Reversible oxidation/reduction of silver supported on silica aerogel: Influence of the addition of phosphate

Ag/SiO(2) and Ag(3)PO(4)/SiO(2) systems supported on silica aerogel were investigated using temperature-programmed reduction (TPR), UV-visible diffuse reflectance spectroscopy (UV-vis DRS), and infrared spectroscopy. The formation of highly dispersed silver particles, uniformly distributed along the surface and stabilized with silanol groups, was observed for Ag/SiO(2) system. Phosphate and silanol groups produce two states of silver localization in phosphate-containing system. The addition of phosphate onto the silica surface leads to the reversible oxidation/reduction of silver in the temperature range of 100-300A degrees C with transitions of silver (particles 10-30 nm in size) to charged states (ions, clusters stabilized by phosphate groups). This reversible behavior of silver is stable, and the amount of silver involved in these processes remained constant (similar to 50%) for the series of consistent cyclic oxidation/reduction treatments.