Hongtao Zhong

In this work, spatially and temporally resolved atomic hydrogen profiles were quantified using femtosecond two-photon absorption laser-induced fluorescence (fs-TALIF) at the plasma-biodiesel interface, at low pressure and room temperature. A pronounced near-surface hydrogen depletion was observed, corresponding to an incident H-atom flux of 1.9 × 10 ¹⁸ cm ^-2 s ^-1 , approximately four orders of magnitude higher than molecular hydrogen fluxes typical of thermal catalytic hydrogenation. Within 2 h of plasma processing, the H-atom density gradually recovered to the no-fuel baseline, indicating progressive elimination of the surface C=C bonds. Ex situ gas chromatography mass spectroscopy (GC-MS) showed that the saturated component such as octadecanoic acid (C18:0) increased from 39% to 86%. With Ni catalyst addition, near-surface H density was further decreased by 50% and remained depleted throughout the plasma processing. Kinetic modeling reveals that non-equilibrium hydrogenation proceeds via two distinct regimes: a surface-limited, self-terminating process in the plasma-only case, and a persistent first-order, H-flux-controlled process in the plasma-catalysis case. These findings establish a quantitative mechanistic link between plasma-generated H flux and hydrogenation kinetics, offering fundamental understanding of upgrading biofuels with renewable electricity and electricity-derived hydrogen.

The increasing demand for sustainable energy has spurred the exploration of advanced technologies for biodiesel production. This paper investigates the use of Dielectric Barrier Discharge (DBD)-generated low-temperature plasmas to enhance the conversion of fatty acid methyl esters (FAMEs) into hydrogenated fatty acid methyl esters (H-FAMEs) and other high-value hydrocarbons. A key mechanistic advance is achieved via in situ distillation: at the reactor temperature, unsaturated C18 and C20 FAMEs remain liquid due to their low melting points, while the corresponding saturated C18:0 and C20:0 FAMEs (with melting points of approximately 37–39 °C and 46–47 °C, respectively) solidify and deposit on a glass substrate. This phase separation continuously exposes fresh unsaturated FAME to the plasma, driving further hydrogenation and thereby delivering high overall conversion efficiency. The non-thermal, energy-efficient nature of DBD plasmas offers a promising alternative to conventional high-pressure, high-temperature methods; here, we evaluate the process efficiency, product selectivity, and scalability of this room-temperature, atmospheric-pressure approach and discuss its potential for sustainable fuel-reforming applications.

Cold plasmas powered by the renewable electricity can facilitate CO ₂ desorption for carbon capture materials (CaCO ₃ ) at low temperatures.

In plasma discharges, the acceleration of electrons by a fast varying electric field and the subsequent collisional electron energy transfer determines the plasma dynamics, chemical reactivity, and breakdown. Current in situ electric field measurements require reconstruction of the temporal profile over many observations. However, such methods are unsuitable for non-repetitive and unstable plasmas. Here, we present a method for creating “movies” of dynamic electric fields in a single acquisition at sample rates of 500 × 106 fps. This ultrafast diagnostic was demonstrated in radio frequency electric fields between two parallel plates in air, as well as in Ar nanosecond-pulsed single-sided dielectric barrier discharges.

We combine in situ laser spectroscopy, quantum chemistry, and kinetic calculations to study the reaction of a singlet oxygen atom with dimethyl ether. Infrared laser absorption spectroscopy and Faraday rotation spectroscopy are used for the detection and quantification of the reaction products OH, H₂O, HO₂, and CH₂O on submillisecond time scales. Fitting temporal profiles of products with simulations using an in-house reaction mechanism allows product branching to be quantified at 30, 60, and 150 Torr. The experimentally determined product branching agrees well with master equation calculations based on electronic structure data and transition state theory. The calculations demonstrate that the dimethyl peroxide (CH₃OOCH₃) generated via O-insertion into the C-O bond undergoes subsequent dissociation to CH₃O + CH₃O through energetically favored reactions without an intrinsic barrier. This O-insertion mechanism can be important for understanding the fate of biofuels leaking into the atmosphere and for plasma-based biofuel processing technologies.

We investigate the conversion of CO₂ into CO and O₂ with nanosecond repetitively pulsed (NRP) discharges in a high-pressure batch reactor. Stable discharges are obtained at up to 12 bar. By-products are measured with gas chromatography. The energy efficiency is determined for a range of processing times, pulse energy, and fill pressures. It is only weakly sensitive to the plasma operating parameters, i.e the extent of CO₂ conversion is almost linearly-dependent on the specific energy invested. A conversion rate as high as 14% is achieved with an energy efficiency of 23%. For long processing times, saturation in the yield and a drop in efficiency are observed, due to the increasing role of three-body recombination reactions, as described by zero-dimensional detailed kinetic modeling. The modeling reveals the presence of three-stage kinetics between NRP pulses, controlled by electron-impact CO₂ dissociation, vibrational relaxation, and neutral elementary kinetics. Transport effects are shown to be important for CO₂ conversion at high pressures. For fill pressures beyond 10 bar, CO₂ may locally transit into supercritical states. The supercritical plasma kinetics may bypass atomic oxygen pathways and directly convert CO₂ into O₂. This work provides a detailed analysis of plasma-based high-pressure CO₂ conversion, which is of great relevance to future large-scale sustainable carbon capture, utilization, and storage.