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

摘要

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 O-2 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, H-2-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.