Catalyst

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Types of Catalyst Deactivation

Poisoning

the poisoning molecules become irreversibly chemisorbed to active sites, thereby reducing the no of sites availablefor the main rxn

Fouling

It results from a carbonaceous (coke)material being deposited on the surface of catalyst.btopic

This mechanism common for the rxn involve the hyrocarbons.

Aging

the lost of catalytic activitydue to loss of active site surface resulting from the prolonged exposure to high gas-phase temperature

Deactivation» the decline in a catalytic activity as time progresses.

Catalyst

Application of catalyst

industrial gas

oil rige

power station

Types of catalyst

Unsupported

A catalyst distinguishes from supported catalyst.

used for high temp

Usually very active catalyst that do not require high surface area

Supported

A catalyst consists of minute particles of an active material dispersed over a less active substance

Require a high surface area supportto disperse the primary catalyst

Monolithic

A catalyst that can be either porous or non-porous which is normally encountered in processes where pressure dropand heat removalare major consideration.

Require a high surface area supportto disperse the primary catalyst.

The active materialis a pure metalor metal alloy.

Molecular Sieves

A catalyst that admit small moleculesbut prevent the large molecules from entering it

Porous

A catalyst has a large area resulting from porous.

The porescan control the residence time of various molecules

regeneration of catalyst

Redispersion of sintered

High-temperature treatment oxychlorination

Coked catalyst

gasification with O2, H2O, CO2 and H2

Poisoned catalyst

treatment with steam at 700-800 degree celcius

treatment with oxygen at low oxygen partial pressure

Catalysts properties

Typical silica

provide by inner porous structure

a large interfacial area

Solid interface

Catalytic process

Heterogeneous

Reaction between gasses and liquids are usually mass transfer limited

Occurs at or very near the fluid-solid interface

More common type used in industrial

A process involves more than one phase (usually the catalyst is a solid)

Example : Production of benzenefrom the hydrogenation of cyclohexane (obtained from distillation of crude petroleum) using platinum-on-alumina as the catalyst.

Homogeneous

A cataltic process in which a catalyst is in solution with atleast one of thw reactants

Example : Industrial Oxo processfor manufacturing normal isobutylaldehyde.

Definition

catalysis

The study and use of catalyst and catalytic processes

A substance that affects the rate of a reaction but emerges from the process unchanged

Change only the rate of reaction (not affect the equilibrium)

Catalyst speed up reaction accelerate or slow the formation of a particular product species

Catalyst can affect both the yield and productivity(create different pathway with a lower energy barrier)