(287i) Pathways to Make the Precious Platinum Metals Even More Valuable

• Paper 676a: "Impact of Pt Nuclearity on CO₂ Reduction and Aldol Condensation Reactions", Wednesday November 8, 12:30-12:48 pm, Plaza International Ballroom D (https://aiche.confex.com/aiche/2023/meetingapp.cgi/Paper/669877)

Research Interests:

As a group of the most widely used heterogenous catalysts, platinum-group metals have been reported to be active in a variety of industrial applications such as chemical manufacturing, automotive catalytic converters, and petroleum refining. The economic feasibility of their use, however, is dependent on the ability to use the Pt metal in minimal quantities with maximized catalytic performance. In this poster, I am going to show three cases from my past research experience of designing suitable nanostructured catalysts to make the precious Pt more remarkable for applications in the field of renewable chemical/fuel production. During this process, I have used a combination of nanocatalyst synthesis, characterization, kinetics study, and computational collaborations that I have found to be extremely enjoyable and highly productive during my doctoral and postdoctoral works.

Case #1: Remarkable Bimetallic Effect by the Alloyed Nanoparticles

A highly active and selective Pt−Fe alloy catalyst on CeO₂ support is reported in this work for aqueous phase oxidation of ethylene glycol (EG) to glycolic acid. The Pt−Fe nanoparticles are highly alloyed with a face-centered cubic (fcc) type of crystal structure and a chemical state of Pt⁰/Fe⁰, as confirmed from X-ray diffraction and extended X-ray absorption fine structure characterizations, respectively. Compared to the monometallic Pt catalyst, the Pt−Fe catalyst shows more than a 17-fold higher initial turn-over-frequency (TOF), while achieving complete EG conversion in 4 h at 70 °C and ambient O₂ pressure under alkaline conditions. The synergistic bimetallic effect occurs due to significantly changing the O₂ adsorption-dissociation characteristics on the catalyst surface. The addition of a base shows a promotional effect on both Pt and Pt−Fe catalysts at low NaOH concentrations, but an inhibition effect is observed for both catalysts at sufficiently high NaOH concentrations. Furthermore, the base enhances the synergistic effect observed with the Pt−Fe catalyst.

Case #2: Shape-Controlled Catalysis on Nanoparticles with Tailored Structures

Bimetallic nanoparticles have been synthesized and studied extensively in heterogeneous catalysis, however, there are few strategies for the facile synthesis of morphology-controlled structures. In this letter, we developed a one-pot synthesis of highly selective and monodispersed bimetallic nanoparticles on titanium oxide (TiO₂) with tunable shapes (cubic, octahedral, and stellated octahedral structures). The synthesized catalysts were tested for glucose oxidation in the aqueous phase to understand the shape dependence of activity and selectivity. Experimentally, it is shown bimetallic Pt-Cu with dominant {100} crystal facets favor both reaction rate and glucaric acid selectivity under mild conditions. In addition, the C-C cleavage products were negligible by using the morphology-controlled nanocatalysts developed in this work. The optimal catalyst is a Pt-Cu nanoparticle with a cubic structure that showed the highest catalytic activity to date for producing glucaric acid under base-free conditions (TOF_glucaric=113 h^-1).

Case #3: Maximizing the Atomic Use and Creating Electronic Effects by Single-Atoms and Rafts

Catalysts consisting of atomically dispersed Pt species on metal oxide support have received tremendous research interest due to their potential in tuning the surface electronic density for remarkable catalytic performances. However, it is still unclear at what nuclearities downsizing nanoparticles to single atoms, the chemistry required for the transition to higher activity or selectivity could take place. In this work, a series of Pt catalysts supported on Fe₃O₄ were prepared and characterized by Transmission Electron Microscopy (TEM), X-ray Absorption Spectroscopy (XAS) and X-ray Diffraction (XRD). Depending on the metal loading, the synthesized Pt catalysts demonstrated three different regimes in geometry (single atoms, rafts, and nanoparticles), and they are tested on two important gas-phase reactions: reduction of CO₂ and the self-coupling of acetone. Reactivity measurements showed that the rates of CO₂ reduction and acetone aldol condensation follow different trends in the presented structures. In the reaction of CO₂ reduction, the raft catalysts demonstrate the same turn-over-frequency (TOF) but significantly improved stability compared to the single atoms. In addition, the nuclearity of the Pt structures is found to be crucial in determining the phase transition and involvement of the Fe₃O₄ support in CO₂ reduction. On the other side, the raft and nanoparticle catalysts cannot compete with the single atoms regarding the activity in the aldol-condensation reaction. A series of prevailing characterizations on the acid-base properties were performed on different Pt structures, and the results underline our hypothesis that doping Pt single atoms to the surface of Fe₃O₄ creates stronger Pt^δ+-O^2- pairs facilitating the acetone adsorption and α-H abstraction steps, which eventually results in the remarkable high activity of the Pt single atoms in the self-coupling of acetone.

Postdoc Projects:

1. “Ozonolysis of aromatic compounds using liquid CO₂ as a green reaction medium” under the supervision of Dr. Bala Subramaniam, Department of Chemical and Petroleum Engineering, University of Kansas
2. “Impact of nuclearity of Pt supported on iron oxide for CO₂ hydrogenation and aldol-condensation reactions” under the supervision of Dr. Johannes A. Lercher, Pacific Northwest National Laboratory (PNNL)

PhD Dissertation:

“Oxidation of Sugars and Polyols for Sustainable Production of Value-added Chemicals” under the supervision of Dr. Raghunath V. Chaudhari, Department of Chemical and Petroleum Engineering, University of Kansas

Service Experiences:

Reviewer for (journals):

Applied Catalysis B: Environmental

ACS Sustainable Chemistry & Engineering

Journal of CO₂ Utilization

Frontiers in Chemistry

Journal of Nanomaterials

Chemistry Select

Volunteer for Get to Know Nuclear Girl Scout Event at Tri-cities, WA (November 2022)

Judge for 14^th Annual Postgraduate Research Symposium, Pacific Northwest National Laboratory (August 2022)

Invited Speaker for the “Women in Engineering” Panel Discussion, University of Kansas (October 2019)

Judge for the Undergraduate Research Symposium, University of Kansas (April 2016 and April 2017)

Selected Awards:

Pacific Coast Catalysis Society Meeting (PCCS): 1^st Place Poster Award 2022

17^th International Congress on Catalysis (ICC): Young Scientist Presenter Award 2020

University of Kansas: Department Honor for the Ph.D. Final Defense 2019

North American Catalysis Society: Kokes Award for the NAM26 Conference 2019

4^th North American Symposium for Chemical Reaction Engineering: Travel Award

University of Kansas: Honored Doctoral Candidate for the Comprehensive Exam 2019

Great Plains Catalysis Society: GPCS Spring Symposium Graduate Travel Award 2019

American Chemical Society: Scholarship for the ACS Summer School on Green Chemistry and Sustainable Energy 2018

University of Kansas: Graduate Travel Fund by Department of Chemical & Petroleum Engineering 2017

University of Kansas: Graduate Engineering Association Travel Fund 2016

University of Calgary: Graduate Excellence Scholarship 2014

University of Calgary: Schulich Student Activity Fund (SSAF) 2014

University of Calgary: URGC International Student Travel Award 2014

Selected Publications:

Shi, H.; Lundin, M.; Danby, A.; Go, E. P.; Patil, A.; Zhou, H.; Jackson, T. A.; Subramaniam, B., Selective ozone activation of phenanthrene in liquid CO₂. RSC advances 2022, 12 (1), 626-630.

Shi, H.; Yin, X.; Subramaniam, B.; Chaudhari, R. V., Liquid-Phase Oxidation of Ethylene Glycol on Pt and Pt–Fe Catalysts for the Production of Glycolic Acid: Remarkable Bimetallic Effect and Reaction Mechanism. Ind. Eng. Chem. Res. 2019, 58 (40), 18561-18568.

Shi, H.; Thapa, P. S.; Subramaniam, B.; Chaudhari, R. V., Oxidation of glucose using mono-and bimetallic catalysts under base-free conditions. Organic Process Research & Development 2018, 22 (12), 1653-1662.

Shi, H.; Mahinpey, N.; Aqsha, A.; Silbermann, R., Characterization, thermochemical conversion studies, and heating value modeling of municipal solid waste. Waste Management 2016, 48, 34-47.

Dominguez, A. A. T.; Shi, H.*; Subramaniam, B.; Chaudhari, R. V., Aqueous-Phase Glycerol Catalysis and Kinetics with in Situ Hydrogen Formation. ACS Sustainable Chem. Eng. 2019, 7 (17), 15146-15146.

Jin, X.; Zeng, C.; Yan, W.; Zhao, M.; Bobba, P.; Shi, H.; Thapa, P. S.; Subramaniam, B.; Chaudhari, R. V., Lattice distortion induced electronic coupling results in exceptional enhancement in the activity of bimetallic PtMn nanocatalysts. Applied Catalysis A: General 2017, 534, 46-57.

Chen, L.; Meyer, L. C.; Kovarik, L.; Meira, D.; Pereira-Hernandez, X. I.; Shi, H.; Khivantsev, K.; Gutiérrez, O. Y.; Szanyi, J., Disordered, Sub-Nanometer Ru Structures on CeO₂ are Highly Efficient and Selective Catalysts in Polymer Upcycling by Hydrogenolysis. ACS Catal. 2022, 12 (8), 4618-4627.