Monometallic advantage: highly selective benzyl alcohol oxidation catalyzed by Cu/TiO2 nanosheets with exposed (001) facets, compared to Cu-Ni/TiO2

초록

This study investigates the selective oxidation of benzyl alcohol, focusing on the catalytic performance of both monometallic Cu/TiO2 and bimetallic Cu-Ni/TiO2 nanosheets, each engineered to expose a high percentage of reactive (001) facets. While our initial aim was to develop a novel Cu-Ni bimetallic catalyst, the research revealed that monometallic Cu/TiO2 provided the highest overall selectivity and yield under the present reaction conditions, while Cu-Ni/TiO2 still showed a pronounced selectivity-regulation effect relative to Ni/TiO2. TEM and HRTEM imaging revealed well-dispersed Cu-Ni nanoparticles on the unique TiO2 nanosheet morphology. XPS analysis confirmed the presence of oxidized copper (Cu2+) and nickel (Ni2+) species interacting with the Ti4+ of the TiO2 support. The catalyst exhibited a mesoporous texture (N2 adsorption-desorption) and specific surface acidity (NH3-TPD). In catalysis, Cu-Ni/TiO2 achieved a benzyl alcohol conversion of 40.4% with a high selectivity of 91.0% towards benzaldehyde, yielding 36.7%. While this bimetallic catalyst showed enhanced selectivity compared to Ni/TiO2, its conversion was slightly lower than both Cu/TiO2 and Ni/TiO2 under the tested conditions. Notably, Cu/TiO2 exhibited superior selectivity and yield (46.4%), suggesting that under these specific reaction conditions, the copper active sites on the monometallic catalyst are more effective at directing the reaction pathway almost exclusively towards the desired benzaldehyde, minimizing the formation of side products more efficiently than the combined copper-nickel active sites. These findings indicate that while Cu/ TiO2 exhibits the highest overall selectivity and yield, the incorporation of Cu into the Cu-Ni/TiO2 system significantly improves the selectivity behavior of Ni-containing catalysts by suppressing non-selective oxidation pathways.

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