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Lecture 23 Thursday 4/1/08 OCNB Explosion Noble Prize 2007 Catalytic Steps

Lecture 23 Thursday 4/1/08 OCNB Explosion Noble Prize 2007 Catalytic Steps. 400. Temperature o C. Cooling Restored. Q r = 0. Isothermal Operation. 200. 175. 9:55 t = 0. 10:40 10:50. midnight 12:18. Temperature-time trajectory. fuse. Catalysts and Catalysis.

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Lecture 23 Thursday 4/1/08 OCNB Explosion Noble Prize 2007 Catalytic Steps

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  1. Lecture 23 Thursday 4/1/08OCNB ExplosionNoble Prize 2007Catalytic Steps

  2. 400 Temperature oC Cooling Restored Qr = 0 Isothermal Operation 200 175 9:55 t = 0 10:40 10:50 midnight 12:18 Temperature-time trajectory fuse

  3. Catalysts and Catalysis A Catalyst is a substance that affects the rate of chemical reaction but emerges from the process unchanged. Catalysis is the occurrence, study, and use of catalysts and catalytic processes. Approximately 1/3 of the GNP of materials produced in the U.S. involves a catalytic process.

  4. Catalysts affect both Selectivity and Yeild

  5. Steps in a Catalytic Reaction

  6. Active Site • Reactions are not catalyzed over the entire surface but only at certain active sites or centers that result from unsaturated atoms in the surface. • An active site is a point on the surface that can form strong chemical bonds with an adsorbed atom or molecule.

  7. The Adsorption Step

  8. The Surface Reaction Step

  9. The Rate Limiting Step:Which Step Has the Largest Resistance?

  10. Octane Numbers Catalytic Reforming Normal Pentane Octane Number = 62 Iso-Pentane Octane Number = 95

  11. Intro to Catalysis • Reforming catalyst – • Algorithm • Postulate a mechanism • Postulate a rate-limiting step • Express Ci·s in terms of partial pressures • Site balance (Total number of sites constant) • Derive rate law • Evaluate parameters Pt (sputtered on) Al2O5 (scaffold)

  12. CV=concentration of vacant sites Postulate a mechanism: (single site) In 75% of heterogeneous catalysis, surface reaction is the slow step

  13. Site Balance: Is this consistent with the data? Linear when PNi0 is low Low slope when PNi0 is large rNi0 PNi0 Consistent!!

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