David W. Flaherty - US grants

Flaherty, 1511819

Global energy consumption will increase dramatically in the next several decades, thus stimulating demand for fuels and chemicals produced from renewable sources such as biomass. While the processes for converting biomass to chemicals such as ethanol are well-known, the further processing of those fermentation products to the larger molecules that make up fuels and chemicals is presently inefficient and not well understood. This project will investigate new combinations of catalytic materials specifically designed to promote the coupling of fermentation products into diesel fuel, lubricants and chemical feedstocks. By understanding the detailed catalytic chemistry and its relationship to the structure and composition of the catalytic materials, the research will lay the groundwork for a new class of catalyst materials that can convert fermentation products into higher-value products both more efficiently and with significant energy savings compared to existing processes. The work will also provide opportunities for the training of both graduate students and undergraduates in science, technology, and engineering, with special emphasis on providing opportunities to female students.

Most biomass upgrading processes rely on acidic catalysts. Basic catalysts have generally been avoided because of poisoning by water and carbon dioxide associated with fermentation processes. These researchers have recognized an opportunity to combine both acidic and basic catalytic functions into a single catalyst in a way that promotes aldol type condensation (i.e. chain growth) reactions without the usual poisoning effects. They will do this by investigating more than 25 technologically relevant catalysts containing a range of acid sites, base sites, and acid-base site pairs. Using a combination of experimental tools, they will characterize the number and strength of acid, base, and acid-base pair sites and then relate alcohol and aldehyde adsorption on those sites to detailed aldol condensation kinetics and identification of critical transition states. The broader scientific impact of this work will be to produce guiding principles for the design of more active and stable catalysts for the production of carbon-neutral biofuels and chemicals. In addition, the principal investigator is building an undergraduate research program that focuses on developing graduate-student female mentors to work with undergraduate mentees in the STEM areas.

Abstract (Flaherty; 1553137)

Currently millions of tons of hazardous chlorinated compounds are used for selective oxidation and bleaching reactions in the manufacture of pulp, paper, and commodity chemicals each year. Hydrogen peroxide (H2O2) represents a "green" alternative to chlorinated compounds, but it is not widely used because the current production method is economically viable only at very large scales. The proposed study will investigate an alternative catalytic approach - direct synthesis of H2O2 from hydrogen (H2) and oxygen (O2) gases - that would enable H2O2 production on-site for use in smaller, more common processing facilities. The proposed research is integrated with educational programs focusing on young women with emphasis on building research and research-mentoring skills.

The research will combine catalytic kinetic and in situ spectroscopic measurements in a systematic investigation to determine: 1) the mechanism for direct synthesis of H2O2, 2) the roles of surfaces, solvents, and liquid-phase intermediates in forming reactive intermediates, and 3) the combined effects of catalyst composition and solvent properties on reaction rates and selectivities. The initial work will focus on palladium (Pd) and palladium-gold (PdAu) clusters as the active catalytic materials, but learning derived from those materials will be used to generate guiding principles and activity descriptors to identify inexpensive alternatives to PdAu catalysts. To achieve these goals, a combination of kinetic and (ex situ and in situ) infrared spectroscopic techniques will be employed to probe the catalytic chemistry at the liquid-solid interfaces of supported metal clusters. This investigation will involve design parameters such as: size and composition of the metal clusters, the role of electrophilic adsorbates, and solvent properties such as pH and polarity. Although these studies specifically target the direct synthesis of H2O2, the work will develop tools and expertise needed for future investigations of a broad range of oxidative and reductive chemistries at liquid-solid interfaces.

This project will address the grand challenge of achieving a sustainable global society by moving towards carbon-neutral, energy-efficient, and distributable chemical manufacturing technology. The PIs will develop the scientific principles and technology to make distributed electrochemical reactors that simultaneously remediate CO2 and upgrade stranded regional feedstocks in order to generate commodity chemicals and transportation fuels. Specifically, the electrochemical process will enable the use of renewable energy (e.g., wind and solar power) to consume CO2 emissions from stationary sources (e.g., power plants, chemical refineries) but will do so with lower energy requirements. The team will accomplish this by using a single reactor to consume CO2 and to perform selective oxidation reactions that upgrade regional feedstocks (e.g., biomass, biogas) into useful building block chemicals. The PIs will develop fundamental insight into interfacial chemistry to design new catalysts for electrochemical oxidations; apply reaction engineering principles to increase the productivity and effectiveness of the reactors; and analyze the availability and costs of critical resources to identify promising sets of reactions and reactors for distinct regions in the United States. The team will benefit from the inclusion of persons from underrepresented groups among senior personnel, graduate students, and undergraduate students and will engage local K-9 native Spanish speaker, Girl Scouts of Central Illinois, and other future members of the STEM workforce through unique educational programs related to electrochemistry, manufacturing, and sustainability.

The transformative nature of the proposed research resides in linking the reduction of CO2 with the oxidative upgrading of regional feedstocks in a co-electrolysis process. This effort leverages the team's recent technological advances for energy-efficient flow electrocatalytic reduction of CO2 to C2-products such as ethylene and ethanol under alkaline conditions in tandem with oxidation of waste, such as glycerol from the biofuels industry. Specifically, the PIs will develop molecular insight into surface chemistry and catalysis at anodes in alkaline conditions under flow, by synthesizing and characterizing new electrocatalysts with multifunctional active sites needed for selective oxidations. The team will design, evaluate, and optimize liquid electrolyte and membrane-based co-electrolysis reactors for coupled CO2 reduction and selective oxidations with a focus on process intensification (e.g., by varying temperature, pressure, pH) for reactant-catalyst pairs. The team will use technoeconomic analysis and life cycle assessment (TEA-LCA) with spatially-resolved resource data to quantify system-level water, energy, and greenhouse gas impacts to identify potential opportunities to deploy these co-electrolysis devices via geographic information system based multicriteria decision analysis (GIS-MCDA). Constant feedback between the research thrusts will ensure that surface chemistry informs reactor design and process intensification; the performance metrics update the TEA-LCA; and TEA-LCA guides catalysis and reactor engineering efforts for promising reaction and identifies pressure points for the process. The PIs will deliver multiple co-conversion solutions, each optimized for a distinct geographical region in the US.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

PART 1: NON-TECHNICAL SUMMARY

Dense microbial films called ?biofilm? often foul medical tools, household items, and infrastructures such as an endoscopes, bathroom tiles, and water supply pipes, and can lead to dangerous infections. These biofilms are slimy aggregates of bacterial cells surrounded by scaffolds adhering to anything they touch. About 80 percent of all medical infections originate from biofilms that invade the inner workings of clinical devices and implants inside patients. Cleaning of biofilms in such a hard-to-reach area is extremely difficult because traditional disinfectants and antibiotics cannot penetrate a biofilm's tough scaffolds. How can we let antibacterial reagents cross over such a barrier of biofilms? This proposed study attempts to develop a small particle that can penetrate and destroy tough scaffolds by generating oxygen bubbles. The particle named ?self-propelling microbubbler? would be prepared by loading an oxygen-generating chemical on diatoms ? the tiny skeletons of algae. As a consequence, this system would improve the delivery of antibacterial deathblow to the bacterial cells living inside. While tuning the oxygen bubble generation rate and subsequent propulsion speed of the micrububblers, this proposed study will examine extents that the microbubblers can penetrate biofilm clinging to a material with complex topology, damages the scaffold of biofilms, kill bacterial cells protected by the scaffolds, and, ultimately, prevent the return of biofilm formation. In parallel, for broad impacts, the unique microbubblers will be used as education and training tools for a new generation of bioscientists and bioengineers. Overall, this project will serve to improve people?s health, safety, and life quality against infectious diseases and fouling.

PART 2: TECHNICAL SUMMARY

Biofilms composed of microbial cell colonies and surrounding extracellular polymer substances (EPS) are major causes of medical infection and material deterioration, thus threatening both human health and sustainability. A variety of disinfectants were developed to date, but none of these systems are active in removing biofilms forming in confined spaces. To this end, this proposed study aims to assemble and analyze a ?self-propelling microbubbler? that can invade biofilms grown in the hard-to-reach area and, subsequently, clean out both bacterial colonies and EPS. This study hypothesizes that diatom particles doped with zinc oxide (ZnO) or manganese dioxide (MnO2) catalysts decomposing hydrogen peroxide (H2O2) eject oxygen bubbles and, in turn, act as the self-propelling microbubbler in the antiseptic 3% H2O2 solution. After the invasion, the microbubblers would continue to generate oxygen bubbles that fuse to produce a wave of mechanical energy capable of destroying the biofilms. The self-propulsion of microbubblers will be studied by analyzing the activation energy for H2O2 decomposition, the H2O2 decomposition rate, and the kinetic energy. In parallel, the extent that the microbubblers remove biofilm in the micro-grooved substrate will be examined by monitoring invasion of particles into the biofilm and subsequent changes in stiffness, adhesion force, and chemical composition of the biofilms formed by Escherichia coli and Pseudomonas aeruginosa. Finally, the efficacy of microbubblers to killing biofilm bacteria will be evaluated by monitoring the increase of intracellular oxidative stress, the reduction of viable cells, and the recurrence of biofilm. The successful completion of this study will elucidate the unique cleaning mechanism attained by chemical-to-mechanical energy conversion and transform current disinfection strategies that rely on chemicals mostly. In parallel, this project will make broad impacts by incorporating the proposed research modules into several educational programs developed for students at various educational levels and also disseminating the research outcomes to a broad spectrum of communities.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.