Now showing 1 - 5 of 8
- ItemDirect Conversion of Ethane to Oxygenates, Ethylene, and Hydrogen in a Noncatalytic Biphasic Plasma Microreactor(ACS Sustainable Chemistry and Engineering, 2023-05-29) Cameli, Fabio; Dimitrakellis, Panagiotis; Vlachos, Dionisios G.We selectively upgrade ethane (C2H6) to ethanol (C2H5OH), methanol (CH3OH), and acetic acid (CH3COOH) in a catalyst-free, continuous, argon/water biphasic plasma microreactor. The water (H2O) evaporates and electron- dissociates into OH· radicals. OH· recombines with alkyl radicals, produced via electron dissociation of ethane, to generate the oxygenates that absorb into H2O. A plasma-assisted path, reminiscent of the low-temperature thermocatalytic ethane steam reforming, leads to significant H2 coproduction. The gaseous stream also comprises CO2 and C2H4. Up to 1.3 and 1 μmol min–1 of liquid C2H5OH and CH3OH are attained, respectively. Compared to CO2-assisted ethane plasma conversion, which produces many oxygenates with low selectivity, the carbon selectivity can range from >70% C2H5OH, CH3OH, and CH3COOH to 60% C2H4. The low carbon footprint, electrified, modular, intensified process using a reactive evaporation and separation plasma could pave the way for the valorization of underutilized shale gas resources in remote areas.
- ItemDeducing subnanometer cluster size and shape distributions of heterogeneous supported catalysts(Nature Communications, 2023-04-08) Liao, Vinson; Cohen, Maximilian; Wang, Yifan; Vlachos, Dionisios G.Infrared (IR) spectra of adsorbate vibrational modes are sensitive to adsorbate/metal interactions, accurate, and easily obtainable in-situ or operando. While they are the gold standards for characterizing single-crystals and large nanoparticles, analogous spectra for highly dispersed heterogeneous catalysts consisting of single-atoms and ultra-small clusters are lacking. Here, we combine data-based approaches with physics-driven surrogate models to generate synthetic IR spectra from first-principles. We bypass the vast combinatorial space of clusters by determining viable, low-energy structures using machine-learned Hamiltonians, genetic algorithm optimization, and grand canonical Monte Carlo calculations. We obtain first-principles vibrations on this tractable ensemble and generate single-cluster primary spectra analogous to pure component gas-phase IR spectra. With such spectra as standards, we predict cluster size distributions from computational and experimental data, demonstrated in the case of CO adsorption on Pd/CeO2(111) catalysts, and quantify uncertainty using Bayesian Inference. We discuss extensions for characterizing complex materials towards closing the materials gap.
- ItemDynamic Electrification of Dry Reforming of Methane with In Situ Catalyst Regeneration(ACS Energy Letters, 2023-02-10) Yu, Kewei; Wang, Cong; Zheng, Weiqing; Vlachos, Dionisios G.We report the design and performance of a rapid pulse Joule heating (RPH) reactor with an in situ Raman spectrometer for highly endothermic, reversible reactions. We demonstrate it for methane dry reforming over a bimetallic PtNi/SiO2 catalyst that shows better performance than its monometallic counterparts. The catalyst temperature ramp rate can reach ∼14000 °C/s, mainly owing to the low thermal mass and resistivity of the heating element. Joule heating elements afford temperatures unachievable by conventional technology to enhance performance and more than double the energy efficiency. Dynamic electrification can increase syngas productivity and rate. Extensive characterizations suggest that pulse heating creates an in situ catalyst regeneration strategy that suppresses coke formation, sintering, and phase segregation, resulting in improved catalyst stability, under many conditions. Potentially driven by renewable electricity, the RPH can provide superb process advantages for high-temperature endothermic reactions and lead to negative carbon emissions.
- ItemA Life Cycle Greenhouse Gas Model of a Yellow Poplar Forest Residue Reductive Catalytic Fractionation Biorefinery(Environmental Engineering Science, 2022-09-13) Luo, Yuqing; O’Dea, Robert M.; Gupta, Yagya; Chang, Jeffrey; Sadula, Sunitha; Soh, Li Pei; Robbins, Allison M.; Levia, Delphis F.; Vlachos, Dionisios G.; Epps, Thomas H. III; Ierapetritou, MarianthiThe incentive to reduce greenhouse gas (GHG) emissions has motivated the development of lignocellulosic biomass conversion technologies, especially those associated with the carbohydrate fraction. However, improving the overall biomass valorization necessitates using lignin and understanding the impact of different tree parts (leaves, bark, twigs/branchlets) on the deconstruction of lignin, cellulose, and hemicellulose toward value-added products. In this work, we explore the production of chemicals from a yellow poplar-based integrated biorefinery. Yellow poplar (Liriodendron tulipifera L.) is an ideal candidate as a second-generation biomass feedstock, given that it is relatively widespread in the eastern United States. Herein, we evaluate and compare how the different proportions of cellulose, hemicellulose (xylan), and lignin among leaves, bark, and twigs/branchlets of yellow poplar, both individually and as a composite mix, influence the life-cycle GHG model of a yellow poplar biorefinery. For example, the processing GHG emissions were reduced by 1,110 kg carbon dioxide (CO2)-eq, 654 kg CO2-eq, and 849 kg CO2-eq per metric ton of twigs/branchlets, leaves, and bark, respectively. Finally, a sensitivity analysis illustrates the robustness of this biorefinery to uncertainties of the feedstock xylan/glucan ratio and carbon content.
- ItemA review of thermal and thermocatalytic valorization of food waste(Green Chemistry, 2021-04-08) Ebikade, Elvis Osamudiamhen; Sadula, Sunitha; Gupta, Yagya; Vlachos, Dionisios G.Food waste (FW) remains a global challenge due to the increasing demand for food production to support a growing global population and the lack of effective waste management technologies for recycling and upcycling. Unique compounds in FW – such as carbohydrates, proteins, lignin, fats, and extractives – can be repurposed to produce important biobased fuels, bulk chemicals, dietary supplements, adsorbents, and antibacterial products, among many others. We review the thermal and thermocatalytic FW valorization strategies and the fundamental pathways. We discuss the potential integration of various valorization processes, their economic viability, the technical and marketing challenges, and the need for further developments. By overcoming several technical hurdles, repurposing FW into modular plants can create exciting economic and environmental prospects.