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1 Heterogeneous Catalysis 6 lectures Dr. Adam Lee Surface Chemistry & Catalysis Group.

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1 1 Heterogeneous Catalysis 6 lectures Dr. Adam Lee Surface Chemistry & Catalysis Group

2 2 Synopsis Topics: Heterogeneous catalysts: definitions, types, advantages Catalyst surfaces: adsorption processes, kinetics Structure-sensitivity: dispersion, active site Bimetallic catalysts: selectivity control Catalyst preparation Catalyst characterisation Heterogeneous Catalysis is crucial to diverse industries ranging from fuels to food and pharmaceuticals. This course will introduce a wide range of heterogeneous catalysts and associated industrial processes. Methods for the preparation, characterisation and testing of solid catalysts will be discussed. Fundamentals of surface reactions and catalyst promotion are addressed, and finally some applied aspects of catalyst reactor engineering will be considered. Recommended Texts: Basis and Applications of Heterogeneous Catalysis: Mike Bowker,Oxford Primer, (1998) Catalytic Chemistry: B.C.Gates, Wiley (1992) Heterogeneous Catalysis: G.C.Bond OUP 2nd Ed (1987)

3 3 What are catalysts and why are they beneficial ‘Why haven’t they been used more widely when so many examples in petrochemical industry?’ Types of catalysts Properties of catalysts Calculation of TON & measurement of kinetic parameters Overview of typical classes of reactions and catalysts used Environmental considerations Lecture 1 Overview

4 4 Organic Chemistry (1805) Physical Chemistry Discovery of Catalysis (1835) - Petrochemical & oil refining industry recognise promise - Catalytic technology generates >10 trillion $/yr - Clean technology (1990?) - applications in plastics, fabrics, food, fuel Why don’t we use a catalyst? How can we accelerate a chemical reaction? Use reagents - stoichiometric - separation problems - TOXIC waste - Industrial fine chemicals processes developed - Carry on using reagents

5 5 Typical Reagents Oxidation Permanganate, Manganese dioxide, Chromium (VI) (<0.10 ppm) Reduction Metal Hydrides, (NaBH, LiAlH) 44 Reducing metals (Na, Fe, Mg,Zn) Basic reagents Potassiumbutoxide,diisopropylamine Tetramethyl guanidine Acidic reagents SO, HAlCl 3, BF 3, ZnCl 224 C-C Coupling Homogeneous Pd based complexes

6 6 Importance of Heterogeneous Catalysis Chemicals Industry: >90% of global chemical output relies upon heterogeneous catalysed processes Economics: ~20% of world GNP dependent on processes or derived products Equates to $10,000 billion/year!! Environment: Ozone depletion catalysed over aerosol surfaces in Polar Stratospheric Clouds Pollution control (catalytic converters, VOC destruction) Clean synthesis (waste minimisation, benign solvents, low temperature) Power generation Nobel Prize in Chemistry 2007 – Gerhard Ertl

7 7 Faujasitic zeolites Polymerisation (1957/1991) Zeigler-Natta /Metallocene nC 2 H 2 Catalytic Cracking (1964) C x H 2x+2 C x-2 H 2x-2 C x H 2x+2 C x-2 H 2x-4 HDPELDPE Historical Evolution

8 8 Automotive Emission Control (1976) Pt/Rh/Al 2 O 3 HC + CO + NO X CO 2 + H 2 O + N 2 Chiral Catalysis (1988) Chiral pocket

9 9 ‘A catalyst is a material that enhances the rate and selectivity of a chemical reaction without itself being consumed in the reaction.’ Swedish Chemist - Jöns Jakob Berzelius (1779-1848) Minimize FEEDSTOCK and reduce ENERGY costs More efficient use of raw materials. Advantages of Catalytic Technology

10 10 Heterogeneous - active site immobilised on solid support - tuneable selectivity - easily separated Homogeneous - organometallic complexes widely used - more active than heterogeneous, - high selectivity - difficult to separate Bio-catalysts - enzymes, bacteria, fungi - highly selective Phase transfer - Reagent soluble in separate phase to substrate - use PTC to transfer reagent into organic Classes of Catalyst

11 11 Catalyst: a material that enhances the rate and selectivity of a chemical reaction without itself being consumed in the reaction. Catalyst Definitions Rates (kinetics): Rate = rate constant x [reactant] n Rate constant (k or k’) = A exp (-E Act /RT) Consider, All catalysts work by providing alternative pathways: - different, lower E Act - accelerates both forward AND reverse reactions (increase k f and k b ) - catalysts do not influence how MUCH product forms Reactants Products k forward k back

12 12 http://www.chemguide.co.uk/physical/basicrates/catalyst.html#top Catalyst Definitions Uncatalysed Catalysed Energetics: Reactants do not all have same energy: Boltzmann distribution So what determines theoretical product yield?? - thermodynamic driving force,  G = -nRT ln(K) Large –ve  G  large +ve ln(K)  huge K  ~100 % Yield Catalysts do not affect K!

13 13 Goal of catalytic research is improved activity & selectivity Alter rate constants: k For simple reax.A  B + C Activity = Selectivity = = Yield of Desired Product x 100 % Total Yield of all Product Catalyst Definitions mol. s -1 rate of reaction % relative formation of specific product

14 14 Conversion The % of reactant that has reacted Conversion = (Amt of Reactant at t 0 ) - (Amt of Reactant at t 1 ) x 100 (Amt of Reactant at t 0 ) Catalyst Efficiency: 1 Triglyceride transesterification Biodiesel Activity = -d[Tributyrin] = 20 = 1 mmol.s -1 dt 20 Conversion = 20 %

15 15 Triglyceride transesterification Tri-glyceride Di-glyceride Methyl-butanoate (FAME) Selectivity to FAME? [FAME] [Diglyceride]+[Monoglyceride]+[FAME] x 100 45 20+10+45 x 100 = = 60 %

16 16 Reagents are often stoichiometric - single use By definition catalysts must be regenerated once product formed. Need a parameter to compare efficiency of catalysts. Turn over number (TON) - Number of reactions a single site can achieve e.g. 1 mmol Pd converts 1000 mmols of CO  CO 2 Turn over frequency (TOF) - Number of reactions per site per unit time. e.g. 1 mmol Pd converts 1000 mmols of CO  CO 2 in 10 s To be valid TOF must be measured in absence of: - mass transport limitations - deactivation effects Catalyst Efficiency: 2 TON = 1000 TOF = 100 s -1

17 17 C - Catalytic cracking S, Pb - Car exhaust catalysts Active Phase - transition-metal - highly dispersed - reduced/oxidic/sulphided state ‘Inert’ Support - high surface area oxide - high porosity - high thermal/mechanical stability Sn - Naptha reforming Cl - Ethylene epoxidation K 2 O - NH 3 synthesis Catalyst Constituents

18 18 Active Component Responsible for the principal chemical reaction Features: activity, selectivity, purity surface area, distribution on support, particle size Types: Metals Semiconductor oxides and sulphides Insulator oxides and sulphides Platinum particles on a porous carbon support Transmission Electron Micrograph

19 19 Other features include: porosity mechanical properties stability dual functional activity modification of active component Types: high melting point oxides (silica, alumina) clays carbons Main function is to maintain high surface area for active phase Support

20 20 Ease of removal from reaction and possible to recycle Diffusional effects - reaction rates may be limited by diffusion into/out of pores. May need to re-optimise plants (often batch reactors) for solid-liquid processes - separation technology Opportunity to operate continuous processes Advantages and Limitations of Heterogeneous Catalysts

21 21 Apathy - Fine chemicals synthesis often on small scale, magnitude of waste not appreciated. Cost - Conventional reagents are cheap, catalysts require development………(i.e. Investment !) Time - Fine chemicals have a short life cycle compared to bulk chemicals:‘Time to market’ is critical. ‘…classical methods are broadly applicable and can be implemented relatively quickly...…the development of catalytic technology is time consuming and expensive.’ R.A.Sheldon & H.Van Bekkum - Eds. Fine chemicals through heterogeneous catalysis Why the Implementation Delay??

22 22 The 12 Principles of Green Chemistry 1) It is better to prevent waste than to treat or clean up waste after it is formed. 2) Synthetic methods should be designed to maximise the incorporation of all materials used into the final product. 3) Wherever practicable, synthetic methodologies should be designed to use and generate substances that possess little or no toxicity to human health and the environment. 4) Chemical products should be designed to preserve efficacy of function while reducing toxicity. 5) The use of auxiliary substances (e.g. solvents, separation agents, etc) should be made unnecessary wherever possible and, innocuous when used. 6) Energy requirements should be recognised for their environmental and economic impacts & should be minimised. Synthetic methods should be conducted at ambient temperature and pressure. 7) A raw material of feedstock should be renewable rather than depleting wherever technically and economically possible. 8) Unnecessary derivatisation (blocking group, protection/deprotection, temporary modification of physical/chemical processes) should be avoided whenever possible. 9) Catalytic reagents (as selective as possible) are superior to stoichiometric reagents. 10) Chemical products should be designed to preserve efficacy of function while reducing toxicity. 11) Analytical methodologies need to be developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances. 12) Substances and the form of a substance used in a chemical process should be chosen as to minimise the potential for chemical accidents, including releases, explosions and fires. Dr. Paul Anastas Director of Green Chemical Inst. Washington D.C. ex. White House Asst. Director for Environment

23 23 “It is better to prevent waste than to treat or clean up waste after it is formed” Chemical Process No waste

24 24 “Synthetic methods should be designed to maximise the incorporation of all materials used into the final product” A + B C + D + E + F... Only required product C (only product) Selectivity

25 25 “Energy requirements should be recognised for their environmental impacts and minimised. Synthetic methods should be conducted at ambient pressure and temperature” Heating Cooling Stirring Distillation Compression Pumping Separation Energy requirement (electricity) Burn fossil fuel CO 2 to atmosphere Global warming High Activity Filtration

26 26 “Unnecessary derivatisation (blocking group, protection/deprotection..) should be avoided wherever possible” Selectivity

27 27 CONCLUSION: “Selective catalysts are superior to stoichiometric reagents” Stoichiometric Catalytic 4-Chlorobenzophenone

28 28 Catalysis in Action: C 2 H 2 on Pd(111) Scanning Tunnelling Microscope movie - real-time molecular rotation Further Info Even More Info!

29 29 Reaction kinetics and diffusion limitations Langmuir adsorption isotherm Unimolecular reaction Bimolecular reactions Surfaces Lecture 3/4 Overview

30 30 Kinetics of heterogeneously catalysed liquid phase reactions are largely governed by diffusion limitation within the porous solid Require a new range of heterogeneous catalysts tailored for liquid phase organic reactions offering... - pore structure - ease of separation - high activity - high selectivity to desired products. Kinetics of Catalysed Reactions

31 31 Batch Reactor Batch/Flow Reactor Comparison

32 32 Diffusional effects - (Mass Transfer) Adsorption strength- Mechanism- Heat transfer- Key Considerations Solvent polarity Ratio of reactant Competitive adsorption Adsorption of product/by products (e.g. H 2 O) Site blocking Solvent adsorption Study rate as function of concentration and compare theoretical profile Hot spots? In exothermic reactions rapid removal of heat from active site is essential

33 33 Porous catalyst structure k 1 k 7 k 2 k 6 k 3 k 4 k 5 k 1 = Film mass transfer to ext. surface k 2 = Diffusion into Catalyst Pore (Bulk or Knudsen Diffusion) k 3 = Adsorption on surface k 4 = Reaction k 5 = Desorption of Product k 6 = Diffusion of Product k 7 = Film mass transfer away ext. surface A B Diffusion Parameters Reactant film Gas diffusion kinetics important in liquid oxidation/hydrogenation - high pressure needed to increase solubility Reax. Mix O2O2

34 34 For dissolution of oxygen in water, O 2 (g) O 2 (aq), enthalpy change under standard conditions is -11.7 kJ/mole. Dissolution is EXOTHERMIC Henry’s Law Raise PRESSURE Not temperature

35 35  At low T reaction processes dominate  At high T diffusional effects become rate limiting  Typical Arrhenius plot Reaction control Diffusion control ln k app 1/T Activation Energy - Diffusion Limitation? k app = Aexp (-E app /RT) lnk app = LnA - E app /RT Activation Energy Arrhenius const

36 36  Rate  [Cat] n n=1 if no diffusion limitation  Rate  with agitation, or gas flow  E app is low 10-15 kJmol -1 Diffusional Step Chemical Step Small T dep (T 1/2 or T 3/2 )High T dep E a ~ 20-200kJmol -1 Test for Diffusion Limitation

37 37 Surface Terminology Substrate (adsorbent) - the solid surface where adsorption occurs  Adsorbate - the atomic/molecular species adsorbed on the substrate

38 38 Adsorption - the process in which species ‘bind’ to surface of another phase Coverage - the extent of adsorption of a species onto a surface (  ) Adsorbed NH 3 reacting over Fe Langmuir Adsorption Isotherm  = 1 

39 39 Langmuir Adsorption Isotherm:refresher Predicts adsorbate coverage (  )  calculate reaction rates  optimise reaction conditions (T, pressure) Chemical equilibria exist during all reactions - stabilities of adsorbate vs. gas/liquid - temperature (surface and reaction media) - pressure (liquid conc.) above catalyst GAS/LIQUID reactants, products solvents CATALYST absorbate

40 40 Equilibrium between the gas molecules M, empty surface sites S and adsorbates e.g. for non-dissociative adsorption S * + M S----M Assumption 1: Fixed number of identical, localised surface sites [S----M]   adsorbate coverage [S * ]  vacancies  (1-  ) [M]  gas pressure  P ReactantsProducts

41 41 Equilibrium constant, b is Rearrange in terms of , Langmuir Adsorption Isotherm - b called sticking-probability and depends on  H ads Assumption 2:  H ads and thus b is temperature & pressure independent b

42 42 Consider the surface decomposition of a molecule A, i.e. A (g)  A (ads)  Products Let us assume that : decomposition occurs uniformly across surface sites (not restricted to a few special sites) products are weakly bound to surface and, once formed, rapidly desorb the rate determining step (rds) is the surface decomposition step Under these circumstances, the molecules of A on the surface are in equilibrium with those in the gas phase  predict surface conc. of A from Langmuir isotherm Unimolecular Decomposition  = b.P / ( 1 + b.P ) Assumption 3:  H ads is coverage independent Assumption 4: Only 1 adsorbate per site

43 43 Rate of surface decomposition (  reaction) is given by an equation: Rate = k  (assuming that the decomposition of A ads occurs in unimolecular elementary reaction step and that kinetics are 1 st order in surface concentration of intermediate A ads ) Substituting for the  gives us equation for the rate in terms of gas pressure above surface Two extreme cases: Limit 1 : b.P << 1 ; i.e. a 1 st order reaction (with respect to A) with an 1 st order rate constant, k' = k.b. This is low pressure (weak binding) limit : Rate = k b P / ( 1 + b P ) then( 1 + b.P ) ~ 1 and Rate ~ k.b.P  steady state surface  of reactant v. small

44 44  Limit 2 : b.P >> 1 ; then ( 1 + b.P ) ~ b.P and Rate ~ k i.e. zero order reaction (with respect to A) This is the high pressure (strong binding) limit : steady state surface  of reactant ~100% Rate shows the same pressure variation as  (not surprising since rate   !) Rate = k b P / ( 1 + b P )

45 45 Langmuir-Hinshelwood type reaction : Assume that surface reaction between two adsorbed species is the rds. If both molecules are mobile on the surface and intermix then reaction rate given by following equation for bimolecular surface combination step: Rate = k     Since  b.P / ( 1 + b.P ), when A& B are competing for same adsorption sites the relevant equations are: A (g)  A (ads) B (g)  B (ads) A (ads) + B (ads) AB (ads) AB (g) rdsfast Bimolecular Reactions:1

46 46 Look at several extreme limits:  Limit 1 :b A P A << 1 & b B P B << 1 In this limit  A &  B are both very low, and Rate  k. b A P A. b B P B = k'. P A. P B 1 st order in both reactants  Limit 2 : b A P A << 1 << b B P B In this limit  A  0,  B  1, and Rate  k. b A P A / (b B P B ) = k'. P A / P B Substituting these into the rate expression gives : 1 st order in A negative 1 st order in B  = b.P / ( 1 + b.P ) Rate Pure APure B [A]/[B] Competitive Adsorption

47 47

48 48 Eley-Rideal type reaction : Consider same chemistry A (g)  A (ads) A (ads) + B (gas) AB (ads) AB (gas) last step is direct reax between adsorbed A* and gas-phase B. A + B  AB rdsfast Rate = k    where [B] is pressure/conc in gas or liquid phase [A ]/ [B] Rate A varied Bimolecular Reactions:2

49 49 However Without extra evidence cannot conclude above reaction is Eley-Rideal mechanism… last step may be composite and consist of the following stages B (g)  B (ads) A (ads) + B (ads) AB (ads) AB (g) with extremely small steady-state coverage of adsorbed B  Test by monitoring rate vary   vary ratio of or over wide range fast slow Langmuir-Hinshelwood not Eley-Rideal. need free sites

50 50 Calculated energy diagram Langmuir-Hinshelwood: CO oxidation over Pt Highest rate of CO 2 production under slightly oxidising conditions: - a high concentration (~0.75 monolayer) of surface O - significant no. of O a vacancies (empty sites) - CO adsorbs in vacancy with only small energy barrier Reaction pathway CO O Example 1 CO(g)+O(a) CO(g)+½O 2 (g )

51 51 Ru catalyst O atoms Eley-Rideal: CO oxidation over Ru Highest rate of CO 2 production under oxidizing conditions: - a high concentration (1 monolayer) of surface O - no surface CO detectable Example 2 Calculated energy diagram Transition state GAS SURFACE CO(g)+O(a)

52 52 Oscillating reactions of carbon monoxide oxidation on platinum. Good for oxididation ‘Inert’ towards O 2 Can adsorb CO

53 53 Important to verify whether reaction kinetics (esp. liquid phase) are determined by mass transport limitations. Homogeneous reaction conditions may not be directly transferable Reactions involving Solid-Liquid-Gas particularly challenging! Relative ‘sticking probability’ of reactants plays a major role in determining surface coverage and optimum reaction conditions. Use of promoters can help with coverage effects.... Kinetics Summary

54 54 Surfaces Structure Geometric factors - dispersion, particle size effects Electronic factors - alloys Lecture 4 Overview

55 55 Surfaces Most technologically important catalysts contain active metal surfaces Most possess simple fcc structures e.g. Pt, Rh, Pd Face Centred Cubic unit cell Low index faces are most commonly studied surfaces with unique: - Surface symmetry - Surface atom coordination - Surface reactivity

56 56 Surface Symmetry (111) (100)(110) Surface are regions of high energy - cohesive energy is lost in their creation “Close-packed” surfaces have higher coord. nos - more stable  low surface energy Open (rough) surfaces low coord. nos - unstable  high surface energy Principle Low Index Surfaces

57 57 For any reaction the pathway depends on: - reactant geometry - reactant energy relative to transition complex Monitor adsorption geometry via vibrational spectroscopy (RAIRS, HREELS, ARUPS) Geometric Factors Reax. Co-ordinate T.S. E R P e.g. C 2 H 4 dehydrogenation

58 58 Calculate Ni-C-C bond angle, for different Ni surfaces, Ni-Ni= 0.25   = 103 , bond twists to stabilise ethene “= 0.35   = 123 , destabilisation of C-H bond Observe R(110) > R(100) > R(111) Ni CH 2  x 5

59 59 Spectroscopy shows - same adsorption mode (HREELS) - strength (TPD) Geometric Factors: C 2 H 4 dehydrogenation Volcano Plot Trend reflects C 2 H 4 geometry  surface structure important (111) (110)

60 60 Quadrupole Mass Spectrometer H2H2 Temperature-programmed desorption Pt(111) Stepwise decomposition C2H3C2H3 CH 3 CH 2

61 61  Supported metal particle can expose different crystal faces.  In addition there are steps & defects within each particle. - these are low coordination sites - region of high potential energy  facilitate bond dissociation Structure Sensitivity

62 62 Structure Sensitivity occurs when reaction requires specific active sites: ( any mix of step, terrace, kink atoms) The density of steps and dominant crystal face reflects the metal particle size  changing particle size modifies rate Stepped surfaces Stepped + kinked surface (100) square (111) hex

63 63 Consider total fraction of available surface sites: Spherical particles if N s = total no. of surface atoms N T = total atoms in particle For small particles (< 20Å) Dispersion  1  if Activity  SA, then  particle size will  rate (per mass of catalyst) provided exposed surface atom arrangement unchanged

64 64 Structure sensitive test: Consider CO + 3H 2  CH 4 + H 2 O Compare specific TON (per surface site) Ni (100) 9% Ni/Al 2 O 3 5% Ni/Al 2 O 3 If reaction requires specific (4-coord) active site expect constant  E act observed higher rate over surfaces with most (100) sites larger particles

65 65 Structure sensitive vs insensitive reaction: Cyclohexane hydrogenolysis High step/kink densities  high rates Reaction requires defect sites contrast with (de)hydrogenation which proceeds over diverse surface arrangements Reaction kinetics tell us about the active site -H 2 -CH x

66 66 Electronic Factors: Alloys  Electronic properties of crystalline solids described by Band Theory  Bimetal may transfer e - to/from active metal  changes adsorbate binding strength 1s-band 2s-band Energy Bimetal Alkali-metals → 1 valence e - /atom

67 67 Bimetallic Alloys ‘True’ alloy versus surface decoration? Requirements: - Intimate contact between components - Direct chemical coordination (bonding) between metal neigbours Minimise excess bimetal deposits on support

68 68 Acetylene Coupling over Pd/Au  Reaction mechanism well understood  Unique chemistry - low temperature (25°C) & high selectivity - operates from 10 -13 - 10 atmospheres  Reaction requires 7-atom ensemble

69 69 Pd(111) C2H2C2H2 C6H6C6H6  Methodology - construct relevant model catalyst - add gold (Au) promoter - perform chemistry over Pd/Au alloys Pd(111) Au C2H2C2H2 C6H6C6H6 Incorporation of Au  improved activity, selectivity & lifetime Zoom Au

70 70  Chemistry - products include C 6 H 6, C 6 H 14, C 6 H 14 - add heteroatoms O, S..  C 5 heterocycles BUT~50 % of C 2 H 2 decomposes over Pd

71 71

72 72 Summary Au/Pd alloys  reactant/product decomposition vs. Pd  Au  selectivity to benzene  Au  long-term activity Both ensemble & ligand effects are important  Au breaks up active site  Au ‘softens’ Pd chemistry

73 73 Sol-gel synthesis Formation of inorganic oxide via acid or base initiated hydrolysis of liquid precursor (e.g. Si(OEt) 4 ). Can incorporate active sites directly in ‘one-pot’ route. Post modification Active site is ‘grafted’ onto pre-formed support via reaction with surface groups (often OH) Lecture 6 Preparation of Heterogeneous Catalysts

74 74 Impregnation Pore filling with catalyst precursor followed by evaporation of solvent Traditional method for supported metals Ion Exchange Equilibrium amount of cation or anion is adsorbed at active sites containing H + or OH - SOH + C + = SOC + H + S(OH) - + A - = SA - + (OH) - Precipitation Catalyst precursor is precipitated in form of hydroxide or carbonate.

75 75 Incipient-Wetness (wet-impregnation)

76 76 Increased rate of drying  temperature gradient across pore  forces precursor to be deposited at the pore mouth. Concentration of solution for impregnation will alter loading and particle size

77 77 Precipitation

78 78 Surfactant micelle Alumino-surfactant mesostructure Ordered (hexagonal) array Mesostructured Al 2 O 3 Surfactant + Solvent  Micelle Lauric Acid (coconut oil) Template extraction Al precursor Templated Sol-Gel Surfactant

79 79 Porosimetry N 2 physisorption used to surface area, pore structure, pore shape Typical adsorption isotherms BET model  surface area during monolayer adsorption Characterisation

80 80 A B E Use hysteresis on desorption to deduce pore shape According to IUPAC Type A = cylindrical pores Type B = slit shaped pores Type E = Bottle neck pores

81 81 Well developed laboratory technique Gives satisfactory results (<5 h per sample) Powder X-Ray Diffraction Complications - Minimum amount of material is required (usually 1-5wt%) - Diffraction lines broaden as crystallite size decreases  hard to measure crystallites < 2nm diameter  peakwidth yields particle size - Lines from different components often overlap or interfere with each other B = line width at ½ height (in degrees) d = crystallite size (in nm) = X-Ray wave length (0.154nm for Cu K  )  = Diffraction angle (in degrees) Measure intensity of diffraction peaks as a function of sample and analyser angle (2  )

82 82 XRD of Cu/CeO 2 Catalyst

83 83 Typical XRD lattice parameter for MCM = 35Å Estimate pore wall thickness d(100) XRD of modified MCM supports

84 84 Can make vibrational measurements of adsorbates on catalyst surface! Transmission Mode – using KBr Self Supporting Wafer - e.g. CO adsorption on metal crystallites Diffuse Reflectance Mode (DRIFTS) – acquire data directly from a catalyst powder Infrared Spectroscopy

85 85 COURSE SUMMARY Learning Objectives Catalysis Definitions - activity, selectivity, conversion, TON and TOF Reaction Kinetics - diffusion limitations, Langmuir adsorption, unimolecular and bimolecular reactions Surface structure - terminology, symmetry, geometric vs. electronic factors Structure-Sensitivity - definition, particle size effects, dispersion Catalyst Preparation - simple methodologies Catalyst Characterisation - simple methodologies, surface vs. bulk insight


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