Ethanol Dehydrogenation over Copper-Silica Catalysts: From Sub-Nanometer Clusters to 15 nm Large Particles
Tomáš Pokorný, Vít Vykoukal, Petr Macháč, Z. Moravec, Nicola Scotti, Pavla Roupcová, Kateřina Karásková, Aleš Stýskalík
Abstract
High Resolution Image Download MS PowerPoint Slide 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 2 O, 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.