A major goal of modern catalysis research is design and fabrication of catalysts that are selective toward reaction of a particular functional group. In attempting to tailor catalytic surfaces for selectivity, not only is it important to have a high level of control over the surface composition, but also to achieve this control using methods that can be scaled up for the economical production of large amounts of catalyst. One promising technique is electroless deposition (ED), which allows one metal component to be deposited in controlled quantities on the surface of a second metal. Because ED is a scaleable method that can be used to prepare truly bimetallic surfaces on supported catalyst particles, it shows great promise for catalytic applications in which selectivity can be tuned through adjustment of the surface composition. In the proposed effort, ED will be employed as a tool for tailoring bimetallic catalysts for the selective oxidation of biomass-related alcohols. In addition to being very important for the future production of fuels and chemicals, they serve as excellent probe molecules for assessing the capability of ED to prepare highly selective catalysts this class of reactions. The proposed effort will integrate a wide-ranging set of characterization techniques in pursuit of selective catalysts:
1. ED will be used to prepare a series of Au, Ag, and Cu-modified Pt and Pd catalysts having targeted metal compositions; these catalysts will be characterized using an array of spectroscopic techniques, and will be evaluated for glycerol oxidation.
2. DFT computational studies on the bimetallic compositions will be used to better understand and corroborate the characterization results and to suggest directions for further bimetallic catalyst compositions.
3. Catalyst evaluation results will be interpreted within the guidelines predicted by catalyst characterization and computation to make subsequent generations of catalysts. This iterative cycle should facilitate catalyst development leading to improved alcohol oxidation catalysts.
The overall goal is to use these diverse capabilities to assess the utility of ED for preparation of bimetallic oxidation catalysts, and to take steps toward making rational improvements in catalyst design based on a fundamental understanding of electronic and structural features of the bimetallic catalysts.
Intellectual Merit. The proposed work will help to develop ED as a potentially important technique for large-scale production of bimetallic catalysts. These efforts will also provide a template for programs aimed at identification of selective catalysts for reactions of multifunctional molecules. Furthermore, the close integration between (a) preparation and characterization of supported metal catalysts and (b) fundamental modeling and surface science studies will help to further develop the integration of basic science with applied catalysis, ultimately promoting rational design approaches for catalysis and materials synthesis.
Broader Impact. The selective oxidation of biomass-related alcohols represents an important industrial target for production of a new class of bio-derived products. ED-prepared catalysts that facilitate higher selectivity can help to reduce process separations costs, over-use of feedstocks, and emissions to the environments. This collaborative effort will also allow graduate and undergraduate students to be involved in the integration of diverse research approaches within the catalysis community, ranging from surface science experiments to computational chemistry to selectivity probes of realistic catalysts. The broad experience gained by the students who work on this project, as well as the interactions with multiple PIs at different institutions, will allow those students to recognize the important contributions available from these different types of catalysis studies.
In this project, a combination of experimental and computational techniques was used to investigate how the surfaces of catalysts could be tailored to improve the efficiency of chemical reactions, including reactions important in the conversion of biomass to renewable fuels and chemicals. The intellectual merit was partly based in model studies were used to understand how the composition of metal surfaces controlled adsorption of reactants through oxygen and carbon atoms, which (along with hydrogen) are the primary constituents of biomass-derived compounds. The model studies revealed that selectivity to desired products could be tuned by selecting metal compositions that altered the repulsive interactions between adsorbates and surfaces. They also revealed that mixing of metals that are less reactive (e.g., gold) with metals that are more reactive (e.g., palladium) can improve the efficiency of catalysis by preventing strong adsorption of reaction intermediates. With palladium-gold catalysts, the reduction in adsorption strength was found to improve access to active sites, and was accompanied by a lower activation energy for the reaction. Finally, a new self-limiting method for preparing bimetallic catalysts containing a precious metal component and a more abundant metal (nickel) were pioneered to control the surface properties of catalysts. These results can have broader impacts for design of catalysts in numerous processes in the chemical industry. They also may be applicable toward related scientific fields such as separations and sensing. The grant provided a portion of the support for four students who completed their PhD training.
