Bruce E. Koel

We report retention of deuterium (D), a proxy for tritium (T), from D ₂ neutral gas and D ⁺ ion exposures on commercial boron (B) powder, a proxy for B dust potentially formed in fusion reactors. D removal behavior from B powder is reported as a means of estimating a potential T inventory in B dust in advanced fusion reactors, such as SPARC and ITER, the latter currently plans to employ B wall conditioning by glow-discharge boronization. B wall conditioning forms surface coatings of chemical compounds on tungsten (W) plasma-facing components (PFCs), thus suppressing plasma contamination by impurities such as oxygen, carbon, and tungsten. However, B–based slag or dust particles are expected to form. Such B dust particles can retain hydrogen isotope species, thereby causing a T inventory issue. In this work, the commercial B powder was exposed to D ₂ neutral gas or D ⁺ ions and analyzed by temperature-programmed desorption to quantify D retention and the desorption temperature. The experiment confirmed D retention from D ₂ neutral gas exposure. A strong D ₂ desorption peak at 700 K, corresponding to B–D bonding, was observed for all D ₂ gas and D ⁺ ion exposure cases. For D ₂ gas exposures, D retention was significantly enhanced at a B powder temperature of 550 K. B powder bakeout under vacuum at 600 K for 22 h after D ₂ exposure exhibited efficient D removal. In contrast, the B powder bakeout at 420 K, even for 1 d, did not remove D efficiently. D retention yields from D ⁺ ion exposure, emulating charge–exchange involving D atoms, were determined. Experiments confirmed that D retention was suppressed by oxidation of the B powder surface, which naturally occurs in reactor environments.

Nonthermal plasma (NTP)-assisted dry methane reforming (DMR) on supported metal catalysts has emerged as a promising method for sustainable, electrified conversion of methane (CH4) and carbon dioxide (CO2) into carbon monoxide (CO) and hydrogen (H2), which are valuable chemical/fuel precursors and energy carriers. NTP-assisted DMR has been reported to enhance reaction rates and reduce catalyst deactivation relative to purely thermal operation. However, the complex interactions between the plasma, metal nanoparticles, and catalyst support under reaction conditions complicate mechanistic interpretation and limit informed catalyst design. Here, plasma-assisted DMR on platinum (Pt) nanoparticles supported on alumina (Al2O3), silica (SiO2), and zeolite 3A was investigated in a coaxial packed-bed dielectric barrier discharge (DBD) reactor to increase understanding of how the plasma, metal, and support interact to govern activity, selectivity, and catalyst stability. The plasma enhanced DMR turnover rates, altered selectivity among DMR, reverse water–gas shift (RWGS), and direct coupling of methane (DCM) pathways as indicated by CO, H2, water (H2O), and ethane (C2H6) formation rates, and reduced the apparent activation barriers. The extents of all these plasma-induced changes were impacted by the catalyst identity. Properties of the support (e.g., basic site density and dielectric constant) affected the plasma power and catalytic performance, and the Pt nanoparticle size impacted the plasma and product selectivity. Post-reaction characterization and extracted deactivation rate constants revealed support-dependent catalyst stability, including coke formation and Pt restructuring, with minimal sintering on Al2O3, significant agglomeration on 3A after plasma exposure, and reduced deactivation of Pt/SiO2 under plasma-assisted conditions relative to thermal conditions. These results provide insight into the interplay of plasma, metal nanoparticles, and support in NTP-assisted DMR, with implications for informed catalyst design and process optimization in similar plasma-assisted catalytic C1 upgrading systems.

Brønsted (BAS), Lewis (LAS), and surface Brønsted (SBAS) acid sites have been investigated for polyethylene (PE) upcycling by zeolite catalysts, but there is no clear consensus regarding their catalytic roles, partly due to the complexity of the catalysts used and varying reaction conditions across studies. This work systematically determined how these sites impact PE conversion rates and product distributions by utilizing a suite of microporous MFI catalysts with varying Si/Al ratios, acid site densities, and inherent mesoporosities. PE conversion rates did not trend with total BAS or LAS densities due to a combination of internal mass transfer limitation and the apparent inability of LAS alone to cleave C–C bonds, but a strong, statistically significant correlation was present with respect to SBAS density and mesopore surface area, jointly, owing to accelerated polymer activation on external surfaces to smaller diffusion-limited chains. However, ingress of these SBAS-derived fragments ultimately remained rate limiting, as demonstrated by solid conversion rates that increased with mesopore surface area at similar SBAS density and likewise increased with SBAS density at similar mesopore surface area. In batch PE cracking reactions, light gaseous product selectivities were most sensitive to total BAS, with higher densities generally exhibiting higher selectivity to C3 and linear C4–C7 products and higher alkane/alkene product ratios, consistent with increased β-scission turnovers. Insights from this work help systematically clarify the roles of BAS, LAS, SBAS, and mesopores in PE cracking reactions and inform the development of tailored zeolite catalysts for efficient polyolefin upcycling.

Thermal plasma decomposition of natural gas is a scalable pathway for the production of hydrogen alongside high‐value carbon nanotubes (CNTs). Metals evaporate from an electrode and condense to form seed nanoparticles that nucleate and grow CNTs. However, the lack of mechanistic understanding of the CNT nucleation and growth processes in thermal plasma makes control over CNT diameter, chirality, length, and yield difficult. We debundled and separated CNTs from soots produced using iron (Fe) nanocatalysts, and distributed them on monolayer graphene for high‐resolution transmission electron microscopy (HRTEM) imaging to gain mechanistic insights. Full graphene encapsulation was found for relatively small Fe nanoparticles that were molten at high temperatures. Zigzag single‐wall or double‐wall CNTs (SWCNTs or DWCNTs) appeared to have grown out directly from the graphene covering on the conical or cylindrical bodies of small molten Fe nanodroplets with high curvature. Also, SWCNTs likely grew out from H‐ or O‐atom etched single‐wall carbon nanocones observed on conical Fe nanoparticles. A SWCNT/DWCNT could also be generated from the cracked opening of the graphene covering on a face‐centered cubic (FCC) Fe nanoparticle. A simple, plausible pathway is proposed for the growth of an open, H‐passivated, zigzag SWCNT involving reaction of CH ₂ and CH radicals at high temperatures.

We have investigated the thermodynamic, structural, and transport properties of lithium–oxygen (Li–O) and lithium–oxygen–deuterium (Li–O–D) systems using molecular dynamics over a temperature range of 100–1500 K. Rapid quenching yields glassy and amorphous phases, enabling comparisons with liquid and crystalline states. Deuterium addition suppresses crystallization and enhances hydrogen mobility, especially in non-stoichiometric regimes. For the Li2O stoichiometry, structural metrics and diffusivity trends are benchmarked against available ab initio and experimental data. For other Li–O compositions, no ab initio molecular dynamics or experimental data exist for amorphous or molten states; the only exception is the binary Li–D system, which serves as a limiting case of the ternary Li–O–D mixture. These results provide insight into hydrogen isotope behavior, structural frustration, and phase stability in fusion-relevant lithium-based materials.

We report the in situ formation of Ni nitride for plasma-assisted ammonia synthesis. Both the surface nitrogen concentration and the ammonia formation rate exhibit dependence on the N₂:H₂ feed ratio. The maximum surface nitrogen concentration occurs at a N₂:H₂ ratio of 4:1, and the maximum catalytic activity occurs at 2:1. In contrast, the formation of gas phase radicals is less sensitive to feed composition, indicating that Ni nitride is more kinetically relevant to ammonia production than gas-phase radicals. The plasma-induced formation of Ni nitride is therefore proposed to be a critical contributor to the synergistic effects in plasma-assisted catalytic ammonia synthesis. Additionally, Ni nitride alters the surface reaction mechanism of plasma-assisted ammonia synthesis, with the rate-determining-step (RDS) shifting to surface-bound NH₃ formation rather than N₂ activation at temperatures below 373 K. These findings provide mechanistic insight that opens opportunities for optimizing the performance of plasma-assisted catalytic ammonia synthesis.