H1: Setting the scene
History of (heterogeneous) catalysis
General
Heterogeneous catalysis as a “phenomenon”
Jean-Jacques Thenard (1813)
- Contacting Pt with NH3 allows its decomposition into N2 & H2, provided metal = hot
𝑃𝑡
- 2 𝑁𝐻3 ↔𝑁2 + 3 𝐻2 (endotherm; ΔH = 90 kJ mol-1)
𝑇
Humphry Davy (1817)
- Reactions of coal-gas & oxygen on Pt, Pd (active) & Co, Ag, Au, Fe (ineffective) wires
- Developed safety lamp for miners
- Detected anesthetic effect of N2O (breathing it became highlight of social events)
𝑃𝑡
- 𝐶𝐻4 + 2 𝑂2 → 𝐶𝑂2 + 2 𝐻2 𝑂
𝐴𝑢
- 2 𝐶𝑂 + 𝑂2 → 2 𝐶𝑂2
Synthesis and decomposition of NH3
𝑁2 + 3 𝐻2 ↔ 2 𝑁𝐻3
Sir William Grove (1835)
- Water can be splitted in H2 & O2 in presence of hot Pt filament
- Metals have special powers to force such chemical reactions
𝑃𝑡
- 2 𝐻2 𝑂↔2 𝐻2 + 𝑂2
𝑇
1
,Michael Faraday (1835)
- 1st description of surface phenomena during catalysis
- Water splitting in its elements on Pt is suppressed by presence of CO & ethylene
- Adsorption processes on specific sites are crucial in heterogeneous catalysis & preferred
adsorption can lead to inhibition
Start of “Heterogeneous catalysis”
2
,Challenges with heterogeneous catalysis
- Selective functionalization of natural gas: methane, ethane, butane
- Biomass: ligno(hemi)cellulose conversion to biofuels & bio-based chemicals
- Production of bio-based chemicals materials: PLA but also new building blocks & novel
functional materials
- CO2 conversion & water splitting to hydrogen: input of renewable energy like sunlight
(directly with semiconductors / indirectly via electricity) required in this chemistry
- Plastic waste: sorting plastics, polymer additives, catalyst properties (pore architecture),
catalytic reactors …
Mode of action of catalysis: the three criteria of a catalytic industrial
process
General
- Activity: effective catalyst converts reagents at appreciable reaction rate (conversion rate)
- Selectivity: product type depends on catalyst used
- Stability: ideally catalyst converts reagents endlessly
3
, Activity
Reaction rate r
𝑟
𝐴→𝑃
𝑐𝑜𝑛𝑣𝑒𝑟𝑡𝑒𝑑 𝑎𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡
𝑟= [𝑚𝑜𝑙 𝐿−1 ℎ−1 𝑜𝑟 𝑚𝑜𝑙 𝑘𝑔−1 ℎ−1 ]
𝑐𝑎𝑡𝑎𝑙𝑦𝑠𝑡 𝑣𝑜𝑙𝑢𝑚𝑒 (𝑜𝑟 𝑚𝑎𝑠𝑠) ∙ 𝑡𝑖𝑚𝑒
- Not volume of reactor in denominator (is sometimes used but we will use volume / mass of
catalyst)
-
- How does [A] change in function of time? This allows to n & k
o A ifv time → can see if reaction is 0, 1st, 2nd order
o Watch y-axis of graphs!!
- How does k change with temperature? This allows determining Ea
- Note for heterogeneous catalysis
𝑘𝑠𝑟 𝑏𝐴 𝑏𝐵 𝑃𝐴 𝑃𝐵
𝑅𝑎𝑡𝑒 =
(1 + 𝑏𝐴 𝑃𝐴 + 𝑏𝐵 𝑃𝐵 + 𝑏𝑅 𝑃𝑅 + 𝑏𝑆 𝑃𝑆 )2
o Not only rate constants ksr, but also adsorption coefficients b take part in kinetics
o Observed activation energy Ea,obs may not be equal to intrinsic activation energy of
chemical reactions for 2 reasons
▪ Reaction may be infected by mass transfer issues
▪ There may also be contribution of heat of adsorption (Q) in temperature
dependency of reaction, catalysed heterogeneously
4
History of (heterogeneous) catalysis
General
Heterogeneous catalysis as a “phenomenon”
Jean-Jacques Thenard (1813)
- Contacting Pt with NH3 allows its decomposition into N2 & H2, provided metal = hot
𝑃𝑡
- 2 𝑁𝐻3 ↔𝑁2 + 3 𝐻2 (endotherm; ΔH = 90 kJ mol-1)
𝑇
Humphry Davy (1817)
- Reactions of coal-gas & oxygen on Pt, Pd (active) & Co, Ag, Au, Fe (ineffective) wires
- Developed safety lamp for miners
- Detected anesthetic effect of N2O (breathing it became highlight of social events)
𝑃𝑡
- 𝐶𝐻4 + 2 𝑂2 → 𝐶𝑂2 + 2 𝐻2 𝑂
𝐴𝑢
- 2 𝐶𝑂 + 𝑂2 → 2 𝐶𝑂2
Synthesis and decomposition of NH3
𝑁2 + 3 𝐻2 ↔ 2 𝑁𝐻3
Sir William Grove (1835)
- Water can be splitted in H2 & O2 in presence of hot Pt filament
- Metals have special powers to force such chemical reactions
𝑃𝑡
- 2 𝐻2 𝑂↔2 𝐻2 + 𝑂2
𝑇
1
,Michael Faraday (1835)
- 1st description of surface phenomena during catalysis
- Water splitting in its elements on Pt is suppressed by presence of CO & ethylene
- Adsorption processes on specific sites are crucial in heterogeneous catalysis & preferred
adsorption can lead to inhibition
Start of “Heterogeneous catalysis”
2
,Challenges with heterogeneous catalysis
- Selective functionalization of natural gas: methane, ethane, butane
- Biomass: ligno(hemi)cellulose conversion to biofuels & bio-based chemicals
- Production of bio-based chemicals materials: PLA but also new building blocks & novel
functional materials
- CO2 conversion & water splitting to hydrogen: input of renewable energy like sunlight
(directly with semiconductors / indirectly via electricity) required in this chemistry
- Plastic waste: sorting plastics, polymer additives, catalyst properties (pore architecture),
catalytic reactors …
Mode of action of catalysis: the three criteria of a catalytic industrial
process
General
- Activity: effective catalyst converts reagents at appreciable reaction rate (conversion rate)
- Selectivity: product type depends on catalyst used
- Stability: ideally catalyst converts reagents endlessly
3
, Activity
Reaction rate r
𝑟
𝐴→𝑃
𝑐𝑜𝑛𝑣𝑒𝑟𝑡𝑒𝑑 𝑎𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡
𝑟= [𝑚𝑜𝑙 𝐿−1 ℎ−1 𝑜𝑟 𝑚𝑜𝑙 𝑘𝑔−1 ℎ−1 ]
𝑐𝑎𝑡𝑎𝑙𝑦𝑠𝑡 𝑣𝑜𝑙𝑢𝑚𝑒 (𝑜𝑟 𝑚𝑎𝑠𝑠) ∙ 𝑡𝑖𝑚𝑒
- Not volume of reactor in denominator (is sometimes used but we will use volume / mass of
catalyst)
-
- How does [A] change in function of time? This allows to n & k
o A ifv time → can see if reaction is 0, 1st, 2nd order
o Watch y-axis of graphs!!
- How does k change with temperature? This allows determining Ea
- Note for heterogeneous catalysis
𝑘𝑠𝑟 𝑏𝐴 𝑏𝐵 𝑃𝐴 𝑃𝐵
𝑅𝑎𝑡𝑒 =
(1 + 𝑏𝐴 𝑃𝐴 + 𝑏𝐵 𝑃𝐵 + 𝑏𝑅 𝑃𝑅 + 𝑏𝑆 𝑃𝑆 )2
o Not only rate constants ksr, but also adsorption coefficients b take part in kinetics
o Observed activation energy Ea,obs may not be equal to intrinsic activation energy of
chemical reactions for 2 reasons
▪ Reaction may be infected by mass transfer issues
▪ There may also be contribution of heat of adsorption (Q) in temperature
dependency of reaction, catalysed heterogeneously
4
