We present a computational study for the conversion of CH4 and CO2 into value-added chemicals, i.e., the so-called “dry reforming of methane”, in a dielectric barrier discharge reactor. A ...zero-dimensional chemical kinetics model is applied to study the plasma chemistry in a 1:1 CH4/CO2 mixture. The calculations are first performed for one microdischarge pulse and its afterglow, to study in detail the chemical pathways of the conversion. Subsequently, long time-scale simulations are carried out, corresponding to real residence times in the plasma, assuming a large number of consecutive microdischarge pulses, to mimic the conditions of the filamentary discharge regime in a dielectric barrier discharge (DBD) reactor. The conversion of CH4 and CO2 as well as the selectivity of the formed products and the energy cost and energy efficiency of the process are calculated and compared to experiments for a range of different powers and gas flows, and reasonable agreement is reached.
CO2 hydrogenation to methanol is a promising process for CO2 conversion and utilization. Despite a well-developed route for CO hydrogenation to methanol, the use of CO2 as a feedstock for methanol ...synthesis remains underexplored, and one of its major challenges is high reaction pressure (usually 30–300 atm). In this work, atmospheric pressure and room temperature (∼30 °C) synthesis of methanol from CO2 and H2 has been successfully achieved using a dielectric barrier discharge (DBD) with and without a catalyst. The methanol production was strongly dependent on the plasma reactor setup; the DBD reactor with a special water-electrode design showed the highest reaction performance in terms of the conversion of CO2 and methanol yield. The combination of the plasma with Cu/γ-Al2O3 or Pt/γ-Al2O3 catalyst significantly enhanced the CO2 conversion and methanol yield compared to the plasma hydrogenation of CO2 without a catalyst. The maximum methanol yield of 11.3% and methanol selectivity of 53.7% were achieved over the Cu/γ-Al2O3 catalyst with a CO2 conversion of 21.2% in the plasma process, while no reaction occurred at ambient conditions without using plasma. The possible reaction mechanisms in the plasma CO2 hydrogenation to CH3OH with and without a catalyst were proposed by combined means of electrical and optical diagnostics, product analysis, catalyst characterization, and plasma kinetic modeling. These results have successfully demonstrated that this unique plasma process offers a promising solution for lowering the kinetic barrier of catalytic CO2 hydrogenation to methanol instead of using traditional approaches (e.g., high reaction temperature and high-pressure process), and has great potential to deliver a step-change in future CO2 conversion and utilization.
Increasing attention has been drawn to carbon dioxide (CO2) conversion into higher-value platform chemicals and synthetic fuels due to global warming. These reactions require a large amount of ...thermal energy in order to proceed, which is ascribable to the high stability of the bonds in CO2. Non-thermal plasma (NTP)-catalytic CO2 conversion has emerged as a promising method to significantly reduce the reaction temperature as plasma can activate CO2 at as low as room temperature and atmosphere pressure. However, this technology requires a paradigm shift in process design to enhance plasma-catalytic performance. CO2 conversion using plasma-catalysis has great potential to increase reaction efficiencies due to the synergetic effects between the plasma and catalysts. It is crucial to present the recent progress in CO2 conversion and utilization whilst providing a research prospects framework and direction for future research in both industries and laboratories. Herein, a comprehensive review of recent, encouraging research achievements in CO2 conversion using NTP is provided. The topics reviewed in this work are: i) the recent progress in different NTP sources in relation to product selectivity, conversion, and energy efficiency; ii) plasma-based CO2 reactions and applications; iii) CO2 conversion integrated with CO2 capture; and iv) current challenges and future perspectives. The high market value of the possible products from this process, including chemicals and fuels, make commercialization of the process feasible. Furthermore, the selectivities of these products can be further improved by developing suitable catalysts with effective sensitivities and performances under the intricate conditions needed to make these products. There is an urgent need for further studies to be performed in this emerging field.
•Non-thermal plasma is an emerging and promising technology for the conversion of CO2.•Current technology development on CO2 capture and conversion has been reviewed.•Plasma catalysis has great potential to generate a synergistic effect and enhance the selectivity of target products.
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•Steam reforming of toluene was carried out in a gliding arc plasma reactor.•Adding steam significantly enhanced the toluene conversion and energy efficiency.•Best performance of the ...plasma process was achieved at an S/C molar ratio of 2–3.•Formation of OH radicals opens a new reaction route for toluene conversion.
Non-thermal plasma is considered a promising and attractive approach for the removal of tars from biomass gasification to deliver a clean and high quality syngas (a mixture of H2 and CO). In this study, an AC gliding arc discharge (GAD) reactor has been developed for the conversion of toluene as a tar model compound using nitrogen as a carrier gas. The presence of steam in the plasma reaction produces OH radicals which open a new reaction route for the conversion of toluene through a stepwise oxidation of toluene and intermediates, resulting in a significant enhancement in both the conversion of toluene and the energy efficiency of the plasma process. The effects of steam-to-carbon (S/C) molar ratio, toluene feed rate and specific energy input (SEI) on the performance of the plasma steam reforming of toluene have been investigated. The optimal S/C molar ratio was found to be between 2 and 3 for high toluene conversion and energy efficiency. The maximum toluene conversion of 51.8% was achieved at an optimal S/C molar ratio of 2, a toluene feed flow rate of 4.8ml/h and a SEI of 0.3kWh/m3, while the energy efficiency of the plasma process reached a maximum (∼46.3g/kWh) at a toluene feed flow rate of 9.6ml/h and a SEI of 0.19kWh/m3. H2, CO and C2H2 were identified as the major gas products with a maximum syngas yield of 73.9% (34.9% for H2 and 39% for CO). Optical emission spectroscopy (OES) has been used to understand the role of steam on the formation of reactive species in the plasma conversion of toluene. The possible reaction pathways in the plasma conversion of toluene have also been proposed by combined means of the analysis of gas and liquid samples and OES diagnostics.
An alternating-current (AC) gliding arc reactor has been developed offering a new route for the co-generation of syngas and value-added carbon nanomaterials by plasma dry reforming of methane. ...Different carbon nanostructures including spherical carbon nanoparticles, multi-wall carbon nanotubes and amorphous carbon have been obtained as by-products of syngas generation in the plasma system. Optical emission spectra of the discharge demonstrate the formation of different reactive species (Al, CO, CH, C2, Hα, Hβ and O) in the plasma dry reforming reaction. The effect of different operating parameters (feed flow rate, input power and CH4/CO2 molar ratio) on the performance of the plasma process has been evaluated in terms of the conversion of feed gas, product selectivity and energy conversion efficiency. It is interesting to note that gliding arc plasma can be used to generate much cleaner gas products of which syngas is the main one. The results also show that the energy efficiency of dry reforming using gliding arc plasma is an order of magnitude higher than that for processing using dielectric barrier or corona discharges. Both of these can be attributed to the higher electron density in the order of 1023 m−3 generated in the gliding arc plasma.
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•Gliding arc offers a new route to co-generate syngas and carbon nanomaterials.•Three different carbon nanomaterials are generated as by-products of syngas.•Gliding arc dry reforming process generates much cleaner gas products.•High electron density of the order of 1023 m−3 is generated in the gliding arc.•The energy efficiency of the gliding arc dry reforming is much higher than for other cold plasmas.
Defects are now recognized to be a useful tool in tailoring the properties of metal-organic frameworks (MOFs). The introduction of missing linker and cluster defects into MOFs provides additional ...active sites, optimizes the acidity/basicity, improves the conductivity, tailors mechanical responses and creates more pore space to enhance diffusion and mass transfer in MOFs. Structural defects in MOFs have been demonstrated to be beneficial in areas such as catalysis, decontamination, bio-applications, adsorption, separation, energy storage, energy conversion, electronics, magnetics, optical functional materials and others. Defective MOFs are also excellent model materials for the fundamental study of defect chemistry. In this review, we provide a general overview of the commonly available methods that are feasible for the creation and characterization of structural defects in MOF materials. Additionally, recent studies on various applications of defective MOFs are highlighted, aiming to provide new insights into the design and introduction of structural defects to synthesize MOF materials with high performance and to promote the wide application of defective MOFs in various fields. Challenges and future perspectives on defect engineering of MOFs are also addressed.
An overview of important recent advances on synthesis, characterization and application of defective metal-organic frameworks is provided.
A coaxial packed-bed dielectric barrier discharge (DBD) reactor has been developed for plasma-catalytic CO 2 hydrogenation at low temperatures and atmospheric pressure. Reverse water-gas shift ...reaction and carbon dioxide methanation have been found dominant in the plasma CO 2 hydrogenation process. The results show that the H 2 /CO 2 molar ratio significantly affects the CO 2 conversion and the yield of CO and CH 4 . The effect of different γ-Al 2 O 3 supported metal catalysts (Cu/γ-Al 2 O 3 , Mn/γ-Al 2 O 3 , and Cu-Mn/γ-Al 2 O 3 ) on the performance of the CO 2 hydrogenation has been investigated. Compared with the plasma CO 2 hydrogenation without a catalyst, the combination of plasma with these catalysts enhances the conversion of CO 2 by 6.7%-36%. The Mn/γ-Al 2 O 3 catalyst shows the best catalytic activity for CO production, followed by the Cu-Mn/γ-Al 2 O 3 and Cu/γ-Al 2 O 3 catalysts. The presence of the Mn/γ-Al 2 O 3 catalyst in the plasma process significantly increases the yield of CO by 114%, compared with the plasma reaction in the absence of a catalyst. In addition, we find that combining plasma with the Mn/γ-Al 2 O 3 catalyst significantly enhances the energy efficiency of CO production by 116%, whereas packing the Cu/γ-Al 2 O 3 catalyst into the DBD reactor only increases the energy efficiency of CO production by 52%.
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•Plasma reforming of naphthalene as a tar surrogate was carried out using a gliding arc.•Adding steam enhanced the conversion of tar and energy efficiency of the process.•The presence ...of OH radicals enhanced the conversion of naphthalene.•Introducing steam reduced the formation of by-products.•The optimal S/C ratio of 2 was found to achieve the highest process performance.
The contamination of producer gas with tars from biomass gasification remains a significant challenge in the bioenergy industry and a critical barrier, limiting the commercial applications of biomass gasification. Non-thermal and non-equilibrium plasma offers an unconventional and emerging technology for the effective reduction of problematic tars from gasification. In this study, we investigated plasma reforming of naphthalene as a two-ring tar model compound using a gliding arc discharge (GAD) reactor with/without steam. The influence on the plasma conversion of naphthalene based on the inlet naphthalene concentration, discharge power and steam-to-carbon ratio was examined to understand the effects of these operating parameters on the destruction of tar, gas selectivity/yield and energy efficiency. Adding H2O in the plasma process generates oxidative OH radicals, creating additional reaction routes for the step-wised oxidation of naphthalene and its fragments towards the CO, CO2 and water. The optimum ratio (2.0) of steam-to-carbon was identified to achieve the highest naphthalene conversion (84.8%), C2H2 yield (33.0%), total gas yield (72.2%) and energy efficiency (5.7 g/kWh). The effect of the amount of steam on the plasma reduction of tars was dependent on the balance between two opposite effects due to the presence of steam: positive effect of OH radicals and the negative effect of electron attachment on water molecules. Introducing an appropriate amount of steam to the plasma reduction of naphthalene also substantially minimized the formation of by-products and enhanced the carbon balance. Plausible reaction mechanisms for the plasma decomposition of naphthalene were proposed through a comprehensive analysis of gaseous and condensable products combined with plasma spectroscopic diagnostics.
This study of loneliness across adult lifespan examined its associations with sociodemographics, mental health (positive and negative psychological states and traits), subjective cognitive ...complaints, and physical functioning.
Analysis of cross-sectional data.
340 community-dwelling adults in San Diego, California, mean age 62 (SD = 18) years, range 27-101 years, who participated in three community-based studies.
Loneliness measures included UCLA Loneliness Scale Version 3 (UCLA-3), 4-item Patient-Reported Outcomes Measurement Information System (PROMIS) Social Isolation Scale, and a single-item measure from the Center for Epidemiologic Studies Depression (CESD) scale. Other measures included the San Diego Wisdom Scale (SD-WISE) and Medical Outcomes Survey- Short form 36.
Seventy-six percent of subjects had moderate-high levels of loneliness on UCLA-3, using standardized cut-points. Loneliness was correlated with worse mental health and inversely with positive psychological states/traits. Even moderate severity of loneliness was associated with worse mental and physical functioning. Loneliness severity and age had a complex relationship, with increased loneliness in the late-20s, mid-50s, and late-80s. There were no sex differences in loneliness prevalence, severity, and age relationships. The best-fit multiple regression model accounted for 45% of the variance in UCLA-3 scores, and three factors emerged with small-medium effect sizes: wisdom, living alone and mental well-being.
The alarmingly high prevalence of loneliness and its association with worse health-related measures underscore major challenges for society. The non-linear age-loneliness severity relationship deserves further study. The strong negative association of wisdom with loneliness highlights the potentially critical role of wisdom as a target for psychosocial/behavioral interventions to reduce loneliness. Building a wiser society may help us develop a more connected, less lonely, and happier society.
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