In situ EPR study of chemical reactions in Q-band at higher temperatures: a challenge for elucidating structure-reactivity relationships in catalysis.
For the first time, heterogeneous catalytic reactions have been monitored by in situ EPR spectroscopy in the Q-band using a homemade heatable probe head equipped with a flow reactor. The reactions of Al(2)O(3)-supported TEMPO with NO and H(2) as well as of SiO(2)/Al(2)O(3)-supported H(4)PVMo(11)O(40) with methanol and formaldehyde were studied up to 400 degrees C. TEMPO radicals are immobilized on the support in positions which impose a different reactivity to NO and H(2). This may be due to different accessibility, which changes during thermal treatment. By combined evaluation of anisotropic X- and Q-band spectra with a complex hyperfine structure (e.g., from VO(2+)), spin Hamiltonian parameters can be derived with higher precision, since limits of the specific resolution in both frequency bands are compensated for. In addition to VO(2+), Mo(5+) is formed above 180 degrees C depending on the O(2) content of the feed, which is easily discriminated in the Q-band but not in the X-band.
Stösser
Reinhard
R
Institute of Chemistry, Humboldt University of Berlin, Brook-Taylor-Strasse 2, D-12489 Berlin, Germany.
Marx
Ulrich
U
Herrmann
Werner
W
Jabor
Jabor K
JK
Brückner
Angelika
A
D002384:Catalysis; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D006358:Hot Temperature; D013329:Structure-Activity Relationship