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Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous....

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Page 1: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

CatalystsCatalysts

Page 2: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

Learning ObjectivesLearning Objectives Catalysts can be classified as either heterogeneous Catalysts can be classified as either heterogeneous

or homogeneous.or homogeneous.

Heterogeneous catalysts work by the adsorption of Heterogeneous catalysts work by the adsorption of reactant molecules.reactant molecules.

The surface activity of a catalyst can be reduced by The surface activity of a catalyst can be reduced by poisoning.poisoning.

Impurities in the reactants result in the industrial Impurities in the reactants result in the industrial catalysts having to be regenerated or renewed.catalysts having to be regenerated or renewed.

Catalytic converters are fitted to cars to catalyse the Catalytic converters are fitted to cars to catalyse the conversion of poisonous carbon monoxide and conversion of poisonous carbon monoxide and oxides of nitrogen to carbon dioxide and nitrogen.oxides of nitrogen to carbon dioxide and nitrogen.

Page 3: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

Definition of CatalystsDefinition of Catalysts

Speed up the rate of a chemical reactionSpeed up the rate of a chemical reaction

Are not chemically changed or used up Are not chemically changed or used up in the reactionin the reaction

May be May be specificspecific for a particular reaction for a particular reaction

Page 4: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

Types of catalysts

HomoHomogeneous catalysts –geneous catalysts –reactants and catalyst in same statereactants and catalyst in same state

HeteroHeterogeneous catalysts – geneous catalysts – reactants and catalysts in different reactants and catalysts in different statesstates

Page 5: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

How do heterogeneous catalysts work?How do heterogeneous catalysts work?

Catalyst is usually solidCatalyst is usually solid

Reactants are Reactants are adsorbedadsorbed onto surface onto surface

Adsorb – Adsorb – formation of weak bondsformation of weak bonds

Page 6: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

CatalystCatalyst

Page 7: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

CatalystCatalyst

Reactant AReactant A

Page 8: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

CatalystCatalyst

Adsorption occurs at Adsorption occurs at active siteactive site

Page 9: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

CatalystCatalyst

Page 10: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

CatalystCatalyst

Reactant BReactant B

Page 11: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

CatalystCatalyst

Page 12: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

CatalystCatalyst

Page 13: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

CatalystCatalyst

Page 14: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

CatalystCatalyst

Page 15: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

CatalystCatalyst

ProductsProducts

Page 16: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.
Page 17: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.
Page 18: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

H H C CH H

H H

E.g Hydrogenating alkenes (turning oils into fats)

H H

Page 19: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

Bonds within reactant molecules are Bonds within reactant molecules are weakened and breakweakened and break

H H C CH H

H HH H

Page 20: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

New bonds form between the reactantsNew bonds form between the reactants

H H C CH H

H HH H

Page 21: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

H

H

H

C

C

H

H

•New bonds form between the reactant molecules

H HH

Page 22: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

The product(s) leave the catalyst The product(s) leave the catalyst surfacesurface

H H C CH H

HHH H

Page 23: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

CatalystsCatalystsN

UM

BE

R O

F M

OL

EC

UE

S W

ITH

A P

AR

TIC

UL

AR

EN

ER

GY

MOLECULAR ENERGY Ea

NUMBER OF MOLECULES WITH SUFFICIENT ENERGY TO OVERCOME THE ENERGY BARRIER

Page 24: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

CatalystsCatalysts Catalysts lower the activation energy for a Catalysts lower the activation energy for a

reactionreaction

Ea

EXTRA NUMBER OF MOLECULES WITH SUFFICIENT ENERGY TO OVERCOME THE ENERGY BARRIER

NU

MB

ER

OF

MO

LE

CU

ES

WIT

H A

PA

RT

ICU

LA

R E

NE

RG

Y

MOLECULAR ENERGY

Page 25: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

EXAMPLES OF CATALYSTS

• MetalsMetals Ni, Pt Ni, Pt hydrogenation reactionshydrogenation reactions FeFe Haber ProcessHaber Process Rh, PdRh, Pd catalytic converterscatalytic converters

• Format is FINELY DIVIDED Format is FINELY DIVIDED

• This increases the surface area and provides more This increases the surface area and provides more active sitesactive sites

Page 26: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

Catalyst poisoningCatalyst poisoning

In heterogeneous catalysis Catalyst In heterogeneous catalysis Catalyst poisoned by a chemical binding to surfacepoisoned by a chemical binding to surface

Poison bonds irreversibly with catalystPoison bonds irreversibly with catalyst

Sulphur and lead are two examples of Sulphur and lead are two examples of catalyst poisonscatalyst poisons

Page 27: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

PoisoningPoisoning

CatalystCatalyst

Page 28: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

PoisoningPoisoning

CatalystCatalyst

Page 29: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

PoisoningPoisoning

Active site taken up by poisonActive site taken up by poison

Effectiveness of catalyst reduced.Effectiveness of catalyst reduced.

CatalystCatalyst

Page 30: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

Cleaning a catalystCleaning a catalyst

Catalysts can sometimes be Catalysts can sometimes be regeneratedregenerated by blowing hot air over by blowing hot air over catalyst – oxidises chemicals on surfacecatalyst – oxidises chemicals on surface

Used to remove carbon (soot) after Used to remove carbon (soot) after catalytic crackingcatalytic cracking

Page 31: Catalysts. Learning Objectives Catalysts can be classified as either heterogeneous or homogeneous. Catalysts can be classified as either heterogeneous.

Catalytic ConvertersCatalytic Converters

Found in car exhaust systemsFound in car exhaust systems Reduce levels of pollutant gasesReduce levels of pollutant gases Pollutants react in exhaust to form less Pollutants react in exhaust to form less

harmful gases.harmful gases.


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