Lecture 23

Chemical Reaction Engineering (CRE) is the field that studies the rates and mechanisms of

chemical reactions and the design of the reactors in which they take place.

Lecture 23

Today’s lectureInterstage CoolingNoble Prize 2007Catalytic Steps

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Catalysts and CatalysisA 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.

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Catalysts affect both Selectivity and Yield

Different reaction Paths

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Different shapes and sizes of catalyst.

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Catalytic packed-bed reactor, schematic.

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Steps in a Catalytic Reaction

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Active SiteReactions 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.

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The Adsorption Step

Vacant and occupied sitesFor the system shown, the total

concentration of sites isCt = Cv + CA.S + CB.S

N

SNVNAAD K

CCPkr

SNSN

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AdsorptionSASA

AASVAAAD k/CCPkr

VAAASAAD

VAAASAD

CPkC 0k/r

CPkC 0r :mequilibriu @

VAAVSAVT CPkCCCC

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AA

AAT

T

AS

AA

AATAS

VAA

TV

Pk1PkC

CC

Pk1PkCC

CPk1CC

More Catalysis

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Langmuir Adsorption Isotherm

AP

T

AS

CC Increasing T

Slope=kA

More Catalysis

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The Surface Reaction Step

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The Surface Reaction Step

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The Surface Reaction Step

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The Surface Reaction Step

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The Surface Reaction Step

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SBSB

Desorption from surface

Vacant and occupied sites

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Steps in a Catalytic ReactionBA

Adsorption on Surface SASA

Surface Reaction Single Site SBSA

Dual Site SSBSSA

Desorption from Surface SBSB

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

Electrical analog to heterogeneous reactions

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Collecting information for catalytic reactor design

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Octane NumbersCatalytic Reforming

Normal Pentane Octane Number = 62Iso-Pentane Octane Number = 95

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Steps in a Catalytic ReactionBA

Adsorption on Surface SASA

Surface Reaction Single Site SBSA

Dual Site SSBSSA

Desorption from Surface SBSB

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Steps in a Catalytic ReactionDCBA

Adsorption on Surface SASA SBSB

Surface Reaction Dual SiteSDSCSBSA

'SDSC'SBSA

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Steps in a Catalytic ReactionSurface Reaction Eley-Rideal

gDSCgBSA

Desorption form Surface SCSC SDSD

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End of Lecture 23

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