CeNiXAl0.5HZOY nano-oxyhydrides for H2 production by oxidative dry reforming of CH4 without carbon formation Yaqian Wei, Xiu Liu, Noura Haidar, Hervé Jobic, Sébastien Paul, Louise Jalowiecki-Duhamel To cite this version: Yaqian Wei, Xiu Liu, Noura Haidar, Hervé Jobic, Sébastien Paul, et al.. CeNiXAl0.5HZOY nano- oxyhydrides for H2 production by oxidative dry reforming of CH4 without carbon formation. Applied Catalysis A : General, Elsevier, 2020, 594, pp.117439. 10.1016/j.apcata.2020.117439. hal-03022420 HAL Id: hal-03022420 https://hal.archives-ouvertes.fr/hal-03022420 Submitted on 26 Nov 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. CeNiXAl0.5HZOY nano-oxyhydrides for H2 production by oxidative dry reforming of CH4 without carbon formation Yaqian Weia, Xiu Liua, Noura Haidar a, Hervé Jobicb, Sébastien Paula, and Louise Jalowiecki- Duhamela,* a Univ. Lille, CNRS, Centrale Lille, ENSCL, Univ. Artois, UMR 8181 – UCCS – Unité de Catalyse et Chimie du Solide, F-59000 Lille, France. b Institut de Recherches sur la Catalyse et I’Environnement de Lyon (IRCELyon), 69626 Villeurbanne Cedex, France. Corresponding author. Tel.: +33 (0)3 20 33 77 35; fax: +33 (0)3 20 33 65 61. E-mail address: [email protected] (L. Jalowiecki-Duhamel) Highlights: Mixed oxides based hydride reservoirs with Ni2+ cations are performant catalysts. CO2 conversion overcomes the predicted value at 500-600°C. H2/CO ratio of 1.3 is obtained at 600°C. No carbon formation at 600°C in O2/CH4 ratio of 0.3. Keywords: Hydrogen; Oxyhydride; CH4; CO2; Ceria, Nickel ABSTRACT The oxidative dry reforming of CH4 (ODRM) was studied at 500-800°C in harsh conditions -1 -1 (CH4/CO2/O2/N2 = 1:0.7::N2 with 20% of CH4, 96,000 mLh gcat and varying from 0 up to 0.5) on CeNiXAl0.5HZOY (0.5 ≤ x ≤ 5) nano-oxyhydride catalysts. At low temperature (500-600°C), the conversion of CH4 reaches the thermodynamic limit while those of CO2 overcomes the predicted value in particular at 500°C. At 600°C with an O2/CH4 ratio of 0.3, the CeNi2Al0.5HZOY catalyst allows getting CH4 and CO2 conversions of about 63% and 50 %, respectively, and a H2/CO ratio of about 1.3, without carbon 1 formation. The physico-chemical characterizations performed before and after test show the existence of strong interactions existing between Ni2+ cations with other cations and the presence of nano- oxyhydride compound. The mixed oxide based nano-materials corresponding to hydride reservoirs with the presence of Ni2+ cations are shown to be highly active, selective and stable catalysts. 1. Introduction Access to clean, affordable and reliable energy has been a cornerstone of the world’s increasing prosperity and economic growth since the beginning of the industrial revolution. Our use of energy in the 21th century must also be sustainable [1]. Hydrogen is seen as the “green” energy of the future while it is already largely used in chemical industry as an indispensable raw material. However up to date, hydrogen is mainly produced from fossil fuels and the main hydrogen production in industrial scale is the steam reforming of methane (SRM), an endothermic process, requiring high energy consumption. It is urgently desirable to produce hydrogen from renewable energy sources, such as biomass-derived materials and/or biogas. Biogas, a mixture of gases mainly containing CH4 and CO2, can be obtained by the anaerobic digestion of various bio-resources and the transformation of biogas has received growing interest [2-8]. Although operating at low temperature is of enormous importance because of environmental, economic and maintenance reasons; it remains a great challenge for CH4 and CO2 transformations in the same time [9,10]. The CO2 reforming with CH4 is an endothermic process, so called dry reforming (DRM, Eq.1). This type of reaction is attractive from an environmental point of view, since it consumes two major greenhouse gases [5-7,9-14]. However, the main drawback of DRM is the deactivation of the catalyst due to heavy carbon deposition (particularly at low temperature) [2-6,15] and the sintering of the active phase [5,6,11]. Co-feeding O2 with CH4 and CO2 (ODRM, Eq. 2) provides several advantages such as reducing the global energy requirement and enhancing catalyst stability, 2 by increasing deactivation resistance and inhibiting the carbon deposition rate by gasifying carbon species, however it decreases the CO2 conversion [10,11,16-27]. Avoiding carbon formation (Eqs. 3-6) at low temperature (500-600°C) and sintering of the active phase are still challenges. In the meantime, as for DRM, another drawback is the reverse water gas shift reaction (RWGS) that can decrease the selectivity in H2 by consuming it while it allows to transform CO2 (Eq. 7). Moreover, maintaining stability of the catalyst in presence of water that can be formed during reaction is also important, while water gas shift reaction (WGS) can increase H2 formation (Eq. 8). 0 1 CH4 + CO2 → 2CO + 2H2 ΔH 298K = + 247 kJ mol (1) 0 1 CH4 + aCO2 + (1-a)/2O2 → (1+a)CO + 2H2 ΔH 298K = (285a-41) kJ mol 0≤ a ≤1 (2) 0 1 2CO CO2 + C ΔH 298K = -171 kJ mol (3) 0 1 CH4 2H2 + C ΔH 298K = +76 kJ mol (4) 0 -1 CO2 + 2H2 C +2H2O ΔH 298K = 90 kJ mol (5) 0 -1 CO + H2 C + H2O ΔH 298K = 131 kJ mol (6) 0 1 CO2 + H2 → CO + H2O ΔH 298K = + 41 kJ mol (7) 0 1 CO + H2O CO2 + H2 ΔH 298K = - 41 kJ mol (8) Because of its high performance, Ni is one of the most studied metals for DRM of CH4 [5, 28-30], in particular in association with ceria [12-14] or when the catalyst is promoted with cerium allowing improving stability [31]. On some performant catalysts for dry reforming it has been shown that they are also effective in presence of O2 and even better performance could be obtained [ 32 ]. Coking phenomenon was found to be limited in case of highly dispersed metal species at the surface of the support. Moreover, among the different supports allowing high dispersion, CeO2 is widely known and largely studied due also to its excellent oxygen storage capacity, which might be favoring the oxidation 3 of the carbon deposits formed upon direct methane decomposition [5]. In general, better catalytic performance and lower carbon content are obtained. Besides, it has been shown that CO2 can be directly dissociated to CO and active oxygen species by the metal-ceria catalyst, donating oxygen to a lattice vacancy and producing CO [33] and that CO2 is activated in the defect sites of ceria, without noble metals, if the concentration of Ce3+ is high enough [34]. In the meantime, many studies have shown that the redox properties can be considerably enhanced if additional elements are introduced into the CeOY lattice by forming a solid solution [13,35]. It is known that CeO2-MOx solid solution has good thermal stability and better oxygen storage capacity than CeO2 alone [36]. Furthermore, it is often reported that the preparation method is of high importance [5], and usually, the coprecipitation method is used to increase the interactions between the cations [37] that can favor C-H bond activation at low temperature [12,13,38 , 39 ] . Besides, CO2 activation requires high temperature/pressure conditions and/or active reductants, such as hydrogen or can be activated under ambient conditions with the help of a solid state catalyst [40,41]. In particular, it has been shown that the presence of hydride species can be of great help for CO2 activation [42-45]. Our previous studies showed that CeNiXOY mixed oxides once transformed into oxyhydrides (solids storing hydride species, after pretreatment in H2 at particular temperature) are efficient catalysts in CH4 partial oxidation in presence of O2 [38,39], while beside adding another cation to the system allows increasing the hydrogen storage of the catalyst [46]. The current challenge is to tune and maintain nano- oxyhydrides containing cations in strong interaction to favor C-H bond activation at low temperature, with hydride species stored in the solid to facilitate CO2 activation. Herein we report the successful development of CeNiXAl0.5HZOY nano-oxyhydrides as highly active, selective and stable catalysts that are applied to low temperature CO2 and CH4 transformations for H2 production. The effect of different 4 parameters is studied such as the Ni content in the catalyst and the O2/CH4 ratio in the reaction mixture. Different physico-chemical characterizations are performed before and after test. In particular, Inelastic Neutron Scattering (INS) proves the presence of hydride species (H–). Furthermore, correlations between the catalyst properties and the catalytic performances are discussed, allowing us to participate to the open debate on this catalytic process and to propose an active site and a possible mechanism. 2. Experimental 2.1. Catalyst preparation CeNiXAl0.5Oy catalysts where x is the Ni/Ce atomic ratio, were prepared by coprecipitation of cerium, nickel and aluminum hydroxides from a mixture of their nitrate solutions. At first, the nitrate precursors (nickel nitrate hexahydrate 99%) Ni(NO3)2·6H2O, Ce(NO3)3·6H2O, and Al(NO3)3·6H2O were dissolved in distilled water, respectively, to get 0.5M solutions.