A single source method to generate Ru-Ni-MgO catalysts for methane dry reforming and the kinetic effect of Ru on carbon deposition and gasification
TL;DR: In this paper, a single precursor RuxNiyMg1-x-y(OH) derived from solvothermal synthesis was used to generate Ru-Ni-MgO catalysts for methane reforming with CO2.
Abstract: A single precursor RuxNiyMg1-x-y(OH)(OCH3) derived from solvothermal synthesis was used to generate Ru-Ni-MgO catalysts for methane reforming with CO2. Calcination-reduction pretreatment of precursors could easily cause segregation of Ru and formation of both large and small metallic particles as RuO2 has limited solubility in NiO-MgO solid solution. Uniform small Ru-Ni alloy particles could only be produced within their limited alloying composition range through direct reduction pretreatment of the precursor. Catalysts derived from calcination-reduction exhibited low initial activity that increased with time-on-stream, whereas catalysts derived from direct reduction demonstrated high and steady activity. Over spent catalysts, Ru was found to have changed the type of deposited carbon from a recalcitrant graphitic one that could only be gasified by O2 to a soft type that can be facilely gasified by CO2. Kinetic studies showed that Ru increased the activation barrier for the rate determining CH4 dissociation step and thereby slows down the carbon deposition rate. A first order reaction dependence for CH4 pressure variation and zeroth for CO2 pressure change for pristine Ni- and Ru-catalysts was identified, while a first order and a deviation from zeroth order for CH4 and CO2 pressure variation were observed on bimetallic Ru-Ni catalyst. Such a deviation is associated with the oxyphilic nature of Ru that is enriched in the alloy surface under reforming conditions. The effects of Ru on carbon gasification over spent catalysts were investigated using a modified CO2-TPO measurement based on an extrapolated Wigner–Polanyi equation for carbon gasification. Ru was found to accelerate carbon gasification by increasing the pre-exponential factor for CO2 oxidation of carbon, albeit a disfavored elevated activation barrier was obtained, thus showing a strong compensation effect. Carbon gasification is favored in high concentration of CO2 and at high temperatures for Ru-Ni catalyst.
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TL;DR: A review of the recent literature achievements on DRM using bimetallic catalyst formulations is provided in this paper in a comprehensive and comparative manner, where the authors provide a detailed analysis of the current state-of-the-art.
Abstract: Dry (CO2) reforming of methane (DRM) for syngas production, a critical feedstock for the production of hydrogen, ammonia, and Fischer-Tropsch derived liquid energy carriers, unequivocally ranks among the top issues of applied catalysis in the light of environmental protection, renewable energy production and circular economy. This mainly because DRM involves the simultaneous reduction of two key greenhouse gases (CO2 and CH4) and provides an efficient way for CO2 utilization/recycling and the direct implementation of biogas. The same advantages make DRM a more favorable process compared to steam- or oxi- reforming ones. The design of cost-effective, efficient and robust (coking- and sintering-resistant) DRM catalysts is a grand challenge in the topic. Bimetallic catalysts, providing synergistic effects via metal-to-metal interactions seem to be an effective strategy for achieving these goals. A review of the recent literature achievements on DRM using bimetallic catalyst formulations is provided herein in a comprehensive and comparative manner.
140 citations
TL;DR: In this article, a series of catalysts with varied Fe/(Ni+Fe) ratios (0 to 0.17) and homogeneous metal distribution were prepared from a single FexNi0.07-xMg0.93O-R (x = 0.003-0.06) precursor derived from solvothermal synthesis.
Abstract: Dry reforming of methane (DRM) converts two major greenhouse gases into syngas, a versatile chemical feedstock, requiring the identification of a robust catalyst. In this contribution, we explored the promoting effect of Fe in MgO supported Ni-Fe alloy catalysts in DRM. Towards this end, a series of catalysts with varied Fe/(Ni+Fe) ratios (0 to 0.17) and homogeneous metal distribution were prepared from a single FexNiyMg1-x-y(OH)2 (x = 0.00–0.07, y = 0.00–0.07) precursor derived from solvothermal synthesis. Catalytic evaluations at 760 °C and 800 °C showed that Fe passivated the activity of Ni surface while promoting the coke-tolerant property. Structural evolution and coke deposition of catalysts were extensively characterized by using XRD, SEM, TEM, HAADF-HRTEM, H2-TPR, CO2 (O2)-TGA and CO2-TPO techniques, manifesting that alloying of Fe with Ni had enhanced catalyst stability. Lowered amount of coke was found on spent Ni-Fe alloy catalysts with respect to pristine Ni catalyst, and Fe also changed the type of surface carbon from a refractory type to a soft one that can be readily gasified by CO2. Fe also increased the surface oxyphilicity of alloy particle surface via balancing the otherwise carbon affinity of Ni surface. Optimized catalytic performance was attained by FexNi0.07-xMg0.93O-R (x = 0.003–0.006) catalyst. Kinetic studies and coke gasification kinetic disclosed that Fe slowed down coke deposition rate and concomitantly accelerated surface coke gasification rate, without changing the essential reaction mechanism or kinetic features of pristine Ni catalyst. The promoting effect of Fe was found to be highly dependent on CO2 contents in the contacting atmosphere, as well as Fe/Ni ratios in the alloy. The stability of Ni-Fe alloy catalyst in DRM can be ascribed to combined effects from both ensemble size reduction and surface oxyphilicity change. The role Fe plays in enhancing DRM coke-resistant property is potentially useful for alike reforming catalyst and process design.
101 citations
17 Jun 2015
TL;DR: In this paper, a low temperature dry reforming of methane was studied over platinum (0.2-2.5% Pt)-Ni/Mg/Ce 0.6 Zr 0.4 )O 2 catalyst.
Abstract: Abstract Low temperature dry reforming of methane was studied over platinum (0.2–2 wt.%) and/or nickel (8 wt.%) and magnesium (8 wt.%) immobilized onto a ceria–zirconia support. Ceria–zirconia (0.6:0.4) solid solutions were synthesized by precipitation and the metals were loaded by the incipient wetness method. XRD patterns demonstrated that the support was a cubic fluorite structure and Ni and Mg were deposited onto it. Temperature-programmed reduction showed that Pt addition substantially decreased the reduction temperature and the impact became less prominent with increasing Pt loading. The Ni–Mg/(Ce 0.6 Zr 0.4 )O 2 had the highest number of basic sites and the amounts decreased with the addition of platinum. The lowest CH 4 and CO 2 conversion ( X 10 ) temperatures were achieved at 454 °C and 437 °C, respectively, using a 0.5% Pt–Ni–Mg/(Ce 0.6 Zr 0.4 )O 2 catalyst. This catalyst was optimum because it balanced between the enhanced reducibility and decreasing number of basic sites, which both occurred with increasing Pt loading. Dry reforming experiments also indicated that Pt decreased the reaction onset temperature for methane and CO 2 and correlated to a slight decrease in the H 2 :CO ratio (though still higher than for the 0.5% Pt–Ce 0.6 Zr 0.4 O 2 control catalyst). Steady-state reaction experiments were conducted between 430 and 470 °C for the best catalyst and the results showed TOFs increasing from 2.69 to 4.74 s −1 with increasing temperature and minimal deactivation when left on stream for 100.5 h. A comparison to literature indicates that the Pt/Ni/Mg/Ce 0.6 Zr 0.4 O 2 catalyst has among the highest activities, especially if Ir and Rh catalysts are not included.
94 citations
TL;DR: In this article, the application of perovskite catalysts for methane reforming is discussed in details, and a summary with future outlooks is raised for the future development of Perovskites catalysts.
Abstract: Hydrogen is regarded as one of the promising sustainable energy carriers for human society. Methane reforming is crucial to hydrogen energy industry since it is the main route to obtain hydrogen. Ni-based catalyst has been extensively explored because of its low price and good catalytic activity. However, it suffers from fast deactivation caused by carbon deposition. Perovskite with its unique structure, has been a popular candidate for catalyst precursors and lots of related literature is published. In this review, the application of perovskite catalysts for methane reforming is discussed in details. Typical LaNiO3 has shown its superb carbon-resistance due to the strong interaction between La2O3 and CO2. The substitution of A and B sites could modify the structure and improve the catalytic performance further. Recent advances on this topic are presented as well. It is beneficial to increase the surface area by preparation supported and porous perovskite. Finally, a summary with future outlooks is raised for the future development of perovskite catalysts.
87 citations
TL;DR: In this article, the recent progress in the development of efficient and robust DRM catalysts is highlighted, after a brief introduction of the thermodynamics and general reaction mechanisms for DRM, and with a firm belief in the great promise of DRM technology, the remaining challenges for DRM catalyst development are discussed along with their perspectives on the future research directions.
Abstract: The increasing amount of greenhouse gases, especially CO2, in the atmosphere during the past decades has been a matter of great concern. Meanwhile, with the extensive exploration of natural gas resources, there is abundant CH4 waiting for valorization. CO2 or dry reforming of methane (CRM/DRM) is a promising approach to simultaneously utilize the two gases for the production of syngas. High-quality (free of sintering and carbon deposition during the reaction) and cost-effective catalysts are the key to the practical application of DRM. In this review article, the recent progress in the development of efficient and robust DRM catalysts is highlighted, after a brief introduction of the thermodynamics and general reaction mechanisms for DRM. The key factors in constructing highly efficient catalysts are addressed and the two major types of DRM catalysts, i.e., conventional supported catalysts and reduced solid solution catalysts, are clearly classified. Furthermore, with a firm belief in the great promise of DRM technology, the remaining challenges for DRM catalyst development are discussed along with our perspectives on the future research directions.
69 citations
References
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10 Jul 1997
TL;DR: This paper presents a meta-modelling system that automates the very labor-intensive and therefore time-heavy and therefore expensive and expensive process of characterization and activation of Solid Catalysts.
Abstract: Preparation of Solid Catalysts. Characterization of Solid Catalysts. Model Systems. Elementary Steps and Mechanisms. Kinetics and Transport Processes. Deactivation and Regeneration. Special Catalytic Systems. Laboratory Reactors. Reaction Engineering. Environmental Catalysis. Inorganic Reactions. Energy-related Catalysis. Organic Reactions.
4,227 citations
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: Time-resolved, high-resolution in situ transmission electron microscope observations of the formation of carbon nanofibres from methane decomposition over supported nickel nanocrystals show that metallic step edges act as spatiotemporal dynamic growth sites and may be important for understanding other types of catalytic reactions and nanomaterial syntheses.
Abstract: The synthesis of carbon nanotubes with predefined structure and functionality plays a central role in the field of nanotechnology1,2, whereas the inhibition of carbon growth is needed to prevent a breakdown of industrial catalysts for hydrogen and synthesis gas production3. The growth of carbon nanotubes and nanofibres has therefore been widely studied4,5,6,7,8,9,10. Recent advances in in situ techniques now open up the possibility of studying gas–solid interactions at the atomic level11,12. Here we present time-resolved, high-resolution in situ transmission electron microscope observations of the formation of carbon nanofibres from methane decomposition over supported nickel nanocrystals. Carbon nanofibres are observed to develop through a reaction-induced reshaping of the nickel nanocrystals. Specifically, the nucleation and growth of graphene layers are found to be assisted by a dynamic formation and restructuring of mono-atomic step edges at the nickel surface. Density-functional theory calculations indicate that the observations are consistent with a growth mechanism involving surface diffusion of carbon and nickel atoms. The finding that metallic step edges act as spatiotemporal dynamic growth sites may be important for understanding other types of catalytic reactions and nanomaterial syntheses.
1,357 citations
TL;DR: In this article, self-consistent density functional calculations using the LMTO-ASA method of the variations in the surface electronic structure for pseudomorfic overlayers and impurities of Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au on the other metals are presented.
Abstract: We present self-consistent density functional calculations using the LMTO-ASA method of the variations in the surface electronic structure for pseudomorfic overlayers and impurities of Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au on the other metals. Knowledge of these variations is of importance in understanding trends in the reactivity of metal surfaces. A simple model is presented which gives a description of the overall trends in the self-consistently calculated results.
1,061 citations
TL;DR: Based on density functional theory calculations, kinetic measurements, microkinetic and Monte Carlo simulations, thermogravimetric analysis (TGA) experiments, extended X-ray absorption spectroscopy (EXAFS) measurements, and experimental results from the literature, this paper presented a detailed and comprehensive mechanistic picture of the steam reforming process on a Ni catalyst.
1,002 citations