Chapter 10: Catalysis and Catalytic Reactors

Learning Resources

Example CD10-1: Analysis of a Heterogeneous Reaction

[Class Problem, Winter 1997]



		Experimental data for the gas-phase catalytic reaction



		are shown below. The limiting step in the reaction is known to be irreversible, so that the overall reaction is irreversible. The reaction was carried out in a differential reactor to which A, B, and C were all fed.

		(a) Sketch as a function of P_A , as a function of P _B , and as a function of P _C^. (b) From your observations in part (a), which species would appear in the numerator of the rate expression? Which species would appear in the denominator of the rate expression? To what power is the denominator raised? (c) From your conclusions from part (b), suggest a rate law consistent with the experimental data.
		(d) Evaluate the rate law parameters. (e) From your rate expression, which species can you conclude are adsorbed on the surface? (f) From your conclusions in part (e), suggest a mechanism and rate-limiting step for this reaction. (g) For an entering partial pressure of A of 2 atm in a PBR, what is the ratio of sites of A to C sites at 80% conversion of A? (h) At what conversion are the number of A and C sites equal?

		Solution (a) Compare runs 1, 3, 6, and 7. P _B and P _C are fixed. As P _A increases the rate first increases then levels off. Therefore, P _A must be in both the numerator and denominator.

		Compare runs 4 and 5. P_A and P_B are fixed. Because the reaction is irreversible, P_C must be in the denominator.

		Compare runs 2 and 7. P_A and P_C are fixed. increases by a factor of 10 when P_Bincreases by a factor of 10. P_B is only in the numerator.

		(b) A and B are in the numerator, C and A are in the denominator. (c) (d) For fixed P _C and P _B ,



		For fixed P _A and P _B



		We note that the non-linear regression techniques described in Chapter 5 could have easily been used.