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•Demand for H2 necessitated the development of a compact reformer.•Core unit process of compact reformer includes SRM, WGS, and PROX.•Scale-down of reformer decrease thermal ...efficiency and increase processing capacity.•This review introduces the studies about each core unit and provides a guide.•It especially focuses on the selection of appropriate materials in catalysts.
Climate change triggered by the excessive use of fossil fuels has resulted in an increased focus on the use of hydrogen. In addition to its clean property, hydrogen exhibits a higher efficiency for fuel cell applications compared to heat engines. Although hydrogen is one of the most common elements on Earth, it is not readily available in its elemental form in nature, indicating that it is a secondary energy source that requires the processing of hydrocarbons or water. Currently, hydrogen is predominantly produced using fossil fuels (96%), and the large-scale production of hydrogen from natural gas has already been commercialized. However, the increasing demand for on-site/distributed power generation systems has necessitated the development of a small-scale hydrogen production process. This scale-down induces a decrease in thermal efficiency and an increase in processing capacity, which compels the development of an integrated and harmonized technology. Studies are being conducted on compact reformers in this regard. The core unit processes of compact reformer include steam reforming of methane (SRM), water–gas shift (WGS), and preferential CO oxidation (PROX), with each process requiring the development of customized catalysts. This review introduces the basic thermodynamics and kinetics of these core unit processes, details their various issues, and provides a guide regarding current research trends on the development of customized catalysts for the unit processes of SRM, WGS, and PROX in compact reformers. State of the art for compact reformers are also introduced, showing that there are only several types of commercial compact reformers yet compared to their importance.
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•This review introduces the WGS reaction and catalyst of diverse types of syngas.•Natural gas-, biomass-, waste-, and coal-derived syngas are categorized.•Customized reaction ...conditions/catalysts are compared based on syngas type.•Some similarities were identified through the comparison of syngas characteristics.•CO concentration and the presence of H2S are the main consideration factors.
The conventional hydrogen production process from natural gas includes a water–gas shift reaction (WGSR) as a core step to remove carbon monoxide and produce additional hydrogen. The WGSR can be further applied to the upcycling of other types of synthesis gases, such as biomass, municipal solid waste, and coal-derived synthesis gas. We have focused on the reaction conditions and catalysts for the WGSR dealing with diverse types of feed gases for the last 10 years to understand the development progress. Based on the categorization (by the type of feed gas), the tested catalysts, capacity, temperature, feed gas composition, steam-to-carbon ratio, and the performance of the catalyst are carefully compared. This review provides insight into the current research trends and perspectives for target-oriented WGSR in each type of feed gas, which can give clues for customization.
The perirhinal cortex (PER) supports multimodal object recognition, but how multimodal information of objects is integrated within the PER remains unknown. Here, we recorded single units within the ...PER while rats performed a PER-dependent multimodal object-recognition task. In this task, audiovisual cues were presented simultaneously (multimodally) or separately (unimodally). We identified 2 types of object-selective neurons in the PER: crossmodal cells, showing constant firing patterns for an object irrespective of its modality, and unimodal cells, showing a preference for a specific modality. Unimodal cells further dissociated unimodal and multimodal versions of the object by modulating their firing rates according to the modality condition. A population-decoding analysis confirmed that the PER could perform both modality-invariant and modality-specific object decoding—the former for recognizing an object as the same in various conditions and the latter for remembering modality-specific experiences of the same object.
The hippocampus and parahippocampal region are essential for representing episodic memories involving various spatial locations and objects, and for using those memories for future adaptive behavior. ...The “dual‐stream model” was initially formulated based on anatomical characteristics of the medial temporal lobe, dividing the parahippocampal region into two streams that separately process and relay spatial and nonspatial information to the hippocampus. Despite its significance, the dual‐stream model in its original form cannot explain recent experimental results, and many researchers have recognized the need for a modification of the model. Here, we argue that dividing the parahippocampal region into spatial and nonspatial streams a priori may be too simplistic, particularly in light of ambiguous situations in which a sensory cue alone (e.g., visual scene) may not allow such a definitive categorization. Upon reviewing evidence, including our own, that reveals the importance of goal‐directed behavioral responses in determining the relative involvement of the parahippocampal processing streams, we propose the Goal‐directed Interaction of Stimulus and Task‐demand (GIST) model. In the GIST model, input stimuli such as visual scenes and objects are first processed by both the postrhinal and perirhinal cortices—the postrhinal cortex more heavily involved with visual scenes and perirhinal cortex with objects—with relatively little dependence on behavioral task demand. However, once perceptual ambiguities are resolved and the scenes and objects are identified and recognized, the information is then processed through the medial or lateral entorhinal cortex, depending on whether it is used to fulfill navigational or non‐navigational goals, respectively. As complex sensory stimuli are utilized for both navigational and non‐navigational purposes in an intermixed fashion in naturalistic settings, the hippocampus may be required to then put together these experiences into a coherent map to allow flexible cognitive operations for adaptive behavior to occur.
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•Nickel-based catalyst tolerates high gas hourly space velocity of 1,620 L g−1h−1.•Developed catalyst was compared with commercial carbon dioxide reforming catalyst.•Reformer size is ...reduced by 23% due to the developed catalyst’s high space velocity.•Efficient heat utilization diminishes production cost by a factor of 2.5.•Improved methanol production cost (36%) and energy efficiency (∼6%p) are reported.
The economic viability of a methanol production process through carbon dioxide reforming of landfill gas using a newly developed nickel-based catalyst was assessed. The development of the catalyst and techno-economic analysis of the designed process were targeted. The nickel-based catalyst showed a highly active and stable performance even at an extremely high gas hourly space velocity of 1,620,000 mL g−1h−1. The high activity of the catalyst was due to the abundant nickel active sites (metallic nickel particles) on its surface. Coke formation was suppressed by the small particle size of nickel and relatively high oxygen storage capacity, resulting in a stable catalytic performance. In the process simulation, the methanol production system based on the nickel-based catalyst (new process) leveraged its smaller reformer size and more efficient heat utilization compared to those of a previously reported system based on a rhodium-based catalyst (base process) because of its higher gas hourly space velocity. The process simulation was conducted based on the gas hourly space velocity of 312,346 mL g−1h−1. The unit production costs of methanol were reduced from 184.0 $ ton−1 in the base process to 117.5 $ ton−1 in the new process. In addition, profitability analysis based on the global market price of methanol demonstrated that the new process exhibited a positive net present value, indicating economic feasibility, whereas the base process was not viable in the worst-case scenario (lowest market price of methanol).
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•Key steps of GTL process include methane reforming and FTS.•Connectivity at each step is critical to increase the efficiency of the GTL process.•Reforming for producing syngas with a ...desired H2/CO ratio targeting FTS is dealt with.•FTS conditions and catalysts considering the syngas composition are addressed.•This review introduces the studies about nano-catalysts for reforming and FTS.
Gas-to-liquids (GTL) has attracted attention as a commercial process capable of producing clean fuels and petrochemical products from natural gas. It has the potential to be a competitive alternative during a period of elevated global oil prices. The key steps of GTL involve the preparation of syngas (CO + H2) through the methane reforming and the production of hydrocarbons through Fischer–Tropsch synthesis (FTS) from the syngas. In this review, nano-catalyst technology that is directly related to the increase in the efficiency of GTL will be introduced with a focus on reforming and FTS. This review will provide insights into current research trends and issues in the development of customized catalysts for reforming and FTS, as well as the thermodynamics and kinetics. Further, it places emphasis on the connection between the reforming and FTS, with a particular focus on the development of tailored reforming catalysts that can produce syngas with a H2/CO ratio of 2 to 2.15 to suit the requirements of FTS. In that regard, various studies are being conducted on the catalyst design to inhibit the carbon deposition of the Ni-based catalyst for combined steam and CO2 reforming. CeO2 has been employed as major components for reforming based on its excellent physicochemical properties. This review also highlights the importance of customized FTS catalysts that consider the reactant gas composition. A considerable volume of literature has been published on the impact of Ru noble metal as the other active metal or promoter to improve the performance of Co-based catalysts for FTS.
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•Me-CeO2 and Me-Ni-CeO2 catalysts were prepared and explored in the HT-WGS reaction.•Doping of CeO2 with transition metal led to increased lattice strain.•Doping of Ni into Me-CeO2 ...further improved activity and thermal stability.•The higher lattice strain introduced higher oxygen vacancies in the Me-Ni-CeO2.•Co-Ni-CeO2 showed the excellent activity and stability among the tested catalysts.
A comparative study between monometallic (Me−CeO2, Me=Zn, Cu, Fe and Co) and Ni-doped bimetallic (Me−Ni−CeO2) catalysts has been performed in the high temperature water-gas shift (HT−WGS) reaction using waste derived synthesis gas. Experimental results revealed that Me−Ni−CeO2 exhibited higher catalytic performance than simple Me−CeO2 catalysts. Within the Me−Ni−CeO2 series, Co−Ni−CeO2 exhibited excellent and stable catalytic performance (CO conversion>90%) at a very high GHSV of 143,000h−1. The existence of high concentration of Ce3+ ions and oxygen vacancies on the catalyst surface were responsible for the increased WGS activity of Co−Ni−CeO2. In addition, Co−Ni−CeO2 maintains a stable performance for 50h. However, commercial Fe2O3-Cr2O3 catalyst showed a steep decline from their initial CO conversion values 15–10% within 5h.
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•Cu/CeO2 catalysts were prepared using different impregnation orders for Cu and Ce.•Cu–Ce/CeO2 (prepared by co-impregnation) exhibited the highest catalytic activity.•Cu dispersion ...and Cu particle size are important factors in reaction < 280 °C.•Oxygen vacancy concentration and active Cu species are important factors > 360 °C.
To investigate the effect of Cu/CeO2 catalysts preparation methods for low temperature water−gas shift reaction, Cu/CeO2 catalysts were prepared with various impregnation sequences and applied to the water−gas shift reaction at a high gas hourly space velocity of 36,080 mL/g·h. The catalyst preparation method affected both the Cu−Ce synergistic effect and the physico−chemical properties of the Ce promoted Cu/CeO2 catalysts, such as specific surface area, Cu particle size, Cu dispersion, amount of active Cu species and oxygen vacancy concentration. Among the prepared catalysts, Cu–Ce/CeO2 showed the highest CO conversion because of the high contents of active Cu species and high concentration of oxygen vacancies.
Various noble metals (Pt, Rh, Ru, and Pd) were supported on CeO2 to understand their sulfur-tolerant catalytic activity. The synthesized catalysts were applied to the water-gas shift reaction in the ...waste-to-hydrogen process with the injection of 500 ppm H2S. Among the samples, the PtCe catalyst showed the highest sulfur tolerance and recovery of catalytic activity. Considering the catalytic reaction results and physicochemical properties, the sulfur tolerance of the catalyst is affected by oxygen vacancies and redox properties, which are closely related to the interaction between the metal and the CeO2 support. In addition, the oxygen storage capacity concentration was used as an indicator for classifying the recovered catalyst and the non-recovered catalyst which had been poisoned by sulfur.
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•CeO2-based noble metal catalysts are tested for sulfur-injected water gas shift.•Pt-loaded catalyst showed strong sulfur tolerance and regeneration.•Sulfur tolerance is strongly related to oxygen storage capacity of the catalyst.•Regeneration trends are clearly classified based on the oxygen storage capacity.•Certain oxygen vacancy is required for the regeneration of sulfur-poisoned catalyst.
Dry reforming of methane (DRM) is an attractive route to simultaneously consume both methane (CH4) and carbon dioxide (CO2) for the production of valuable syngas. Although nickel catalysts are ...considered to be the most promising in both cost and activity, catalysts having high stability with low coke formation are highly coveted for commercialization. Here, we report a one-pot synthesis for mesoporous supported nickel catalysts with high activity and stability in a DRM reaction by using a spray pyrolysis-assisted evaporation-induced self-assembly (EISA) method. Two different strategies were introduced to prepare the catalysts of mesoporous alumina supports with highly dispersed active nickel sites from one pot of precursor solutions. One is phase segregation of nickel from alumina supports already in the self-assembly step by using a hydrophobic nickel oleate precursor, a hydrophilic alumina precursor, and an amphipathic triblock copolymer, which was achievable owing to the unique characteristics of spray pyrolysis, especially its fast drying-pyrolysis-mediated kinetic quenching, which was used to form catalysts with highly dispersed active sites of nickel (3 nm). The other strategy is exsolution, entailing the release and anchoring of nickel from the bulk to the surface of the alumina phase in the reduction step while using a hydrophilic nickel precursor. Compared with nickel catalysts prepared by conventional wet impregnation, the one-pot catalysts, especially the nickel oleate-based catalyst, showed high coke resistance, maintaining conversion for 30 h with 92% CH4 conversion and 97% CO2 conversion, which originated from the smaller well-dispersed nickel particles, the strong metal–support interaction, and the suppressed particle agglomeration. We envisage the development, by the one-pot processing of multicomponent precursor solutions, of heterogeneous supported catalysts with superior performances for a wider range of applications.
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