It was mentioned in Chapter 7.1 that if more than one active site is required in a unimolecular decomposition reaction, the denominator must be raised to a power greater than unity. Now, if a RDS does not exist, the derivation can become more complicated. An example of this is provided by a study of ammonia decomposition on a 4.8% Ru/carbon catalyst with a dispersion near unity [60]. Using a power rate law of the form rm = kPa NH3 Pb H2 , values of a ¼ 0:75 and 0.69 were obtained at 643 and 663 K, respectively, while values of b were _2.0 and _1.6 at 643 and 663 K, respectively. The elementary steps proposed for the catalytic cycle are given below with their stoichiometric numbers, where * represents an active site