Au−Pd Selectivity‐switchable Alcohol‐oxidation Catalyst: Controlling the Duality of the Mechanism using a Multivariate Approach

• Published in: ChemCatChem 2019-07, Vol.11 (13), p.3022-3034
• Main Authors: da S. Melo, Itaciara E. M., de Sousa, Samuel A. A., dos S. Pereira, Laíse N., Oliveira, Jefferson M., Castro, Karla P. R., Costa, Jean C. S., de Moura, Edmilson M., de Moura, Carla V. R., Garcia, Marco A. S.
• Format: Article
• Language: English
• Subjects: Alcohol; alcohol oxidation; Aldehydes; Au−Pd nanoparticles; Benzyl alcohol; Catalysis; Catalysts; factorial design; Gold; Multivariate analysis; Nanoparticles; Optimization; Oxidation; Palladium; Selectivity; SrCO3; Strontium carbonate
• ISSN: 1867-3880; 1867-3899
• DOI: 10.1002/cctc.201900512

Supported gold‐palladium nanoparticles are highly selective catalysts for the oxidation of alcohols. However, little is known about how integrated reaction conditions can affect the chemoselectivity of a specific catalytic system. Herein, a novel Au−Pd selectivity‐switchable catalyst supported on SrCO3 is reported; and a multivariate optimization was suggested as the key process to better understand the formation of the products. The optimization approach considered temperature, pressure, time of reaction, and Au : Pd molar ratio, and settled that the temperature and Au : Pd molar ratio showed an important effect on the ester yield, while just the metal molar ratio significantly influenced the selectivity for the aldehyde. Thus, taking into consideration the experimental data and optimized conditions, we were able to efficiently switch the selectivity by just changing the pressure of the system in a benzyl alcohol oxidation reaction. In addition, we proposed that the presence of O2 implies that there are two catalytic pathways, which leads to different selectivity, allowing us to bring some mechanistic insights dealing with the duality of the mechanism. Such outcomes are based on dense experimental results and characterizations (FT‐IR, Rietveld refinement, XPS, H2‐TPR, and EDS‐STEM). The catalyst was also very stable, presenting activity up to 6 runs without loss of activity and selectivity, under certain reaction conditions. All about the nano: We have proposed a catalyst comprised of an Au−Pd nanoalloy supported on SrCO3 that can modify the benzyl alcohol selectivity by just changing the pressure of the system. At 5 bar, the chemoselectivity was demonstrated to be for the benzyl benzoate, and at 1 bar, high yields of benzaldehyde were obtained. We were able to prepare a catalyst that is a real selectivity‐switchable material.