Steven P. Crossley

Zeolite Y catalysts contain Brønsted acid sites in accessible large pores, known as supercages, and in sterically inaccessible small pores within sodalite cages. Access to acid sites within sodalite units is precluded due to their 0.26 nm cage windows, which are smaller than the critical diameters of relevant hydrocarbons. By preparing a series of HY catalysts with different acid site densities, including for the first time reported those with theoretical maximum acid site density, the number of acid sites in the inaccessible sodalite cages is shown to be a dominant factor in reactivity for catalysts in which the structural integrity of the sodalite unit is preserved. Using a combination of catalyst preparation, spectroscopy, isotopic exchange measurements with bulky hydrocarbons, and high-temperature isooctane cracking experiments on catalysts with fixed supercage proton amounts but varying sodalite proton concentrations, the dominant contribution of sodalite cage acid sites is quantified. DFT calculations suggest that a plausible mechanism involves framework flexibility in the form of site exchange via rotation of sodalite protons into supercages. In addition to revealing that commonly used acid site density measurements and turnover frequency calculations may exclude contributions from important sites, these data demonstrate that BASs in intact sodalite cages can define and control catalyst reactivity in HY catalysts. Large increases in catalyst activity are obtained by exchanging La³⁺ cations into sodalite cages with maximum acid site densities. These findings extend beyond HY catalysts, as they imply that other zeolite catalysts with sterically occluded acid sites may be tuned for improved performance.

Multilayer plastic films that combine polar barrier polymers, such as ethylene vinyl alcohol (EVOH), with nonpolar polyolefins, such as polyethylene (PE), are widely used in food packaging, but their recycling remains challenging because of phase separation during reprocessing. Here, we address this limitation through the selective deoxygenation of EVOH over a Pd-promoted molybdenum oxide (MoO₃) catalyst, enabling C–O bond cleavage while preserving the polymer backbone. The catalytic performance was evaluated in both a monophasic γ-valerolactone (GVL) system and a biphasic GVL/decalin system. While the monophasic GVL system achieved moderate oxygen removal of up to 31.62% after 8 h, the biphasic GVL/decalin system significantly enhanced performance, reaching up to 41.1% oxygen removal in only 1 h, corresponding to a 2.4–2.8-fold increase in the reaction rate. Notably, the biphasic system enabled in situ product separation, with nonpolar deoxygenated products partitioning into the decalin phase, thereby reducing product accumulation on the catalyst surface. Applied to a commercial multilayer film containing 80 wt % LDPE and 20 wt % EVOH, the system achieved near-complete deoxygenation of 83.5% after 1 h over Pd5%/MoO₃. Kinetic analysis revealed a positive half-order dependence on H₂ over Pd/MoO₃, highlighting the critical role of Pd in H₂ dissociation and spillover, which facilitates the rate-determining step. Overall, this work establishes an efficient biphasic catalytic platform for upgrading oxygen-containing barrier layers in multilayer plastic films into more recyclable polyolefin-like materials.

Hydrogen production from biomass and natural gas has emerged as a prominent research area in response to the growing demand for energy from alternative sources that minimize CO₂ emissions. In this study, we investigate the impact of water, which is present in and generated from biomass-derived streams, on carbon nanotube (CNT) growth and hydrogen production during methane decomposition using Ni–Mo/MgO as a catalyst. We reveal here that the role of water on CNT growth is highly complex; its effect depends on the stage of growth at which the water is incorporated. When water is introduced at the beginning of methane decomposition (t = 0 h), methane conversion rates are negatively impacted. We hypothesize that water inhibits the significant phase changes the Ni–Mo/MgO catalyst undergoes during catalyst carburization. In contrast, the incorporation of a small percentage of water after a stabilization period (t = 3 h) results in methane conversion rate enhancements that scale with the introduced water partial pressure as water selectively reacts with amorphous carbon deposits that lead to catalyst deactivation, thus prolonging the lifetime of some of the most active sites. Moreover, water incorporation after stabilization significantly reduces the apparent activation energy. Density Functional Theory (DFT) calculations reveal that water preferentially interacts with carbon fragments on the catalyst surface to remove carbon deposits with a barrier lower than that required for methane activation, further supporting its role in cleaning active sites on the catalyst surface. Characterization of the resulting carbon nanotubes reveals the formation of more graphitic materials produced in the presence of water, highlighting the impact of water on nanotube properties. These results provide clarity toward the many ways in which water, or cofeeding of biomass-derived materials, may impact catalytic methane pyrolysis rates.

Multilayered plastic films containing polyethylene (PE) and poly(vinyl alcohol-co-ethylene) (EVOH), are of great importance for the food and pharmaceutical industries. However, economical recycling is challenging for these materials, leading to waste accumulation in landfills. Mechanical recycling produces a low-value mixture of immiscible phases. Here, we describe a new approach that employs a biphasic solvent system with interfacially active catalysts to selectively remove oxygen from EVOH within multilayered plastic films to yield a single phase of compatible polymers from this complex feed mixture. This approach offers great potential for selective reactions and separation of plastic waste. An economic evaluation simulates an industrial scale recycling process for the PE product with the minimum selling price of $0.90 per kg, which is below the market price, indicating promise for the economical recycling of multilayered films.

Plastic recycling is an important but complicated issue. Some plastics are currently readily recyclable with existing technologies, whereas others are not. However, the general public often does not appreciate the benefits and costs associated with hard-to-recycle (e.g., multi-material) plastics, potentially causing confusion and, in some cases, backlash. While some methods of relaying information to the public have been previously studied (e.g., infographics, descriptive labeling), educational videos have not. We created an educational video on the properties and functions of single- and multi-material plastic. Participants who viewed the educational video were more knowledgeable about multi-material plastic recycling and had higher intentions to use and be satisfied with a hypothetical recycling company that intends to begin recycling multi-material plastic. Our data suggest that education interventions have the potential to inform and empower the public while protecting common values.

Lanthanum and other rare earth cations are routinely added to commercial zeolite catalysts to increase stability during hydrothermal regeneration steps, as well as to modify catalyst reactivity by changing the distribution of acid sites and operative electric field gradients in working catalysts. Solution ion-exchange procedures are typically used to introduce La cations into zeolite Y, primarily as La³⁺ or its hydroxylated moieties, La^3-n(OH)_n, in the formulation of commercial LaY or ultrastable steam-stabilized Y (USY) catalysts. Within zeolite Y, multiple possible exchange sites exist for La occupation, but quantitative measurement of La siting as a function of La loading in the catalyst is not generally accessible. Specific open questions involve whether La cations reside in both sodalite and supercage sites, which sites are preferred for La incorporation, and whether La can be selectively incorporated into specific site types. In this contribution, a simple quantitative method based on solid-state NMR coupled with the preparation of La-HY catalysts without framework defects reveals that at low La loadings of less than 3 wt %, essentially all La is incorporated into sodalite cages as La³⁺ ions. DFT calculations support these experimental conclusions. Coincident with this incorporation, sodalite Brønsted bridging acid sites (BAS) decrease, but the number of supercage BASs can remain constant depending on the La concentration. Increased La loadings in the catalyst preferentially reduce the number of sodalite BASs compared to supercage acid sites, with both sodalite and supercage BAS amounts, as well as the amount of newly created La^3-n(OH)_n species, quantitatively measured using the methods described here. Flow reactor hexane-cracking experiments, as well as in situ probe reactions, reveal that catalyst reactivity increases relative to that of HY when La resides exclusively in sodalite positions.

Daniel Resasco is widely recognized for his significant contributions to the science and application of heterogeneous catalysis. In this Account, we highlight key points along his career path, demonstrating how fundamental insights─drawn from rigorous kinetic analysis, precise materials synthesis, and in situ characterization─enabled breakthroughs in areas ranging from strong metal–support interactions to biomass upgrading. Daniel’s work on selective ring opening of hydrocarbons influenced the production of cleaner diesel fuels, while his innovative methods for synthesizing single-walled carbon nanotubes accelerated progress in nanomaterial applications. He later pioneered the use of Pickering emulsions in catalysis, employing amphiphilic materials to control selectivity and facilitate product separation at water–oil interfaces. Throughout these varied application areas, Daniel consistently blended a rigorous mechanistic approach with pragmatic goals, ensuring that the concepts he uncovered could be translated across topics and have practical impact. Beyond his scientific contributions, we highlight Daniel’s commitment to supporting the next generation of researchers in catalysis science.