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Catalysis
Catalysis ApplicationsCatalysis Applications
World catalystsWorld catalysts• 9 G$ business in 1999• 24% for Refining, 24% for Chemicals,
23% for Polymers, 29% for Environment
oxidation
According to Dept. Energy, USA, in 2003
Catalysis & Catalytic processes are
•responsible for about 20% of the U.S. gross domestic product (all goods and services)
• the keys to future gains in energy efficiency, environmental stewardship and attendant economic prosperity for the country
The twelve principles of Green Chemistry1. It is better to prevent waste than to treat or clean up
waste after it is formed.
2. Synthesis methods must be designed to maximize the incorporation of all materials used in the process into the final product.
3. Whenever practicable, synthetic methodologies should be designed to use and generate substances that possess little or no toxicity to human health and the environment.
4. - - - -
9. Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.
10.- - - -
Early History of Catalysis
•Neolithic age (新石器時代 ~5000B.C.)
Biocatalytic fermentation in wine manufacture
•500B.C.
Soap manufacture (hydrolysis of animal fats with potash lye)
•1500A.C.
Alchemists formed sulfuric acid by a mysterious catalytic process
•1831
Pelegrine Phillips (a Bristol vinegar manufacturer) obtained the 1st known patent in catalysis for the reaction
SO2 + air → SO3 (Pt sponge as catalyst)
The catalyst used now-a-day is V2O5/ SiO2
•1835
J.J. Berzelius coined the word “catalysis”
Greek words “cata”means “down”
“lysis”means “split”or “break”
“This new force, which is unknown until now, is common to both organic and inorganic nature. I do not believe that it is a force completely independent of electrochemical affinities; … It is more convenient to give this force a separate name. I would therefore call this the catalytic force. I would furthermore, call the decomposition of substances resulting from this force catalysis, just as the decomposition of substances resulting from chemical affinity is calledanalysis.”
•1880 Carl Groebeaccidentally broke a thermometer while stirring a mixture of hot naphthalene and H2SO4
⇒ phthalic anhydride & phthalic acid⇒ dye chemistry
•1899 Arrhenius equation k = A exp(-Ea/RT)
•1903 Ostward process
2NH3 + 7/2 O2 → 2NO2 + 3 H2O (Pt sponge as
catalyst)
⇒ HNO3 industry
•1909 Ostward (German) received Nobel Prize
for studies of reaction rate over catalysts
•1912 Paul Sabatier (French) received Nobel Prize
for studies of catalytic hydrogenation of organic
compounds
•1915 Haber Process
N2 + 3 H2 → 2 NH3 (Fe catalyst)
•1919 Fritz Haber (German) received Nobel Prize
•1920 Sabatier published the 1st book on catalysis
•1923 Methanol synthesis
CO + 2 H2 → CH3OH (Cr2O3-ZnO catalyst)
•1930 Fischer-Tropsch Process
CO + H2 → (CH)n (Fe catalyst)
• 1932 Langmuir (USA) received Nobel Prize
For surface chemistry and Langmuir isotherm
• 1936 Modern era in catalysis
Catalytic cracking of petroleum (acid treated clays as catalyst)
BET surface area
Deuterium discovery ⇒ isotope research
• 1963 Ziegler (German) & Natt (Italian)received Nobel Prize for stereoregulated
polymerization catalyst
Three Classes of Catalysts
• Heterogeneous- The catalyst and the reactants are in different phases
• Homogeneous- The catalyst and the reactants are in the same phase
• Biological - Enzymes
Effect of Catalyst on Reaction Profile and Activation Energy
Reaction profiles for theuncatalyzed and catalyzed decomposition of ozone
⇒ Homogeneous Catalysis
Homogeneous CatalysisProduction of acetic acid
1916 acetylene→acetaldehyde→acetic acid1950-1960 oxidation of n-butane or naphtha1955 homogeneous methanol carbonylation use
Ni catalyst by BASF1960 iodide-promoted CO catalyst under 2300C
600atm yield 90%1970 Monsanto synthesis use Rh complex
(180-2200C 30-40atm) yield 99%1980 Celanese and Daicel improve Monsanto
process adding LiI or NaI1996 use Ir-based process improved Celanese process1997 direct oxidation of ethylene by Denko
Production of acetic acid
Methanol carbonylation- Rh catalyzed methanol carbonylation
CH3OH + CORh complex
CH3COOH180-2200C30-40atm
r.d.s Rate ∝ [cat.][CH3I]
14-15wt.% of H2O is required
Enzyme Catalysis
• Enzymes are high-molecular-mass proteins that usually catalyze one specific reaction – or a set of quite similar reactions – but no others.
• Extremely high selectivity• The reactant substance (S), called the substrate,
attaches itself to an area on the enzyme (E) called the active site, to form an enzyme-substrate complex (ES).
• The rates of enzyme-catalyzed reactions are influenced by factors such as concentration of the substrate, concentration of the enzyme, acidity of the medium, and the temperature.
“Induced-fit” Model of Enzyme Action
“Lock and key” Model by Emil Fischer in 1894
Effect of Substrate Concentrationon Rate: [Enzyme] = Constant
Effect of Enzyme Concentrationon Rate: [Substrate] = Constant
Enzyme Activity as a Functionof Temperature
Heterogeneous Catalysis• Many reactions are catalyzed by the surfaces of
appropriate solids.
• Steps in heterogeneous catalytic reactions1. Diffusion to the surface2. Adsorption of reactants3. Surface diffusion of reactants4. Surface reaction5. Surface diffusion of products6. Desorption of products7. Diffusion away from the surface
• Heterogeneous catalysis requires balance of adsorption, reaction, and desorption
Catalyst strongly adsorbing ––> no rxn.Catalyst weakly adsorbing ––> no rxn.
A Surface-Catalyzed Reaction
Nanostructured Materials ( <100 nm)
•Nanostructures represent the transition from atom to solid.• It is essential to obtain particles or pores with uniform diameters and shapes and, for the purpose of particular applications, to arrange and embed them in a superstructure.•Size quantization effects, high number of surface atoms, and special surface states.•Special optical, electronic, magnetic, and chemical properties•Good applications in the areas of signal transmission, data and energy storage, as well as catalysis.
Catalytic Reaction Steps
Adsorption
CO
O2
Surfacediffusion
Precursor
Surfacereaction
Desorption
2CO
Ni,PtNi, Co, Pt metals
RhPt metalsPtPt metals
PtAu, Pt metals
Ag
AgoxidationPtGroup Ⅷdehydrogenation
PtPt, Ir, Pd, Auskeletal isomerization of (HC)n
Group Ⅷhydrogenation
PdPt metals
double bond shift
Group Ⅷhydrogenolysis
W, Ptmost trans. metalsH-D exchange
High activityCatalystRxn’s catalyzed by Metals
Ru, Rh, PdOs, Ir, Pt
CH2=CH2 CH2 CH2
O+O2
CH3OH HCHOO2+
CO CO2O2+
Ostwald process(i)
NO CO+2 2 CO2+2N2
CH4+ H2O CO+ H2
+ 6454 + O2 H2ONONH3850oC
CatalystRxnCu2O or multimetallic oxidee.g. Bi2O3-MoO3
Transition Metal oxide catalysts
C3H6 CH2 CH CN +O2, NH3
H2OComplex metal molybdatesor multimetallic oxidee.g. CdMoO4,
M8ⅡFeⅢBiⅢ(MoO4)12O12
Co2+, Ni2+
One-step ammoxidationto acrylonitrile
butane butadiene
Oxidativedehydrogenation
C4H8 + O2 C4H6 + H2O12
∆H < 0exo
H2+C4H6C4H8dehydrogenation ∆H > 0
endo
Ferrite spinelse.g. MnFe2O4, Zn(Cr2-xFex)O4
“metal” catalyst, high temp. easily coking
Propylene → acrolein + acrylic acid
CatalystRxn
Naphthalene or o-xylene + air→ phthalic anhydride
Supported V2O5
n-butane → maleic anhydride (VO)2P2O7
Butene (or benzene) + air→ maleic anhydride
(VO)2P2O7 (V2O4/MoO3)
SO2 O2 SO3 H2SO412
+ V2O5 + K2SO4 /SiO2
Transition Metal oxide catalysts (continue)
CH3OH lean – Fe2O3-MoO3CH3OH rich – Ag
Solid acid catalysts
(i) alumina & acid-treated clays(ii) alumino-silicate (incorporation of alumina in silica)
silica-alumina(iii) protonated zeolites – behave as highly acidic solutions
amorphous
crystalline
shape selectivityacid amount α no. of Alacid strength α 1 / no. of Al
(iv) super acids
TiO2ZrO2Fe2O3
H2SSO4
-2
SO2
+ calcination
H0-14.5-16.0-12.9
Acid-Catalyzed Rxn’s
Isomerization (alkene double-bond isomerization;trans, cis-isomerization)
Alcohol dehydrationPolymerizationCrackingSkeletal isomerizationAlkylation
Acylation
AcidStrength
increases
e.g.
Disproportation
CH3
+ CH3OH + +
CH3
CH3
CH3
CH3
CH3
CH3
+CH3 C
O
O CH3
CH3 C
O
Cl
C CH3
O
CH3 CH3
CH3
CH3
CH3
CH3
CH3
+ ++2
Solid basic catalysts – less used, and less developed
MgO (/Li2O), CaOK/Al2O3KNH2/Al2O3
M-zeolites (M: Li < Na <K < Rb< Cs specific activity )
Base-Catalyzed Rxn’s
dehydrogenation
aldol condersation
Side-chain alkylation with methanol
CH3CH2CH3
OH
CH3CH2CH3
O
CH3CH CH2
+
+ H2O
H2
CH3CH2CH3
OCH3CCH2C
O OH
CH3
CH3
CH3CCH
O
C
CH3
CH3
H2O-
+ H2OCH3OH+
CH3 CH2CH3
CH2CN CH3OH+ CHCN
CH3
H2O+623K
acid-catalyzed
base-catalyzed
Nanotechnology of Catalysis
• Catalysts are perhaps the first industrial nanotechnology
• 2-10 nm particles (sometimes larger) on high surface area support (Al2O3, SiO2)
Automotive catalyst:nm Pt on γ-Al2O3
Catalyst Particles
• Catalytic reactions occur on catalyst surfaces
• Small particles maximize surface area- optimize use of catalysts
(more metal atoms at surface)
• Catalyst dispersionfraction of catalyst atomsat surface (10-40%)
O2
O OOOOC
OC
2 CO
2 CO 2
Turn-over
Reactive site
Catalyst TurnoverTurnover rate [=] s–1: number of reaction cycles completed at a catalyst site per second
車輛所排放的廢氣是造成空氣污染的最大來源之一,一般引擎所排放的廢氣主要組成為:
carbon monoxide (CO, 0.5 vol.%)unburned hydrocarbons (HC, 350 vppm)nitrogen oxides (NOx, 900 vppm)hydrogen (H2, 0.17 vol.%)water (H2O, 10 vol.%)carbon dioxide (CO2, 10 vol.%)oxygen (O2, 0.5 vol.%)其中對環境危害最嚴重的是CO,NOx,及HC。
Automotive Emission Control
Automotive Emission Control
• Largest use of Pt, Pd and Rh industrially
• Example of typical heterogeneous catalytic reaction
• Three-way catalyst: Pt/Pd/Rh on CeO2
Pt/Pd: CO + 1/2 O2 ––> CO2
Pt/Pd: HC + O2 ––> CO2 + H2O
Rh: NOx + HC(CO) ––> N2 + CO2 + H2O
The Catalytic ConverterThe catalytic converter consists of Rh, Pt and Pd
particles on an Al2O3/CeO2 wash-coat deposited on a
monolith of cordierite
Three Way Converter
OxygensensorEngine
Catalyst
AcceleratorAir
Fuel
Exhaust
Computer
Pt/Pd/RhCeria washcoat
A/F ratio
14.914.614.3
0
100
Conv. %CO
NOx
HC
stoic
Catalyst Support Effects
• Note cyclic operation of catalytic converterFuel lean: CO, HC oxidationFuel rich: NOx reduction
• Yet oxidation and reduction continue even when the A/F mixture favors the opposite reaction!
• How does this occur?
• CeO2 acts as an oxygen storage medium
Fuel rich: Oc + Ce3+ ––> Ce4+ (i.e. CeO2)
Fuel lean: CeO2 ––> Ce3+ + O
Nanoscale Effects in Catalysis
• Are catalyst particles simply small versions of the catalyst material?
• Does the nanoscale influence catalytic properties beyond simply presenting more surface atoms?
• What possibilities exist for nanoscale modification of catalyst behavior?
1. Modification of electronic structure2. Interaction of different structure surfaces3. Spill-over effects/other support interactions4. Variation in fluid phase transport properties
Fuel cells
• Liquid electrolyte : AFC, PAFC, MCFCsolid electrolyte: PEMFC, SOFC
• Low temperature: AFC, PAFC, PEMFChigh temperature: MCFC, SOFC
Fuel cells
Fuel cells
Fuel cells• Concept of solid oxide fuel cell (SOFC)
Fuel cells• Concept of proton-exchange membrane fuel cell PEMFC
The catalysts for fuel cells
• Electrode catalyst supports:@ AFC: carbon, Ni- or Ag-based @ PAFC: carbon@ MCFC: Ni-based cement@ SOFC: Ni-YSZ cement, LSM/YSZ@ PEMFC: carbon
• Fuel cells with non-hydrogen fuel@ direct methanol FC: Pt-Ru/carbon, Pd-Ru/carbon electrode catalysts
@ CH4, gasoline as fuels: adding component of oxidation catalyst into anode
Figure 2. (a) Cyclic voltammograms of carbon-supported Pt catalyst samples recorded in 0.1 M HClO4 solution; T= 20 °C, scan rate 50 mV/s; currents are normalized to the measured Pt surface area (Hupd charge after double layer correction); HRTEM images of a carbon-supported Pt nanoparticle (b), and the nanostructured Pt film supported on organic whiskers (c).
J. AM. CHEM. SOC. 127, (2005) 6821
Catalyst Size Effect- I
• EXAFS of Pt/C and Pt-alloy/C catalysts[S. Mukerjee, J. McBreen, J. Electrochem. Soc. 146 (1999) 600.]
Change in d-band density
particle size / nm
2 4 10
Effect of change in potential of 0-0.54 V
0
0.22
Pt/C
Pt d-band density
Pt-Pt bond distance / nm
2.66 2.78
Pt-alloy effects
Pt/Ni/C
Pt/Co/CPt/Fe/C
Pt/Cr/C
• Pt/Cr/C optimal for O2 redn. due to optimal d-band vacancy
Active sites on edge
Active sites on terrace
TOF = (AR)/(FE)Atomic rate
Fraction expose
demanding
facile
Catalyst Size Effect- II
structure-insensitive
structure-sensitive
Reaction on NanocatalystsH2/O2 reaction at 1000 K
(nonflammable mixture in Ar)
H2 + 1/2 O2 ––> H2O130 nm Pt/CeO2 fresh and after 10 min of reaction
[S. Johansson, K. Wong, V.P. Zhdanov, B. Kasemo, J. Vac. Sci. Tech. A 17 (1999) 297.]
Equilibrium Particle Shape
Reaction alters particle shape!
• Polycrystalline particles become crystalline
• Large particles disintegrate to faceted crystals
500 nm Pt/CeO2 (a) fresh and (b) after 10 min of reaction
Influence of Surface Reaction
• Role of oxygen as reactant- Oxygen adsorption weakens Pt-Pt bonds- Pt (in oxide form) becomes more mobile- Effects not seen for H2, H2O
• Energy transfer from reaction- Adsorption highly exothermic (2.5 eV/t.o.)- High reaction rates (t.o. ˜ 103!)
• Local temperature increase
Angew. Chem. Int. Ed. Vol. 41, pp. 688-714 (2002)
Nano-porous materials
Development of Zeolites
•1950sLinde company; Synthetic A-type zeolite for separation of
normal and branched paraffins•1960s
X and Y-type zeolites for catalytic cracking•1968
First use of “Shape Selectivity” properties of zeolites in selective hydrocracking on erionite•In the past 40 years
Zeolites are used in refining and petrochemicals worldwide.⇒ Many synthetic zeolites are prepared.Many synthetic zeolites are prepared.•1998
160 x 103 tons in catalysis applications
Shape-Selectivity:Catalytic reactions in
Molecular Sieves
Polymerization in Confined Space• Adsorption of Monomer in Vapor Phase• Conducting Polymerization• Control of Polymer Morphology and Physical
Properties• Molecular blending of different polymers
Extrusion polymerization: Catalyzed synthesis of crystalline linear polyethylene nanofibers within a mesoporous silica
Science; 285 (1999) 2113.
Modify Meso-Pore Properties By:
• Direct Synthesis — Changes Pore Diameter by Change in Surfactant Chain
Length — Changes Pore Diameter by Addition of Solubilization Agents — Changes Reactivity by Co-precipitation with Functional
Silane • Post Functionalization
— Silylation Changes Pore Diameter and Sorption Properties — Changes Reactivity by Adding Reactive Species
Si-OH
Si-OH
Si-OH
H3COSiH3CO
H3CO
SHO
O
OSi SH
H2O2
O
O
OSi
SOH
O
O
Grafting of Sulphonic Acid Groups on Nano-porous Materials
MCM-SO3H
Summary
• Catalysts are an existing nanotechnology
• Nanotechnological aspects of catalysis only just beginning to be understood
• More effects to explore- Modification of electronic structure- Interaction of facets- Interaction with support (spillover effects)- Mass transport resistances- Confined space reactions and catalysis