Plasma-catalytic conversion of CO2 to CO over binary metal oxide catalysts at low temperatures

Non-thermal plasma (NTP) technology is gaining increasing interest for CO2 conversion due to its potential to convert inert and stable CO2 to value-added fuels and chemicals at ambient conditions. Combining catalysts with plasma can enhance conversion and energy efficiency simultaneously, overcoming the trade-off barrier commonly present in plasma processes. This work reports the influence of various ceria-promoted iron oxide catalysts on the decomposition of CO2 to carbon monoxide and oxygen in a packed bed, dielectric barrier discharge (DBD) reactor at low temperatures and ambient pressure. As ceria is an expensive rare earth metal, its combination with a cheap, abundant metal such as iron can make the process far more economical. The optimum CO2 conversion (24.5%) and energy efficiency (13.6%) were achieved using γ-Al2O3 supported 5Fe5Ce, almost twice the conversion attained using 10Fe (13.3%). Catalysts were characterized using N2 adsorption, X-ray diffraction (XRD), Raman spectroscopy, H2-temperature programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) analysis. A solid solution formed from the mixture of iron oxide and ceria. A critical concentration of iron oxide is required to increase the number of oxygen vacancy sites in the solid solution. The synergy between Fe and Ce, and thus the oxygen vacancy sites, can also be optimized via the synthesis method. A reaction mechanism has been proposed for CO2 conversion at the catalyst surfaces

Plasma-catalytic CO2 hydrogenation to ethane in a dielectric barrier discharge reactor

Anthropogenic greenhouse gas emissions have caused changes to the Earth's climate, resulting in catastrophic weather events that are becoming more frequent and intense. Developing carbon-neutral processes for CO2 conversion powered by renewable energy is one way of attaining a circular economy, as waste CO2 is converted to a new carbon-containing product, without also being created as a by-product during the process. Plasma-catalysis is gaining increasing interest for CO2 conversion and utilisation under mild conditions, particularly CO2 conversion to green chemicals and fuels using renewable hydrogen, as this electrified process can easily be combined with clean and renewable energy to ensure a carbon-neutral process. Previous studies have mainly focussed on the production of methane from CO2 and H2; however, ethane (C2H6) is a much more valuable product. In this work, we report a non-thermal plasma-catalytic process for the conversion of CO2 into C2H6 in a dielectric barrier discharge (DBD) reactor. The influence of a variety of alumina-supported metal catalysts (Ru, Cu, Ni and Fe) on the plasma-catalytic CO2 hydrogenation to C2H6 was evaluated. The Ru catalyst attained the highest selectivity towards C2H6, at almost 40%. The Ru catalyst also increased the energy efficiency of the process to around 18%, in comparison to the plasma reaction using pure alumina (12%). The Ru catalyst also achieved the highest H2 conversion at 29%. Plasma-assisted production of C2H6 is a new promising process for the utilisation of CO2 via carbon-neutral electrified gas conversion.</p

Plasma-photocatalytic conversion of CO2 at low temperatures: Understanding the synergistic effect of plasma-catalysis

A coaxial dielectric barrier discharge (DBD) reactor has been developed for plasma-catalytic conversion of pure CO2 into CO and O2 at low temperatures (<150°C) and atmospheric pressure. The effect of specific energy density (SED) on the performance of the plasma process has been investigated. In the absence of a catalyst in the plasma, the maximum conversion of CO2 reaches 21.7% at a SED of 80kJ/L. The combination of plasma with BaTiO3 and TiO2 photocatalysts in the CO2 DBD slightly increases the gas temperature of the plasma by 6-11°C compared to the CO2 discharge in the absence of a catalyst at a SED of 28kJ/L. The synergistic effect from the combination of plasma with photocatalysts (BaTiO3 and TiO2) at low temperatures contributes to a significant enhancement of both CO2 conversion and energy efficiency by up to 250%. The UV intensity generated by the CO2 discharge is significantly lower than that emitted from UV lamps that are used to activate photocatalysts in conventional photocatalytic reactions, which suggests that the UV emissions generated by the CO2 DBD only play a very minor role in the activation of the BaTiO3 and TiO2 catalysts in the plasma-photocatalytic conversion of CO2. The synergy of plasma-catalysis for CO2 conversion can be mainly attributed to the physical effect induced by the presence of catalyst pellets in the discharge and the dominant photocatalytic surface reaction driven by the plasma

Green chemical pathway of plasma synthesis of ammonia from nitrogen and water : a comparative kinetic study with a N2/H2 system

Sustainable ammonia synthesis under mild conditions that relies on renewable energy sources and feedstocks is globally sought to replace the current Haber-Bosch process. Electricity-driven plasma catalysis is receiving increasing attention as a sustainable technology for the efficient synthesis of ammonia. However, the current implementation of nonthermal plasma technology still faces several hurdles, particularly the extensive usage of energy-intensive H2, low energy efficiency and the lack of understanding of the underlying mechanisms of the plasma catalysis process. Here we propose a green chemical pathway of plasma catalysis from nitrogen and water for sustainable ammonia production. In order to understand the different characteristics of the N2/H2O plasma system and seek further improvements in ammonia synthesis, detailed plasma kinetics modelling is presented in comparison with the N2/H2 system at atmospheric pressure. The model includes both electron and vibrational kinetics and updated surface reactions adapted from DFT calculation results on the SiO2 surface. The facile dissociative adsorption of H2O and the Eley-Rideal mechanisms are demonstrated to be important to enable efficient NH3 production as the experimental observation. The model reproduced the measured trends of ammonia production on the different concentrations of H2O input and power density with reasonable accuracy and provided an explanation of the critical influence of temperature and catalyst packing in the N2/H2O system in comparison to the N2/H2 system in relation to the quenching effect of H2O by vibrational-translational relaxation.</p

Application of plasma-printed paper-based SERS substrate for cocaine detection

Surface-enhanced Raman spectroscopy (SERS) technology is an attractive method for the prompt and accurate on-site screening of illicit drugs. As portable Raman systems are available for onsite screening, the readiness of SERS technology for sensing applications is predominantly dependent on the accuracy, stability and cost-effectiveness of the SERS strip. An atmospheric-pressure plasmaassisted chemical deposition process that can deposit an even distribution of nanogold particles in a one-step process has been developed. The process was used to print a nanogold film on a paperbased substrate using a HAuCl4 solution precursor. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that the gold has been fully reduced and that subsequent plasma post-treatment decreases the carbon content of the film. Results for cocaine detection using this substrate were compared with two commercial SERS substrates, one based on nanogold on paper and the currently available best commercial SERS substrate based on an Ag pillar structure. A larger number of bands associated with cocaine was detected using the plasma-printed substrate than the commercial substrates across a range of cocaine concentrations from 1 to 5000 ng/mL. A detection limit as low as 1 ng/mL cocaine with high spatial uniformity was demonstrated with the plasma-printed substrate. It is shown that the plasma-printed substrate can be produced at a much lower cost than the price of the commercial substrate.</p

Publisher Correction: Whole-genome sequencing of a sporadic primary immunodeficiency cohort (Nature, (2020), 583, 7814, (90-95), 10.1038/s41586-020-2265-1)

An amendment to this paper has been published and can be accessed via a link at the top of the paper