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.

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.

No abstract

Nowadays, the production of acetaldehyde heavily relies on the petroleum industry. Developing new catalysts for the ethanol dehydrogenation process, which could sustainably substitute current acetaldehyde production methods, is highly desired. Among ethanol dehydrogenation catalysts, copper-based materials have been intensively studied. Unfortunately, the Cu-based catalysts suffer from sintering and coking, which lead to rapid deactivation with time-on-stream (TOS). Phosphorus doping has been demonstrated to diminish coking in methanol dehydrogenation, fluid catalytic cracking, and ethanol-to-olefin reactions. This work reports a pioneering application of the well-characterized copper phosphinate complexes as molecular precursors for copper-based ethanol dehydrogenation catalysts enriched with phosphate groups (Cu-phosphate/SiO2). Three new catalysts (CuP-1, CuP-2, CuP-3), prepared by the deposition of complexes {Cu(SAAP)}n (1), [Cu6(BSAAP)6] (2), and [Cu3(NAAP)3] (3) on the surface of commercial SiO2, calcination at 500 °C, and reduction in the stream of the forming gas 5% H2/N2 at 400 °C exhibited unusual properties. First, the catalysts showed a rapid increase in catalytic activity. After reaching a maximum conversion, the catalyst started to deactivate. The unusual behavior could be explained by the presence of the phosphate phase, which prevented the Cu2+ reduction. The phosphorus content gradually decreased during time-on-stream, copper was reduced, and the activity increased. The deactivation of the catalyst could be related to the copper diffusion processes. The most active CuP-1 catalyst reaches a maximum of 74 % ethanol conversion and over 98 % acetaldehyde selectivity at 325 °C and WHSV = 2.37 h−1.