Speakers

From fleeting sites to lasting carbon: the molecular catalysis of liquid metal alloys

Molten metal alloys catalyze the conversion of CH4 and CO2 into hydrogen and syngas while producing solid carbon instead of CO2, offering a route to decarbonized fuels and chemicals. Unlike solid catalysts, their active sites are dynamic: surface segregation, solvated [C] and [O] intermediates, and transient site ensembles govern activity, and alloy composition tunes both gas activation and the morphology of the carbon produced. We show how this molecular-level understanding enables the design of alloys that couple clean hydrogen production with the growth of valuable carbon materials, including carbon nanotubes free of residual catalyst.

Mechanistic Insights into Facet-Dependent Water Impact on Alkanol Dehydration on TiO2

Water is ubiquitous in biomass conversion, serving both as a feedstock component and a primary byproduct during dehydration reaction—a critical step in for biomass upgrading. However, the understanding of how water modulates the interaction between alcohol, water, and metal oxide facets as well as reaction mechanisms remains limited. Herein, we leverage facet engineered TiO2 (101) and (001) with minimized structural heterogeneity to probe the facet-dependent influence of water on isopropanol (IPA) dehydration. IPA dehydration rates on TiO2(101) are twice the intrinsic activity of TiO2(001). As H2O partial pressure increases, dehydration rates decrease on both facets, levelling off at 8 kPa. The H2O-induced rate inhibition on (001) is about 3.5-3.7 times more severe than on the (101), as manifested by the respective activation barrier elevations of 40 and 25 kJ/mol. The integration of in situ NMR and DFT calculations provided molecular insight into the impact of water. On (001), pure IPA undergoes primarily dissociative adsorption (70%), characterized by a resonance at 78 ppm. At an equimolar H2O: IPA ratio, the adsorbed isopropoxide transforms into a pseudo molecularly bound complex with water, as evidenced by an upfield shift from 78 to 68 ppm. On (101), pure IPA undergoes primarily molecular adsorption (70%), characterized by a resonance at 68 ppm. Water interacts with molecular IPA via weak hydrogen bonding, as evidenced by an upfield shift from 68 to 64 ppm. Beyond altering adsorption geometries, DFT results indicate that water hinders the C–H bond cleavage during the transition state, further increasing the activation barrier. On dry (001), the transition state is stabilized by Ti-OH∙∙∙H-Cβ interactions, with a theoretical activation barrier of 129 kJ/mol. The presence of water hinders the C-H cleavage, elevating the activation barrier to 179 kJ/mol. For the molecularly adsorbed IPA on (101), the theoretical activation energy is 77 kJ/mol. With weak water-IPA interactions on (101), the activation energy leads to an increase of only 14 kJ/mol. This work demonstrates that water impacts IPA dehydration more significantly on TiO2 (001) than on (101) due to the distinct adsorption configurations and transition states energetics, which provides a fundamental basis for the rational design of water-tolerant catalysts for industrial biomass upgrading.

Cooperative Heterogeneous–Homogeneous Catalysis Enables Aprotic H2O2 Synthesis and Tandem Organic Oxidations

We show that cooperation of heterogeneous metal and homogeneous Brønsted-acid catalysts enables direct synthesis of hydrogen peroxide (H2 + O2 → H2O2) in aprotic solvents. By studying different molecular acids, we discover that the selectivity of H2O2 vs H2O formation is controlled by the steric profile of the acid, which we hypothesize orchestrates the formation of transition states for proton-coupled reduction of metal-bound O2. This mechanistic understanding informs our selection of unhindered Brønsted-acid catalysts that tune H2O2 selectivity by orders–of–magnitude in aprotic solvents and improve H2O2 selectivity by ~60× compared to protic solvents. We show the synthetic value of H2O2 formation in organic solvents by addition of a third catalytic function via Lewis-acidic TS-1 zeolite that activates H2O2 to oxidize thioanisole into the corresponding sulfoxide and sulfone with quantitative yield. This work thus establishes strategies for tunable heterogeneous–homogeneous catalytic cooperativity and synthetic protocols for peroxide-mediated oxidation applicable to a broad expanse of organic substrates.

Bringing Acid Catalysis into Electrocatalysis: How Acid Sites Promote Glycerol Oxidation on Pt

Acid sites are widely used in heterogeneous catalysis, but their role in electrocatalysis remains much less understood. In this work, we investigate the effect of acidic Al sites on the electrocatalytic glycerol oxidation reaction by integrating Pt nanoclusters with a zeolite-templated conductive carbon framework containing acid sites. 

The optimized PtAlYTC catalyst showed significantly enhanced glycerol oxidation performance under neutral conditions, including an approximately 30-fold higher turnover frequency and 17-fold higher reaction rate than an acid-site-free Pt catalyst. The main products were glyceraldehyde and glyceric acid, while product selectivity changed only modestly, indicating that acid sites primarily enhance activity rather than alter the reaction pathway. 

DFT calculations suggest that the acidic Al sites modify the electronic environment of Pt and act as hydrogen acceptors, facilitating dehydrogenation and stabilizing key intermediates. These results highlight a cooperative role between metal and acid sites and demonstrate a strategy for extending concepts of metal–acid catalysis into electrocatalytic systems.

Electrocatalytic Interfaces in CO2 Capture and Conversion

Electrochemical conversion of captured CO2 to fuels and chemicals relies on two catalytic interfaces: (i) the bipolar membrane (BPM) junction, where water dissociation (WD; H2O ⇌ H+ + OH−) generates the protons needed to liberate CO2 from a captured (bi)carbonate stream; and (ii) the porous catalyst layer, where (bi)carbonates are transported and CO2 is reduced to product. Using a (bi)carbonate electrolyser as a platform, we show that a 3D-architected SnO2-catalyzed BPM junction lowers WD overpotential losses relative to planar interfaces at the same catalyst loading.

With WD catalysts exhibiting sufficiently low overpotentials [1], we ask whether proton supply is the kinetically-limiting step for CO2 capture and conversion. An experimentally-validated continuum model coupling gas and ion transport with field-enhanced water dissociation physics shows instead that (bi)carbonate transport through the porous catalyst layer becomes rate-limiting at high current densities. Catalyst layer porosity is identified as a structural lever that governs the transition from kinetic- to mass-transport controlled regimes.

References

1. Wu, Y., Stovall, T.N., Xi, D., Hou, S., Sarma, P., Vulpin, O.T., Sasmal, S., Weber, A.Z., Bui, J.C., and Boettcher, S.W. J. Am. Chem. Soc. 148, 23395 (2026).

The impact of water on zeolite-catalyzed hydrocracking of polyolefins

The chemical recycling of waste plastics is an emerging challenge for the heterogeneous catalysis community. Complications arising from mixed feedstocks, contaminants, and complex product distributions, coupled with the high cost of catalysts and reagents, present challenges for the scalable upgrading of waste plastics to value-added products. One such challenge is the presence of moisture in waste feeds. While water is common in plastic waste feeds, its influence on zeolite-catalyzed polyolefin hydrocracking remains poorly understood. In this talk, I will discuss how water affects Brønsted acid-site accessibility, proton transfer, and hydrogen utilization during hydrocracking over H-BEA zeolites with varying acid-site densities and H-ZSM-5 with comparable acidity. Using alkylamine temperature-programmed reactions, selective acid-site poisoning, and hydrocracking experiments with tetracosane and low-density polyethylene, we examined catalyst behavior in the presence and absence of water. Our results show that water can enhance Brønsted acid-catalyzed olefin formation, likely by promoting proton transfer through hydrogen-bonded water clusters or hydronium-like species within confined zeolite pores. At the same time, increasing water loading suppresses hydrogen conversion while promoting cracking, aromatic formation, and coke deposition, revealing a complex tradeoff between improved acid-catalyzed reactivity and disrupted hydrogen activation. Product analysis, NMR, BET, and thermogravimetric measurements further show that hydrated conditions favor the formation of heavier condensed intermediates and carbonaceous deposits. Selective poisoning experiments indicate that the promotional effect of water on acid-catalyzed pathways is most significant inside the small pores of ZSM-5. Overall, these findings identify hydration-driven changes in proton transfer, hydrogen utilization, and confinement effects as key determinants of water tolerance in zeolite hydrocracking. They also suggest design strategies for improving catalyst resistance to moisture, deactivation, and carbon deposition in realistic plastic waste upgrading processes.

Ethanol upgrading to ketone intermediates – A platform for synthetic aviation fuel (SAF) and chemicals

Demand for synthetic aviation fuel (SAF) continues to grow in the United States and globally. Expanding domestic SAF supply requires the development of technologies that leverage abundant domestic feedstocks to build resilient supply chains, thereby enhancing the potential for successful commercialization. As the largest biobased product manufactured worldwide, ethanol offers tremendous potential owing to its availability in large quantities at competitive prices. In the United States alone, ethanol production reaches approximately 16 billion gallons per year across a distributed network of facilities, providing a reliable and scalable resource. Beyond SAF, ethanol offers significant potential as a platform molecule and building block for a wide range of value-added chemicals. Consequently, developing novel, robust, and economically viable ethanol conversion technologies represents a compelling pathway to advance SAF production, unlock new chemical markets, and create lasting value for ethanol producers.

In the present study we developed a process that utilizes wet ethanol as the feedstock and convert it to SAF in a series of chemical steps. The first step of this process is ketonization of the ethanol which generated mixture of C3-C7 ketones such as acetone, 2-pentanone and 2-heptanone. Over the different mixed metal oxide catalyst, Pd promoted ZnO-ZrO2 exhibited the highest performance. In-situ formation of Pd-Zn alloy was attributed to the active site which promoted rapid dehydrogenation and hydrogen transfer in conjunction of efficient C-C coupling on acid-base sites that form long chain ketones. These long chain ketones are valuable chemicals and are used as solvents in electronic industry as well as serve as intermediate to produce fuel blendstocks. We also developed a downstream condensation process using a Pd/Mg₄AlO catalyst, which generated a pool of C8–C16 ketones via self- and cross-aldol condensation. Upon hydrogenation, these ketones yielded the corresponding alkanes and iso-alkanes ideal for jet fuel applications. When Mg4AlO was obtained as catalyst cyclic ketones were obtained as the products which typically falls beyond the jet range (>C15). Additionally rapid deactivation of the catalysts was also noted in this case. Introducing small amount of Pd as promoter not only prevents the catalyst deactivation but also generates mixture of linear ketones that are required for jet range (C8-C16). Effect of different process parameters was investigated which shows an effect on products obtained. The difference in reactivity was attributed to difference in active sites and the corresponding reaction mechanism which will be discussed in detail. 

Support-induced charge redistribution governs restructuring trajectories in bimetallic Pt oxidation catalysts

Supported Pt bimetallic catalysts often exhibit enhanced performance compared to their monometallic counterparts, but their widespread implementation remains challenging due to reaction-driven surface restructuring and phase segregation under reaction conditions, which often deteriorate performance. Here, we demonstrate that the electronic character of an oxide support dictates the restructuring trajectory of Pt/Cu bimetallic catalysts under reaction conditions by driving charge redistribution across both metal components. In situ X-ray absorption spectroscopy and diffuse-reflectance infrared spectroscopy of highly uniform Pt/Cu nanocrystals supported on nonreducible Al2O3 and reducible Mn2O3, corroborated by first-principles calculations, demonstrated that charge equilibration across all metals at the metal–support interface can stabilize a transient bimetallic oxide configuration that is highly active for the structure-sensitive oxidation of propene. This support-induced charge redistribution alters the initial redox state of supported Pt/Cu nanoparticles and redirects their restructuring trajectory, leading to a more active catalyst with substantially attenuated deactivation.

Characterizing the atomic-level structure and stability of interfaces between Pt nanoparticles and transition aluminas

Metal nanoparticles (NPs) supported on metal-oxides play a critical role in catalytic processes. In this work, transmission electron microscopy (TEM) is used to guide and validate density functional theory (DFT) based models of Pt/-alumina and Pt/-alumina interfaces. Pt NPs were formed in dense - and -alumina through solid-state precipitation into sapphire partially amorphized by ion implantation of Pt. Thermal annealing re-crystallizes the amorphized alumina and precipitates Pt NPs. The NPs in the transition alumina are primarily bound by {111} facets, so these facets were chosen for DFT modelling. Atomic-resolution images of Pt/alumina interfaces are compared to DFT-based models of the interfaces with different alumina terminations (O, Al1, Al2). The O-terminated interface model provides the best match to experiments for both transition phases and is predicted to be the most stable for the processing conditions, based on thermodynamic calculations of the interfacial energy as a function of temperature and oxygen partial pressure. The Pt/-alumina model matches experiments well at the interface, but same model does not capture the bulk structure as well. This is attributed to compromises in the -alumina model made to limit the computational time required for the calculations, which were not required for -alumina. This works furthers the understanding the limits of models of transition aluminas and Pt/alumina interfaces.