Thermal decomposition and reducibility of silica-supported precursors of Cu, Fe and Cu–Fe nanoparticles

Cu–Fe nanocomposites are considered as ecofriendly and low-cost alternative to precious metal catalysts for selective hydrogenation of products derived from biomass and syngas. In this work, the catalytically active nanocomposites have been synthesized by supporting Cu and Fe precursors on a silica carrier using the novel procedure of consecutive incipient wetness impregnation and the method of deposition–precipitation using urea (DPU). The prepared silica-supported precursors are shown to decompose completely at temperatures as low as 300–350 °C, thus giving a possibility to obtain Fe and Cu–Fe oxide nanoparticles of the size 1–4 nm as isolated particles or their aggregates. Interaction of Fe and Cu species in the prepared nanoparticles has been revealed by the method of temperature-programmed reduction with hydrogen, which exhibited the Cu-enhanced reducibility of Fe³⁺ to Fe⁰ and stability to reoxidation for the metallic particles. Variations in the preparation procedures influence the reducibility and the interaction between Cu and Fe components resulting in considerable changes of the catalytic activity and selectivity in hydrogenation of unsaturated carbon bonds. Complete reduction to a metallic state was reached at 500 °C if the DPU preparation method was applied. The nanocomposites prepared by the DPU procedure provide the highest catalytic activity.