Speciation and distribution of copper and zinc in MCM-41

Abstract

Speciation and distribution of copper and zinc in the channels of the surface modified MCM-41 (MCM-41-SH) (pore opening = 2.6 nm) has been studied by X-ray absorption near edge structural (XANES) and X-ray absorption fine structural (EXAFS) spectroscopies in the present work. By least-square fitted XANES spectroscopy, mainly CuO and ZnO are observed in the channels of MCM-41-SH after calcination at 298–1173 K. Interestingly, a small amount of Cu–Zn alloys is also found in the MCM-41-SH at the calcination temperature of 573 K. At T > 573 K, nanosize CuO and Zn 2SiO 4 are the copper and zinc compounds in the MCM-41-SH. Due to aggregation of nanosize CuO at 1173 K, the bond distance of Cu–O is increased to 1.97 Å with the coordination number (CN) of 3.3. A decrease of the Zn–O bond distance (1.94 Å) at 1173 K is also observed. This work is also an example of the usefulness of the XANES and EXAFS spectroscopies for revealing the chemical structure of copper and zinc and possible reaction paths in the channels of MCM-41-SH during calcination at elevated temperatures.