The Art of Heterogenous The Art of Heterogenous Catalytic HydrogenationCatalytic Hydrogenation

Part 1Part 1

An Introduction:An Introduction:

Chemistry 536Chemistry 536

Recommended Books:Recommended Books:

Heterogenous Catalysis for the Synthetic Heterogenous Catalysis for the Synthetic Chemist Chemist Robert L Augustine (1996)Robert L Augustine (1996)

Practical Catalytic Hydrogenation, Practical Catalytic Hydrogenation, Techniques and ApplicationsTechniques and Applications Morris Freifelder 1971Morris Freifelder 1971

Recommended ReferencesRecommended References

Catalytic Hydrogenation over Platinum Catalytic Hydrogenation over Platinum Metals Metals P. N. Rylander 1967P. N. Rylander 1967

What will Not be Covered Here:What will Not be Covered Here:(Topics for Another Class)(Topics for Another Class)

Homogenous catalystsHomogenous catalysts Chiral catalysisChiral catalysis

What will be Covered Here:What will be Covered Here:

Some basic theorySome basic theory CatalystsCatalysts Solvents, and their effectsSolvents, and their effects Structure effectsStructure effects Temperature effectsTemperature effects Common and useful reductions with hydrogenCommon and useful reductions with hydrogen How to use a Parr ShakerHow to use a Parr Shaker Tour of the High Pressure LabTour of the High Pressure Lab

Two Ways to Add Hydrogen:Two Ways to Add Hydrogen:

Hydrogenation: Hydrogenation: addition across Pi addition across Pi bondsbonds

Hydrogenolysis: Hydrogenolysis: Cleavage of Sigma Cleavage of Sigma bondsbonds

A Y A Y

H H

A X A X

H H

Catalysts: OverviewCatalysts: Overview

Discrimination dependent upon:Discrimination dependent upon: MetalMetal SupportSupport SolventSolvent TemperatureTemperature Presence or absence of poisonsPresence or absence of poisons PromotersPromoters

Catalysts Overview, cont’d:Catalysts Overview, cont’d:

Rate of reduction dependent upon:Rate of reduction dependent upon: Catalyst preparationCatalyst preparation Time (in hours) since prep. of catalystTime (in hours) since prep. of catalyst PressurePressure TemperatureTemperature Loading of catalystLoading of catalyst

Why Choose Catalytic Why Choose Catalytic Hydrogenation?Hydrogenation?

Simple work-upSimple work-up Generally clean reactionsGenerally clean reactions No extra ions or compounds to deal with; No extra ions or compounds to deal with;

just remove solvent.just remove solvent. Can be done neat.Can be done neat. Most cost-effective choice for scale-upMost cost-effective choice for scale-up In Process; spent catalyst is usually In Process; spent catalyst is usually

recoverable for cost savingsrecoverable for cost savings

RheniumRhenium

Usually used in an oxide form (recovered Usually used in an oxide form (recovered in an oxide form)in an oxide form)

Requires vigorous conditionsRequires vigorous conditions Best use is in reduction of carboxylic acids Best use is in reduction of carboxylic acids

to alcohols or amides to aminesto alcohols or amides to amines Typical conditions: 200 atm and 150-250 Typical conditions: 200 atm and 150-250

°C°C

RutheniumRuthenium

Used as dioxide or metal on supportUsed as dioxide or metal on support Commercially availableCommercially available Active at 70-80 Active at 70-80 °C/ 60-70 atm°C/ 60-70 atm Very resistant to poisoningVery resistant to poisoning Good choice for reduction of aromatic rings, but Good choice for reduction of aromatic rings, but

does not discriminate.does not discriminate. Reduces COOH, but only at HP; 500-950 atm.Reduces COOH, but only at HP; 500-950 atm. Reduces aldehydes, ketones, even sugars.Reduces aldehydes, ketones, even sugars.

Copper Chromium OxideCopper Chromium Oxide

Commercially availableCommercially available Useful only at elevated temperatures and Useful only at elevated temperatures and

pressures (250-300 pressures (250-300 °C/250-300 atm)°C/250-300 atm) Used for reduction of aldehydes and Used for reduction of aldehydes and

ketones w/o hydrogenolysisketones w/o hydrogenolysis No effect on benzene ringNo effect on benzene ring Used for reduction of amides to amines Used for reduction of amides to amines

and esters to alcohols, but now replaced and esters to alcohols, but now replaced with LAHwith LAH

CobaltCobalt

Mostly used in “Raney” formMostly used in “Raney” form Active primarily at elevated pressures and Active primarily at elevated pressures and

temperaturestemperatures Converts nitriles to primary amines Converts nitriles to primary amines

(absence of ammonia)(absence of ammonia) Can reduce double bonds and carbonyls Can reduce double bonds and carbonyls

at 1 atm, but much less active than Raney at 1 atm, but much less active than Raney NickelNickel

Just what are Raney metals?Just what are Raney metals? An alloy of the metal and aluminum is made by An alloy of the metal and aluminum is made by

melting them together a certain proportions.melting them together a certain proportions. The aluminum is dissolved away using sodium The aluminum is dissolved away using sodium

hydroxide solutionhydroxide solution The remaining metal from the alloy “domains” The remaining metal from the alloy “domains”

become particles with high surface area and are become particles with high surface area and are charged with hydrogencharged with hydrogen

It is extremely flammable in air and must be It is extremely flammable in air and must be handled wet with waterhandled wet with water

Commercially available, but best if prepared just Commercially available, but best if prepared just before use. (See Freifelder, p. 7)before use. (See Freifelder, p. 7)

NickelNickel

Mostly used as Raney NickelMostly used as Raney Nickel Very subject to loss of activity within two weeks Very subject to loss of activity within two weeks

of preparation, especially W-6 and W-7of preparation, especially W-6 and W-7 Only modest temperatures and pressures Only modest temperatures and pressures

neededneeded Can selectively reduce aromatic ringsCan selectively reduce aromatic rings Above 100 Above 100 °C reaction may get out of hand°C reaction may get out of hand Reduces esters, ketones, nitrilesReduces esters, ketones, nitriles

Nickel cont’dNickel cont’d

Other forms are nickel on kieselguhr and Other forms are nickel on kieselguhr and form of Urushibara (form of Urushibara (Bull. Chem Soc. JapBull. Chem Soc. Jap 2525, 280 (1952)), 280 (1952))

Can be used in acid solution (HOAc) and Can be used in acid solution (HOAc) and can give better results than noble metal can give better results than noble metal catalysts (i.e. better discrimination and catalysts (i.e. better discrimination and yields)yields)

PlatinumPlatinum

Don’t use platinum black: highly variableDon’t use platinum black: highly variable Adam’s catalyst (PtOAdam’s catalyst (PtO22)(Stable in storage!) )(Stable in storage!)

and platinum on support are most and platinum on support are most common forms; all commercially availablecommon forms; all commercially available

Wide variety of reductions, including Wide variety of reductions, including hydrogenation and hydrogenolysis, hydrogenation and hydrogenolysis, depending upon conditions; most are milddepending upon conditions; most are mild

Poisoned by amines and sulfurPoisoned by amines and sulfur

Platinum cont’dPlatinum cont’d

If PtOIf PtO22 is pre-treated with HOAc or MeOH is pre-treated with HOAc or MeOH

wash, can reduce benzene rings readily.wash, can reduce benzene rings readily. PtOPtO22 not selective between double and not selective between double and

triple C-C bonds.triple C-C bonds. Many variants of Pt/C, each with its own Many variants of Pt/C, each with its own

selectivity.selectivity.

PalladiumPalladium

Many forms of palladium on support Many forms of palladium on support available, each with its own selectivityavailable, each with its own selectivity

Less than half the cost of platinumLess than half the cost of platinum Gives both hydrogenation and Gives both hydrogenation and

hydrogenolysishydrogenolysis Most reductions under mild conditionsMost reductions under mild conditions Subject to poisoning with sulfur, amines, Subject to poisoning with sulfur, amines,

and lead.and lead.

RhodiumRhodium

Expensive (~Pt), but very versatile.Expensive (~Pt), but very versatile. Best for reductions of aromatic systems Best for reductions of aromatic systems

(incl. heterocycles) under mild conditions (incl. heterocycles) under mild conditions sans acidsans acid

Reduces C=C, nitro, and carbonyls; most Reduces C=C, nitro, and carbonyls; most reducible groupsreducible groups

Aromatic vs carbonyl selectivity can be Aromatic vs carbonyl selectivity can be controlled by pH and nearby groupscontrolled by pH and nearby groups

Catalyst Inhibitors and PoisonsCatalyst Inhibitors and Poisons

Inhibitors diminish the rate , but the effect Inhibitors diminish the rate , but the effect can be reversed by washing it away.can be reversed by washing it away.

Poisons exert an appreciable inhibitory Poisons exert an appreciable inhibitory effect when present in small amounts.effect when present in small amounts.

Both can be used to fine-tune the Both can be used to fine-tune the selectivity of a catalyst.selectivity of a catalyst.

Catalyst Inhibitors and PoisonsCatalyst Inhibitors and Poisons

Metals and metals SaltsMetals and metals Salts Mg, Ni Co have no effect on PdClMg, Ni Co have no effect on PdCl22 reductions. reductions. Al, Fe, Cu, Zn, Ag, Sn, Pb, Hg, Cr their oxides Al, Fe, Cu, Zn, Ag, Sn, Pb, Hg, Cr their oxides

and carbonates inhibit Palladium.and carbonates inhibit Palladium. Pt reductions inhibited by Al, Co, Bi.Pt reductions inhibited by Al, Co, Bi. Pt Reductions increased by Fe, Cu Zn, Ag, PbPt Reductions increased by Fe, Cu Zn, Ag, Pb Raney nickel completely inhibited by mercuric Raney nickel completely inhibited by mercuric

chloride, but 50% inhibited by Agchloride, but 50% inhibited by Ag22SOSO44

Catalyst Inhibitors and PoisonsCatalyst Inhibitors and Poisons

Halogen-Containing CompoundsHalogen-Containing Compounds Halide ions inhibit Ni, sometimes Pt, Pd: IHalide ions inhibit Ni, sometimes Pt, Pd: I-- >> Br >> Br-- > Cl > Cl--

> F> F- - in a concentration-dependent manner. in a concentration-dependent manner. Corresponding acids just as potent, if anhydrous. Tip: Corresponding acids just as potent, if anhydrous. Tip: add water or use acetic acid.add water or use acetic acid.

Non-ionizable organic halides often do not inhibit Pt Non-ionizable organic halides often do not inhibit Pt and Pd, except when directly bonded to the region of and Pd, except when directly bonded to the region of reduction (e.g. aromatic halides reduced to reduction (e.g. aromatic halides reduced to cyclohexane halides).cyclohexane halides).

Potent inhibitors (Ni): carbon tet, chloroform, chloral Potent inhibitors (Ni): carbon tet, chloroform, chloral hydrate, trichloroethanol, di- and trichloroacetic acid, hydrate, trichloroethanol, di- and trichloroacetic acid, alkyl chloride, benzyl chloride, and acetyl chloride.alkyl chloride, benzyl chloride, and acetyl chloride.

An Example of Halide InhibitionAn Example of Halide Inhibition

N+H+

N

HO HO

Cl-

Cl-

Pd/H2/EtOH

RT, 6 hours

N+

HO

I-

H+

N

HO

I-

X

Pd/H2/EtOH

120 C, 48 hrs,900 psi

60 psi

Compounds containing Ar, Sb, O, Compounds containing Ar, Sb, O, P, Se, TeP, Se, Te

Oxygen rarely inhibits, except as COOxygen rarely inhibits, except as CO Other members of this group are inhibitors Other members of this group are inhibitors

if their oxidation state leaves unbonded if their oxidation state leaves unbonded electron pairs on the central atom.electron pairs on the central atom. Example: POExample: PO44

3-3- Inert Inert

PHPH33 InhibitorInhibitor

Compounds containing Ar, Sb, O, Compounds containing Ar, Sb, O, P, Se, Te cont’dP, Se, Te cont’d

Sulfate: inertSulfate: inert Sulfite: InhibitorSulfite: Inhibitor Phosphite, hypophosphite: inhibitorPhosphite, hypophosphite: inhibitor AsHAsH33 and SbH and SbH33 are poisons, as well as are poisons, as well as

organic derivativesorganic derivatives Se and Te in lower oxidation states are Se and Te in lower oxidation states are

inhibitorsinhibitors

Sulfur as an InhibitorSulfur as an Inhibitor

As sulfides, mercaptans, disulfides, and As sulfides, mercaptans, disulfides, and thiosulfates and thiophenes: potent thiosulfates and thiophenes: potent inhibitors.inhibitors.

Beware the rubber stopper! Contains Beware the rubber stopper! Contains sulfur for vulcanizing!sulfur for vulcanizing!

Some sulfoxides and sulfinates are Some sulfoxides and sulfinates are inhibitors.inhibitors.

Sulfonates, sulfuric acid, and sulfoxides Sulfonates, sulfuric acid, and sulfoxides have little effect.have little effect.

The Effect of the Nitrogen AtomThe Effect of the Nitrogen Atom

Compounds with unshielded basic Nitrogen act as Compounds with unshielded basic Nitrogen act as inhibitors.inhibitors.

Compounds which generate basic nitrogen on Compounds which generate basic nitrogen on reduction (e.g. nitro, oxime) act as inhibitors.reduction (e.g. nitro, oxime) act as inhibitors.

Nitrile is an inhibitor (likely due to product), while Nitrile is an inhibitor (likely due to product), while cyanide is a catalyst poison.cyanide is a catalyst poison.

Non-basic nitrogens (e.g. in amide or urea) have little Non-basic nitrogens (e.g. in amide or urea) have little effect.effect.

Non-poisonous: Schiff-bases, imines, azines, Non-poisonous: Schiff-bases, imines, azines, hydrazones & similar cpds with azomethine links.hydrazones & similar cpds with azomethine links.

Other Nitrogen InhibitorsOther Nitrogen Inhibitors

Pyridine and related heterocycles are Pyridine and related heterocycles are inhibitors.inhibitors.

Piperidine is a potent poisonPiperidine is a potent poison Quinoline is only a weak inhibitor, often used Quinoline is only a weak inhibitor, often used

for modifying activityfor modifying activity

Strategies to Counter the Inhibition Strategies to Counter the Inhibition by Nitrogenby Nitrogen

Use a protic solvent such as ethanol, Use a protic solvent such as ethanol, methanolmethanol

Use an organic acid such as acetic acidUse an organic acid such as acetic acid Use 1 equivalent HCl (less preferable)Use 1 equivalent HCl (less preferable) Choose an alternate catalyst not Choose an alternate catalyst not

susceptible to nitrogen inhibition (rarely an susceptible to nitrogen inhibition (rarely an option)option)

Using Catalyst PoisonsUsing Catalyst Poisons

Effect of poisoning Effect of poisoning agents not the same agents not the same for every catalystfor every catalyst

Can be added to stop Can be added to stop a multi-step reduction a multi-step reduction at a given level of at a given level of reduction. Example : reduction. Example : the Rosamund the Rosamund Reduction:Reduction:

Cl

O

H

O

PtO2/thiourea

Useful InhibitionUseful Inhibition Reduction of Reduction of

cinnamaldehyde to 3-cinnamaldehyde to 3-phenylpropionaldehyde phenylpropionaldehyde (added pyridine limits (added pyridine limits reduction):reduction):

Lindlar reduction of Lindlar reduction of acetylenes:acetylenes:

H

O

H

O

RaNi, H2, Pyridine

C13H27

OH

NO2

OH C13H27

OH

NO2

OH

H

H

Pd/CaCO3, H2

Poison: lead acetate

Catalyst PromotersCatalyst Promoters

Substances that produce greater catalytic effect Substances that produce greater catalytic effect than can be accounted for by each component than can be accounted for by each component independently and in proportion to the amount independently and in proportion to the amount presentpresent

Most promotors are inactive as catalysts Most promotors are inactive as catalysts themselves.themselves.

Sometimes are inactivators in another context Sometimes are inactivators in another context and/or at a higher concentrationand/or at a higher concentration

Promoters tend to be specific to an application.Promoters tend to be specific to an application.

Examples of promoters:Examples of promoters:

Added Cerium Added Cerium distinctly promotes distinctly promotes the reduction of the reduction of toluene:toluene:

Addition of 1:1 Addition of 1:1 Mol/mol FeClMol/mol FeCl33 to Pt to Pt increases rate of increases rate of reduction of nitro reduction of nitro 400%400%

175 C/ 125 atm

Nickel on Keiselguhr

R-NO2 RNH3

Pd or Pt/ H2

Metal PromotersMetal Promoters

10 mole% FeCl10 mole% FeCl33 per per

g-atom Pt allows g-atom Pt allows reduction of reduction of Benzaldehyde at a Benzaldehyde at a practical rate:practical rate:

SnClSnCl22 promotes the promotes the

reduction of reduction of heptaldehyde with Pt heptaldehyde with Pt or PtOor PtO22::

Hydrogen/ PtO2

HOOH

H

O

H

OH

H

PtO2/H2

Air as a promoterAir as a promoter Some reductions, esp. aldehydes over platinum Some reductions, esp. aldehydes over platinum

or ruthenium, are very slow if the mixture is not or ruthenium, are very slow if the mixture is not periodically purged with air.periodically purged with air.

Need may arise from depletion of “lower oxide” Need may arise from depletion of “lower oxide” active form of platinum catalyst; purging with active form of platinum catalyst; purging with nitrogen has no effect.nitrogen has no effect.

Pt/C often has less need. Activated C’s contain Pt/C often has less need. Activated C’s contain absorbed oxygen.absorbed oxygen.

Careful! The procedure involves mixing solvent, Careful! The procedure involves mixing solvent, air, catalyst to purge residual hydrogen; recipe air, catalyst to purge residual hydrogen; recipe for an event.for an event.

Noble Metals as Promoters of RaNiNoble Metals as Promoters of RaNi

Addition of Pt, Os, Ir, or their salts had a Addition of Pt, Os, Ir, or their salts had a dramatic effect on rate of reduction of a dramatic effect on rate of reduction of a cholesterol ketone; Rh and Ru not cholesterol ketone; Rh and Ru not effective.effective.

Most effective as platinic chloride; Most effective as platinic chloride; activates for reductions of nitrile and activates for reductions of nitrile and alkylnitro groupsalkylnitro groups

Basic PromotersBasic Promoters

Addition of KOH or NaOH to Nickel-cat. Addition of KOH or NaOH to Nickel-cat. ketone reductions greatly increases rate. ketone reductions greatly increases rate. Improved: reduction of nitroanilines, acyl Improved: reduction of nitroanilines, acyl phenols, phenyl phenols, alkyl phenol and phenols, phenyl phenols, alkyl phenol and free phenols if anhydrousfree phenols if anhydrous

Trace EtTrace Et33N added to RaNi reductions of N added to RaNi reductions of

aldehydes and ketones cut the time in half. aldehydes and ketones cut the time in half. Synergistic with platinum chloride.Synergistic with platinum chloride.

Water as a PromoterWater as a Promoter

Addition of water most frequently improves Addition of water most frequently improves ruthenium reductions.ruthenium reductions.

Ru reductions at low or moderate Ru reductions at low or moderate conditions often do not proceed without conditions often do not proceed without presence of water.presence of water.

Water counteracts effect of chloride or HCl Water counteracts effect of chloride or HCl as inhibitoras inhibitor

Reaction ConditionsReaction Conditions

CatalystCatalyst AdjuvantAdjuvant SolventSolvent SupportSupport LoadingLoading TemperatureTemperature PressurePressure Method of agitationMethod of agitation

SolventSolvent

Hydrogenations can be run sans solvent.Hydrogenations can be run sans solvent. Solvents moderate reactions and exothermsSolvents moderate reactions and exotherms SM does not need to be dissolved or even be SM does not need to be dissolved or even be

significantly soluble, so long as product is.significantly soluble, so long as product is. Effect of solvent choice is reaction-specific.Effect of solvent choice is reaction-specific. Acidic and basic solvents serve a dual purpose.Acidic and basic solvents serve a dual purpose. The effect of a neutral solvent is unpredictable.The effect of a neutral solvent is unpredictable.

Solvents continuedSolvents continued

The neoprene stopper of Parr Shakers is The neoprene stopper of Parr Shakers is attacked by ketones, ethyl acetate, attacked by ketones, ethyl acetate, benzene, THF and pyridine, but is inert to benzene, THF and pyridine, but is inert to alcohols, water, alkane solvents. Solvent alcohols, water, alkane solvents. Solvent choice may require sacrificing stopper or choice may require sacrificing stopper or using alternate closure.using alternate closure.

High pressure autoclaves are consistent High pressure autoclaves are consistent with any organic solvent with any organic solvent but not mineral but not mineral acids.acids.

Solvents continuedSolvents continued

Common Solvent Choices:Common Solvent Choices: Water Water methyl and ethyl alcoholmethyl and ethyl alcohol Ethyl acetate, cyclohexane, Ethyl acetate, cyclohexane,

methylcyclohexane, benzene, pet ether, methylcyclohexane, benzene, pet ether, ligroinligroin

Methyl cellosolve (MeOCHMethyl cellosolve (MeOCH22CHCH22OH)OH) DMFDMF Acetone, MEKAcetone, MEK

Solvents continuedSolvents continued

Solvents are not always inert:Solvents are not always inert: Reduction of pyridine over nickel in lower alkyl Reduction of pyridine over nickel in lower alkyl

solvents results in N-alkylationsolvents results in N-alkylation Reductions in THF and dioxane at high temps Reductions in THF and dioxane at high temps

over nickel make explosive mixtures. So over nickel make explosive mixtures. So DIOXANE AND THF ARE FORBIDDEN DIOXANE AND THF ARE FORBIDDEN

IN THE HIGH PRESSURE LAB!IN THE HIGH PRESSURE LAB!

SupportSupport

Used to increase surface area of catalyst Used to increase surface area of catalyst with consequent higher rateswith consequent higher rates

Modifies SelectivityModifies Selectivity (Process) Minimizes loss of catalyst (Process) Minimizes loss of catalyst

Common SupportsCommon Supports

Carbon (many variations): high surface Carbon (many variations): high surface area, absorbs oxygen and impurities; most area, absorbs oxygen and impurities; most common and reliable.common and reliable.

Alumina: Absorbs impurities. pH of Alumina: Absorbs impurities. pH of Alumina can modulate selectivity.Alumina can modulate selectivity.

Alkaline earth carbonates: impart basicity Alkaline earth carbonates: impart basicity (in some cases impedes polymerization of (in some cases impedes polymerization of alkynes).alkynes).

SupportsSupports

There are many types of support designed There are many types of support designed for specific reductions and situations, for specific reductions and situations, includingincluding

ClaysClays CeramicsCeramics PumicePumice CeliteCelite

Catalyst LoadingCatalyst Loading

Rate is semi-proportional to catalyst Rate is semi-proportional to catalyst loading loading but not linearbut not linear. (Low loading may . (Low loading may give no reaction at all, but doubling at give no reaction at all, but doubling at midrange may give 5-20x effect).midrange may give 5-20x effect).

Use and report loading based upon weight Use and report loading based upon weight percent of total catalyst (not contained percent of total catalyst (not contained metal)vs substrate.metal)vs substrate.

Scale-ups require a smaller loading than Scale-ups require a smaller loading than pilots.pilots.

TemperatureTemperature

Classic rate vs temperature rules applyClassic rate vs temperature rules apply Lower temperatures are preferable, as Lower temperatures are preferable, as

they exaggerate selectivity differences.they exaggerate selectivity differences. Many reductions are exothermic; use more Many reductions are exothermic; use more

solvent, less agitation, or less hydrogen solvent, less agitation, or less hydrogen pressure to moderatepressure to moderate

Parr limit: 80Parr limit: 80°C HP autoclave: 300 °C°C HP autoclave: 300 °C

AgitationAgitation

Shaking (Parr Shaker) Efficient for small Shaking (Parr Shaker) Efficient for small quantities, but difficult to achieve over 2 L.quantities, but difficult to achieve over 2 L.

Rocking (Rocker autoclaves) Less efficient Rocking (Rocker autoclaves) Less efficient than rocking or stirring, but best choice for than rocking or stirring, but best choice for high pressures.high pressures.

Stirring: Depending upon design, can be Stirring: Depending upon design, can be very efficient. Magnetically coupled shafts very efficient. Magnetically coupled shafts permit much more reliable performance.permit much more reliable performance.

Extensive discussion in AugustineExtensive discussion in Augustine

Agitation continuedAgitation continued

Rate of reaction increases with efficiency Rate of reaction increases with efficiency of stirring (e.g. mixing of phases)of stirring (e.g. mixing of phases)

Magnetically stirred microhydrogenators Magnetically stirred microhydrogenators become ineffective above 50 mL.become ineffective above 50 mL.

Why?Why?

Two Standard MixersTwo Standard Mixers

PressurePressure

A great many Pt and Pd reductions can be A great many Pt and Pd reductions can be achieved at 60 psi with proper choice of solvent achieved at 60 psi with proper choice of solvent and promotersand promoters

Rate is (nonlinearly) proportional to pressure.Rate is (nonlinearly) proportional to pressure. Some catalysts (Cobalt, copper arsenite) require Some catalysts (Cobalt, copper arsenite) require

higher pressures (up to 200 atm) to perform. higher pressures (up to 200 atm) to perform. Some substrates such as aromatics are resistant Some substrates such as aromatics are resistant to hydrogenation and require high pressureto hydrogenation and require high pressure

Atmospheric HydrogenatorAtmospheric Hydrogenator

End of Hydrogenation End of Hydrogenation Part OnePart One