The dependence of the decomposition on the total pressure was also investigate By changing the ratio of ammonia to carrier, i.e. the initial partial pressure of ammonia, some changes in decomposition occurs. The onset of decomposition is earlier for a high initial ammonia ratio; around 500 ms, 1 s and 5 s for 1:1, 1:10 and 1:100 ammonia to carrier ratio at 1000 °C, 10 mbar total pressure in nitrogen or argon carrier, Figs. S61, 1 and S65. It can be noticed that the degree of decomposition has a steeper slope when the ammonia ratio is low. The results also show that as the amount of carrier is decreased the decomposition profile becomes less dependent on the carrier type. This is expected as the main inhibitor for decomposition, hydrogen, is lowered if the amount of hydrogen containing carrier is lowered. The evolution of the decomposition rate with time (Fig. ) shows that the decomposition rate is much higher in nitrogen or argon than in hydrogen containing carriers. The decomposition rate in nitrogen and argon follows the same profile; a tailing distribution with a sharp peak of maximum decomposition rate at approximately 2 s, with the main difference between N2 and Ar being that the rate in nitrogen is slightly higher than in argon. The main contributing reaction for ammonia decomposition is the bimolecular decomposition assisted by a hydrogen radical (reaction 21, Table ) followed by dimerization with an already formed NH2 (reaction 22, Table ). Both these reactions cannot start at time 0 since no co-reactant is present, instead the processes start with bimolecular dissociation assisted by a third-body molecule (reaction 19 and 20, Table ).