Synthesis of Colloidal Pd/Au Dilute Alloy Nanocrystals and Their Potential for Selective Catalytic Oxidations

Abstract

Selective oxidations are crucial for the creation of valuable chemical building blocks but often require expensive and unstable stoichiometric oxidants such as hydroperoxides and peracids. To date, many catalysts that contain a single type of active site have not been able to attain the desired level of selectivity for partially oxidized products over total combustion. However, catalysts containing multiple types of active sites have proven to be successful for selective reactions. One category of such catalysts is bimetallic alloys, in which catalytic activity and selectivity can be tuned by modifying the surface composition. Traditional catalyst synthesis methods using impregnation struggle to create catalysts with sufficient control over surface chemistry to accurately tune the ensemble size of the desired active sites. Here we describe the synthesis of colloidal nanocrystals of dilute alloys of palladium and gold. We show that when supported on titania (TiO), tuning the composition of the Pd/Au nanocrystal surface provides a synergistic effect in the selective oxidation of 2-propanol to acetone in the presence of H and O. In particular, we show that certain Pd/Au surface ratios exhibit activity and selectivity far superior to Pd or Au individually. Through precise structural characterization we demonstrate that isolated atoms of Pd exist in the most active catalysts. The synergy between isolated Pd atoms and Au allows for the formation of reactive oxidizing species, likely hydroperoxide groups, responsible for selective oxidation while limiting oxygen dissociation and, thus, complete combustion. This work opens the way to more efficient utilization of scarce noble metals and new options for catalyzed selective oxidations.

Corrosion Motivated ROS Generation Helps Endow Titanium with Broad‐Spectrum Antibacterial Abilities

“…Recent research found that OM is susceptible to reactive oxygen species (ROS), and the Gram‐ bacteria is easier to be killed in an oxidative stress environment . Although various ROS producing agents are available, such as graphene and its derivatives, iron nanoparticles, noble metal, or doping titanium oxides, it remains a challenge to design a broad‐spectrum antibacterial surface fulfilling the various requirements of titanium implants. For instance, the developed surface must be biocompatible.…”

In situ tuning of electronic structure of catalysts using controllable hydrogen spillover for enhanced selectivity

“…For instance, a well-defined model system demonstrated that on the nonreducible alumina support, hydrogen spillover is limited to short distances, with the hydrogen flux decreasing over distance to create a concentration gradient 25 . In-depth understanding of hydrogen spillover can not only help to explain experimental phenomena but also aid the design of advanced catalysts with enhanced catalytic performances [27][28][29][30][31][32][33][34][35] . Being inspired by these researches, we posit that there is an opportunity for an approach to modulating the electronic structure of active sites through regulating hydrogen spillover strength for enhanced catalytic performance.…”

On the behaviour of structure-sensitive reactions on single atom and dilute alloy surfaces

“…3 Surface science and catalysis studies underline the excellent catalytic properties of SAAs for a number of chemistries, such as hydrogenation and dehydrogenation reactions, 2,[4][5][6] C-H activation, 7,8 C-C coupling, 9 and catalytic oxidations. 10 Remarkably, studies by Zhang et al 11 have unveiled that Pt/Cu SAA catalysts exhibit an unprecedented catalytic performance (i.e. extremely high activity, selectivity and stability) during the hydrogenolysis of glycerol to 1,2propanediol; we note that the activation of pertinent reactions usually requires the presence of large PGM metal ensembles on the alloy surface.…”