| AVS 60th International Symposium and Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS-TuA |
| Session: | Metals and Alloys: Structure, Reactivity & Catalysis |
| Presenter: | I. Waluyo, University of Illinois at Chicago |
| Authors: | I. Waluyo, University of Illinois at Chicago Y. Ren, University of Illinois at Chicago M. Trenary, University of Illinois at Chicago |
| Correspondent: | Click to Email |
We used reflection absorption infrared spectroscopy (RAIRS) to experimentally study the kinetics of the NH formation and dissociation reactions on Ru(0001). These reactions are important in ammonia synthesis, for which ruthenium is one of the most effective catalysts. While theoretical values for the heats of adsorption of each species and the activation barriers for each step in the ammonia synthesis reaction have been extensively reported, there are few, if any, direct experimentally measured values for the activation barriers of the elementary steps in the reaction on Ru(0001). In our study, the evolution of the NH stretch peak at 3318 cm-1 was monitored as a function of time during the course of the NH formation reaction between 320 and 370 K and NH dissociation between 370 and 400 K. An atomic N layer was prepared through the thermal decomposition of NH3. During the NH formation reaction, the sample was continuously exposed to a constant background pressure of H2 to compensate for the loss of surface H due to the associative desorption of H2, which occurs in the same temperature range as NH formation. Both NH formation and dissociation were found to follow first-order kinetics, and the experimental rate constants show good agreement with the theoretical values. The experimentally determined activation energies of 69.6 and 104.9 kJ/mol for NH formation and dissociation, respectively, are comparable to the theoretical values of 103.3 and 133.5 kJ/mol.