Download - Heterogeneous catalyst
![Page 1: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/1.jpg)
CHL727(3-0-2):Heterogeneous Catalysis and Reactor Design
Prof. K.K.PantDepartment of Chemical Engineering
L 3
![Page 2: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/2.jpg)
Why R& D in catalysis is important
• 90 % of chemical industry involve products made
using catalysts (food, fuels, polymers, textiles,
pharma/ agrochemicals,etc)
• For discovery/use of alternate sources of energy/fuels/
raw material for chemical industry.
• For Pollution control-Global warming.
• For preparation of new materials (organic & inorganic-
eg: Carbon Nanotubes).
![Page 3: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/3.jpg)
3
WHAT DOES A CATALYST LOOK LIKE
![Page 4: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/4.jpg)
4
![Page 5: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/5.jpg)
5
![Page 6: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/6.jpg)
6
Turnover Frequency TOF
The turnover frequency TOF quantifies the specific activity of a catalytic center for a special reaction under defined reaction conditions by the number of molecular reactions or catalytic cycles occurring at the center per unit time.For most relevant industrial applications the TOF is in the range
10–2 to 102 s–1 (enzymes 103–107 s–1).
TOF (time -1) = volumetric rate of reaction/number of centers /volume
![Page 7: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/7.jpg)
• The reaction activation energy is altered
• The intermediates formed are different from those formed in non-catalytic reaction
• The rates of reactions are altered (bothdesired and undesired ones)
– Reactions proceed under less demanding conditions
• Allow reactions occur under a milder conditions, e.g. at lower temperatures for those heat sensitive materials
• It is important to remember that the use of catalyst DOES NOT vary DG & Keq values of the reaction concerned, it merely change the PACE of the process.
7
Action of Catalysts
![Page 8: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/8.jpg)
oWhether a reaction can proceed or not and to what extent a reaction can proceed is solely determined by the reaction thermodynamics, which is governed by the values of dG & Keq, NOT by the presence of catalysts.
o The reaction thermodynamics provide the driving force for a rxn; the presence of catalysts changes the way how driving force acts on that process.
8
![Page 9: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/9.jpg)
e.g CH4(g) + CO2(g) = 2CO(g) + 2H2(g)
DG°373=151 kJ/mol (100 °C) & DG°973
=-16 kJ/mol (700 °C)
=>At 100°C, DG°373=151 kJ/mol > 0. There is no thermodynamic driving force, the reaction won’t proceed with or without a catalyst
9
![Page 10: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/10.jpg)
=>At 700°C, DG°373= -16 kJ/mol < 0.
The thermodynamic driving force is required. However,
simply putting CH4 and CO2 together in a reactor does not
mean they will react. Without a proper catalyst heating the
mixture in reactor results no conversion of CH4 and CO2 at
all. When Pt/ZrO2 or Ni/Al2O3 is present in the reactor at
the same temperature, equilibrium conversion can be
achieved (<100%).
10
![Page 11: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/11.jpg)
Action of Catalysts• Catalysis action - Reaction kinetics and
mechanism Catalyst action leads to the rate of a reaction to change. This is realised by changing the course of reaction (compared to non-catalytic reaction)
• Forming complex with reactants/ products, controlling the rate of elementary steps in the process.
11
![Page 12: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/12.jpg)
ACTIVITY MEASURE FOR CATALYST: For comparative measurements, such as catalyst screening, determination of process para-meters, optimization of catalyst production conditions, and deactivation studies – Conversion under constant reaction conditions– Space velocity for a given, constant conversion– Space–time yield– Temperature required for a given conversion
12
![Page 13: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/13.jpg)
13
The suitability of a catalyst for an industrial process depends mainly on the followingthree properties:
– Activity– Selectivity– Stability (deactivation behavior)
Which of these functions is the most important is difficult toanswer because the demands made on the catalyst are different for each process.
Activity : how fast one or more reactions proceed in the presence of the catalyst. Activity can be defined in terms of kinetics or from a more practically oriented viewpoint. In a formal kinetic treatment, it is appropriate to measure reaction rates in the temperature and concentration ranges that will be present in the reactor.
Mode of Action of Catalysts
![Page 14: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/14.jpg)
Heterogeneous Catalysis:right specieswith the right coverageat the right temperatureon the right surface
![Page 15: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/15.jpg)
Fundamental Concepts of Catalysis
• Catalysis is a cycle; Sabatier’s Principle•Catalysts break bonds!….How?•Elementary surface reactions (NO + CO reaction)•CO oxidation is structure sensitive (every reaction is…)•Dissociation is the key step•Elementary rate parameters •Lateral interactions affect the kinetics•Reaction design?
![Page 16: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/16.jpg)
Popular Representation of Catalysis
![Page 17: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/17.jpg)
![Page 18: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/18.jpg)
![Page 19: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/19.jpg)
optimum interaction catalyst -adsorbate:not too strongnot too weak
optimum coverage at right surface
The Sabatier Effect
![Page 20: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/20.jpg)
![Page 21: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/21.jpg)
Applications of Catalysis• Industrial applications
Almost all chemical industries have one or more steps employing catalysts
– Petroleum, energy sector, fertiliser, pharmaceutical, fine chemicals.
Advantages of catalytic processes– Achieving better process economics and
productivity
21
![Page 22: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/22.jpg)
Applications of Catalysis• Industrial applications
Almost all chemical industries have one or more steps employing catalysts
– Petroleum, energy sector, fertiliser, pharmaceutical, fine chemicals.
Advantages of catalytic processes– Achieving better process economics and
productivity
22
![Page 23: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/23.jpg)
Research in Catalysis
• Research in catalysis involve a multi-discipline approach– Reaction kinetics and mechanism
• Reaction paths, intermediate formation & action,
• interpretation of results obtained under various conditions,
• generalising reaction types & schemes,• predict catalyst performance…
23
![Page 24: Heterogeneous catalyst](https://reader031.vdocuments.us/reader031/viewer/2022012322/577ccf151a28ab9e788ed5a8/html5/thumbnails/24.jpg)
Industrialecology
Greenengineering
Greenchemistry
Renewableenergy
Practical approaches
Sustainabledevelopment
Strategic goal
Life-cycleassessment
Catalysis
Wastemanagement
E-factor,atom economy
Process intensification
Operational tools
Monitoring tools
The picture of green catalysis