Ethanol Dehydrogenation over Copper-Silica Catalysts: From Atomic Distribution to 15 nm Large Particles

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/SiO2 catalysts (~2.5 wt% Cu) with varying copper distribution: hydrolytic sol-gel (mostly atomic dispersion), dry impregnation (Ā = 3.9 nm; σ = 1.4 nm and particles up to 22 nm), strong electrostatic adsorption (Ā = 2.6 nm; σ = 1.0 nm) and solvothermal hot injection followed by Cu particles deposition (Ā = 14.7 nm; σ = 3.1 nm). All materials were characterized by ICP-OES, XPS, N2 physisorption, STEM-EDS, XRD, and H2-TPR, and tested in ethanol dehydrogenation from 185 to 325 °C. The sample prepared by hydrolytic sol-gel exhibited mostly atomic 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) and 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

Potenciálem řízená spínací strategie zapnutí/vypnuti pro elektrosyntézu polymérů odvozených od [7]Helicenu

New materials bearing thiophene and helicene moieties were prepared by using a potential-driven on/off switch strategy on the surface of glassy carbon and indium tin oxide substrates. Specifically, a 3-([7] helicen-9-yl)-thiophene hybrid monomer was electrooxidized in acetonitrile by using cyclic voltammetry with anodic potential limits of + 1.5 or + 2.5 V, resulting in a conductive and non-conductive polymer, respectively. The electrochemical findings were supplemented by microscopy investigations, UV/Vis, fluorescence and vibrational spectroscopies, and H-1 NMR spectroscopy as well as ellipsometry measurements and computational chemistry. The electrodeposited polymers could be used for the further development of materials applicable in organic electronics, optoelectronics, and sensing technologies.Nové materiály nesoucí thiofenovou a helicenovou část byly připraveny pomocí potenciálem řízené spínací strategie zapnutí/vypnutí na povrchu substrátů ze skleněného uhlíku a indium cín oxidu. Konkrétně, 3-([7]helicen-9-yl)-thiofenový hybridní monomer byl elektrooxidovaný v acetonitrilu za použití cyklické voltampermetrie s limitním anodickým potenciálem +1.5 nebo +2.5 V, mající za následek vodivý a nevodivý polymer. Elektrochemická zjištění byla doplněna mikroskopickým zkoumáním, UV/Vis, fluorescenční a vibrační spektroskopií a 1H NMR spektroskopií a také elipsometrií a chemickými výpočty. Elektrodeponovaný polymer by mohl být využit pro další vývoj materiálů aplikovatelných v organické elektronice, optoelektronice a senzorů

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

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/SiO2 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, N2 physisorption, STEM-EDS, XRD, RFC N2O, and H2-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