Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

PP-I-21the molecular oxygen is predominating. It is coincide with experiments [5]. It is also agreedwith suggested explanation of molecular oxygen participation in the formation complexes atthe surface due to particularities of its electronic structure (the triplet ground state with twounpaired electrons).Table 1. Results of MNDO calculations of the processes on the Fe catalyst duringammonia oxidation.Collision complexes NH 3 …Fe O 2 …Fe O…Fe Fe…O 2 …NH 3 Fe...O...NH 3Total energy, Е tot eV –350,689 –745,635 –427,04 –989,23 –668,7Heat of formation ΔΗ 0 298,kcal/molDistance between particlesand Fe, R, Å164,77 72,00 29,216 211,19 219,941,9 1,95 1,9 2,05 1,75The activation energy, E act 4,03 4,45 6,74 1,16 4,2The next research stage is calculation of ammonia with Fe interaction in the presencemolecular or atomic oxygen. As for as NH 3 …O…Fe, collision complex shows considerableinteraction and energy minimum at R = 1.8Å. According to the electronic density distributionanalysis we can see that oxygen atom almost «seats» on the d-orbitals of iron. There is theweak overlapping between ammonia molecular orbitals and oxygen atomic orbitals. Besides,there is the significant interaction of the oxygen p-orbitals and iron d-orbitals. It can beexplained by stronger influence of the atomic oxygen on the iron, than on the NH 3 . Thecalculation of all collision complexes confirmed significantly deep interaction betweenammonia and atomic oxygen over Fe catalyst. Therefore it is necessary to admit that atomicoxygen can be more active in the ammonia oxidation on the Fe surface. It is agreed withtraditional point of view concerning the ammonia oxidation mechanism.References:1. J.K. Norskov and P. Stolze, Theoretical aspects of surface reactions, Surface Science, 189/190, 91-105(1987) North-Holland, Amsterdam.2. North-Holland, Amsterdam, J.K. Norskov, Progress in Surface Science, V. 38, №2, 1991.3. S. Holloway and J.K. Norskov, Surface science lecture notes, 1991, Liverpool University press.4. Van Santen Rutger A, and Neurock, Catal. Rev.-sci.eng., 1995, 37 (4), 557-698.5. C.T. Au and M.W. Roberts, Nature, 319, 206 (1986).251