. Fogler (Ch 11)
Facile synthesis and hydrogen storage application of nitrogen-doped carbon nanotubes with bamboo-like structure Reference, Liang Chen et.al, international.
INTRODUCTION TO CATALYSIS –KINETICS OF CATALYTIC REACTIONS CH
© 2014 Pearson Education, Inc. Chemistry: A Molecular Approach, 3rd Edition Nivaldo J. Tro Solution The equilibrium constant is the equilibrium concentrations.
CHAPTER 9 BALANCES ON REACTIVE PROCESSES By : Ms. Nor Helya Iman Bt Kamaludin 1 PTT 108: Mass and Energy Balances.
Chapter 10 Gases No…not that kind of gas. Kinetic Molecular Theory of Gases Kinetic Molecular Theory of Gases – Based on the assumption that gas molecules.
CHAPTER 17 – CHEMICAL EQUILIBRIUM 8B-1 (of 37) COLLISION THEORY 1 - Molecules must collide to react 2 -Molecules must collide with sufficient energy to.
UNIT 3 CHEMICAL EQUILIBRIUM. Introduction to Chemical Equilibrium Focus has always been placed upon chemical reactions which are proceeding in one direction.
John A. Schreifels Chemistry Chapter 5 Gases.
Section 1.3. Limiting reactant Excess reactant Yields: Theoretical yield Percentage yield Experimental yield Avogadro’s law Molar volume.
CH4: Gases and their Properties NOTES #5. Diffusion Caused by random motion!!! And collision of molecules Random motion of molecules and their collisions.
I.Dalton’s Law A.The total pressure of a mixture of gases equals the sum of the pressures each gas would exert independently 1.P total = P 1 + P 2 + …
Reaction Rate and Equilibrium. Video: World of Chemistry Chemical Kinetics Use this video as an introduction to this concept.
S OLID S TATE AND S URFACE C HEMISTRY ( LECTURE 10) Dr. Saeda Rwede Al-Mhyawi Assistant professor in physical chemistry Contact Info:
1 Boyle’s Law (T and n constant) Charles’ Law (p and n constant) Combined Gas Law (n constant) Summary of Gas Laws p 1 ×V 1 = p 2 ×V 2.
© 2016 SlidePlayer.com Inc. All rights reserved.