Abstract:
The aim of the paper is to bring insight into the relationship between the structure, redox properties and catalytic activity in propane oxidation of the Cu ions in high-silica zeolites. Previous studies revealed several defined Cu ion sites characteristic of high-silica zeolites, differing in coordination-siting, positive charges, and population depending on Cu concentration, and content of Al in the framework. It has been a highly important to relate this knowledge on the structure of Cu ion sites to the redox properties and oxidation catalytic activity of the Cu-high-silica zeolites. The reducibility and catalytic activity in propane oxidation was investigated for the Cu ions planted in zeolites of structural types ZSM-5 (MFI) with different Cu/Al/Si compositions, where NA(I) or H(I) ions were present as cocations, and Cu ions were exchanged at various conditions (concentration and pH). Reducibility of the CU(II) ions was investigated by temperature-programmed reduction (TPR) with hydrogen, and by vacuum and CO treatment of the zeolities; the relative concentration of the CU(I) ions was monitored by IR spectra of formed CU(I)-(CO)n complexes. Conversion of propane to CO and CO2 was studied in dependence on temperature in an integral through-flow reactor and evaluated in turn-over-frequency (TOF) values, representing the activity per one CO ion.
