EXAFS and optical spectroscopy characterisation of reduction products of binary silver-copper ion mixture in mordenite

摘要

Ag~+, Cu~(2+) and Ag~+-Cu~(2+) binary mixtures with different Ag/Cu ratios were supported on mordenite with Si/Al ratio equal to 10 and reduced in the temperature range 323-673 K. Diffuse Reflectance UV-Visible spectra reveal appearance of Ags clusters and small copper metal particles. Cu K-edge EXAFS show for Cu-rich non-reduced samples the presence of only oxygen shell; but for the Ag-rich sample, the presence of heavier backscatterer is also indicated producing a different EXAFS envelope. Silver EXAFS analysis suggests that, for the reduced samples, there are both Ag-O and Ag-Ag distances (Ag-Ag and Ag-O coordination numbers of approx 2 and of 1.3 respectively for the Ag/Cu = 3:1 and 1:3 samples). Importantly, for the reduced sample, the EXAFS indicates that Ag appears to promote/stabilise Cu cluster formation whereas Cu appears to impede/destabilise Ag cluster formation.