Ethanol Dehydrogenation over Copper-Silica Catalysts: From Sub-Nanometer Clusters to 15 nm Large Particles

Abstract

Non-oxidative ethanol dehydrogenation is a renewable source of acetaldehyde and hydrogen. The reaction is often catalyzed by supported copper catalysts with high selectivity. The activity and long-term stability depend on many factors, including particle size, choice of support, doping, etc. Herein, we present four different synthetic pathways to prepare Cu/SiO ₂ catalysts (∼2.5 wt % Cu) with varying copper distribution: hydrolytic sol–gel (sub-nanometer clusters), dry impregnation ( A̅ = 3.4 nm; σ = 0.9 nm and particles up to 32 nm), strong electrostatic adsorption ( A̅ = 3.1 nm; σ = 0.6 nm), and solvothermal hot injection followed by Cu particle deposition ( A̅ = 4.0 nm; σ = 0.8 nm). All materials were characterized by ICP-OES, XPS, N ₂ physisorption, STEM-EDS, XRD, RFC N ₂O, and H ₂-TPR and tested in ethanol dehydrogenation from 185 to 325 °C. The sample prepared by hydrolytic sol–gel exhibited high Cu dispersion and, accordingly, the highest catalytic activity. Its acetaldehyde productivity (2.79 g g ^–1 h ^–1 at 255 °C) outperforms most of the Cu-based catalysts reported in the literature, but it lacks stability and tends to deactivate over time. On the other hand, the sample prepared by simple and cost-effective dry impregnation, despite having Cu particles of various sizes, was still highly active (2.42 g g ^–1 h ^–1 acetaldehyde at 255 °C). Importantly, it was the most stable sample out of the studied materials. The characterization of the spent catalyst confirmed its exceptional properties: it showed the lowest extent of both coking and particle sintering.

Abstract

Comparison of four preparation methods showed that the simple and cost-effective dry impregnation provides Cu/SiO ₂ material showing the most stable catalytic behavior in potential renewable acetaldehyde production despite having a broad particle size distribution.