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

Abstract

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.

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“…Due to growing environmental concerns, polluting reagent-based stoichiometric oxidants are needed to avoid and replace these harmful stoichiometric oxidants by using selective oxidation processes utilizing environmentally benign oxidants. In the literature, noble metals such as Ru-, Au-, Pd-, and Pt- based catalysts have also shown excellent catalytic activity for the organic transformation of aromatic primary alcohols. However, due to their high cost, these are not industrially favorable catalysts.…”

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“…Another method based on materials design is to utilize the ensemble effects that emerge through alloying the surface with other metals. There is evidence that both alloys [17] and mixtures [18] of Au with other metals outperform pure Au. Of particular interest is the work by Zhao et al [18] who discovered, via measurements Disclaimer/Publisher's Note: The statements, opinions, and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s).…”