Use of In Situ X‑ray\nAbsorption to Probe Reactivity:\nA Catalysis Golden Rule

The decomposition of ozone on supported manganese oxide\ncatalysts,\nstudied here, exemplifies reactions involving electron transfer. In\nsitu extended X-ray absorption fine-structure spectra (Mn K-edge)\non in situ treated samples show that the supported phase in MnO<sub><i>x</i></sub>/SiO<sub>2</sub> resembles Mn<sub>3</sub>O<sub>4</sub> while that in MnO<sub><i>x</i></sub>/Al<sub>2</sub>O<sub>3</sub> samples resembles MnO<sub>2</sub>. In situ Raman\nspectroscopy shows the involvement of a common peroxide surface species.\nKinetic data indicate a nonuniform surface and a rate-determining\nstep (rds) involving electron transfer from the peroxide intermediate.\nThe activation energy for all the catalysts is the same, indicating\nthat the pre-exponential factor controls the rate. This can be associated\nwith the electronic partition function (unoccupied density of states\n(DOS)), and X-ray absorption near-edge spectroscopy duly shows that\nthe areas of the pre-edge peaks due to 1s to 3d transitions track\nthe reactivity trends. The relation to the unoccupied DOS is analogous\nto Fermi’s Golden Rule for electronic transitions, and we denote\nthe finding here, applicable to reactions involving electron transfer,\nas a Catalysis Golden Rule.