Controlling Catalysis at Metal Nanoparticle Surfaces by Direct Photo-excitation of Absorbate-Metal Bonds
Abstract
In this project we will perform fundamental research aimed at elucidating pathways to enable control of chemical reactivity at catalytic metal surfaces through direct photoexcitation of adsorbate-metal bonds. Direct photoexcitation of molecular bonds offers a unique approach to manipulate chemical reactivity by matching photon excitation wavelengths to bond-specific electronic transitions or vibrational modes, but has primarily been utilized in single-phase molecular systems. Developing approaches to confine the direct photoexcitation mechanism to adsorbate-metal bonds has the potential to significantly reduce the required energy input to break bonds, compared to single phase systems, while maintaining high levels of specificity in guided bond breaking and making. Although this approach offers significant promise for controlling catalytic chemistry, experimental evidence and mechanistic insights defining approaches to induce photocatalysis by direct adsorbate-metal bond photoexcitation are scarce. The central hypothesis explored in this proposal is that the use of sub 5 nm nanoparticles as photocatalysts and the inclusion of a background thermal energy source will uniquely enable direct photoexcitation as the dominant mechanism driving catalytic chemistry under low intensity photon flux. The large surface area to volume ratio of sub 5 nm nanoparticles will force photon absorption onto surface sites where direct photoexcitation adsorbate-metal bonds is possible, while background thermal excitation will increase the probability that photoexcitation of adsorbate-metal bonds will result in a chemical reaction. The overall objective of the research proposed here is to develop a holistic understanding of catalysis on metal nanoparticles surfaces driven by direct photoexcitation of adsorbate-metal bonds and the knowhow to exploit this phenomenon to manipulate reaction selectivity. The specific project objectives are: (1) Develop models that relate the nature of adsorbate-metal bond formation to the oscillator strength and energy of induced dipole electronic transitions (2) Uncover governing factors that control the efficiency of chemical reactions on metal nanoparticle driven by direct adsorbate-metal bond photo-excitation. (3) Identify strategies to enhance the efficiency of direct photoexcitation driven chemical reactions on metal nanoparticles. (4) Demonstrate control of reaction selectivity by resonance between visible photon excitation and electronic transitions localized in targeted adsorbate-metal bonds To achieve these objectives we will use in-situ spectroscopic techniques, photocatalytic reaction quantification and quantum chemical calculations. We will focus primarily on the chemistry of (CO, NO, HCN, CH4, CH3OH and furfural) on transition and noble metal surfaces (Pt, Pd, Rh and Cu) to develop mechanistic insights into photocatalysis on metal nanoparticles by direct adsorbate-metal bond photoexcitation. These insights will be applied to demonstrate unique approaches to control selectivity in preferential CO oxidation, selective molecular desorption (CO vs. NO), furfural hydrogenation or decomposition and alkene hydroformylation reactions. The proposed research has the potential to introduce new mechanisms to achieve high selectivity in catalytic reactions at surfaces, which could have significant impact for emerging Army interests in photochemical catalysis for water splitting, CO2 reduction, remediation of waste and others. We expect that the proposed research will have a significant impact on the broad catalysis community, sparking the interest of chemical engineers, chemists, materials scientists and surface physicists. The physical chemistry identified through these studies may prove extremely insightful for various technologies that rely on electron transfer processes at surfaces.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 01, 2019
- Source ID
- W911NF1910116
Entities
People
- Phillip Christopher
Organizations
- Army Contracting Command
- United States Army
- University of California, Santa Barbara