Search

Hydrogen production from seawater remains challenging due to the deactivation of the hydrogen evolution reaction (HER) electrode under high current density. To overcome the activity-stability trade-offs in transition-metal sulfides, we propose a strategy to engineer sulfur migration by constructing a nickel-cobalt sulfides heterostructure with nitrogen-doped carbon shell encapsulation (CN@NiCoS) electrocatalyst. State-of-the-art ex situ/in situ characterizations and density functional theory calculations reveal the restructuring of the CN@NiCoS interface, clearly identifying dynamic sulfur migration. The NiCoS heterostructure stimulates sulfur migration by creating sulfur vacancies at the Ni3S2-Co9S8 heterointerface, while the migrated sulfur atoms are subsequently captured by the CN shell via strong C-S bond, preventing sulfide dissolution into alkaline electrolyte. Remarkably, the dynamically formed sulfur-doped CN shell and sulfur vacancies pairing sites significantly enhances HER activity by altering the d-band center near Fermi level, resulting in a low overpotential of 4.6 and 8 mV at 10 mA cm−2 in alkaline freshwater and seawater media, and long-term stability up to 1000 h. This work thus provides a guidance for the design of high-performance HER electrocatalyst by engineering interfacial atomic migration. Stable and efficient hydrogen production from seawater remains challenging. Here the authors engineer sulfur migration in NiCoS electrocatalyst via N-doped carbon encapsulation, generating S vacancies and S doped CN active sites at the interface that improves electrocatalytic hydrogen evolution activity and durability in both alkaline freshwater and seawater. [ABSTRACT FROM AUTHOR]

The polarized electron source is a critical component in accelerator facilities such as the electron–ion collider, which requires a polarized electron gun with higher voltage and higher bunch charge than existing sources. One challenge we faced was the surface charge limit of the distributed Bragg reflector GaAs/GaAsP superlattice (DBR-SL-GaAs) photocathode. We suppressed this effect by optimizing the surface doping and heat cleaning procedures. We achieved up to 11.6 nC bunch charge of polarized electron beam. In this report, we discuss the performance of tests of a DBR-SL-GaAs photocathode in the high voltage direct current gun. Possible reasons for the observed peak quantum efficiency wavelength shift are analyzed, and we addressed it by using a wavelength tunable laser. In addition, the impact of the DBR layer and laser on the lifetime is investigated in this paper. The optimal DBR-SL-GaAs operating zone has been proposed, which gave us a long lifetime and high polarization at 30 μA operation. The success of this polarized gun will be key to the future of the nuclear sciences. [ABSTRACT FROM AUTHOR]

Spin polarized photocathodes are key to the future operation of electron accelerators such as the ones at Thomas Jefferson National Accelerator Facility and Brookhaven National Laboratory. Currently, these photocathodes come in short supply due to limited production by molecular beam epitaxy. By developing a process to implement similar structures using metal organic chemical vapor deposition, the availability of these devices can be increased. In this paper, we detail the implementation of recent photocathode advancements via metal organic chemical vapor deposition process and show an improvement in both polarization and quantum efficiency of our devices compared to those fabricated via molecular beam epitaxy, with devices reaching 82% polarization and 2.9% quantum efficiency. [ABSTRACT FROM AUTHOR]

Photocathodes based on GaAs and other III–V semiconductors are capable of producing highly spin-polarized electron beams. GaAs/GaAsP superlattice photocathodes exhibit high spin polarization; however, the quantum efficiency (QE) is limited to 1% or less. To increase the QE, we fabricated a GaAs/GaAsP superlattice photocathode with a Distributed Bragg Reflector (DBR) underneath. This configuration creates a Fabry–Pérot cavity between the DBR and GaAs surface, which enhances the absorption of incident light and, consequently, the QE. These photocathode structures were grown using molecular beam epitaxy and achieved record quantum efficiencies exceeding 15% and electron spin polarization of about 75% when illuminated with near-bandgap photon energies. [ABSTRACT FROM AUTHOR]

The lifetime of GaAs photocathodes in polarized electron guns is limited due to the delicate activation layer. An atomically clean and smooth GaAs surface is needed to deposit a robust activation layer, such as Cs 2 Te , with longer lifetime compared to traditional (Cs,O) activation. A previous experiment with Cs 2 Te activation on GaAs used heat cleaning temperatures around 400 ° C to avoid an increase in surface roughness [Bae et al., Appl. Phys. Lett. 112, 154101 (2018)]. High-temperature heat cleaning around 580 ° C , which results in a relatively contamination-free surface, could be one possible way to improve quantum efficiency. However, one should be cautious about surface roughness degradation during high-temperature heat cleaning. In this paper, we report results of surface roughness measurements on native, heat cleaned, and (Cs,O) activated GaAs photocathodes under vacuum. The results, measured by ultrahigh vacuum scanning tunneling microscopy, show that the surface roughness improves as the heat cleaning temperature is increased, by at least a factor of three for 580 ° C heat cleaning, compared to the native sample. Activation with (Cs,O) is shown to increase surface roughness by a factor of four compared to a 580 ° C heat cleaned sample. This confirms that high-temperature heat cleaning can be useful for depositing good quality robust activation layers on GaAs. We also report chemical analysis for each step of preparation for p-doped GaAs photocathodes using X-ray photoelectron spectroscopy (XPS), angle-resolved XPS, and ultraviolet photoelectron spectroscopy. Our results indicate that the (Cs,O) activation layer forms a sandwich structure consists of Cs and oxygen. We found no formation of any specific compound such as Cs 2 O or Cs 11 O 3. [ABSTRACT FROM AUTHOR]

The effects of solute cerium (Ce) on the electrochemical performance of magnesium (Mg) alloy anodes are investigated by the weight loss test, electrochemical measurement, and surface analysis methods. It is found that the added Ce with the content of 0.174 wt.% enhances the corrosion resistance of Mg in seawater through forming the compact corrosion products layer and reducing the grain size of Mg alloys. Moreover, Mg-Ce alloys were applied in Mg-seawater batteries, which obtained a high energy density of 627.53 mWh g−1 with an anode efficiency of 43.49%, around 11 times than that of casting pure Mg. [ABSTRACT FROM AUTHOR]

A Monte Carlo model was developed to simulate electron transport and emission from thin GaAs photocathodes with different active layer thicknesses and dopant concentrations. The simulation accurately predicts expected behavior, namely, quantum efficiency (QE) is enhanced for thicker GaAs photocathodes and for higher dopant concentrations. More significantly, the simulation predicts that electrons excited to the conduction band of the GaAs can be reflected by the band bending regions of the AlGaAs barrier layer, which contributes to enhance QE. The simulation also predicts that electrons in the conduction band suffer more scattering for thicker GaAs photocathodes and for higher dopant concentration, leading to longer emission response time. This Monte Carlo model will improve our understanding and predicting of the performance of more complicated GaAs-based heterojunction structures composed of multiple thin layers. [ABSTRACT FROM AUTHOR]

Zinc/air batteries have received extensive attention due to their low cost, high safety, and high energy density. However, as the zinc/air battery is operated in the practical environment, water exchange between the battery and the environment occurs and affects the specific capacity and service life of the battery. In this paper, high relative‐humidity water‐vapor‐resistant membrane is prepared based on water‐absorbent polyacrylic acid. Using this membrane, water exchange is effectively reduced due to the decreased humidity gradient through gas diffusion electrode. When the thickness of the PAA wet film is 150 μm, the water vapor transmission rate (WVTR) reduced to 51 % of the blank. The excellent discharge performance of zinc/air battery is also achieved with the discharge voltage plateau of 1.10 V and the specific capacity of 612.5 mAh g−1 under the current density of 20 mA cm−2, which is 33.8 % higher than that without PAA membrane. [ABSTRACT FROM AUTHOR]

Mg-air battery is a promising electrochemical system for high-energy–density, long storage application. However, its commercialization is hindered by the low anode utilization rate mainly caused by the serious hydrogen evolution reaction (HER) in traditional NaCl aqueous electrolyte. Herein, we report NaBF4-dimethyl sulfoxide (DMSO)/NaCl-H2O biphasic electrolytes to alleviate the anode HER corrosion by allowing anodic reaction to take place in organic solution DMSO while ensuring high cathode activity with applying cathode reaction to occur in NaCl-H2O solution. The discharge results show that its utilization rate of AZ61 alloy in NaBF4-DMSO/NaCl-H2O biphasic electrolytes is increased to 67% at 1 mA cm−2 which is 17% higher than in NaCl-H2O single electrolyte, and the anode energy density is up to 2020 Wh kg−1. In addition, even at 15 mA cm−2, its discharge voltage is still up to 1.02 V which is higher than that in similar literatures using organic electrolytes for Mg anode. [ABSTRACT FROM AUTHOR]

Summary: Aqueous zinc batteries (AZBs) hold great promise for advancing applications in next‐generation energy storage devices because of their high safety, high energy density, and low cost. However, zinc metal anodes have greatly impeded the application in AZBs due to their poor cycle performance. Short lifespan, which is caused by dendritic growth, deformation, corrosion, and competing hydrogen evolution, is very tricky. Herein, a stable Sn@Cu foam, prepared by plating tin on copper foam, is reported as the substrate of Zn anodes. We evaluate the quality of plating tin layers, which are prepared by using different tin salt solutions, and Na2SnO3 solution is eventually selected. Electrochemical tests show that Sn@Cu foam can not only inherit the merits of Cu foam but also suppress hydrogen evolution reaction and lower the initial heterogeneous nucleation barrier of deposited Zn. Moreover, in situ observation by optical microscope demonstrates that Zn dendrite growth on Sn layer is suppressed during the plating‐stripping process. As a result, a compact Zn layer on Sn@Cu foam is obtained (Zn/Sn@Cu foam), symmetrical cells display superior cycling life of 1800 h at 1 mA cm−2 for 1 mAh cm−2, and full cells with VO2 cathode deliver remarkably better cycling stability and longer lifespan. [ABSTRACT FROM AUTHOR]

The simulation and optimization of an electron injector that operates a high-intensity polarized electron beam are presented. The electron injector would provide a single-bunch electron beam at a repetition rate of 1 Hz with a bunch charge of 10 nC, kinetic energy of 400 MeV and an electron spin polarization of 85 %. A direct current (DC) high-voltage photogun was employed to produce the 10 nC polarized electron beam with a kinetic energy of 350 keV, beam diameter of 1.44 cm (Gaussian distribution with σ of 0.36 cm) and full bunch length of 1.3 ns (Gaussian distribution with σ of 0.325 ns). The beam was compressed to 6 ps of RMS bunch length using one 114.24 MHz standing-wave sub-harmonic buncher, two 571.2 MHz standing-wave sub-harmonic bunchers and one 2.856 GHz traveling-wave buncher. The beam was accelerated finally to 400 MeV via eight 2.856 GHz traveling-wave Linacs. We performed the beam simulation, and the simulated results showed that the optimized RMS bunch length was 4.65 ps, RMS relative energy spread was 0.48 % and normalized RMS transverse emittance was 3 0. 1 3 m m ⋅ m r a d at a beam energy of 400 MeV. [ABSTRACT FROM AUTHOR]

In this work, a multi-interfacial nickel phosphide-nitride/nickel (NiPN/Ni) nanoparticle (NP)-decorated P,N-doped carbon nanotube (CNT) forest on carbon cloth (NiPN/Ni/CC-CNT2) with a high electrochemical active surface area was synthesized by a facile two-step approach involving the CNT forest growth with a subsequent controlled phosphorization/nitridation procedure, in which the initially loaded Ni species (active sites for growing CNT forest) serve as a precursor for synthesizing NiPN/Ni NP active species on CNT forest for water electrolysis. This is the first example that the loaded Ni sites for CNT forest growth were directly converted to active species for water electrolysis rather than be removed by acid treatment, which fully utilizes Ni resources and simultaneously avoids the waste acid environmental pollution. Thanks to the promoted mass/electron transfer by the CNT forest structure and the improved intrinsic activity by the multi-interfacial synergistic effect of nickel phosphide-nitride and nickel, the resultant NiPN/Ni/CC-CNT2 shows high activity toward hydrogen evolution reaction (HER, η10 = 56 mV and η100 = 186 mV) and oxygen evolution reaction (OER, η10 = 204 mV and η100 = 266 mV) in an alkaline medium. In addition, the assembled two-electrode electrolyzer with NiPN/Ni/CC-CNT2 as both the anode and cathode delivers low cell voltages of 1.49 and 1.74 V for 10 and 100 mA cm–2, respectively, associated with an excellent electrocatalytic durability for overall water splitting. The developed low-cost bifunctional NiPN/Ni/CC-CNT2 outperforms most of the reported electrocatalysts in literature and performs even better than the Pt and RuO2 benchmark electrocatalysts for HER and OER, respectively, at a large current density. Therefore, the fabricated NiPN/Ni/CC-CNT2 has shown great potential for large-scale commercial production of green hydrogen as a clean and renewable fuel to support the carbon neutralization strategy. [ABSTRACT FROM AUTHOR]

The development of efficient and stable non-noble metal bifunctional electrocatalysts for overall water splitting in acidic and alkaline media is highly desirable for industrial water electrolysis, but remains a profound challenge. Herein, for the first time, we report a general urea-modulated hydrothermal phosphorization strategy to directly grow hierarchical CoMnP/Ni2P nanosheet-based microplate arrays on Ni foam (NF). Thanks to the unique hierarchical structure, CoP–MnP synergism, and superhydrophilicity and superaerophobicity of the CoMnP/Ni2P/NF arrays, the optimized CoMnP/Ni2P/NF shows high activity for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with low overpotentials in 0.5 M H2SO4 (HER: 84 mV; OER: 165 mV) and 1 M KOH (HER: 108 mV; OER: 209 mV) at a current density of 10 mA cm−2, outperforming most of the reported electrocatalysts. Moreover, the assembled two-electrode electrolyzer with CoMnP/Ni2P/NF as both the anode and cathode delivers a low cell voltage of 1.54 V at 10 mA cm−2 with robust stability in alkaline electrolyte. More importantly, highly active and stable overall water splitting in acidic medium on a non-noble bifunctional electrocatalyst is realized, and only 1.43 V cell voltage is required to achieve 10 mA cm−2 current density. This work not only creates an excellent non-noble bifunctional electrocatalyst for overall water splitting in acidic and alkaline media, but also provides a universal and practical way to prepare other nanostructured metal phosphides for diverse electrocatalytic reactions. [ABSTRACT FROM AUTHOR]

Here, we report a demonstration of electron beam generation in a superconducting radio frequency (SRF) Teraelectronvolt Energy Superconducting Linear Accelerator 1.3 GHz gun equipped with a field emission cathode and operated at 2 K. The cathode is a submicrometer film of nitrogen-incorporated ultrananocrystalline diamond [(N)UNCD] deposited atop a Nb RRR300 cathode plug that is 4 mm in diameter. Measurements of the output current showed that it increased exponentially as a function of the gun gradient. Our results demonstrate a feasible path toward simplified fully cryogenic SRF injector technology. At a maximal gradient of 0.9 MV/m, a current density of 22 μA/cm2 was obtained [calculated as a 2.75 μA current over the total cathode surface area of π(2 mm)2]. One important finding is that the electron emitter made of (N)UNCD, a material long been known as a highly efficient field emission material, demonstrated a record low turn-on gradient of 0.6 MV/m. A hypothesis explaining this behavior is proposed. [ABSTRACT FROM AUTHOR]

GaAs photocathodes are the primary choice for generating spin-polarized electron beam with high brightness, high polarization, and fast polarization reversal. However, it suffers from short lifetime due to the highly reactive nature of the emission surface, resulting in substantial operational difficulties. Activating GaAs with a more robust material, such as Cs2Te, shows comparable polarization to that of Cs–O activation and increases the lifetime due to the robustness of the Cs2Te layer. However, previously reported photocathodes based on Cs–Te activation on GaAs suffer from 10× lower quantum efficiency (QE) compared to that activated with conventional Cs–O activation. Herein, we report activation recipes for GaAs photocathodes using Cs, O2, and Te. For Cs–Te activation, the QE was 6.6% at 532 nm. For Cs–O–Te activation, the QE was 8.8% at 532 nm and 4.5% at 780 nm. The negative electron affinity of the activated GaAs was directly measured and confirmed by low energy electron microscopy. We also report the activation layer chemical states and stoichiometry using in situ micro-spot synchrotron radiation x-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

Al is one of the principal alloying elements for Mg anodes. In this study, a series of Mg–Al alloys has been evaluated as anode materials for optimizing the Al addition amount in Mg anodes with the intention of improving the discharge performance in aqueous batteries. The effect of Al content on the discharge potential and corrosion resistance of the Mg anode has been investigated through microstructure characterization, electrochemical measurements in a half‐cell, discharge morphology analysis, and Mg–water battery tests. The results show that the Mg–1Al alloy possesses a larger corrosion resistance during discharge, with significant increase of the anode utilization efficiency at 1 and 5 mA/cm2 compared with pure Mg. However, a further increase of Al content does not continuously improve the discharge performance of the Mg anode with the decline of utilization efficiency due to the influence of the precipitated phase. This study contributes to a better understanding about the effect of Al on anodic dissolution and corrosion kinetics of the Mg anode. [ABSTRACT FROM AUTHOR]

Zn−Ni secondary battery is a promising candidate as next generation of energy storage battery. However, suffering from the poor cycle performance, its commercialization remains rather challenging. The severe dendrite growth of Zn anode and the rapid capacity decay caused by its uncontrollable dissolution and poor electronic conductivity of ZnO are the main factors. Herein, we report a novel Indium (In) doped ZnO/rGO anode material to inhibit ZnO dissolution through the generated C−O−Zn bond between ZnO and graphene. Meanwhile, the capacity decay decline due to the enhanced electronic conductivity of ZnO by the In doping and combination of graphene. As a result, In doped ZnO/rGO anode material delivers a high specific capacity of 643.4 mAh g−1 (coulombic efficiency 97.63 %) and remains 531.3 mAh g−1 after 125 cycles at 0.5 C, which are significantly higher than bare ZnO. [ABSTRACT FROM AUTHOR]

The gas diffusion electrode (GDE) represents the most significant component in metal–air batteries (MABs). It is essential to understand the underlying behaviors of GDE and optimize its performance. Herein, a polarization separation method from total polarization curve to single activation, ohmic, and mass transport polarizations of GDE in MABs is proposed for the first time, which is then applied in the investigation of detailed polarization behaviors of the GDE by changing the fabrication parameters. As the polytetrafluoroethylene contents in the catalyst and gas diffusion layers and pressing pressure are adjusted, hydrophobicity, porosity, coverage, and thickness are changed to influence the performance of GDE. Through this analysis, a detailed understanding of the structure–performance relationship of GDE is achieved to improve the electrode design, architecture, and fabrication. [ABSTRACT FROM AUTHOR]

The 400 MeV LINAC1 of the proposed eRHIC collider1 is the first acceleration stage of the 18 GeV electron accelerator. The second acceleration stage of the electron accelerator is the Rapid Cycling Synchrotron (RCS), which can increase the energy of the electron bunches to 18 GeV and subsequently extract transfer and inject the 18 GeV electron bunches into the 18 GeV electron Storage Ring (SR) to collide with the hadron bunches of the existing (Relativistic Heavy Ion Collider (RHIC)) accelerator. This paper describes the beam optics of the transfer line between the 400 MeV LINAC and the RCS accelerator (LtRCS). The function of the LtRCS line is twofold, first to transfer the electron beam from the exit of the 400 MeV LINAC to the injection point of the RCS1 and second to rotate the stable spin direction of the polarized electrons from the longitudinal direction to the vertical. A detailed description of the constraints to be satisfied by the LtRCS transfer line will be given. A section will also be devoted to discuss the spin rotator2. [ABSTRACT FROM AUTHOR]

An efficient and durable air cathode is of great importance for the commercial application of zinc‐air fuel cell. In this work, a new air cathode with the hydrophobic pores distributed continuously and in gradient was prepared and characterized by the scanning electron microscope (SEM) combined with energy dispersive X‐ray spectroscopy (EDS). Compared with traditional air cathode, our new cathode exhibits attractive performance and lifetime, by which the maximum power density of 252 mW cm−2 and a stable discharge of 3600 h at 50 mA cm−2 are presented in zinc‐air fuel cells. Further investigation shows that the unique pores with the adequate size and hydrophobic property in current collector layer for the new cathode are helpful to prevent the water accumulation, and inhibit the formation of carbonate. Improving stability! A new air cathode with the hydrophobic pores distributed continuously and in gradient was proposed and successfully prepared for zinc‐air fuel cells. The new cathode shows high performance and long lifetime for the maximum power density 252 mW cm−2 and stably 3600 h discharge in a zinc‐air fuel cells. And this cathode efficiently prevents the accumulation of electrolyte and the formation of carbonate inside the electrodes, and is a potential candidate for zinc‐air fuel cells. [ABSTRACT FROM AUTHOR]

Abstract: Insights into the relationship between the crystal planes of metal oxides and the catalytic activity of the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER) are essential for developing efficient renewable energy technologies. Herein, spinel Co3O4 nanomaterials were synthesized controllably with the specified morphologies of nanocubes, nanosheets, and nanoplates with different exposed planes of {100}, {110}, and {111}, respectively. The effects of the crystal planes of Co3O4 on the activity for the OER, ORR, and HER were subsequently investigated in alkaline media. Different electrocatalytic performances are possibly attributed to the abundance ratios of Co3+/Co2+ over the different exposed planes. The surface Co3+ ions exhibit higher activity for the OER and HER, whereas the surface Co2+ ions exhibit better performance for the ORR; moreover, higher electroconductivity enhances the polarization current for ORR and HER except OER. [ABSTRACT FROM AUTHOR]

Abstract: Insights into the relationship between the crystal planes of metal oxides and the catalytic activity of the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER) are essential for developing efficient renewable energy technologies. Herein, spinel Co3O4 nanomaterials were synthesized controllably with the specified morphologies of nanocubes, nanosheets, and nanoplates with different exposed planes of {100}, {110}, and {111}, respectively. The effects of the crystal planes of Co3O4 on the activity for the OER, ORR, and HER were subsequently investigated in alkaline media. Different electrocatalytic performances are possibly attributed to the abundance ratios of Co3+/Co2+ over the different exposed planes. The surface Co3+ ions exhibit higher activity for the OER and HER, whereas the surface Co2+ ions exhibit better performance for the ORR; moreover, higher electroconductivity enhances the polarization current for ORR and HER except OER. [ABSTRACT FROM AUTHOR]

Abstract: With the increasing demand of energy storage towards increasing the use of renewable energy technologies, electrochemical systems with low cost, high safety levels, and low environmental impact are critically needed. Zinc–air/oxygen batteries, which were always considered to be cheap, are losing their competitive advantages due to poor cyclic performance and energy efficiency. Herein, an effective strategy for oxygen recycling, which reduces the cost of oxygen to as low as ¢ 0.2 kWh−1 per cycle, is reported. With the use of oxygen, the performance of zinc–oxygen batteries is largely increased, with a maximum power density of 290 mW cm−2, stable cycling for more than 1500 cycles, an average energy density of 60 %, and elimination of carbonates. A 1 kW/1 kWh zinc–oxygen battery system is also integrated and exhibits a satisfactory energy efficiency of 58 % and a high working power density of 75 mW cm−2. [ABSTRACT FROM AUTHOR]

Zinc-oxygen batteries are promising candidates for electrical vehicles and electric grid energy storage due to their low cost, high safety levels, and low environmental impact. The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) represent the most significant processes in zinc-oxygen batteries. The development of nonprecious metal catalysts for OER with satisfactory performances and low cost (especially prepared by a straightforward synthesis route), still poses a significant challenge. Herein, we report an exceptionally facile and easily scalable method to produce NiFe layered double hydroxide (LDH) coated nickel foam by immersing nickel foams into aqueous solutions containing NiCl2 and FeCl2 and keeping them standing for a certain period of time. Without any other complicated technique or organic reagent, microflower-shaped NiFe LDHs can be obtained. The resulting electrode shows excellent OER performance with a low overpotential of 210 mV at a 10 mA cm−2 constant current polarization and stable operation for more than 100 charge-discharge cycles in zinc-oxygen batteries. [ABSTRACT FROM AUTHOR]

The Co-Mo-Al and Co-Mo-Ce-Al catalysts were prepared and tested for their activity in the methanation of synthesis gas in the presence of hydrogen sulfide. The results showed that the Co-Mo-Ce-Al series was superior to the Co-Mo-Al system in terms of CO conversion. The former system was used to examine the main factors controlling the methanation behavior. Among these are: HS concentration in the reaction mixture, reaction temperature and pressure, concentrations of CO, CH, and HO, H/CO ratio, and gaseous hourly space velocity. The methanation activity increased with increasing temperature, pressure and H/CO ratio. The reason why adding CO or HO decreases the methanation activity is discussed. [ABSTRACT FROM AUTHOR]

Ceria-alumina composite supports were prepared by the co-precipitation (cop), impregnation (imp) or deposition-precipitation (dp) methods. Co-Mo catalysts supported on these composite supports were prepared by the imp method and their catalytic activities for sulfur-resistant methanation of synthesis gas were investigated. The catalysts were characterized by nitrogen adsorption, X-ray diffraction (XRD), and hydrogen temperature-programmed reduction (TPR). It was found that the preparation method of ceria-alumina composite support had a marked influence on the surface area, the interaction between ceria and alumina, and the catalytic performance for sulfur-resistant methanation. Among them, the ceria-alumina composite support prepared by dp method achieves the best methanation activity due to its smaller ceria particle size, better ceria dispersion, weak interaction between ceria-alumina as suggested by XRD and TPR results. [ABSTRACT FROM AUTHOR]