Effect of zeolite matrices on the redox and catalytic properties of the Cu ions in MFI zeolites

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.