In recent years growing interest has been placed on the role of dopant concentrations of tertiary precious and base metals in modifying the performance of supported AuPd nanoalloys towards the direct synthesis of H2O2. Within this contribution, we expand on these earlier studies, with a focus on Fe-containing systems. Through rational catalyst design, an optimal 0.5%Au–0.5%Pd–0.02%Fe/TiO2 formulation has been developed, which not only outperforms the parent bimetallic analogue but also offers increased reactivity compared to alternative trimetallic formulations previously reported, including those which incorporate Pt. Such observations may be surprising given the propensity for Fe to decompose H2O2 via Fenton pathways. However, detailed analysis by CO-DRFITS and XPS reveals that the enhanced activity can be attributed to the electronic modification of Pd and the formation of domains of mixed Pd2+/Pd0 oxidation state, upon Fe introduction. Notably, the resulting improvement in catalytic performance which results from dopant Fe incorporation, is seen to result from an increase in H2 utilisation, rather than improved catalytic selectivity towards H2O2.@en

In this contribution, we outline the efficacy of Pd-based bimetallic catalysts toward the oxidative upgrading of benzyl alcohol via the in situ synthesis of H₂O₂ (and related reaction intermediates) from the elements. In particular, the formation of PdAu and PdFe nanoalloys is observed to be highly effective, offering high yields of benzaldehyde and near total selectivity to the desired product, with these catalysts outperforming alternative materials reported in the literature. Notably, the PdFe formulation also achieves high selective utilization of H₂, a key requirement if the in situ approach to chemical synthesis is to become economically viable. Correlative studies, focusing on the direct synthesis of H₂O₂ and further experiments utilizing preformed H₂O₂, coupled with Electron Paramagnetic Resonance (EPR) spectroscopy indicate that H₂O₂ itself is not primarily responsible for the observed catalysis, but rather, the performance of the PdAu and PdFe formulations can be related to the generation of reactive oxygen species (ROS). While the origin of these ROS is not fully understood, it is hypothesized that they are generated through a combination of (i) the desorption of reaction intermediates formed during H₂O₂ synthesis and (ii) through Fenton-mediated chemistry involving the synthesized H₂O₂, in the case of the PdFe-based materials. Importantly, our EPR studies also identify the noninnocent nature of the reaction solvent.

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