Discovered almost 130 years ago by P. Sabatier, CO2 hydrogenation to methane (CO2 methanation) is presently attracting attention as one of the most promising methods for storing intermittent renewable energy in the form of chemical fuels. Ni particles supported by CeO2 constitute a very effective, reliable, and reasonably priced catalyst for CO2 methanation. Recently a new type of CO2 methanation catalyst, consisting of cerium oxide (ceria) nanoparticles doped with nickel (NiCeOx) in a specific square‐planar configuration with an extremely high‐Ni mass‐specific activity and almost 100% CH4 selectivity, was reported. Here, a 50% enhancement in the CO2 conversion of the NiCeOx catalyst by carefully adjusting the calcination temperature is demonstrated. Notably, thermal aging at 600 °C enhances methanation performance by partially exsolving Ni to the surface, while higher temperatures (750 °C) lead to larger Ni particles, increased CO production, and surface carbon deposition. Several in situ and operando characterization methods are employed to correlate the thermal activation and deactivation of the catalyst with its nanoscale characteristics. Apart from their clear implications for the design of next‐generation Ni‐based CO2 methanation catalysts, these findings significantly enhance understanding of the complex interplay and nature of various surface sites involved in CO2 hydrogenation.

Germanium is known to occupy tetrahedral sites by substituting silicon in germanosilicate zeolites. In this study, we present pioneering findings regarding the synthesis of zeolites with an MFI structure (GeMFI) incorporating a high germanium amount (16% Ge). Remarkably, the germanium atoms feature a slight electron deficiency with respect to GeO2, and the typical coordination number of 4, as usually reported for the germanosilicate zeolites, is exceeded, giving rise to Ge dimers in a double-bridge configuration. Notably, the compensation of the ammonium template is achieved not through fluorine ions in the [415262] cages of the framework, as conventionally considered, but rather through oxygen. The GeMFI zeolite with the high Ge content reported in this work demonstrated exceptional thermal and hydrothermal stability, surpassing up to 1050 °C, thanks to both the double-bridge configuration and the defect-free structure. The unexpected role of germanium in MFI zeolite challenges previous assumptions, representing a paradigm shift in the understanding of porous germanosilicate structures, paving the way for a reevaluation of their synthesis, hydrolysis, and potential applications.

CO2 methanation, also known as the Sabatier reaction, is of great environmental interest as a sustainable process for energy production and storage. Herein, we report the development of a Ni-La2O3 catalyst for CO2 methanation prepared upon reduction of a LaNiO3 perovskite precursor. The perovskite-based catalyst exhibits enhanced activity, high methane selectivity and improved stability when compared to Ni-La2O3 prepared through conventional impregnation methods. The transformation of the LaNiO3 perovskite precursor upon thermal activation in H-2 was found to have a profound impact on the catalytic properties of the resulting material. The size and stability of exsolved Ni nanoparticles after prolonged reaction were investigated using ex situ electron microscopy. Synchrotron-based X-ray absorption fine structure (XAFS) spectroscopy, as well as soft and tender X-ray photoelectron spectroscopies (AP-XPS/HAXPES), provides detailed insights into the evolution of bulk and surface phases during the transition of the perovskite to its active catalytic state. Our findings indicate that processes beyond the well-established exsolution of nanoparticles, such as lanthana spillover onto nickel, may occur during H-2 activation. More importantly, in situ spectroscopy under CO2 methanation conditions revealed that the surface's affinity for La-hydroxide or La-carbonate formation significantly influences the reactivity. Specifically, we found that La-hydroxide acts as a precursor for the formation of La-oxycarbonate (hexagonal La2O2CO3 phase), a crucial element of the active exsolved catalyst. In contrast, in the absence of La-hydroxide, La-carbonates (La-2(CO3)(3)) formed on the surface, blocking the active sites of the supported catalyst. Our research examines hitherto unrecognized processes affecting the reactivity of exsolved perovskites, highlighting LaNiO3 as a promising catalyst for CO2 methanation.

The prismatic and basal plane surfaces of carbon materials dictate most of their anisotropic physicochemical properties. For many applications where interfacial interactions are key, high-temperature treatments are performed to achieve their graphitization. Such treatment changes edge and basal plane configuration, impacting the energetical behavior of the carbon surfaces, particularly for carbon nanomaterials, with consequences for their properties. Therefore, efforts should be devoted to probing the prismatic and basal plane surfaces of such materials to understand their surface properties for the development of high-performance carbon materials. Herein, we investigate the effect of high-temperature graphitization (3073 K) on the structural, textural, chemical, and magnetic properties of graphitic carbon nanomaterials presenting different prismatic/basal surfaces. The evolution of the prismatic/basal surfaces has been probed by nitrogen adsorption, temperature-programmed desorption, and X-ray photoelectron spectroscopy (XPS). Although these three techniques are in agreement for the starting materials, they diverge in the case of materials that have undergone thermal annealing. This is linked in particular to the formation of loops following the heat treatment, which are identified as belonging to the prismatic surface by XPS and modified the N2 adsorptive potentials. Formed small vacancies on closed loops and nonperfect closure of certain loops can contribute to the accumulation of very reactive defects at the loop level. The thermal annealing also has a pronounced influence on the magnetic properties of these materials. Interestingly, we show that a positive correlation exists between the spin density of the annealed graphitic carbons and their prismatic and basal surfaces.

Nickel/yttria-stabilized zirconia (YSZ) composites are the most commonly used fuel electrodes for solid oxide cells. While microstructural changes of Ni/YSZ during operational conditions have been thoroughly investigated, there is limited knowledge regarding Ni/YSZ surface chemistry under working conditions. In this study, we examine the interaction between Ni/YSZ electrodes and water vapor under open circuit and polarization conditions, utilizing near ambient pressure soft and hard X-ray photoelectron spectroscopies. Miniature cells with conventional porous Ni/YSZ composite cermet cathodes were modified to facilitate the direct spectroscopic observation of the functional electrode's areas close to the interface with the YSZ electrolyte. The results highlight dynamic changes in the oxidation state and composition of Ni/YSZ under H2 and H2O atmospheres. We also quantify the accumulation of impurities on the electrode surface. Through adjustments in the pretreatment of the cell, the correlation between the nickel surface oxidation state and the cell's electrochemical performance during H2O electroreduction is established. It is unequivocally shown that nickel surface oxidation in H2O electrolysis favors NiO over Ni(OH)x, providing critical insights into the mechanism of Ni-phase redistribution within the electrode during long-term operation. Depth-dependent photoemission measurements, combined with theoretical quantitative simulations, reveal that NiO and Ni phases are uniformly mixed on the surface during H2O electrolysis. This differs from the conventional expectation of a NiO-shell/Ni-core configuration in gas phase oxidation. These findings provide crucial insights into the surface chemistry of Ni/YSZ electrodes under conditions relevant to H2O electrolysis, elucidating their impact on the electrochemical performance of the cell.

The direct CO2 conversion to liquid fuels by catalytic hydrogenation (CO2-based Fischer-Tropsch synthesis, FTS), is a sustainable approach to reduce CO2 emissions. This challenging reaction proceeds through tandem catalysis involving reverse water gas shift reaction to produce CO and subsequent traditional CO-FTS. Unmodified Cobased catalysts allow performing the reaction at low temperatures (<250 C-degrees), albeit producing mainly methane. In this study, we modified a commercial TiO2-P25 support by NaBH4 reduction so as to introduce controlled amounts of promoters and oxygen vacancies. The modified and unmodified supports were used to prepare Co-based catalysts, which were evaluated for CO2-based FTS at 220-250 C and 20 bar. The promoted catalysts outperform the one prepared on commercial TiO2 in terms of activity and selectivity towards C5+. Detailed characterizations of the catalysts were performed to decipher the role of promoters. We show that, besides improving CO2 activation and limiting H2 activation, the presence of alkali on the support allows a modulation of hydrogen spillover in the system. The best catalyst in terms of activity and selectivity is the one for which sodium is deposited in sufficient amount to modulate the hydrogen spillover, which allows an optimal surface C/H ratio on cobalt.

Frustrated Lewis pairs (FLPs), discovered in the last few decades for homogeneous catalysts and in the last few years also for heterogeneous catalysts, are stimulating the scientific community's interest for their potential in small-molecule activation. Nevertheless, how an FLP activates stable molecules such as CO2 is still undefined. Through a careful spectroscopic study, we here report the formation of FLPs over a highly defective CeO2 sample prepared by microwave-assisted synthesis. Carbon dioxide activation over FLP is shown to occur through a bidentate carbonate bridging the FLP and implying a Ce3+-to-CO2 charge transfer, thus enhancing its activation. Carbon dioxide reaction with methanol to form monomethylcarbonate is here employed to demonstrate active roles of FLP and, eventually, to propose a reaction mechanism clarifying the role of Ce3+ and oxygen vacancies.

To address energy requirements via an optimally sustainable way is of high interest. A ternary hybrid based on natural protein, few layer graphene, and a nonprecious metal component is obtained by a rapid and green method bypassing high-temperature calcination. Its significant activity in H2 production via photo-reforming of methanol is related to the factors combining the nanosized related quantum confinement effect and small band gap, increased conduction band edge, and enhanced reducibility of FexO3 nanoparticles (size up to 2 nm). The albumin homogeneously decorating the FLG surface helps in the catalyst dispersion, reduction of photogenerated charge recombination, and MeOH adsorption. FexO3/Album/FLG shows great photostability and superior activity to the TiO2 based catalysts of reference.

CO2 hydrogenation to methane is gaining increasing interest as one of the most promising ways to store intermittent renewable energy in the form of chemical fuels. Ni particles supported on CeO2 represent a highly efficient, stable and inexpensive catalyst for this reaction. Herein, Ni-doped CeO2 nanoparticles were tested for CO2 methanation showing an extremely high Ni mass-specific activity and CH4 selectivity. Operando characterization reveals that this performance is tightly associated with ionic Νi and Ce3+ surface sites, while formation of metallic Ni does not seem to considerably promote the reaction. Theoretical calculations confirmed the stability of interstitial ionic Ni sites on ceria surfaces and highlighted the role of Ce-O frustrated Lewis pair (FLP), Ni-O classical Lewis pair (CLP) and Ni-Ce pair sites to the activation of H2 and CO2 molecules. To a large extent, the theoretical predictions were validated by in situ spectroscopy under H2 and CO2  : H2 gaseous environments.

Despite the considerable efforts to develop innovative electrode materials, nickel/yttria-stabilized zirconia (Ni/YSZ) electrodes are still employed in nearly all commercial and industrial solid oxide cell units. This is because Ni/YSZ cermets have good electrocatalytic activity in both electrolysis and fuel cell modes, while they are cost-effective as compared to alternative electrodes under development at the lab scale. Infiltration of nanoparticles has immersed as a promising concept to enhance the performance and robustness of conventional Ni/YSZ. Herein, we apply a relatively simple procedure to infiltrate Ni/YSZ electrodes with hexane solution containing prefabricated Ni-doped CeO2 nanoparticles. Cells with modified Ni/YSZ electrodes show a great improvement in the electrocatalytic activity and stability towards direct CO2 reduction as compared to unmodified cathodes. Besides, a single infiltration step is sufficient to achieve the optimum cell performance, streamlining the preparation process. More importantly, we show that this strategy can be equally efficient to fully reactivate previously degraded Ni/YSZ electrodes and restore their electrochemical performance at levels even higher than the initial ones. In addition, due to the high viscosity of the hexane solution, Ni-doped CeO2 nanoparticles access the entire electrode volume all the way close to the YSZ interface, while it penetrates the micro cracks between Ni and YSZ particles. In this way the electrocatalytic reaction zone is recovered, and the degraded Ni/YSZ electrode is reactivated. Physicochemical, microstructural and electrochemical characterization of the cells evinces several effects that contribute to the performance improvement of Ni/YSZ after infiltration, such as the enhanced surface reducibility of Ni and the amelioration of charge transfer processes within the electrode. The simplicity of the proposed infiltration method and the significant promotion in CO2 electroreduction activity, advocate it as a cost-efficient strategy to improve or regenerate conventional Ni/YSZ electrodes without significantly altering the already well-established fabrication process.

Since many decades nickel yttria-stabilized zirconia cermet (Ni/YSZ) has been the most frequently used fuel electrode material for high temperature solid oxide cells (SOCs). However, in recent years there has been considerable effort to improve the Ni/YSZ performance through surface engineering. In this work, we report a simple strategy to apply nanosized un-doped (CeOx) and Ni-doped (NiCeOy) ceria particles into porous Ni/YSZ cermet electrodes via infiltration from hexane solution. Detailed characterization of the particles in their solution revealed differences in the ease of agglomeration, with NiCeOy nanoparticles being better dispersed and thus forming smaller aggregates. This property is critical for the effectiveness of the solution in filling the pores of Ni/YSZ cermet and the consequent ceria deposition. In particular, morphological and microstructural characterization reveals that NiCeOy nanoparticles decorate uniformly the pores of Ni/YSZ backbone, deep up to the interface with the electrolyte. More importantly, this can be done with relatively high ceria loading per infiltration/co-firing step. Electrochemical tests demonstrate that infiltrated Ni/YSZ fuel electrodes have improved I-V performance in CO2 electrolysis as compared to pristine Ni/YSZ. Synchrotron-based operando NAP-XPS experiments using both soft and tender X-rays revealed the formation of an ultrathin Ni-Ce3+ layer on the electrode surface, which can rationalize the ameliorated CO2 electrolysis performance.

The oxidation of porous Ni-yttria-stabilized zirconia(YSZ)and Ni-gadolinia-doped ceria(GDC)ceramic-metal(cermet)electrodes in H2O and CO2 atmospheres was studied by near-ambient pressure X-ray pho-toelectron spectroscopy(NAP-XPS).We show that the oxidation of nickel by the two gases is not similar,as is commonly believed,but it depends on the ceramic type.Nickel is vulnerable to oxidation in H2O but it resists to CO2 in Ni-GDC,as compared to the Ni-YSZ electrode.Inspired by this observation we concep-tualize and fabricate Ni-YSZ electrodes modified by ceria nanoparticles,which show significantly higher resistance to CO2 oxidation as compared with conventional Ni-YSZ electrodes.The preparation of tailor-made cermet electrodes with identical bulk/mechanical characteristics but very different surface proper-ties offers a promising fabrication strategy for high-performance and durability solid oxide electrolysis cells for CO2 conversion.

This work presents an original approach to preparing pure and Ni-doped CeO2 nanoparticles (NPs) that can be directly drop-casted on a substrate or calcined to form powders. The reduction of the NPs in H-2 is very different than the one usually anticipated for supported Ni-CeO2 catalysts. In situ soft X-ray absorption and infrared spectroscopies revealed that the reduction of Ce4+ into Ce3+ in H-2 proceeds via simultaneous oxidation of Ni2+ ions into Ni delta+(2<delta<3). Comparison with reference samples indicates that Ce4+ ions reduction is promoted over Ni-doped CeO2 NPs, whereas that of Ni2+ is hindered. Theoretical simulation of Ni L-edge spectra suggested that Ni dopant into ceria is in a square planar four-coordinate environment, in contrast to the familiar octahedral symmetry of bulk nickel oxides. Our results reveal that the surface chemistry of Ni-doped CeO2 is quite distinct as compared to that of the individual bulk oxides, which potentially can lead to a different performance of this material, notably in catalytic applications. (C) 2022 Elsevier Ltd. All rights reserved.

Although sulfur has long been identified as a poison for Ni catalysts in CO-methanation, its association with Ni on a reducible support allows the selective formation of CO in CO2 hydrogenation.

A new high‐temperature detector dedicated to the collection of backscattered electrons is used in combination with heating stages up to 1050°C, in high‐vacuum and low‐vacuum modes in order to evaluate its possibilities through signal‐to‐noise ration measurements and different applications. Four examples of material transformations occurring at high temperature are herein reported: grain growth during annealing of a rolled platinum foil, recrystallisation of a multiphased alloy, oxidation of a Ni‐based alloy and complex phase transformations occurring during the annealing of an Al‐Si coated boron steel. The detector could be potentially adapted to any type of SEM and it offers good opportunities to perform high‐temperature experiments in various atmospheres.

Preferential oxidation of CO (COPrOx) is a catalytic reaction targeting the removal of trace amounts of CO from hydrogen-rich gas mixtures. Non-noble metal catalysts, such as Cu and Co, can be equally active to Pt for the reaction; however, their commercialization is limited by their poor stability. We have recently shown that CoO is the most active state of cobalt for COPrOx, but under certain reaction conditions, it is readily oxidized to Co3O4 and deactivates. Here, we report a simple method to stabilize the Co2+ state by vanadium addition. The V-promoted cobalt catalyst exhibits considerably higher activity and stability than pure cobalt. The nature of the catalytic active sites during COPrOx was established by operando NAP-XPS and NEXAFS, while the stability of the Co2+ state on the surface was verified by in situ NEXAFS at 1 bar pressure. The active phase consists of an ultra-thin cobalt-vanadate surface layer, containing tetrahedral V5+ and octahedral Co2+ cations, with an electronic and geometric structure that is deviating from the standard mixed bulk oxides. In addition, V addition helps to maintain the population of Co2+ species involved in the reaction, inhibiting carbonate species formation that are responsible for the deactivation. The promoting effect of V is discussed in terms of enhancement of CoO redox stability on the surface induced by electronic and structural modifications. These results demonstrate that V-promoted cobalt is a promising COPrOx catalyst and validate the application of in situ spectroscopy to provide the concept for designing better performing catalysts.

The preferential oxidation of CO in H2-rich mixtures (COPrOx) is a major catalytic reaction utilized for hydrogen purification. In the exploration of alternatives to noble metals, cobalt-based catalysts appear to be a very promising choice. The activity and stability of cobalt in the COPrOx reaction can be improved by the addition of transition metals and manganese is maybe the most prominent among them. Yet, the arrangement of the two components in the catalytically active state is largely unknown, which hinders in-depth understanding of the manganese promotion effect. Here, we compare pure and Mn-modified cobalt catalysts and correlate their structural and chemical characteristics with their COPrOx performance. The Mn-promoted cobalt catalyst is significantly more active than pure cobalt especially at intermediate reaction temperatures (around 200 degrees C). The addition of Mn improves the structural stability of the catalyst and helps to maintain higher specific surface areas. Chemical and microstructural analysis using various operando and in situ techniques revealed that Mn promotes CO conversion by partially stabilizing CoO phase during reaction conditions. It is also suggested that at high temperature, Mn suppress CO methanation reaction but promotes H2 oxidation. Apart of the particular interest in COPrOx reaction, in a general context, this work shows how the spatial distribution of the different catalyst components at nanoscopic level, may affect the surface chemistry and consequently control the reactivity.

Ethylene dehydroaromatisation (EDA) was investigated at 700 °C under 1 bar of ethylene (5 mol% in N2) over a micro-(M) and a nano-sized (N) H-ZSM-5. On the M zeolite an induction period followed by deactivation was observed, which could be related to the presence of long diffusion path lengths in this sample, leading to mass transfer resistance. During the induction step, the aromatics yield increases, despite a significant loss of the acid site concentration as a result of coking. This induction period corresponds to the formation of an active hydrocarbon pool (HCP) composed of units of 2 to 5 aromatic rings with a molecular weight ranging from 130 to 220 g mol−1 (light coke). A kinetic study revealed that the developing HCP species is two times more active than Brønsted acid sites in the fresh zeolite. Diffusion limitations yet impact the product desorption by promoting coke growth and, therefore the deactivation of the HCP and hence of the catalyst. From MA-LDI/LDI-TOF MS (Matrix Assisted Laser Desorption Ionization—Time of Flight Mass Spectroscopy) characterisation was deduced that even after complete catalyst deactivation, the as-deposited coke continues growing at the external surface of the zeolite by condensation reactions, thus leading to heavy coke composed of more than 100 carbon atoms and a molar mass exceeding 1300 g mol−1. Unlike the micro-sized zeolite, the nano-scaled zeolite features a short diffusion path length and promotes fast formation of the active HCP. As a result, higher activity and selectivity into benzene were observed, whilst catalyst deactivation was significantly mitigated.

The Selective Catalytic Reduction (SCR) is one of the most efficient process for NOx removal from Diesel exhaust gas. However, the urea/NH3-SCR process implemented in recent vehicles still suffers from a poor activity in the low temperature range (T < 250 degrees C). One main reason is its dependency against the NO2/NOx ratio, limiting the expected fast-SCR reaction in this temperature range. Recently, we shown that the addition of ethanol to ammonia led to a significant increase of the activity of a Ag/Al2O3 catalyst in this low temperature range. Moreover, in a dual-bed configuration (Ag/Al2O3 + WO3/Ce-x-ZryO2), a remarkable improvement was achieved at low temperature using only NO as NOx. The present work aims to highlight the DeNO(x) chemistry encountered over the WO3/Ce-x-ZryO2 catalyst in a bifunctional (EtOH + NH3) mixture. In addition to the fact that this process takes advantage of the low temperature NO2 formation over the upstream Ag/Al2O3 catalyst, this work also puts in evidenced unexpected interactions between NO2 and CH3CHO (resulting from ethanol oxidation over Ag/Al2O3) thus leading to NO emission.

High-temperature scanning electron microscopy allows the direct study of the temperature behavior of materials. Using a newly developed heating stage, tilted images series were recorded at high temperature and 3D images of the sample surface were reconstructed. By combining 3D images recorded at different temperatures, the variations of material roughness can be accurately described and associated with local changes in the topography of the sample surface.