MSc course Adsorption, Kinetics & Catalysis

Transcription

1 MSc course Adsorption, Kinetics & Catalysis Kinetics Chapter.-.6 Prof. Fran de Groot MSc Nanomaterials Chemistry and Physics Utrecht University

2 master / University of Nijmegen / 987 / Theoretical Chemistry PhD / University of Nijmegen / 99 / Solid State Chemistry post-doc / LURE, CNRS Orsay, France / 993 post-doc / Groningen (KNAW academy researcher) / 995 assistant professor (UD) / Utrecht / 999 (00 vidi) associate professor (UHD) / Utrecht / 003 (006 vici) professor / Utrecht / 009

3 Research

4 Introduction to the course Course objectives General nowledge on main catalytic processes Key concepts in catalysis Adsorption Kinetics Catalysis - mechanisms Porosity and surface area physisorption Diffusion 4

5 Introduction to the course () Solid catalyst Pore Steps in diffusion, adsorption and catalysis 5

6 Introduction to the course (3) Course material I. Chorendorff and J.W. Niemantsverdriet. Concepts of Modern Catalysis and Kinetics, nd Edition, Wiley-VCH (007) Handouts, slides 6

7 Introduction to the course (4) Course lay-out see also lecture schedule Oil refining, petrochemistry (Ch 9) KdJ Synthesis gas (Ch 8) KdJ Kinetics (Ch ) FdG Reaction rate theory (Ch 3) FdG Diffusion (Ch 5) KdJ Surface reactivity (Ch 6) FdG Physisorption PdJ Examination NIOK course Catalytic Surface Science, optional 7

8 Chapter Kinetics (lecture ) classical inetics Rate Equation Arrhenius Equation Order of a reaction Steady State Approximation Chain reactions Concentration in coupled reactions

9 Chemical reaction: Methanol synthesis (a, b, p, q) >> stoichiometric coefficients (A, B) >> Reactants (P, Q) >> Products

10 Chemical reaction: Methanol synthesis (a, b, p, q) >> stoichiometric coefficients (A, B) >> Reactants (P, Q) >> Products

11 Chemical reaction: Methanol synthesis (a, b, p, q) >> stoichiometric coefficients (A, B) >> Reactants (P, Q) >> Products

12 Chemical reaction: Methanol synthesis (a, b, p, q) >> stoichiometric coefficients (A, B) >> Reactants (P, Q) >> Products

13 Chapter Kinetics (lecture ) classical inetics Rate Equation Arrhenius Equation Order of a reaction Steady State Approximation Chain reactions Concentration in coupled reactions

14 Rate Equation = change in concentration/ = d[a]/dt change in time

15 Chemical reaction aa bb pp qq (a, b, p, q) >> stoichiometric coefficients (A, B) >> Reactants (P, Q) >> Products

16 Chemical reaction aa bb pp qq r d A a dt b (a, b, p, q) >> stoichiometric coefficients (A, B) >> Reactants (P, Q) >> Products d B dt P dq r d p dt q dt

17 Rate equation aa bb pp qq r r r r a A B b P p Q q

18 Equilibrium constant aa bb pp qq K p eq a P Q q eq A B b eq eq

19 Chapter Kinetics Rate Equation Arrhenius Equation Order of a reaction Steady State Approximation Chain reactions Concentration in coupled reactions

20 History In 8, the Russian chemist Kirchhof found that when a water suspension of starch is boiled, no change occurs in the starch. When a few drops of concentrated sulfuric acid are added to the same suspension before boiling, the starch breas down into glucose. The acid can be recovered unchanged from the reaction. Kirchhof concluded that it had played a helping role in the breadown of the starch, without itself having undergone any change. Starch [H SO 4 ] glucose

21 Arrhenius equation

22 Arrhenius equation ( T ) Ae E A / RT

23 Arrhenius equation ( T) Ae E A / RT Discovered by: Jacobus van t Hoff (884)

24 Arrhenius equation

25 Arrhenius equation ( T) Ae E A / RT = The fraction of the molecules present in a gas which have energies equal to or in excess of activation energy at a particular temperature. (Boltzman distribution; More in chapter 3)

26 Arrhenius equation ( T) Ae E A / RT = A term which includes factors lie the frequency of collisions and their orientation. It varies slightly with temperature, although not much. It is often taen as constant across small temperature. (more in chapter 3: reaction rate theory)

27 Gas constant R R= J K - mol - R = N a * b = Avogadro * Boltzmann = * ºC Rate E E E ( T ) Ae E A / RT

28 Arrhenius equation ( T) Ae E A / RT

29 Arrhenius equation ( T) Ae E A / RT ln ( T ) ln A ln e E A / RT ln ( T ) ln A EA / RT

30 Arrhenius equation ln ( T ) ln A EA / RT

31 Arrhenius equation ºC Rate E E E

32 Arrhenius equation E A = 03 KJ/mol ln ln ( T ) ln A EA / RT /T (K - )

33 Chapter Kinetics Rate Equation Arrhenius Equation Order of a reaction Steady State Approximation Chain reactions Concentration in coupled reactions

34 First order reaction Equation Time evolution (integrated equation) Half time Linearized equation

35 First order reaction Equation R P r R d dt R

36 First order reaction (time evolution) r R d dt R R R d dt R R 0 R R d t 0 dt

37 First order reaction (time evolution) R R 0 R R d t 0 dt ln R ln e t R 0 R R e t 0

38 First order reaction (time evolution) R P R R e t 0 P R R 0 P R R 0 R e ) 0 ( 0 e t t

39 First order reaction (half time) R R e t 0 R R 0 t R e R 0 0 t e

40 First order reaction (half time) t e ln e t ln t ln t t ln

41 First order reaction (half time) S - R R e t 0

42 First order reaction (linearize) R R e t 0 R R 0 e t ln R ln e t R 0

43 First order reaction (linearize) ln R ln e t R 0 ln R R 0 t R ln 0 t R

44 First order reaction (linearize) R ln 0 t R

45 First order reaction Equation Time evolution (integrated equation) Half time Linearized equation

46 First order reaction (exercise) The decomposition reaction SO Cl (g) ---> SO (g) + Cl (g) is a first order reaction with rate constant =. x 0-5 sec - at 30C. What percent of SO Cl is decomposed at 30C after 90 minutes?

47 Zeroth order reaction R P Excess R r d R dt

48 Zeroth order reaction (time evolution) R R 0 d R t 0 dt t R R 0

49 Zeroth order reaction (half time) R R t 0 R R 0 R t R 0 0 t R 0 R t 0

50 Zeroth order reaction (half time) t R R 0

51 Reaction order (units) Order one, the rate coefficient has units of s - Order zero, the rate coefficient has units of mol L- s-

52 Reaction order (units) Order one, the rate coefficient has units of s - Order zero, the rate coefficient has units of mol L- s- Order two, the rate coefficient has units of L mol- s- Order n, the rate coefficient has units of mol-n Ln- s-

53 Second order reaction R P r R R d dt d R R dt

54 Second order reaction (time evolution) R R 0 d R R t 0 dt t R R 0

55 Second order reaction (time evolution) R R 0 t R R 0 t R R 0 t

56 Second order reaction (half time) R R 0 R 0 R 0 t R t 0 t R 0

57 Second Zeroth order reaction (half time) R R 0 t R R t 0

58 Second order reaction (linearize) R R 0 t

59 Exercise The following data were obtained on the rate of hydrolysis of 7 % sucrose in 0.99 mol L- HCl aqueous solution at 35 C. t / min Sucrose remaining, % What is the order of the reaction with respect to sucrose, and what is the value of the rate constant?

60 Zero-Order First-Order Second-Order Rate Law r R d dt r R d dt R r R d dt R Integrated Rate Law R R0 t t R R 0e R R 0 t Linear Plot to determine ln R0 R t Half-life R t 0 t t ln t R 0

61 Chapter Kinetics Rate Equation Arrhenius Equation Order of a reaction Steady State Approximation Chain reactions Concentration in coupled reactions

62 Steady State Approximation R I P R I P R I P

63 Steady State Approximation R I P R R I d dt I R I I d dt d P dt I

64 Steady State Approximation R I P d I dt 0

65 Steady State Approximation R I P d I dt 0

66 Steady State Approximation d I dt 0 R I I 0 ( ) I R I R ( )

67 Steady State Approximation d I dt 0 I R ( ) P d dt I ( R )

68 Steady State Approximation R K R dt P d ) ( R R dt P d ) ( P I R ) ( R I dt P d

69

70

71

72

73 Example:

74 Example: = 0

75 Example:

76 Alternatives to the Steady State Approximation R Coupled reactions: - =0 Pre-equilibrium solution: [I]= + [R] Exact solution I P

77 Coupled reactions (concentrations) R I P d R dt R R R e t 0

78 Coupled reactions (concentrations) R I P I R I d dt I R 0 t ( e e t )

79 Coupled reactions (concentrations) P I R I R R P 0 ) ( ) ( 0 t t e e R P

80 Coupled reactions (concentrations),0 0,8 0,6 [R] [I] = 0. [P] 0,4 0, 0,0 concentration,0 0,8 0,6 0,4 0, 0,0 [R] [I] [P] =,0 0,8 [R] [P] = 0 0,6 0,4 0, 0,0 [I] t Figure.5

81 I R P

82 P I R

83 P R I

84 Alternatives to the Steady State Approximation R Coupled reactions: - =0 Pre-equilibrium solution: [I]= + [R] Exact solution I P

85 Chapter Kinetics Rate Equation Arrhenius Equation Order of a reaction Steady State Approximation Concentration in coupled reactions Chain reactions

86 O N Chain reaction O N O 3 O NO NO O 4 O { N 5 N } N O eff N O NO

87 Chain reaction d NO dt O N N O 3 N d dt O N N O 3 O O N N O d dt 3 O O 4

88 Chain reaction: steady state d N 0 dt d O dt 0

89 Chain reaction: steady state 0 dt O d O O O N N O 0 4 O O

90 Chain reaction: steady state d O dt 0 O O 4 O O 4

91 Chain reaction: steady state 0 3 O N N O dt N d O N N O 3 4 O N N O

92 Chain reaction: steady state N O N O 3 4 N 3 4 N O

93 Chain reaction: steady state 4 3 O N N 3 O N N O dt NO d 4 O O

94 Chain reaction: steady state 3 O N N O dt NO d O O N N O dt NO d

95 Chain reaction: steady state d NO O N dt 4

96 Exercise The decomposition of N O 5 NO + NO 3 is postulated to tae place via two elementary steps: a. N O 5 + N O 5 N O 5 * + N O 5 b. N O 5 * NO + NO 3. Calculate the rate equation, using the steady-state approximation. Assume that reaction b is much faster than the bacreaction of reaction a. What is the reaction order? 3. Assume that reaction b is much slower than the bac-reaction of reaction a. Reaction order?

97 a. N O 5 + N O 5 N O 5 * + N O 5 b. N O 5 * NO + NO 3 Exercise * 5 * * 5 O N O N O N O N dt O N d

98 Exercise * 5 * O N O N O N O N ) ( 5 5 * 5 O N O N O N

99 Exercise * 5 3 O N r dt NO d ) ( 5 5 O N O N r

100 Exercise ) ( 5 5 O N O N r ) ( O N K O N O N r 5 5 ) ( O N O N r Lindemann-Hinshelwood mechanism

101 Exercises Exercises (page 47 and further).5 and.6 Questions via to or room N07 (went) Next time the exercises will be discussed

102 Exercises