Binary [Cu2O/MWCNT] and ternary [Cu2O/ZnO/MWCNT] nanocomposites: formation, characterization and catalytic performance in partial ethanol oxidation

Abstract

Cuprous oxide agglomerates composed of 4–10 nm Cu₂O nanoparticles were deposited on multiwalled carbon nanotubes (MWCNTs) and on ZnO/MWCNTs to give binary [Cu₂O/MWCNT] and ternary [Cu₂O/ZnO/MWCNT] composites. Di-aqua-bis[2-(methoxyimino)propanoato]copper Cu[O₂CCCH₃NOMe]₂·2H₂O 1 in DMF was used as single source precursor for the deposition of nanoscaled Cu₂O. The precursor decomposes either in air or under argon to yield CuO₂ by in situredox reaction. Thermogravimetric coupled mass spectroscopic analysis (TG-MS) of 1 revealed that methanol formed during the decomposition of 1 acts as a potential in situ reducing agent. Scanning electron microscopy (SEM) of the binary [Cu₂O/MWCNT] nano-composite shows an increase of cuprous oxide loading depending on the precursor amount, along the periphery of the MWCNTs as well as formation of larger particle agglomerates. Transmission electron microscopy (TEM) of the sample shows crystalline domains of size 4–10 nm surrounded by an amorphous region within the larger particles. SEM and TEM of ternary [Cu₂O/ZnO/MWCNT] clearly reveal that Cu₂O nanoparticles are primarily deposited on ZnO rather than on MWCNTs. The catalytic activities of the [Cu₂O/MWCNT] and [Cu₂O/ZnO/MWCNT] binary and ternary composites were studied for the selective partial oxidation of ethanol to acetaldehyde with molecular oxygen. While using binary [Cu₂O/MWCNT] (13.8 wt% Cu) as catalyst, acetaldehyde was obtained with a yield of 87% at 355 °C (selectivity 96% and conversion 91%). When nanoscale ZnO is present, the resulting [Cu₂O/ZnO/MWCNT] composite shows preferential hydrogen and CO₂ formation due to the fact that the dehydrogenation and total oxidation pathway is more favoured compared to the binary composite. Significant morphological changes of the catalyst during the catalytic process were observed.