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catalyst.pptx

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catalyst.pptx

  1. 1. Chemical Surface and Catalyst Masters Lectures Lecture : 1 catalyst Asst. Prof. Firas H. Abdulrazzak Physical chemistry College of Education for Pure Science Chemistry Dep. Diyala University
  2. 2.  What is catalyst  What is CATALYSIS  TYPES OF CATALYSIS  HOMOGENEOUS CATALYSIS  HETEROGENEOUS CATALYSIS  CHARACTERISTICS OF CATALYTIC  REACTIONS  PROMOTERS  CATALYTIC POISONING  AUTOCATALYSIS  NEGATIVE CATALYSIS  ACTIVATION ENERGY AND CATALYSIS
  3. 3. A catalyst is as a materials can alters the rate of reactions, without any chemically changed such consumed or destroyed at the end of the reaction. Catalysis is an action by catalyst.  Positive catalyst :A catalyst which enhances the rate of a reaction and the process Positive catalysis.  Negative catalyst :A catalyst which retards the rate of a reaction and the process Negative catalysis.
  4. 4. Classification of catalysts which depend on many physiochemical properties: Classification by physical state gas liquid solid Classification by nature of materials Inorganic Organic Classification by the mechanism of reactivity Homogeneous Heterogeneous Classification by activity Acid-base catalysts Enzymatic Photocatalysis Electrocatalysis
  5. 5. The ideal properties of catalyst o The mass of catalyst remains without any lose with kept the content after the reaction. o The mass of the catalyst which needed to catalysis the reaction mostly needed small amounts. o selectivity Byproducts should be minimized. o can not initiate the reaction or create new equilibrium state o Stability o Particle size mostly nanometres in diameters
  6. 6. Catalyst components  Active phase Where the reaction occurs (active sites) (mostly metal/metal oxide)  Promoter or stimulus  Modified with Electric groups  Poison resistant promoters  Selectivity enhancement  Support / carrier  Increase • mechanical strength • surface area • activity Promoter A substance which, though itself not a catalyst, promotes the activity of a catalyst MOSTLY IN HETROGENOUS REACTION
  7. 7. Theories of promoter reactivity I. Change of Lattice Spacing. II. Increase of Peaks and Cracks.  AUTOCATALYSIS $$$-When one of the products of reaction itself acts as a catalyst for that reaction. Hydrolysis of an Ester Oxidation of Oxalic acid Decomposition of Arsine
  8. 8. CATALYTIC POISONING A substance which destroys the activity of the catalyst to accelerate a reaction Explanation of Catalytic Poisoning #The poison is adsorbed on the catalyst surface in preference to the reactants -------------------------------------- ---------- #The catalyst may combine chemically with the impurity  poisoning a catalyst  breaking a chain reaction Negative Catalysis
  9. 9. ACTIVATION ENERGY AND CATALYSIS
  10. 10. Preparation of catalysts Home work???????? Precipitation To form non-soluble precipitate by desired reactions at certain pH and temperature Adsorption & ion-exchange Cationic: S-OH+ + C+  SOC+ + H+ Anionic: S-OH- + A-  SA- + OH- I-exch. S-Na+ + Ni 2+ D S-Ni 2+ + Na+ Impregnation Fill the pores of support with a metal salt solution of sufficient concentration to give the correct loading. Dry mixing Physically mixed, grind, and fired
  11. 11. 1-Intermediate Compound Formation theory (Homogeneous ) THEORIES OF CATALYSIS 2-The Adsorption theory. (Heterogeneous)  an intermediate compound produce with one of the reactants.  an intermediate compound reacts with the second reactant to yield the product, releasing the catalyst A + B ⎯C⎯→ AB A + C → AC Intermediate AC + B → AB + C  a reaction between two gases catalyzed by a solid.  the catalyst functions by adsorption of the reacting molecules on its surface. Step 1. Adsorption of Reactant molecules Step 2. Formation of Activated complex Step 3. Decomposition of Activated complex Step 4. Desorption of Products
  12. 12. Activated complexes -----------------------------------------------------------
  13. 13. Active Centres on Catalyst Surface pore porous solid Active site An Active site is a point on the surface that can form strong CONACTION with an adsorbed atom or molecule.
  14. 14. Classification of Solid Catalysts 1-Unsupported (Bulk) Catalysts  Metal Oxides • Simple Binary Oxides • Complex Multicomponent Oxides  Metals and Metal Alloys  Carbides and Nitrides  Carbons  Ion-Exchange Resins and Ionomers  Molecularly Imprinted Catalysts  Metal – Organic Frameworks  Metal Salts  Supported Metal Oxide Catalysts  Supported Metal Catalysts  Supported Sulfide Catalysts  Hybrid Catalysts  Ship-in-a-Bottle Catalysts  Polymerization Catalysts 3-Coated Catalysts 2-Supported Catalysts  Supports  Surface-Modified Oxides
  15. 15. Thank you

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