Copper-dependent modification of structural and functional properties of potassium silicate glasses for catalytic applications

Abstract

Mainly due to their tunable structural and physicochemical properties, glassy systems belong to an interesting class of materials, exhibiting wide potential applications in electronics, medicine, civil engineering, the chemical industry, etc. In this work, the effect of copper doping (0–7 mol.%) on the structural and functional properties of potassium silicate glasses was systematically investigated. Glasses were synthesized by high-temperature melting, characterized by a plethora of methods (XRF, XRD, RS, FTIR, NMR, XPS, XAS, UV/Vis-DR, TPR, DRIFT, SEM/EDX), and tested as catalysts in soot combustion as a model oxidation reaction. The structural analysis confirmed that the amorphous character of the glass matrix was largely preserved upon copper incorporation, although local nanocrystalline domains were also detected. Surface studies revealed pronounced hydroxylation and carboxylation, largely independent in their nature of copper concentration. It was demonstrated that copper is predominantly located within the bulk of the glass matrix and coexists in two oxidation states, Cu⁺ and Cu²⁺, with a Cu⁺/Cu²⁺ ratio that varies non-monotonically with the copper content.

The synthesized materials exhibited high catalytic activity in soot combustion, with T₅₀ values of 350–380 °C under tight contact and 450–500 °C under loose contact conditions. Importantly, a clear correlation between catalytic activity under loose contact conditions and the fraction of Cu²⁺ species was observed, indicating that the catalytic performance is controlled by a redox mechanism involving the Cu²⁺/Cu⁺ couple. The reported findings highlight the decisive role of copper redox speciation in determining the catalytic behavior of alkali silicate glasses and demonstrate the potential of copper-doped glassy materials as stable catalysts for such important environmental applications as soot combustion.