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

Abstract

Comparison of four preparation methodsshowed that the simpleand cost-effective dry impregnation provides Cu/SiO2 materialshowing the most stable catalytic behavior in potential renewableacetaldehyde production despite having a broad particle size distribution. Non-oxidative ethanoldehydrogenation is a renewable source ofacetaldehyde and hydrogen. The reaction is often catalyzed by supportedcopper catalysts with high selectivity. The activity and long-termstability depend on many factors, including particle size, choiceof support, doping, etc. Herein, we present four different syntheticpathways to prepare Cu/SiO2 catalysts (& SIM;2.5 wt %Cu) with varying copper distribution: hydrolytic sol-gel (sub-nanometerclusters), dry impregnation (A = 3.4 nm; & sigma;= 0.9 nm and particles up to 32 nm), strong electrostatic adsorption(A = 3.1 nm; & sigma; = 0.6 nm), and solvothermalhot injection followed by Cu particle deposition (A = 4.0 nm; & sigma; = 0.8 nm). All materials were characterized byICP-OES, XPS, N-2 physisorption, STEM-EDS, XRD, RFC N2O, and H-2-TPR and tested in ethanol dehydrogenationfrom 185 to 325 & DEG;C. The sample prepared by hydrolytic sol-gelexhibited high Cu dispersion and, accordingly, the highest catalyticactivity. Its acetaldehyde productivity (2.79 g g(-1) h(-1) at 255 & DEG;C) outperforms most of the Cu-basedcatalysts reported in the literature, but it lacks stability and tendsto deactivate over time. On the other hand, the sample prepared bysimple and cost-effective dry impregnation, despite having Cu particlesof various sizes, was still highly active (2.42 g g(-1) h(-1) acetaldehyde at 255 & DEG;C). Importantly,it was the most stable sample out of the studied materials. The characterizationof the spent catalyst confirmed its exceptional properties: it showedthe lowest extent of both coking and particle sintering.Comparison of four preparation methodsshowed that the simpleand cost-effective dry impregnation provides Cu/SiO2 materialshowing the most stable catalytic behavior in potential renewableacetaldehyde production despite having a broad particle size distribution. Non-oxidative ethanoldehydrogenation is a renewable source ofacetaldehyde and hydrogen. The reaction is often catalyzed by supportedcopper catalysts with high selectivity. The activity and long-termstability depend on many factors, including particle size, choiceof support, doping, etc. Herein, we present four different syntheticpathways to prepare Cu/SiO2 catalysts (& SIM;2.5 wt %Cu) with varying copper distribution: hydrolytic sol-gel (sub-nanometerclusters), dry impregnation (A = 3.4 nm; & sigma;= 0.9 nm and particles up to 32 nm), strong electrostatic adsorption(A = 3.1 nm; & sigma; = 0.6 nm), and solvothermalhot injection followed by Cu particle deposition (A = 4.0 nm; & sigma; = 0.8 nm). All materials were characterized byICP-OES, XPS, N-2 physisorption, STEM-EDS, XRD, RFC N2O, and H-2-TPR and tested in ethanol dehydrogenationfrom 185 to 325 & DEG;C. The sample prepared by hydrolytic sol-gelexhibited high Cu dispersion and, accordingly, the highest catalyticactivity. Its acetaldehyde productivity (2.79 g g(-1) h(-1) at 255 & DEG;C) outperforms most of the Cu-basedcatalysts reported in the literature, but it lacks stability and tendsto deactivate over time. On the other hand, the sample prepared bysimple and cost-effective dry impregnation, despite having Cu particlesof various sizes, was still highly active (2.42 g g(-1) h(-1) acetaldehyde at 255 & DEG;C). Importantly,it was the most stable sample out of the studied materials. The characterizationof the spent catalyst confirmed its exceptional properties: it showedthe lowest extent of both coking and particle sintering.