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

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

6. 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.

7. Catalysts affect both Selectivity and Yeild

10. Steps in a Catalytic Reaction

11. 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.

12. The Adsorption Step

14. The Surface Reaction Step

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

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

27. Intro to Catalysis Reforming catalyst – Algorithm 1)Postulate a mechanism 2)Postulate a rate-limiting step 3)Express C i·s in terms of partial pressures 4)Site balance (Total number of sites constant) 5)Derive rate law 6)Evaluate parameters Pt (sputtered on) Al 2 O 5 (scaffold)

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

29. Site Balance: Is this consistent with the data? Linear when P Ni0 is low Low slope when P Ni0 is large Consistent!! P Ni0 r Ni0