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A Short Review on the Catalytic Activity of Hydrotalcite-Derived Materials for Dry Reforming of Methane

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A Short Review on the Catalytic Activity of Hydrotalcite-Derived Materials for Dry Reforming of Methane catalysts Review A Short Review on the Catalytic Activity of Hydrotalcite-Derived Materials for Dry Reforming of Methane Radosław D˛ebek 1,2, Monika Motak 1, Teresa Grzybek 1, Maria Elena Galvez 2 and Patrick Da Costa 2,* 1 Faculty of Energy and Fuels, AGH University of Science and Technology, 30 A.Mickiewicza Av., 30-059 Kraków, Poland; [email protected] (R.D.); [email protected] (M.M.); [email protected] (T.G.) 2 Institut Jean Le Rond d’Alembert, Sorbonne Universités, UPMC, Univ. Paris 6, CNRS, UMR 7190, 2 Place de la Gare de Ceinture, 78210 Saint-Cyr-L’Ecole, France; [email protected] * Correspondence: [email protected]; Tel.: +33-1-30-85-48-62 Academic Editor: Simon Penner Received: 29 October 2016; Accepted: 12 January 2017; Published: 18 January 2017 Abstract: Nickel-containing hydrotalcite-derived materials have been recently proposed as promising materials for methane dry reforming (DRM). Based on a literature review and on the experience of the authors, this review focuses on presenting past and recent achievements on increasing activity and stability of hydrotalcite-based materials for DRM. The use of different NiMgAl and NiAl hydrotalcite (HT) precursors, various methods for nickel introduction into HT structure, calcination conditions and promoters are discussed. HT-derived materials containing nickel generally exhibit high activity in DRM; however, the problem of preventing catalyst deactivation by coking, especially below 700 ◦C, is still an open question. The proposed solutions in the literature include: catalyst regeneration either in oxygen atmosphere or via hydrogasification; or application of various promoters, such as Zr, Ce or La, which was proven to enhance catalytic stability. Keywords: hydrotalcites; layered double hydroxides; dry reforming of methane; carbon dioxide; nickel 1. Introduction Our worldwide natural gas consumption increases yearly, i.e., in 2014, 12.9 Gtoe were consumed, which is 22.5% higher with the respect to the year 2004. Only in the last year, an increase of 1% in natural gas consumption has been observed [1]. This trend is predicted to develop even faster, since natural gas is the cheapest fossil fuel and possess the highest H/C ratio, contributing to lower CO2 emissions with respect to other fossil fuels [2]. Nevertheless, CO2 is still emitted in the energetic utilization of natural gas, e.g., 6.9 Gt of CO2 were emitted only in 2013, accounting for ca. 22% of total CO2 emissions [3]. Natural gas and carbon dioxide are therefore closely connected. Finding an appropriate solution to ease the environmental impact of these two gases is crucial for sustainable development in view of a low-carbon dioxide economy, and stays in line with international agreements and policies [4–7]. One of the routes considering the simultaneous energetic valorization of methane and CO2 is dry reforming of methane (DRM, Equation (1)). ◦ CH4 + CO2 2CO + 2H2 DH = 247 kJ/mol (1) The first investigations concerning the transformation of CO2 and CH4 into synthesis gas were reported in 1888. The process was further studied by Fischer and Tropsch in 1928 [8]. Although DRM is not quite a new concept, the dry reforming reaction has again gained considerable attention Catalysts 2017, 7, 32; doi:10.3390/catal7010032 www.mdpi.com/journal/catalysts Catalysts 2017, 7, 32 2 of 25 in our days, due to the possibility of utilizing two greenhouse gases for the production of a very valuable mixture of H2 and CO—a building block for the production of synthetic fuels and chemicals. Moreover, DRM can be used as a way of valorizing natural gas fields containing high amounts of CO2, whose extraction is currently economically unprofitable. The concentration of CO2 in such gas fields can vary from a few percent up to even 70%, as reported for a natural gas field in Indonesia [9]. The studies carried out by Suhartanto et al. [9] confirmed the feasibility of using DRM technology for the energetic valorization of this field, which contains ca. 1320 billion cubic meters of gaseous hydrocarbons.Catalysts 2017 Another, 7, 32 possibility is the use of dry reforming in exothermic-endothermic2 of 25 reaction cycle systemsand storage for of transport energy using andthe waste storage heat from of renewables energy or using nuclear theenergy waste to power heat endothermic from renewablesreactions [10–12], oras nuclear energy todepicted power in Figure endothermic 1. reactions [10–12], as depicted in Figure1. Figure 1.FigureChemical 1. Chemical energy energy storage storage concept, concept, using using heat from heat renewables from renewables or nuclear and or dry nuclear reforming and of methane dry reforming of methane(DRM (DRM)) and methanation and methanation as energy carriers. as energy carriers. The industrial applications of dry reforming are thus far limited to a combination of steam and dry reforming reactions. TheThe industrial addition of applicationsCO2 into the feed allows of dry a more reforming accurate control are of thus product far distribution, limited toi.e., agenerally combination resulting inof lower steam and dry reformingH2/CO molar reactions. ratios. Depending The addition on their application of CO2 ,into the different the feed processes allows differ a morein operating accurate parameters control and feed of product composition (e.g., SPARG–Sulfur Passivated Reforming or CALCOR–CO through CO2 Reforming processes) [13–17]. Their distribution, i.e., generally resulting in lower H2/CO molar ratios. Depending on their application, main goal is, however, to adjust syngas quality to the needs of its subsequent use, and not the valorization of CO2 itself. The the different processes differ in operating parameters and feed composition (e.g., SPARG–Sulfur particular conditions needed for DRM, are a direct consequence of its thermodynamic and kinetic barriers and hinder its Passivatedpractical Reforming industrial application. or CALCOR–CO The commercialization through of DRM CO process2 Reforming for syngas processes)production and [CO132– valori17].zation Their is yet main goal is, however,dependent to adjust on the offer syngas of a new qualityactive and stable to the catalyst. needs of its subsequent use, and not the valorization of During the last few decades, great efforts have been undertaken to develop highly active and stable DRM catalysts. The CO2 itself. The particular conditions needed for DRM, are a direct consequence of its thermodynamic deactivation of DRM catalysts is mainly caused by: (i) the formation of catalytic coke, which may result in the blockage of and kinetic barriers and hinder its practical industrial application. The commercialization of DRM pores and active sites; (ii) sintering of active materials, since DRM is carried out at a rather high temperature; and/or (iii) process foroxidation syngas of metallic production active sites. and The COuse of2 valorizationdifferent types of materials is yet dependent as catalyst supports, on the promoters offer and of apreparation new active and stable catalyst.methods can lead to overcoming these problems. DuringIn the general last, transition few decades, metals belonging great to 8, efforts 9 and 10 groups have of been the periodic undertaken table are active to materials develop for a DRM highly reaction. active and Despite the better performance of noble-metal-based catalysts, most of the reported research currently focuses on nickel-based stable DRM catalysts. The deactivation of DRM catalysts is mainly caused by: (i) the formation systems, since Ni is much cheaper and more available [18]. In comparison to other non-noble metals such as Fe or Co, nickel- of catalyticbased coke, catalysts which are less prone may to result coking [19]. in theThe research blockage on Ni-based of pores catalysts and is currently active dedicated sites; mainly (ii) sintering to increasingof active materials,their since stability. DRM The high is carried endothermicity out atof adry rather reforming high of methane temperature; requires high and/or temperatures (iii) (800 oxidation–1000 °C). This of metallic active sites.unavoidably Theuse leadsof to differentthe sintering typesof nickel ofparticles, materials since its asTammann catalyst temperature supports, is equal promoters to 600 °C [20]. and Moreover, preparation deactivation is substantially accelerated as a consequence of carbon deposition, since carbon-forming reactions are methodsthermodynamically can lead to overcoming favoured in the thesesame temperature problems. window and proceed more easily on large nickel crystallites [21]. In general,Several approaches transition have been metals therefore belonging proposed in order to to 8, increase 9 and the 10stability groups of Ni-based of thecatalysts periodic [22], such as: table are active materials for a DRM reaction. Despite the better performance of noble-metal-based catalysts, most (i) Employing an appropriate preparation method in order to control Ni crystal size and thus inhibit coke growth. of the reported(ii) Using metal research oxides with currently strong Lewis focuses basicity as on supports nickel-based or promoters, since systems, basic sites since enhance Ni CO is2 adsorption. much cheaperMetal and more availableoxides [ can18]. promote In comparison the oxidation of tocarbon other deposits non-noble (i.e. via the metalsreverse Boudouard such as reaction), Fe or but, Co, on nickel-basedthe other hand, the catalysts are less pronesupports to exhibiting coking Lewis [19 acidity]. The enhance research formationon of coke Ni-based deposits. catalysts is currently dedicated mainly (iii) Addition of a second metal, i.e., a noble metal, which may enhance the transport of hydrogen and/or oxygen between to increasingactive their sites and stability. support by spillover, The high and can endothermicity influence the mechanism of of dry coke reforming formation. Addition of methane of promoters, requiressuch as high ◦ temperaturesCe, Zr (800–1000 or La, in the aimC). of modifying This unavoidably the selectivity of the leads DRM process to the and/or sintering enhancing ofthe gasification nickel particles, of the carbon since its ◦ Tammann temperaturedeposits.
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