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Abstract: Methane conversion to C2 hydrocarbons and hydrogen has been investigated in a needle-to-plate reactor by pulsed streamer and pulsed spark discharges and in a wire-to-cylinder dielectric barrier discharge (DBD) reactor by pulsed DC DBD and AC DBD at atmospheric pressure and ambient temperature. In the former two electric discharge processes, acetylene is the dominating C2 products. Pulsed spark discharges gives the highest acetylene yield (54%) and H2 yield (51%) with 69% of methane conversion in a pure methane system and at 10SCCM of flow rate and 12W of discharge power. In the two DBD processes, ethane is the major C2 products and pulsed DC DBD provides the highest ethane yield. Of the four electric discharge techniques, ethylene yield is less than 2%. Energy costs for methane conversion, acetylene or ethane (for DBD processes) formation, and H2 formation increase with methane conversion percentage, and were found to be: in pulsed spark discharges (methane conversion 18–69%), 14–25, 35–65 and 10–17eV/molecule; in pulsed streamer discharges (methane conversion 19–41%), 17–21, 38–59, and 12–19eV/molecule; in pulsed DBD (methane conversion 6–13%), 38–57, 137–227 and 47–75eV/molecule; in AC DBD (methane conversion 5–8%), 116–175, 446–637, and 151–205eV/molecule, respectively. The immersion of the γ-Al2O3 pellets in the pulsed streamer discharges, or in the pulsed DC DBD, or in the AC DBD has a positive effect on increasing methane conversion and C2 yield. [Copyright &y& Elsevier]

Challenges still remain in catalysts cost, activity and durability for the commercialization of polymer electrolyte membrane (PEM) fuel cells. To preferably alleviate the durability problems with carbon corrosion (but secondarily not to compromise any activities), here we demonstrate composites supported Pt nanoparticles electrocatalysts (Pt/WP x -C 4- x) for oxygen reduction reaction (ORR). Of interest the composite of warm plasma-synthesized TiO 2 (WP, lab-made) and Vulcan® carbon, was used to support Pt nanoparticles using a simple ethylene glycol reduction method. In terms of physicochemical structures and properties, complimentary characterizations (e.g., SEM, TEM-EDX, XRD, XPS, EPR) and the electrochemical measurements have been conducted. This composite support definitely contributes to the uniform dispersion on surface and the electronic reconfiguration of Pt nanoparticles. Our Pt/WP 1 –C 3 catalyst has an ultrasmall Pt size (ca. 2.15 nm), and surprisingly outperforms commercial Pt/C catalyst. It has achieved 1.24 times electrochemical active surface area (ECSA), 1.85 times mass activity, and 1.5 times specific activity, compared to commercial Pt/C. More importantly, our synthesized catalysts with WP exhibited almost half the activities losses (in ECSA, mass activity, specific activity) after accelerated stress test (AST, a DOE protocol) compared to Pt/C and commercial Pt/C catalysts. Based on the extraordinary achievements on both high activity and enhanced durability, it is attributed to the synergistic effect of WP (of strong metal support interaction, oxygen vacancies, corrosion resistance), and carbon (of high surface area, electrical conductivity). [Display omitted] • The composite support consists of WP (a synthetic TiO 2 by warm plasma) and carbon. • Pt/WP x -C 4- x catalysts were achieved by a simple ethylene glycol reduction method. • Pt/WP 1 –C 3 exhibited excellent activity and stability for ORR than commercial Pt/C. • It provides a new pathway for designing high performance and durable ORR catalysts. [ABSTRACT FROM AUTHOR]

A cyclic adsorption and plasma-desorption (CAPD) process is applied to remove ppm-level carbon monoxide (CO) from the H 2 -rich stream for the first time. In the CAPD process, CO is first selectively adsorbed on CuCl/γ-Al 2 O 3 till adsorption saturation; Then, the adsorbed CO is in-situ desorbed by plasma generated in dielectric barrier discharge (DBD) and the adsorbent is regenerated simultaneously. The effects of discharge power (P dis) and flow rate of discharge gas (F D) on performances of plasma-desorption are investigated. The time to reach desorption of 50% (t 50) and 90% (t 90) significantly decreases with P dis but is weakly correlated to the F D. At the investigated conditions, t 50 and t 90 are lower than 2.6 min and 4.5 min, respectively, which indicates that plasma-desorption features high desorption rate. In addition, desorption efficiency of plasma-desorption is higher than 98%. Moreover, CAPD process stability is preliminarily confirmed by six consecutive adsorption-desorption cycles. [Display omitted] • A CAPD process to remove ppm-level CO for on-board H 2 production of PEMFC is reported. • The adsorbed CO can be in-situ, fast and efficiently desorbed by plasma. • Time-dependent CO desorption curve accords with discharge characteristics variation. • The stability of CAPD process is preliminarily confirmed. [ABSTRACT FROM AUTHOR]

• Visible-light activity of Au/TiO 2 catalysts treated by various plasmas in formaldehyde oxidation is reported. • Oxygen plasma treatment remarkably promotes visible-light activity of Au/TiO 2 catalyst. • Oxygen plasma endows Au/TiO 2 catalyst with high content of surface oxygen species. • Abundant surface oxygen on Au/TiO 2 catalyst benefits the transfer of hot electrons under visible-light irradiation. As a promising plasmonic photocatalyst under visible-light irradiation, Au/TiO 2 nanocatalyst commonly suffers from risk of Au nanoparticles aggregation and relatively long activation period by using the conventional calcination activation method. We report here that a short-term O 2 plasma treatment enables the Au/TiO 2 catalyst to exhibit higher visible-light photocatalytic activity for formaldehyde (HCHO) oxidation compared with the calcination activated sample. X-ray photoelectron spectroscopy characterization suggests that Au/TiO 2 catalyst activated by O 2 plasma achieves metallic Au content of 72.4% and surface oxygen species content of 29.8%, which not only lead to rapid reduction of cationic Au in HCHO oxidation but also facilitate the preliminary oxidation of HCHO to dioxymethylene and formate on catalyst surface. UV–vis diffuse reflectance spectra, photoluminescence spectra and diffuse reflectance infrared Fourier transform spectra measurements indicate that O 2 plasma activated Au/TiO 2 catalyst presents an enhanced visible-light absorption and surface charge transfer efficiency in HCHO oxidation, which accelerates the formation of superoxide (O 2 −) and OH radicals via hot electron transfer mechanism under visible-light irradiation, remarkably promoting formate oxidation to carbonate, carbonate decomposition and thus HCHO oxidation. [ABSTRACT FROM AUTHOR]

• Methanol steam reforming in a heat-insulated warm plasma-catalytic (WPC) reactor is reported. • Methanol mainly converts via pyrolysis in warm plasma and steam reforming over the catalyst. • H 2 selectivity of higher than 97% is achieved in both warm plasma and WPC case. • Energy efficiency of 84% with methanol conversion of 94% are achieved in this WPC reactor. Efficient hydrogen production from methanol steam reforming is carried out in a heat-insulated warm plasma-catalytic (WPC) reactor. Methanol steam reforming in warm plasma and warm plasma-catalytic cases is investigated. For warm plasma alone, methanol mainly converts via pyrolysis reaction and its conversion linearly increases with specific energy input (SEI). The arc channel temperature and electron density of warm plasma are respectively measured to be around 2500 K and 3 × 1014 cm−3, based on optical emission spectra. To take advantage of energy from plasma, Fe-Cu/γ-Al 2 O 3 catalyst for methanol steam reforming and water gas shift is placed after the warm plasma. Compare with plasma alone, methanol conversion in WPC case is nearly double therefore the energy cost decreases from 1.71 kW h/Nm3 to 0.85 kW h/Nm3. Energy efficiency of 84% and H 2 selectivity of 98% with methanol conversion of 94% are achieved in this warm plasma-catalytic reactor. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Excellent reforming performance is achieved in plasma catalytic reduction of CO 2 with CH 4. • H 2 /CO ratio of 1 is achieved in plasma catalytic reduction of CO 2 with CH 4. • Reduction pathways of CO 2 with CH 4 in plasma and plasma catalytic reforming are identified. Abstract Toward developing an efficient plasma-based technique for CO 2 reduction with CH 4 , warm-plasma catalytic (WPC) reduction of CO 2 with CH 4 in a reactor using gliding arc discharge and Ni/CeO 2 /Al 2 O 3 catalyst is reported. In the warm plasma (WP) case, besides dry reforming reaction, reverse water gas shift (RWGS) reaction also comparably contributes for CO 2 reduction. Although the contribution of dry reforming reaction is significantly enhanced by the increase of CH 4 /CO 2 ratio, it accounts for only 60% due to the limitation of maximum CH 4 /CO 2 ratio by the serious carbon deposition at CH 4 /CO 2 >1/2. In addition, the low CH 4 /CO 2 ratio also results in the low CO 2 conversion, H 2 /CO ratio and H 2 selectivity. In the WPC case, extra CH 4 was fed after plasma to increase the CH 4 /CO 2 ratio to 1, dry reforming reaction becomes the major contributor of CO 2 reduction. Under the conditions of specific energy input of 86 kJ/mol, total flow rate of 2.67 SLM, catalyst-bed temperature of 850 °C and gas hourly space velocity of 3200 h−1, CO 2 conversion of 91% and CH 4 conversion of 94% with H 2 /CO = 1 and nearly 100% H 2 selectivity are achieved with a CO 2 energy cost of 598 kJ/mol and an energy efficiency of 72%. [ABSTRACT FROM AUTHOR]

To achieve on-board hydrogen production with high energy efficiency and low energy cost, the oxidative pyrolysis reforming (OPR) of methanol using air as an oxidant in a heat-insulated gliding arc plasma reactor is explored. Effects of dioxygen/methanol (O 2 /C) ratio, steam/methanol (S/C) ratio and specific energy input ( SEI ) on the OPR are investigated. The reaction rate ratio (α) of pyrolysis reforming to oxidative reforming in the OPR is deduced. The OPR of methanol strongly depends on the O 2 /C ratio, with which methanol conversion increases rapidly. In the OPR, methanol conversions occur mainly by the oxidative reforming (partial oxidation) at the O 2 /C ratios below 0.20, but by the oxidative reforming and the promoted pyrolysis reforming at the O 2 /C ratios above 0.20, which is confirmed by the enthalpy change for the overall reaction of OPR. Higher O 2 /C ratio results in higher energy efficiency and lower energy cost, however, higher S/C ratio or larger SEI leads to lower energy efficiency and higher energy cost. Under conditions of O 2 /C = 0.30, S/C = 0.5, SEI = 24 kJ/mol, energy efficiency of 74% and energy cost of 0.45 kWh/Nm 3 with methanol conversion of 88% are achieved. [ABSTRACT FROM AUTHOR]

As alternative photocatalysts, titania semiconductors have been extensively investigated for energy and environmental applications. However, amorphous titania is often considered not to be photoreactive catalyst. Here we demonstrate an amorphous titania thin film deposited at room temperature for a photocatalytic removal of formaldehyde from air, which features abundant hydroxyl groups and large surface area. Amorphous titania exhibited surprisingly higher apparent quantum yield of 60.4% than crystalline titania (the most active anatase). This exceptional activity is attributed to greatly reduced recombination of electron-hole pairs and abundant adsorption sites towards formaldehyde. The reduced recombination should result from rapid electron transfer along conduction band (>Ti III OH) that allocates abundant terminal hydroxyl groups, and minimized transfer length from bulk to surface in small particles. The abundant adsorption sites are related to surface hydroxyl groups and large surface area. With the exceptional activity, amorphous titania nanofilm achieved at room temperature substantively enables photocatalysis on heat-susceptible substrates, while it is nearly impossible for crystalline films calcined at high temperature. [ABSTRACT FROM AUTHOR]

Highly efficient warm plasma catalytic reforming of biogas in a compact and heat-insulated reactor using gliding arc discharge with a co-axial electrode configuration and Ni-based catalyst was reported. The effect of inlet flow rate at a special energy input ( SEI ) of 20 kJ/mol for the plasma alone was first investigated and the inlet flow rate was selected at 4 SLM. Then, it was found that the Ni-based catalyst could be auto-reduced by the outgoing gas from the warm plasma via comparing with the pre-reduced catalyst in the reforming reaction testing and characterizations of Brunauer–Emmett–Teller (BET) surface area, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effect of catalyst-bed position ( l ) was also examined. Feeding with the molar ratio of CH 4 :CO 2 :O 2 = 3:2:1.8, for the warm plasma with the auto-reduced Ni/CeO 2 /Al 2 O 3 catalyst located at l = 4 cm, dry-basis concentration of syngas rose substantially to 81% and energy efficiency improved dramatically to 86%. Syngas energy cost reduced significantly to 0.21 kW h/N m 3 , which is nearly a threefold reduction compared with the plasma alone. The stability of the warm plasma catalytic reforming was preliminarily evaluated over time-on-stream (TOS) of 13.5 h. [ABSTRACT FROM AUTHOR]

Biogas reforming with added O 2 through a spark-shade plasma was conducted under O 2 /CH 4 ratio of 0.60 and a specific energy input (SEI) of 69 kJ/mol with energy efficiency of around 75%. Effect of CO 2 /CH 4 ratio ranging from 0.17 to 1.00 on the biogas reforming was investigated, and the discharge characteristics of the plasma showed nearly same. With the increase in CO 2 /CH 4 ratio, the conversions of O 2 and CH 4 decreased, however, that of CO 2 apparently increased followed by a little reduction. Also the effect of CO 2 /CH 4 ratio on C-based and H-based selectivities, C-balance and H-balance, and dry-basis concentration and energy cost of syngas were examined. The effective factor of syngas production per CH 4 conversion increased with CO 2 /CH 4 ratio, indicating that CH 4 conversion to syngas was promoted with the increase in CO 2 /CH 4 ratio. The combination coefficients of independent reactions confirmed that partial oxidation of methane mostly contributed to CH 4 conversion and reverse water gas shift solely did CO 2 conversion. [ABSTRACT FROM AUTHOR]

Highlights: [•] MnO x /CeO2 (DP) is a superior low-temperature NH3-SCR catalyst. [•] The catalytic stability is totally different at 80°C and 120°C. [•] A [NH3⋯NO−] complex is proved to be the intermediates. [•] Decomposition of the intermediates is the rate-limiting step. [ABSTRACT FROM AUTHOR]

Highlights: [•] LaMn0.9Fe0.1O3 perovskite catalyst was used as a LNT catalyst. [•] Employing H2-plasma in rich phase to assist reduction of the stored NO x . [•] High NO x conversion can be obtained at low temperatures (<300°C). [ABSTRACT FROM AUTHOR]

Highlights: [•] Pompom-like K-promoted iron-based catalysts were prepared on calcined shell. [•] A mechanism for the formation of pompom-like microspheres was proposed. [•] An excellent catalytic activity were exhibited for the steam reforming of tar. [ABSTRACT FROM AUTHOR]

Abstract: Adding O2 into biogas to achieve partial oxidation and CO2 mixed reforming can not only increase H2 +CO concentration, but also reduce energy cost for H2 production. In this study, optimized mixed reforming of biogas with O2 addition in spark-discharge plasma was pursued in combination with thermodynamic-equilibrium calculation. With respect to mixed reforming of biogas with O2 addition in spark-discharge plasma, combination coefficients of independent reactions were given to quantitatively evaluate the mixed extent at various O2/(CH4–CO2) ratios. Compared thermodynamic-equilibrium with experimental results, it can be concluded that the optimal O2/(CH4–CO2) ratio for optimized mixed reforming of biogas in spark-discharge plasma was about 0.7. When total-carbon conversion was relatively high (>75%), H2 +CO concentration on wet basis was the highest and energy cost for H2 production was the lowest at O2/(CH4–CO2)=0.7, and their experimental results were closest to their thermodynamic-equilibrium values. [Copyright &y& Elsevier]

Abstract: At room temperature, the enhanced effect of water vapor on ozone catalytic oxidation (OZCO) of formaldehyde to CO2 over MnO x catalysts and the reaction stability was reported. In a dry air stream, only below 20% of formaldehyde could be oxidized into CO2 by O3. In humid air streams (RH≥55%), ∼100% of formaldehyde were oxidized into CO2 by O3 and the reaction stability was significantly enhanced. Meanwhile, in situ Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectra of OZCO of HCHO demonstrate that the amount of both monodentate and bidentate carbonate species on MnO x , in the dry stream, increased gradually with time on stream (TOS). However, in the humid stream, almost no accumulation of carbonate species on the catalysts was observed. To clarify the enhanced mechanism, formaldehyde surface reactions and CO2 adsorption/desorption on the fresh, O3 and O3 +H2O treated MnO x catalysts were examined comparatively. [Copyright &y& Elsevier]

Abstract: Driven by excellent CO oxidation capability of gold nanocatalysts at room temperature, a TiO2 supported Au nanocatalyst (Au/TiO2) was synthesized by deposition–precipitation method. To solve the deactivation issue of Au/TiO2 catalyst during CO oxidation, in-situ regeneration by N2/O2 plasma was employed. Pure O2 plasma could reversibly regenerate the deactivated Au/TiO2 catalyst, however, N2 addition resulted in an extra catalyst poisoning during regeneration. The extra poisoning effect was the most severe at 10% N2 and became much weaker at 80% N2. To investigate the formation of any surface poisoning species [NO y ]s on Au/TiO2 catalyst, gaseous product of N2/O2 plasma over fresh Au/TiO2 catalyst was on-line analyzed by FT-IR, followed by catalyst characterization with temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The Au/TiO2 catalysts before and after plasma regeneration were also measured by transmission electron microscopy (TEM), in order to exclude the poisoning effect arisen from the change in gold particle size or morphology. [Copyright &y& Elsevier]

Abstract: To produce high-concentration syngas (CO+H2) from biogas, the effect of pressurization on dry reforming of biogas (CH4/CO2 =60%/40%) in kilohertz spark-discharge plasma was reported for the first time by elevating the pressure from 1 bar to 2 bar. It was found that elevating the pressure could not only increase the reactant conversions, but also reduce energy cost and increase fuel-production efficiency at the same specific energy input (SEI). In particular, pressurization exhibited a significantly positive effect on increasing CO2 conversion and decreasing energy cost for converting CO2. Syngas concentration as high as 83% (H2/CO=1.4) was achieved with a ratio of the flow rates of product gas (dry basis) to feeding gas, 1.7, at 2 bar and SEI=753kJ/mol. The by-product, H2O, was produced with only about 5% of hydrogen-based selectivity in this work. At 2 bar, the effect of SEI was investigated by varying the power and flow rate, respectively. Compared with those at 1 bar, with the increase in SEI, reactants conversion increased fast, energy cost rose slowly and fuel-production efficiency decreased slowly at 2 bar. [Copyright &y& Elsevier]

Abstract: Cycled storage–discharge (CSD) plasma catalytic process was applied to low-concentration formaldehyde removal from air for the first time. HZSM-5, Ag/HZSM-5 (Ag/HZ), Cu/HZSM-5 (Cu/HZ) and AgCu/HZSM-5 (AgCu/HZ) catalysts were used for the process and their performance for formaldehyde storage and plasma catalytic oxidation of stored formaldehyde towards carbon dioxide was investigated in details. AgCu/HZ exhibited the highest formaldehyde adsorption capacity among these catalysts due to the synergistic effect of Ag and Cu, and it was very selective for oxidizing stored formaldehyde into CO2 by either oxygen or air plasmas at the discharge stage. The CSD process for low-concentration formaldehyde removal had extremely low energy cost, excellent humidity tolerance and almost no secondary pollution. At the discharge stage, in addition to pure oxygen, air can also be used as the discharge gas for complete oxidation of formaldehyde, and the nitrogen oxides produced can be negligible because the discharge period was much shorter than the storage period. The stability of the AgCu/HZ catalysts during the CSD process was also investigated. [Copyright &y& Elsevier]

• Atmospheric-pressure plasma treatment of sequentially-prepared Au-Ag/TiO 2 is reported. • Au-Ag plasmonic nanocatalysts are achieved by O 2 plasma treatment. • O 2 plasma treatment contributes simultaneously restructuring and activation. • The Au-Ag plasmonic nanocatalyst exhibits a strongly enhanced photocatalytic activity. Plasmonic Au-Ag/TiO 2 bimetallic nanocatalyst is regarded as a promising visible-light (VL) photocatalyst due to its wide light absorption and potentially enhanced activity. For its preparation, Au precursors usually contain Cl and co-impregnation/co-deposition suffers from AgCl precipitation, and consequently Au and Ag have to be sequentially supported. However, Au and Ag species of the sequential preparation are individually isolated and difficult to be homogeneously mixed. Here we report an Au-Ag plasmonic nanocatalyst achieved by plasma restructuring and activation from the sequential preparation. The isolated cationic Au and Ag species on the sequentially-prepared Au-Ag/TiO 2 sample are restructured to be homogeneously mixed and highly activated by O 2 plasma, which can be partially auto-reduced to Au-Ag bimetallic nanoparticles within the induction period of a few minutes in VL photocatalytic oxidation of CO. The Au-Ag plasmonic nanocatalyst exhibits a strongly enhanced activity in the VL photocatalytic reaction. The contribution of O 2 plasma treatment and the enhancement mechanism for the Au-Ag plasmonic nanocatalyst are disclosed. [ABSTRACT FROM AUTHOR]