To obtain the proper catalyst activity for direct coal liquefaction, the iron-oxides, as a precursor of iron-based catalysts, were sulfurized in the liquid medium before use. The hydrogen-donating ...solvent, a promising liquid medium, benefited the process design. However, it was found to be not conducive to the catalyst activity. Herein, the influence on catalysts from aromatics was investigated. Synthetic iron-oxides were sulfurized under H2S flow in the mixtures of decalin and selected aromatics including xylene, naphthalene, phenanthrene and pyrene. The catalyst activity was evaluated based on its performance in the catalytic hydrogenation of naphthalene. It was found that pyrene had a significant negative effect on catalyst activity, which was mainly related to the condensation of pyrene on the catalyst. The fact was that the amount and condensation degree of carbon deposits on the tested catalysts were inversely proportional to their activities. The condensation of pyrene was related to both elemental sulfur and iron species. The effect from the two factors separately on pyrene condensation was limited, while the synergetic effect when they worked together made the condensation extent increased significantly. The elemental sulfur reacted with pyrene at elevated temperatures and induced the condensation of pyrene. Besides, density-functional-theory calculation results revealed that the chemical bonds of both elemental sulfur and pyrene were weakened by iron-sulfides.
•Pyrene inhibit the activity of obtained catalyst during sulfurization of iron-oxides.•Carbon deposits on catalyst is found to be responsible for the low activity.•Elemental sulfur produced from H2S during sulfurization induce pyrene condensation.•Iron sulfides promote condensation by activating chemical bonds of sulfur and pyrene.
For intermediate temperature solid oxide fuel cell (IT-SOFC) using hydrocarbon gases as fuels, the carbon deposition resistance of the anode is the most critical factor affecting its long-term ...stability. In this study, Ba(Ce0.9Y0.1)0.8Ni0.2O3-δ (BCYN) decorated Gd0.1Ce0.9O1.95 (GDC) composite is prepared by solution impregnation as anode for SOFC. And metal Ni nanoparticles are in-situ exsolved from BCYN as catalyst for the fuel gas cracking. At 750 °C, the polarization resistance of the optimized cell with Ni-BCYN/GDC composite anode are as low as 0.085 and 0.12 Ω cm2 in H2 and CH4, respectively. The related electrolyte-supported full cell's peak power density up to 211 mW cm−2 can be achieved in CH4 at 750 °C. In the long-term polarization test (200 mA cm−2), single cell with Ni-BCYN/GDC composite anode maintains stable output for 100 h without obvious attenuation and carbon deposition.
K doping improves the catalytic activity and stability of ordered mesoporous nickel-alumina catalyst in steam reforming of toluene as a tar model compound.
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•K doping improves the ...water adsorption capability of Ni-OMA catalysts.•K doping reduces the acidity of the support.•K doping reduces the amount of carbon deposition and the degree of graphitization.•The carboxyl pathway occurs preferentially over the catalyst.•Introduction of K by EISA method can suppress the loss of K.
Nickel-based catalysts have been broadly studied for the steam reforming of coal/biomass tar due to their inexpensiveness and good activity. Nevertheless, their industrial application has long been restricted by the deactivation induced by carbon deposition and Ni sintering in the reforming process. Herein, ordered mesoporous nickel-alumina catalysts with varying K contents were prepared. Their performance in steam reforming of toluene as a model compound of tar was evaluated to reveal the effects of K doping. Among them, the catalyst with 2 wt% K loading displayed the best catalytic activity and stability. Experimental and theoretical calculation results suggested that K doping enhances the water adsorption capability of the catalysts, which thereby reduces the amount and graphitization degree of carbon deposits. Moreover, the K doping reduces the acid amount of the support and thereby inhibits the formation of carbon deposits as well. However, K doping does not affect the reaction pathway of the catalysts in toluene steam reforming, and the main reaction intermediates detected with in-situ DRIFTS remain the carbonate groups. Furthermore, the confinement effects of the ordered mesoporous structures inhibit the sintering of Ni particles and the formation of carbon deposits. In addition, the influence of different spatial positions of K on the catalysts was explored. It was found that the K introduction via the one-pot solvent evaporation induced self-assembly method can suppress the loss of K from the catalysts.
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•CuO/SiO2 OC can avoid carbon formation while NiO/ZrO2 OC facing serious carbon deposition issue.•Composite filling reaction unit can greatly improve the CLC performance.•Synergy ...among the different OCs enables the systematic self-regulation function for carbon elimination.
Chemical-looping combustion (CLC) is a promising technology which can realize CO2 capture with low energy consumption. Carbon deposition is one of the main challenges in CLC of methane, which decreases the efficiency of combustion and CO2 capture. In this work, the carbon formation behaviors of four typical oxygen carriers (OCs) including NiO/ZrO2, Fe2O3/Al2O3, MnO2/ZrO2 and CuO/SiO2 were investigated, and a strategy for carbon elimination was proposed by arranging the four OCs with suitable sequences in fixed-bed reactor. It is found that carbon is easy to form on the NiO/ZrO2 OC, although it shows high CH4 conversion. The reduction of Fe2O3/Al2O3 is a stepwise process and carbon will be generated in the deep reduction from Fe3O4 to FeO/Fe. MnO2/ZrO2 OC exhibits poor activity for CH4 conversion, but it shows high resistance to carbon deposition. For CuO/SiO2 OC, it shows high CH4 conversion (89.1%) and CO2 selectivity (97.6%) with almost no formation of carbon. When combing the four OCs in the CuNiFeMn sequence, high-performance CuO/SiO2 and NiO/ZrO2 OCs in front of the filling fixed-bed can oxidize most of CH4. CuO/SiO2 OC will oxidize CH4 to CO2 and H2O, then the formed CO2/H2O may gasify the carbon deposition on the NiO/ZrO2 OC to produce CO and H2. Thereafter, these reducible gases as well as the residual CH4 can be oxidized by the following Fe2O3/Al2O3 and MnO2/ZrO2 OCs with relatively poor activity. In this way, the synergistic effect among the sequenced OC mixtures can significantly enhance the CLC efficiency and resistance to carbon deposition.
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•A 2D transient SOFC multi-physical model is developed.•The degradation analysis and life prediction are conducted.•The current density decreases by 1.6 %/1000 h.•The strategies to ...prevent carbon deposition are proposed.•Reduction in ratio of CH4 to H2O improves durability by 50%.
Carbon deposition is a thorny issue for the SOFC fueled by low carbon hydrocarbons such as biomass syngas. Moreover, long-term large temperature gradients would reduce SOFC durability. Regarding these two issues, a two dimensional transient multi-physical model considering carbon deposition and temperature effect is developed for SOFC in this work. Typically due to the carbon deposition, the SOFC anode porosity decreases from 0.5 to 0.267, and the reaction activity decreases from 1.0 to about 0.45 after running 140 day. Accordingly, the current density decreases by 1.6 % at t = 42 d and 6% at t = 140 d, which indicates the damage of SOFC durability compared to the durability target (1%/1000 h) of commercial SOFC. The maximum temperature difference of the cell is predicted to be about 106 °C. It was found that the carbon deposition and large temperature gradient are closely related to the operating parameters. With the increase of operating voltage from 0.4 V to 0.8 V, the porosity and reaction activity respectively increase by 50% and 55%, and the maximum temperature difference is reduced from 150 °C to 16 °C after running 140 day. The increase of the inlet temperature could improve the overall temperature and decrease the porosity. Besides, the reduction in the ratio of CH4 to H2O helps to suppress carbon deposition, thus to improving the performance.
•H2 production systems coupled with CCS based on methane reforming are proposed.•CO2 reinjection is creatively integrated for high conversion of CH4 and CO2.•Carbon deposition risk has been eased by ...constructing a high CO2/CH4 reforming process.•From the angle of H2 production, new steam reforming one has an advanced performance.•New dry reforming technology has large potential to applied into multifunctional systems.
The combination of methane steam reforming technology and CCS (Carbon Capture and Storage) technology has great potential to reduce carbon emissions in the process of hydrogen production. Different from the traditional idea of capturing CO2 (Carbon Dioxide) in the exhaust gas with high work consumption, this study simultaneously focuses on CO2 separation from fuel gas and recycling. A new hydrogen production system is developed by methane steam reforming coupled with carbon capture. Separated and captured high-purity carbon dioxide could be recycled for methane dry reforming; on this basis, a new methane-dry-reforming-driven hydrogen production system with a carbon dioxide reinjection unit is innovatively proposed. In this study, the energy flow and irreversible loss in the two newly developed systems are analyzed in detail through energy and exergy balance analysis. The advantages are explored from the perspective of hydrogen production rate, natural gas consumption and work consumption. In addition, in consideration of the integrated performance, an optimal design analysis was conducted. In terms of hydrogen production, the new system based on dry reforming is better, with an advantage of 2.41%; however, it is worth noting that the comprehensive thermal performance of the new steam reforming system is better, reaching 10.95%. This study provides new ideas for hydrogen production from a low carbon emission perspective and also offers a new direction for future distributed energy system integration.
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•Nickel (10 wt. %) catalysts supported on nanostructured ceria were prepared.•High temperature steam reforming of ethanol for hydrogen production was studied.•At 550 °C rod-shaped ...sample was the most stable with higher hydrogen yield.•Carbon removal was easier in rod-shaped catalysts due to its higher OSC.
Ceria nanostructures (particles, rods and cubes) were used as support of 10 wt. % Ni/CeO2 catalysts and tested in the steam reforming of ethanol (SRE) reaction at stoichiometric conditions. Supports were prepared by precipitation and hydrothermal methods. Nickel was incorporated by incipient wetness impregnation. Catalysts were characterized by N2 adsorption, EDS, X-ray diffraction, transmission electron microscopy, Raman spectroscopy, N2O chemisorption, temperature programed reduction and CO-oxidation. Characterization of materials showed differences in the nickel particle size, nickel dispersion and its interaction with the ceria support, all these features dependent on the morphology of ceria; trends observed in calcined samples are retrieved in the reduced catalysts. Nickel supported on ceria rods (Ni/Ce-r) exhibited the best activity and hydrogen yield in the SRE reaction at 550 °C for 24 h under stream. Moreover, temperature-programmed oxidation of spent catalysts showed that the Ni/Ce-r sample presented the lower amount of carbon deposits which were also removed at lower temperatures. These characteristics of the rod-shaped catalyst were ascribed to the enhanced oxygen storage capacity presented by ceria rods and the higher dispersion of nickel over this ceria nanostructure.
Despite the importance of subsoil carbon (C) deposition by deep-rooted crops in mitigating climate change and maintaining soil health, the quantification of root C input and its microbial utilization ...and stabilization below 1 m depth remains unexplored. We studied C input by three perennial deep-rooted plants (lucerne, kernza, and rosinweed) grown in a unique 4-m deep RootTower facility. 13C multiple pulse labeling was applied to trace C flows in roots, rhizodeposition, and soil as well as 13C incorporation into microbial groups by phospholipid fatty acids and the long-term stabilization of microbial residues by amino sugars. The ratio of rhizodeposited 13C in the PLFA and amino sugar pools was used to compare the relative microbial stability of rhizodeposited C across depths and plant species. Belowground C allocation between roots, rhizodeposits, and living and dead microorganisms indicated depth dependent plant investment. Rhizodeposition as a fraction of the total belowground C input declined from the topsoil (0–25 cm) to the deepest layer (360 cm), i.e., from 35%, 45%, and 36%–8.0%, 2.5%, and 2.7% for lucerne, kernza, and rosinweed, respectively, where lucerne had greater C input than the other species between 340 and 360 cm. The relative microbial stabilization of rhizodeposits in the subsoil across all species showed a dominance of recently assimilated C in microbial necromass, thus indicating a higher microbial stabilization of rhizodeposited C with depth. In conclusion, we traced photosynthates down to 3.6 m soil depth and showed that even relatively small C amounts allocated to deep soil layers will become microbially stabilized. Thus, deep-rooted crops, in particular lucerne are important for stabilization and storage of C over long time scales in deep soil.
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•Rhizodeposition strongly declined with depth across all plant species.•Microbial stabilization of rhizodeposits increases with depth.•Deep-rooted crops are important for storage and stabilization of rhizodeposition.
Addition of rare earth oxide, especially lanthanide oxide, was regarded as a promising strategy to improve the carbon resistance for Nickel-based catalysts in dry reforming of methane (DRM). In this ...work, Nickel-based catalysts containing lanthanide oxides (NiLa/SiO2, NiCe/SiO2, NiSm/SiO2, and NiGd/SiO2) were prepared and employed to catalyze DRM. Lanthanide oxide affected the formation of Ni nanoparticles in different size. In NiLa/SiO2 and NiCe/SiO2, Ni nanoparticles maintained relatively small size (4 nm), while in NiSm/SiO2 and NiGd/SiO2, nickel particles were in large size (8 nm). NiLa/SiO2 and NiCe/SiO2 exhibited better stability than the other two catalysts, with CH4 conversion decreasing from 64.6 to 57.6% and 61.6 to 60.3%, respectively in 10 h on stream. The kinetic study confirmed that adding lanthanide oxide significantly affected the activation energy of CH4 dissociation and CO2 dissociation. Compared to monometallic Ni/SiO2, the presence of Sm and Gd suppressed CO2 dissociation, and introduction of Ce and La effectively promoted CO2 dissociation. These characters contributed to the higher carbon resistance and good stability for NiLa/SiO2 and NiCe/SiO2 catalysts in DRM reaction.
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•Nickel-based silica catalysts containing lanthanide oxides were synthesized.•Addition of CeO2 and La2O3 showed high carbon resistance for CH4 dry reforming.•Introduction of CeO2 and La2O3 to nickel catalyst promoted the CO2 dissociation.•Nickel catalyst modified with Sm2O3 and CeO2 facilitated the CH4 dissociation.
The main features in cationic LTA zeolites that are likely to impact its potential hydrothermal stability are interconnected. The Al content and the compensating cation play an important role in the ...water adsorption but their influence on the zeolite performance in thermal cycles is yet to be understood. In this study, four LTA zeolite samples were synthetized with distinct Si/Al ratios in sodium and potassium forms. They underwent a Premature Aging Protocol (PAP) that took into account the operating conditions typically found in temperature swing adsorption processes. The Si/Al ratio per se did not impact in the crystallinity upon aging, but the presence of a high amount of potassium cations (Si/Al = 1) led to the amorphization of the zeolite structure. The results from XPS and NMR techniques indicate the Al migration from the outer surface to the inner cages occurs upon aging. Chemical analysis by XRF and ICP-OES associated with 27Al NMR analysis reveal that the presence of EFAl is particularly significant in the sample with the largest Si/Al ratio (5) and is correlated to a much larger C deposition upon aging. TG/DTG and TPD-NH3 experiments suggest that acid sites in the zeolite structures act as a double-edged sword, by enhancing water adsorption while also leading to carbon accumulation. CO2 isotherms at 0 ºC reveal the reduction of the microporosity after aging, whereas the Al content is proportional to the water adsorption uptake, particularly at low pressures (below 10 mbar). The material with an intermediate Si/Al ratio and in Na-form (LTAc-SiAl2-Na) combines excellent hydrothermal stability with a high-water affinity and uptake.
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•LTA zeolite with an intermediate _Si/Al_ ratio and in Na-form combines hydrophilicity and hydrothermal stability.•The presence of Extra-Framework Al is vehemently correlated to a much larger C deposition upon aging.•The Si/Al ratio per se did not impact the crystallinity upon aging.
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