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 catalysis

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•What is Catalysis?

• Catalysts

• Catalyst components

• Properties and Characteristics of Industrial C

• Preparation of Solid Catalysts

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What is Catalysis?

A phenomenonin which a smallquantity of a

substance (thecatalyst) increasesthe rate of achemical reaction

without being

P!"#C$ %C&$&'S$

Catalyst

&

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Catalysis is a

cycle of elementarystep

three); catalytic sites are regenerated 

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*nergy pro+le of a catalytic reaction

Energy barrier of the catalytic route muc

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Catalysts• increase the rate oreaction

• without being consumed in the process

Do not aect the state of equiliof reaction

simply allow equilibrium to bereached faster

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Catalysts !,er alternati-e. energetically fa-orable path

for reactions *nable reactions to occur under industrially

achie-able conditions

&llow selecti-e production routes without or w

undesirable byproducts

&re the wor/ horses of the chemical industry

&re the /ey enablers for sustainable

(green)production

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 $ypes of Catalysts 0 Homogene-s1 Heterogeneous

Homogeneous catalysisSingle phase

($ypically liquid)'ow temperature

Separations are tric/y

Heterogeneous 2ultiphas

(2ostly solid3liquidgas)

High tempera"esign and optimi4

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Heterogeneous Catalysis

Catalyst is a solid

eactants5 gas or liquidphase

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'ength Scales in Heterogeneous Catalys

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• Haber3osch process• 67 % 8 H7 9 7 6H8

• :e;u catalysts. high pressure and temperature• Critical for fertili4er and nitric acid production

• :ischer3$ropsch chemistry• n C! % 7n H7 9 (CH7)n % n H7! . syn gas to liquid fuels

• :e;Co catalysts• Source of fuel for &<is in WWII

• :luidi4ed catalytic crac/ing• High 2W petroleum 9 low 2W fuels. li/e gasoline• =eolite catalysts. high temperature combustor• In your fuel tan/>

• &utomoti-e three3way catalysis• 6!<;C!;HC 9 H7!;C!7;H7!

• Pt;h;Pd supported on ceria;alumina• 2a/es e<haust @ cleaner

Important Heterogeneous Catalytic Proc

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Catalyst components

• catalytically acti-e component• generate the acti-e sites that participa

chemical reaction

Catalytic

agent

• pro-ides large surface area for dispersamount of catalytically acti-e agent

• adsorb reactant and contribute to the r

Support or

carrier• impro-e the acti-ity or selecti-ity or st

catalytic agents• present in a small amount and by itself

acti-ityPromoters

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l

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macro-poresmeso-pores

Pt crystallites

high SA alumina

(10 nm)

(100-200 nm)

(1-5 n m)

 Heterogeneous Catalyst

 Pt supported on alumina 

f i i

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TEM of platinum supported on alumina

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Automotive catalyst:Pt, Pd, h on alumina (Al 2!") promoted #y ceria,$irconia, etc%

S& catalyst:'anadium oide (' 2!5) on titania (i!2) promoted #ymoly#denum oide (*o! ")

Ammonia oidation catalyst:Pt-h gau$e (unsupported)

hus, not all catalysts are supported+

 Examples of typical Heterogeneous Catalys

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rties and Characteristics of Industrial

•   high producti-ity from relati-ely small reactors•  catalyst -olumes• 2ild operating conditions

&cti-ity

•  High yields of a desired product

• Suppress un3 desirable competiti-e and consecuti-e reactio

Selecti-ity

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•   change only -ery slowly o-er the course of time•  under conditions of use and regeneration

 Stability

•  *<ternal morphological characteristics of a catalyst

• its form and grain si4e. must be suited to the correspondingprocess

 2orphology

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2orphology

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• esistance to crushing. pass undamaged through all the str• esistance of the grains to attrition through rubbing• esistance to abrasion on the walls or to erosion by the Auid

  2echanical Strength

• High thermal conducti-ity reduced temperature gradientswithin the grain. as well as in the catalytic bed

• High speci+c heat permits a catalytic crac/ing catalyst to caa large thermal load

 $hermal Characteristics

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•  &ll catalysts age. their acti-ities or their selecti-i

ha-e become insuBcient

• urning o, of carbon

•  eu-enation5 scrubbing with suitable gases .

hydrogenolysis of hydrocarbons. inection of chem

compounds

  egenerability

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 $he preparation of supported catalysts aim

attach the acti-e phase onto the support

Impregnation. co3precipitation (controlled p

not). homogeneous deposition. deposition

surfactant (organic agent) stabili4ed metal

 $he support is either a powder or a pre3sha

the most common ones being D3&l7!8. E3&

Si!7. $i!7or carbons

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Precipitation

a crystalli4ation process and can occur in the bul/ of tliquid or on a relati-ely inert surface1 $he support pa

act as crystalli4ation nuclei for the acti-e site precurs

ion3e<change ; adsorption processes and the interactiwith the support is dominant

Impregnation

Coprecipitation!ne or more metals are precipitated together with thsupport or precursor

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"ry impregnation (pore -olume impregnation) the e<act amount of liquid tpore -olume of the support is used -s Wet impregnation the amount of liquonly FcontrolledG by the solubility of the metal precursor