Lecture 23 thursday 4 1 08 ocnb explosion noble prize 2007 catalytic steps
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Lecture 23 Thursday 4/1/08 OCNB Explosion Noble Prize 2007 Catalytic Steps PowerPoint PPT Presentation


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Lecture 23 Thursday 4/1/08 OCNB Explosion Noble Prize 2007 Catalytic Steps. 400. Temperature o C. Cooling Restored. Q r = 0. Isothermal Operation. 200. 175. 9:55 t = 0. 10:40 10:50. midnight 12:18. Temperature-time trajectory. fuse. Catalysts and Catalysis.

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Lecture 23 Thursday 4/1/08 OCNB Explosion Noble Prize 2007 Catalytic Steps

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Lecture 23 thursday 4 1 08 ocnb explosion noble prize 2007 catalytic steps

Lecture 23 Thursday 4/1/08OCNB ExplosionNoble Prize 2007Catalytic Steps


Temperature time trajectory

400

Temperature oC

Cooling Restored

Qr = 0

Isothermal

Operation

200

175

9:55

t = 0

10:40 10:50

midnight 12:18

Temperature-time trajectory

fuse


Catalysts and catalysis

Catalysts and Catalysis

A Catalyst is a substance that affects the rate of chemical reaction but emerges from the process unchanged.

Catalysis is the occurrence, study, and use of catalysts and catalytic processes.

Approximately 1/3 of the GNP of materials produced in the U.S. involves a catalytic process.


Catalysts affect both selectivity and yeild

Catalysts affect both Selectivity and Yeild


Steps in a catalytic reaction

Steps in a Catalytic Reaction


Active site

Active Site

  • Reactions are not catalyzed over the entire surface but only at certain active sites or centers that result from unsaturated atoms in the surface.

  • An active site is a point on the surface that can form strong chemical bonds with an adsorbed atom or molecule.


The adsorption step

The Adsorption Step


The surface reaction step

The Surface Reaction Step


The rate limiting step which step has the largest resistance

The Rate Limiting Step:Which Step Has the Largest Resistance?


Octane numbers

Octane Numbers

Catalytic Reforming

Normal Pentane Octane Number = 62

Iso-Pentane Octane Number = 95


Lecture 23 thursday 4

  • Intro to Catalysis

  • Reforming catalyst –

  • Algorithm

  • Postulate a mechanism

  • Postulate a rate-limiting step

  • Express Ci·s in terms of partial pressures

  • Site balance (Total number of sites constant)

  • Derive rate law

  • Evaluate parameters

Pt (sputtered on)

Al2O5 (scaffold)


Lecture 23 thursday 4

CV=concentration of vacant sites

Postulate a mechanism: (single site)

In 75% of heterogeneous catalysis, surface reaction is the slow step


Lecture 23 thursday 4

Site Balance:

Is this consistent with the data?

Linear when PNi0 is low

Low slope when PNi0 is large

rNi0

PNi0

Consistent!!


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