Raspberry-colloid-templated catalysts as a versatile and stable thermocatalytic platform

Abstract

Nanoparticle (NP)-supported catalysts are critical to the production of over 90% of chemicals and raw materials used today. Their catalytic performance is predicated on a combination of geometric and electronic descriptors associated with the properties of the NPs, support, and the interactions between them. However, existing catalyst preparative methods of nucleating or immobilizing NPs on support surfaces do not permit independent variation of either NP or support properties as NP nucleation and growth characteristics are dependent on the support chemistry and vice versa. Consequently, such interconnected material properties cannot enable systematic investigations whereby individual NP or support properties are independently tuned to elucidate the catalytic role(s) of each structural descriptor or their combination, especially if their contributions exert orthogonal effects on catalytic performance. To address this gap, we devised a raspberry-colloid-templating (RCT) strategy. In this Account, we outline the RCT synthetic methodology and highlight two key design features: partial NP embedding into the support which enhances catalytic stability against NP sintering while maintaining high reactant accessibility, and synthetic modularity for independent combinatorial variations of the catalyst’s building blocks and in their spatial organization. These two features yield thermomechanically stable RCT catalysts with multiple degrees of freedom at different length scales to isolate and independently tune potential catalytic descriptors, thereby deriving unambiguous structure–property relationships to guide future catalyst designs. We describe how we leveraged these two key design features to employ the RCT strategy as a well-defined and synthetically robust model thermocatalytic platform to deconvolute the individual effects of traditionally coupled structural descriptors and elucidate important insights into catalyst design that cannot be easily achieved using conventional catalyst preparative methods. We highlight our recent investigations into three structural features found in all NP-supported catalysts: individual NP properties, properties of NP ensembles as a collective entity, and NP–support interfaces. First, we show how using pre-formed colloidal NPs in the RCT method decouples the NP and support formation steps to facilitate systematic evaluations of individual NPs properties. We exemplify this point through separate studies into the nanoscale effects of Pd ensemble sizes on the surfaces of PdAu alloyed NPs on reactant adsorption energetics, and the sintering behavior of Pt and Pd NP diesel oxidation catalysts. Second, we demonstrate how the colloidal templating steps in the RCT strategy controls the NP spatial localization to tune NP proximity, a collective NP ensemble property, at a fixed NP size, to induce local enrichment of reaction intermediates within the pore structure to direct catalytic selectivity. Third, we illustrate how partial embedding of NPs in RCT catalysts not only accentuates catalytic contributions arising from NP–support interfacial sites, but also reveals nanoscale wetting effects at the interface that we exploited to direct bimetallic catalyst synthesis. Interspersed throughout this Account, we also describe the advanced characterization and modelling tools adapted to probe the RCT catalyst structure and establish structural insights underpinning some of our main results. Finally, we provide an outlook on the RCT catalyst platform and speculate on its future opportunities, challenges, and practical applications.