Synthesis of Cu/SiO2 catalysts via ionic exchange: Influence of copper loading on chemical structure and alcohol dehydrogenation

Abstract

The study analyzes the effect of copper content in Cu/SiO₂ catalysts (0.3–3.9 % w/w) obtained by the ion exchange method, comparing them with a catalyst prepared by wet impregnation (3.8 % w/w). Several characterization techniques, including XRD, DRUV-Vis, FTIR, and XPS, as well as a study of pyridine adsorption by FTIR, were employed to elucidate the structural and catalytic properties of the catalyst series. Results show that the copper-support interaction varies with concentration: at low concentrations, copper ions are effectively grafted onto the support, whereas at higher concentrations, a partial deposition of hydroxo-ammoniacal complexes begins as ion exchange reaches its limit. Textural properties of the support remain essentially unchanged during synthesis. DRUV-Vis and XPS spectra indicate the presence of dispersed Cu²⁺ species on the support surface, with the Cu/Si intensity ratio growing with copper loading. Catalytic activity increases with copper content up to a maximum, attributed to the formation of SiO–Cu–O–Cu–OSi and small Cu aggregates active sites. The materials exhibit strong selectivity to dehydrogenation reactions, with higher activity towards 2-propanol than ethanol. The paper explains the relationship between copper content, catalyst structure, and catalytic performance in Cu/SiO₂ catalysts.