Plasma-assisted dry reforming of methane over Mo2C-Ni/Al2O3 catalysts: Effects of β-Mo2C promoter
TL;DR: In this article, β-Mo2C was employed as an effective component to activate CO2 and collaborated with Ni/γ-Al2O3 for the dry reforming of methane (DRM) reaction to occur at low temperatures.
Abstract: Non-thermal plasma (NTP) coupled with catalysis provides a way to enable the dry reforming of methane (DRM) reaction to occur at low temperatures. While assistance of NTP brings the negative issue of coke deposition due to the faster rate of CH4 dissociation induced by NTP. Herein, β-Mo2C was employed as an effective component to activate CO2 and collaborated with Ni/γ-Al2O3 for the plasma-assisted DRM reaction. Addition of β-Mo2C facilitated the charge deposition, and Ni nanoparticles were found to re-disperse over the β-Mo2C surface due to the strong interaction between Ni and β-Mo2C. Benefiting from the new active interface of Ni-Mo2C, the mechanically mixed Mo2C-Ni/Al2O3 catalyst exhibited much better activity and stability as compared with the undoped Ni/Al2O3 catalyst. The present study reveals the crucial roles of β-Mo2C additives, providing practical solutions to depress carbon deposition, and thereby enhance the catalytic stability in plasma-assisted DRM reaction.
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TL;DR: In this article , the electronic structure and acidic properties of copper-based catalysts were exploited as strategies to tune the distribution of oxygenates (alcohols and acids) in the plasma-catalytic conversion of CO2 and CH4 at a reaction temperature of 60 °C and atmospheric pressure.
Abstract: Direct conversion of CO2 and CH4 into value-added oxygenates under mild conditions is highly desirable since it has great potential to deliver a sustainable low-carbon economy and a carbon-neutral ecosystem. However, tuning the distribution of oxygenates in this process remains a major challenge. Here, the electronic structure and acidic properties of copper-based catalysts were exploited as strategies to tune the distribution of oxygenates (alcohols and acids) in the plasma-catalytic conversion of CO2 and CH4 at a reaction temperature of 60 °C and atmospheric pressure. We use support, on which copper is anchored, to regulate the distribution of Cu2+ and Cu+ in the Cu-based catalysts. Comprehensive characterization of the catalysts together with the reaction performances reveals that Cu2+ species are favorable to the formation of alcohols, whereas Cu+ species are critical to enhancing acetic acid production. Furthermore, the Brønsted acid sites of HZSM-5 significantly improved the selectivity of acetic acid, while the synergy of isolated Cu+ center and Brønsted acid sites, developed via Cu-exchange HZSM-5, exhibits potential for acetic acid formation. Finally, possible pathways for the formation of alcohols and acetic acid have been discussed. This work provides new insights into the design of highly selective catalysts for tuning the distribution of alcohols and acids in the plasma-catalytic conversion of CO2 and CH4 to oxygenates.
16 citations
TL;DR: In this paper , a flake-like nanocrystalline molybdenum carbide (α•MoC) is surface-engineered via Pd doping, and the synergy between the in-situ generated Mo vacancies and doped Pd species is shown to promote the selective hydrogenation of naphthalene to decalin.
Abstract: Although the hydrogenation of aromatics is important for the processing of fossil fuels and biofuels, it typically requires costly (e.g., noble metal‐based) catalysts and exhibits unsatisfactory selectivity. Herein, flake‐like nanocrystalline molybdenum carbide (α‐MoC) is surface‐engineered via Pd doping, and the synergy between the in‐situ generated Mo vacancies and doped Pd species is shown to promote the selective hydrogenation of naphthalene to decalin. Experimental and theoretical evidence reveal that this enhanced performance is due to the optimization of naphthalene adsorption energy and the establishment of a unique surface structure due to (i) surface environment modulation, (ii) the adjustment of electron density around Mo atoms, and (iii) the change in the strength of Mo‐H bonding caused by d‐band center optimization. Benefiting from the unique surface structure, the obtained optimum 0.5% Pd‐α‐MoC catalyst exhibits excellent performance. The developed strategy is successfully used to fabricate other noble metal (Pt, Ru)‐doped α‐MoC catalysts, thus holding promise as a universal method for the rational design of high‐performance metal carbide‐based hydrogenation catalysts.
13 citations
TL;DR: In this paper , a review of plasma-assisted reforming of methane (PARM) is presented from the perspective of reactor development, thermal and nonthermal PARM routes, and catalysis.
Abstract: Methane (CH4) is inexpensive, high in heating value, relatively low in carbon footprint compared to coal, and thus a promising energy resource. However, the locations of natural gas production sites are typically far from industrial areas. Therefore, transportation is needed, which could considerably increase the sale price of natural gas. Thus, the development of distributed, clean, affordable processes for the efficient conversion of CH4 has increasingly attracted people's attention. Among them are plasma technology with the advantages of mild operating conditions, low space need, and quick generation of energetic and chemically active species, which allows the reaction to occur far from the thermodynamic equilibrium and at a reasonable cost. Significant progress in plasma‐assisted reforming of methane (PARM) is achieved and reviewed in this paper from the perspectives of reactor development, thermal and nonthermal PARM routes, and catalysis. The factors affecting the conversion of reactants and the selectivity of products are studied. The findings from the past works and the insight into the existing challenges in this work should benefit the further development of reactors, high‐performance catalysts, and PARM routes.
11 citations
TL;DR: In this article , the authors developed a water-cooled dielectric barrier discharge (DBD) reactor for dry reforming of CH 4 (DRM) using a plasma-enabled catalytic process.
Abstract: Dry reforming of CH 4 (DRM) using a plasma-enabled catalytic process is an appealing approach for reducing greenhouse gas emissions while producing fuels and chemicals. However, this is a complex process that is influenced by both catalysts and discharge plasmas, and low energy efficiency remains a challenge for this technology. Here, we developed a water-cooled dielectric barrier discharge (DBD) reactor for plasma DRM reactions over supported catalysts (Ni/γ-Al 2 O 3 , Ag/γ-Al 2 O 3 and Pt/γ-Al 2 O 3 ) prepared via plasma-modified impregnation. Results show that metal loading on γ-Al 2 O 3 enhanced the basic nature of the catalysts and promoted the formation of discharge channels and reactive species. The maximum conversion of CO 2 (21.4 %) and CH 4 (27.6 %) was obtained when using Ag/γ-Al 2 O 3 . The basic nature of the catalytic materials dominated CO 2 conversion, whereas the properties of the catalyst and discharge plasma determined CH 4 conversion. The highest selectivity of hydrogen (∼34.5 %) and carbon-containing gas products (∼81.0 %) were attained when using the noble metal catalysts (Ag/γ-Al 2 O 3 and Pt/γ-Al 2 O 3 ), while the highest total selectivity of liquid products (14.1 %) was achieved in the presence of Ni/γ-Al 2 O 3 . Compared with γ-Al 2 O 3 , the supported catalysts demonstrated higher stability, especially for Ag/γ-Al 2 O 3 and Pt/γ-Al 2 O 3 , which also provided higher energy efficiency for gas conversion and product formation. • Plasma-catalytic CH 4 reforming with CO 2 was carried out in a DBD reactor. • Three γ-Al 2 O 3 supported catalysts were prepared by a modified impregnation method. • CO 2 conversion and CO selectivity are closely related to the catalyst basicity. • Ag/γ-Al 2 O 3 had the highest conversion of CO 2 (21.4%) and CH 4 (27.6%). • Ni/γ-Al 2 O 3 showed the highest total selectivity of liquid products.
9 citations
TL;DR: In this article, the most important methods of titanium, molybdenum, and tungsten carbide synthesis and the influence of their properties on activity in catalyzing the reaction of methane with carbon dioxide are presented.
Abstract: Dry reforming of hydrocarbons (DRH) is a pro-environmental method for syngas production. It owes its pro-environmental character to the use of carbon dioxide, which is one of the main greenhouse gases. Currently used nickel catalysts on oxide supports suffer from rapid deactivation due to sintering of active metal particles or the deposition of carbon deposits blocking the flow of gases through the reaction tube. In this view, new alternative catalysts are highly sought after. Transition metal carbides (TMCs) can potentially replace traditional nickel catalysts due to their stability and activity in DR processes. The catalytic activity of carbides results from the synthesis-dependent structural properties of carbides. In this respect, this review presents the most important methods of titanium, molybdenum, and tungsten carbide synthesis and the influence of their properties on activity in catalyzing the reaction of methane with carbon dioxide.
8 citations
References
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TL;DR: Dry (CO2) reforming of methane literature for catalysts based on Rh, Ru, Pt, and Pd metals is reviewed, including the effect of these noble metals on the kinetics, mechanism and deactivation of these catalysts.
Abstract: Dry (CO2) reforming of methane (DRM) is a well-studied reaction that is of both scientific and industrial importance. This reaction produces syngas that can be used to produce a wide range of products, such as higher alkanes and oxygenates by means of Fischer–Tropsch synthesis. DRM is inevitably accompanied by deactivation due to carbon deposition. DRM is also a highly endothermic reaction and requires operating temperatures of 800–1000 °C to attain high equilibrium conversion of CH4 and CO2 to H2 and CO and to minimize the thermodynamic driving force for carbon deposition. The most widely used catalysts for DRM are based on Ni. However, many of these catalysts undergo severe deactivation due to carbon deposition. Noble metals have also been studied and are typically found to be much more resistant to carbon deposition than Ni catalysts, but are generally uneconomical. Noble metals can also be used to promote the Ni catalysts in order to increase their resistance to deactivation. In order to design catalysts that minimize deactivation, it is necessary to understand the elementary steps involved in the activation and conversion of CH4 and CO2. This review will cover DRM literature for catalysts based on Rh, Ru, Pt, and Pd metals. This includes the effect of these noble metals on the kinetics, mechanism and deactivation of these catalysts.
1,472 citations
TL;DR: It is reported that platinum atomically dispersed on α-molybdenum carbide (α-MoC) enables low-temperature (150–190 degrees Celsius), base-free hydrogen production through APRM, with an average turnover frequency reaching 18,046 moles of hydrogen per mole of platinum per hour.
Abstract: Polymer electrolyte membrane fuel cells (PEMFCs) running on hydrogen are attractive alternative power supplies for a range of applications, with in situ release of the required hydrogen from a stable liquid offering one way of ensuring its safe storage and transportation before use. The use of methanol is particularly interesting in this regard, because it is inexpensive and can reform itself with water to release hydrogen with a high gravimetric density of 18.8 per cent by weight. But traditional reforming of methanol steam operates at relatively high temperatures (200-350 degrees Celsius), so the focus for vehicle and portable PEMFC applications has been on aqueous-phase reforming of methanol (APRM). This method requires less energy, and the simpler and more compact device design allows direct integration into PEMFC stacks. There remains, however, the need for an efficient APRM catalyst. Here we report that platinum (Pt) atomically dispersed on α-molybdenum carbide (α-MoC) enables low-temperature (150-190 degrees Celsius), base-free hydrogen production through APRM, with an average turnover frequency reaching 18,046 moles of hydrogen per mole of platinum per hour. We attribute this exceptional hydrogen production-which far exceeds that of previously reported low-temperature APRM catalysts-to the outstanding ability of α-MoC to induce water dissociation, and to the fact that platinum and α-MoC act in synergy to activate methanol and then to reform it.
944 citations
TL;DR: A catalyst composed of layered gold clusters on molybdenum carbide (MoC) nanoparticles to convert CO through its reaction with water into H2 and CO2 at temperatures as low as 150°C is developed.
Abstract: The water-gas shift (WGS) reaction (where carbon monoxide plus water yields dihydrogen and carbon dioxide) is an essential process for hydrogen generation and carbon monoxide removal in various energy-related chemical operations. This equilibrium-limited reaction is favored at a low working temperature. Potential application in fuel cells also requires a WGS catalyst to be highly active, stable, and energy-efficient and to match the working temperature of on-site hydrogen generation and consumption units. We synthesized layered gold (Au) clusters on a molybdenum carbide (α-MoC) substrate to create an interfacial catalyst system for the ultralow-temperature WGS reaction. Water was activated over α-MoC at 303 kelvin, whereas carbon monoxide adsorbed on adjacent Au sites was apt to react with surface hydroxyl groups formed from water splitting, leading to a high WGS activity at low temperatures.
484 citations
TL;DR: In this paper, three different packing methods are introduced into the single-stage plasma-catalysis system to investigate the influence of catalysts packed into the plasma area on the physical properties of the DBD and determine consequent synergistic effects in the plasmacatalytic dry reforming reactions.
Abstract: A coaxial dielectric barrier discharge (DBD) reactor has been developed for plasma-catalytic dry reforming of CH 4 into syngas over different Ni/γ-Al 2 O 3 catalysts. Three different packing methods are introduced into the single-stage plasma-catalysis system to investigate the influence of catalysts packed into the plasma area on the physical properties of the DBD and determine consequent synergistic effects in the plasma-catalytic dry reforming reactions. Compared to the fully packed reactor, which strongly changes the discharge mode due to a significant reduction in the discharge volume, partially packing the Ni/γ-Al 2 O 3 catalyst either in a radial or axial direction into the discharge gap still shows strong filamentary discharge and significantly enhances the physical and chemical interactions between the plasma and catalyst. Optical emission spectra of the discharge demonstrate the presence of reactive species (CO, CH, C 2 , CO 2 + and N 2 + ) in the plasma dry reforming of methane. We also find the presence of the Ni/γ-Al 2 O 3 catalyst in the plasma has a weak effect on the gas temperature of the CH 4 /CO 2 discharge. The synergistic effect resulting from the integration of the plasma and catalyst is clearly observed when the 10 wt% Ni/γ-Al 2 O 3 catalyst in flake form calcined at 300 °C is partially packed in the plasma, showing both the CH 4 conversion (56.4%) and H 2 yield (17.5%) are almost doubled. The synergy of plasma-catalysis also contributes to a significant enhancement in the energy efficiency for greenhouse gas conversion. This synergistic effect from the combination of low temperature plasma and solid catalyst can be attributed to both strong plasma–catalyst interactions and high activity of the Ni/γ-Al 2 O 3 catalyst calcined at a low temperature.
462 citations
TL;DR: This tutorial review describes the recent efforts made toward the development of nickel-based catalysts for the production of hydrogen from oxygenated hydrocarbons via steam reforming reactions and proposes three strategies to address these challenges.
Abstract: Owing to the considerable publicity that has been given to petroleum related economic, environmental, and political problems, renewed attention has been focused on the development of highly efficient and stable catalytic materials for the production of chemical/fuel from renewable resources. Supported nickel nanoclusters are widely used for catalytic reforming reactions, which are key processes for generating synthetic gas and/or hydrogen. New challenges were brought out by the extension of feedstock from hydrocarbons to oxygenates derivable from biomass, which could minimize the environmental impact of carbonaceous fuels and allow a smooth transition from fossil fuels to a sustainable energy economy. This tutorial review describes the recent efforts made toward the development of nickel-based catalysts for the production of hydrogen from oxygenated hydrocarbons via steam reforming reactions. In general, three challenges facing the design of Ni catalysts should be addressed. Nickel nanoclusters are apt to sinter under catalytic reforming conditions of high temperatures and in the presence of steam. Severe carbon deposition could also be observed on the catalyst if the surface carbon species adsorbed on metal surface are not removed in time. Additionally, the production of hydrogen rich gas with a low concentration of CO is a challenge using nickel catalysts, which are not so active in the water gas shift reaction. Accordingly, three strategies were presented to address these challenges. First, the methodologies for the preparation of highly dispersed nickel catalysts with strong metal–support interaction were discussed. A second approach—the promotion in the mobility of the surface oxygen—is favored for the yield of desired products while promoting the removal of surface carbon deposition. Finally, the process intensification via the in situ absorption of CO2 could produce a hydrogen rich gas with low CO concentration. These approaches could also guide the design of other types of heterogeneous base-metal catalysts for high temperature processes including methanation, dry reforming, and hydrocarbon combustion.
395 citations