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Introduction to Catalysis

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Introduction to Catalysis CHEM-E1130 Introduction to catalysis Prof. Riikka Puurunen 14.1.2018 Contents 1. Definition of catalysis and catalyst 2. Classification of catalysts 3. Seven steps of a heterogeneously catalyzed reaction 4. Catalysis: a tool for manipulating selectivity 5. Significance of catalysis? 6. Components of a solid heterogeneous catalyst 7. Engineering features of a solid heterogeneous catalyst + Conclusion & take-home message Definition of catalysis and catalyst Definition of ”catalysis”? • IUPAC Gold Book, Compendium of Chemical Terminology • https://goldbook.iupac.org • ”Catalysis: The action of a catalyst” • Merriam-Webster: “a modification and especially increase in the rate of a chemical reaction induced by material You can also check: unchanged chemically at the end of the reaction” 4 Definition of ”catalyst”? • IUPAC:” A substance that increases the rate of a reaction without modifying the overall standard Gibbs energy change in the reaction ” • Richardson: A catalyst is a substance that increases the rate at which a chemical reaction approaches equilibrium without itself becoming permanently involved in the reaction • You can look also in: Oxford English Dictionary, Merriam- Webster Richardson, Principles of Catalyst Development, Plenum Press, 1989. 5 In other words, a catalyst: 1. Increases the chemical reaction rate 2. Does not influence the position of thermodynamic equilibrium 3. Is not (permanently) changed in the catalysed reaction • <is present in minute concentrations> 6 Timeline of catalysis Jöns Jacob From alchemy to chemistry Berzelius, … - 1834 seminal From empirics to science work 1835 1835-1897 The birth of industrial catalysis 1898-1918 The increase in global mobility by developing catalytic fuel processes https://dx.doi.org/10.1023/A:1025001809516 1919-1945 From war to peace 1946-1970 Environmental catalysis 1970-20?? J. J. Berzelius 1835 • Berzelius coined the word catalysis, combining the Greek words 휅훼휏훼´ (down) and 휆휐휄 ´ (solution, loosening). • In Chinese, catalyst = a marriage broker [Cuīhuàjì] 催化剂 You can also check: More, e.g.: http://dx.doi.org/10.1002/9781119181286 Ross, Heterogeneous Catalysis, Chapter 1, Figure (daguerrotype): https://en.wikipedia.org/wiki/J%C3%B6ns_Jacob_Berzelius Wikipedia: Jöns Jacob Berzelius (1779-1848) 8 Catalyst introduces a less difficult path for molecules to follow Grey: uncatalyzed Green: catalyzed Energy Reaction 9 Catalyst introduces a less difficult path for molecules to follow Grey: uncatalyzed Green: catalyzed New reaction intermediate Energy Reaction 10 Catalyst introduces a less difficult path for molecules to follow Example: ammonia synthesis, Haber-Bosch process Energy Reaction Richardson, Principles of Catalyst Development, Plenum Press, 1989, p. 2. 11 Catalyst introduces a less difficult path for molecules to follow Example: ammonia synthesis, Haber-Bosch process Energy • Exothermic reaction • Catalyst does not change the overall energetics • Activation energy: Ehomogeneous >> Ecatalytic Reaction Richardson, Principles of Catalyst Development, Plenum Press, 1989, p. 2. Also: https://www.chemguide.co.uk/physical/equilibria/haber.html 12 Interactions between catalyst & substrate should be not too storng nor too weak but ”just right” (Sabatier) Volcano curves often encountered. There, measure of catalytic activity… • Reaction rate • Turn-over frequency (TOF) • etc … plotted against a measure of binding energy More, e.g.: http://dx.doi.org/10.1002/9781119181286 Richardson, Principles of Catalyst Development, Plenum Press, 1989 Classification of catalysts Typically divided to homogeneous vs heterogeneous catalysis 1. Homogeneous: catalyst is in the same phase as reactants (and products) • Gas-gas, liquid-liquid, solid-solid 2. Heterogeneous: reactants and catalyst in a different phase • Phase not only solid, liquid, and gas, but also immiscible liquids, e.g. oil and water. • Most often: solid catalyst with gaseous and/or liquid reactant 3. Enzymes form their own (biocatalyst) group (will not be dealt further in this course) (4. Photocatalysts, will not be dealt with further in 2018-2019) More: Ross book, Chapter 1, Box 1.1 15 Some examples 1. Homogeneous catalysts: most typically liquids. Examples: • Liquid-liquid: hydrolysis of esters by acids (more examples to follow in this coures) • Vapor-vapor: oxidation of SO2 by NO2 - • Solid-solid: decomposition of potassium chlorate (K+ ClO3 ) by MnO2 2. Heterogeneous catalysts: most typically solids. Examples • NH3 process; many more examples to follow during course Seven steps of a heterogeneously catalyzed reaction Seven steps of a heterogeneously catalyzed reaction 1. External diffusion 2. Internal diffusion 3. Adsorption 4. Surface reaction 5. Desorption of product 6. Internal diffusion of product 7. External diffusion of product Figure 4.1: Julian Ross: Heterogeneous Catalysis - Fundamentals and Applications, © Elsevier 2012. Link to electronic book here. Catalysis: a tool for manipulating selectivity Catalyst: tool for selectivity. Case: synthesis gas H2 + CO Methane Paraffinic hydrocarbons H2 + CO [Co/ThO2] Alcohols, aldehydes, and acids Methanol Richardson, Principles of Catalyst Development, Plenum Press, 1989, p.5. 20 Catalysis: tool of Green Chemistry Anastas et al. Applied Catalysis A: General 221 (2001) 3–13, https://doi.org/10.101 6/S0926- 860X(01)00793-1 Significance of catalysis? Timeline Lead chamber Berzelius: “Catalysis” process, H2SO4 From alchemy to chemistry Ostwald: “there is probably no chemical reaction which … - 1834 can not be influenced From empirics to science catalytically” 1835-1897 The birth of industrial catalysis ”The nitrogen problem” 1898-1918 NH3 synthesis Fluid Catalytic Cracking (Haber-Bosch) The increase in global Fischer-Tropsch mobility by developing catalytic fuel processes 1919-1945 Petrochemical industry & polymers (& explosive automotive market) From war to peace 1946-1970 (1962 Rachel Carson’s Silent Spring) Environmental catalysis Pollution control 1970-20?? https://dx.doi.org/10.1023/A:1025001809516 How a centrury of ammonia synthesis changed the world, Erisman et al., Nature Geoscience 1 (2008) 636-639. ”Carbon dioxide crisis”, 2018 • Empty shop shelves in summer for beer & soft drinks (with Fifa World Cup!) • Shortage of CO2 because of… • … shutdowns & maintenance in NH3 production https://www.chemistryworld.com/news/explainer-the-carbon-dioxide-crisis- /3009216.article, accessed 12.1.2019 Significance of catalysis? Without catalysts, there would not be • Modern chemical industry • Oil refining • Polymer production • Possibility to control emissions • Enough food for the earth’s population How large is the catalyst market? • Market studies in 2013 have estimated the total sales of catalysts to be between $15 and $19 billion per year, and to rise 4−5% per year. • Munnik, de Jongh, de Jong, Recent developments in the synthesis of supported catalysts, Chem. Rev. 115 (2015) 6687. (Open Access) http://dx.doi.org/10.1021/cr500486u --> • https://www.transparencymarketresearch.com/global-refinery-catalyst-market.html • https://www.freedoniagroup.com/world-catalysts.html • ~850 catalysts commercially available • Source: Prof. Jiri Cejka, plenary lecture at EuropaCat 2017 Munnik, de Jongh, de Jong, Recent developments in the synthesis of supported catalysts, Chem. Rev. 115 (2015) 6687. (Open Access) http://dx.doi.org/10.1021/cr500486u Components of a solid heterogeneous catalyst Three typical components of a solid heterogeneous catalyst Richardson, Principles of Catalyst Development, Plenum Press, 1989, p. 27. Active component: chemical activity Types, e.g.: • Metals • Semiconductor oxides and sulfides • Insulator oxides and sulfides Richardson, Principles of Catalyst Development, Plenum Press, 1989, p. 27. 30 Transition metals are typical active components Source: https://iupac.org/what-we-do/periodic-table-of-elements/ , 31 accessed 12.1.2019 https://en.wikipedia.org/wiki/Transition_metal, accessed 14.1.2019 Active component: chemical activity • Types, e.g.: • Metals • Semiconductor oxides and sulfides • Insulator oxides and sulfides Richardson, Principles of Catalyst Development, Plenum Press, 1989, p. 27. 32 Support: high surface area etc • Function: • High surface area; Porosity • Mechanical properties; Stability • Dual functional activity • Modification of active component • Types, e.g.: • High melting point oxides • Clays • Carbon Richardson, Principles of Catalyst Development, Plenum Press, 1989, p. 27. 33 Some catalyst supports + ZrO2, CeO2-ZrO2, TiO2, … Richardson, Principles of Catalyst Development, Plenum Press, 1989, p. 31. 34 Catalysts contain ”finely disintegrated metals” Dispersion defined as • D = Ns / Nt • Ratio surface atoms vs total atoms (typically used for metals) Image: Ross, Heterogeneous catalysis, Chapter 3 (Fig. 3.5) Image: Richardson, Principles of Catalyst Development, Plenum Press, 1989, p. 31. More, e.g.: http://dx.doi.org/10.1002/9781119181286 Sabatier Nobel lecture 1912: https://www.nobelprize.org/prizes/chemistry/1912/sabatier/lecture/ 35 Distribution of surface sites varies with crystallite size corner edge face Image: Richardson, Principles of Catalyst Development, Plenum Press, 1989. Promoters:”spices” of a catalyst • Function, on support: • Structural • Activity inhibition • Activity promotion • Function, on active component: • Electronic • Morphology • Poisoning Richardson, Principles of Catalyst Development, Plenum Press, 1989, p. 27. 37 Examples of promoters Typical: K basic Cl acidic Richardson, Principles of Catalyst Development,
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