Hydrogen spillover is a catalytic phenomenon involving an activated hydrogen species migrating from a metal cluster to a conventionally inert support. Over the past several decades, catalytic systems that are hydrogen spillover active have been repeatedly shown to increase kinetic rates. To date, the mechanism for hydrogen spillover is still heavily disputed. My project seeks to answer the unresolved questions of hydrogen spillover including the identity of the activated hydrogen species, the active sites present on the supports, and the change in reaction mechanism on the catalyst with a hydrogen spillover active support. Hydrogenation reactions are used as model reactions to study the mobility of hydrogen species. This work will shed light on the effects of catalyst and support interactions and kinetic rates and reactivity.

Zeolites have the capability to alter product distributions and reaction rates through shape selectivity and molecular sieving of chemical species. Small pore zeolites, in particular, offer a unique opportunity to selectively impose intraparticle concentration gradients on methane. Combining this with recent advances in encapsulating metal clusters developed within our group, we have the capability to control local reaction stoichiometry inside the zeolite crystal and enhance the performance of catalysts in certain processes. My project focuses on exploring the types of systems for which this control would be beneficial and tuning the catalyst to the reaction. For example, methane reforming over conventional Ni supported catalysts is known to deactivate due to coking unless a large excess of steam or carbon dioxide is supplied. Imposing a concentration gradient in methane would allow for a stoichiometric ratio in the bulk phase, while retaining an excess of co-reactant at the metal sites. This research will give insights into diffusional effects in small pore zeolites, and the implications of the work can help lower the cost of a variety of systems where an excess of reactant is currently needed. Furthermore, the diffusional effects may be leveraged to couple certain reactions in C1 processes and lower energy requirements.

The selective catalytic conversion of light alkanes to alkenes and arenes offers a viable starting point for the production of many high-value chemicals. Dehydrogenation rates are often limited by thermodynamics but undesired side reactions are not as limited, necessitating that conversions be kept low in order to maintain sufficient selectivity. The thermodynamics of the dehydrogenation reaction can be improved by oxidizing the hydrogen formed, but this needs to be done selectively so that the hydrocarbons are not oxidized as well. My work involves the use of encapsulated metal clusters within small-pore zeolites to impose diffusional constraints for bulky hydrocarbons, while allowing the hydrogen and oxygen molecules access to the active sites, in order to facilitate the selective oxidation of hydrogen. The synthesis and tunability of these encapsulated metal clusters within zeolites will be explored so that their ability to impose intracrystalline diffusional constraints may be exploited for other reactions as well.

Catalytic oxidation reactions are essential in fine chemical production and in gas purification technology. Dioxygen (O2) is commonly used as an oxidant in oxidation reactions, and O2-derived surface species are therefore formed during catalytic cycle. This project aims to identify which O2-derived surface species form via O2 activation, how they work in catalysis, and ultimately how to predict oxidation catalysis by metal oxides. DFT calculations are utilized for theoretical description of O2 activation, and kinetic experiments and UV-Vis analysis are then carried out for validation of thoery. Findings from this project will provide fundamental understanding of oxidation catalysis and method to find improved catalysts.

The reactivity and selectivity of metal-oxo species in oxidation reactions depends on the nature of the O₂-derived species. Particularly, on their nucleophilic or electrophilic nature which controls their activity to abstract H-atoms or insert O-atoms into C-H bonds. The objective of this research is to understand the specific electronic and morphological properties that determine the type and reactivity of the O₂-derived species, through appropriate descriptors. The result will advance our understanding of structure-function relationship in oxidation catalysis.

Non-oxidative catalytic hydrogenation of light alkanes is also of great importance for the chemical and petrochemical industries. The most common catalysts for these processes are Cr-based systems. This project aims to replace the use of toxic Cr-based catalysts and explore the properties of W-oxide based catalysts, due to their ability to form stable and non-volatile sub-oxides, carbides and oxycarbides, required for dehydrogenation processes.

This project will address the formation and scavenging of reactive and thermodynamically unstable intermediates without a C-C bond, which can be formed from C1 molecules, specifically natural gas or biogenic feedstocks, through the precise positioning for their formation and scavenging functions. The intermediate of interest is formic acid (HCOOH) formed in situ from CO/H2O mixtures on metals and oxides that catalyze selective HCOOH dehydration, and thus its microscopic reverse. Subsequent HCOOH dehydrogenation would lead to the formation of H2 and CO2, thus completing a water-gas shift turnover without requiring interfacial contact among functions, or use the H2, after desorption or directly from HCOOH, in transfer hydrogenation reactions.