A synthesis strategy combining an impregnation approach with a self-combustion process to develop Ni-based catalysts (5–15 wt% of Ni) supported on mesoporous CeO2 is proposed. This strategy favors an intimate Ni–CeO2 coupling enabling a fine NiO dispersion in form of ultrasmall particles/clusters on CeO2. Comprehensive characterization, including XRD, Raman, N2-physisorption, HRTEM, STEM-EDXS/EELS, H2-TPR, CO2-TPD, and H2-TPD, revealed a strong metal–support interaction and promotion of oxygen vacancy formation. CO2 methanation testing under atmospheric pressure demonstrated high CO2 conversion and near-complete CH4 selectivity. At lower reaction temperatures, CO₂ conversion increased with Ni loading, which can be reasonably attributed to the higher concentration of oxygen vacancies. However, above 325 °C, the catalyst with the lowest Ni content exhibited performances comparable to the other samples, likely due to its very high Ni dispersion. Notably, a critical comparison with state-of-the-art systems, despite differences in operating conditions, highlighted the outstanding performance of the catalysts, particularly in terms of methane productivity (256-486 ), CO2 conversion (68-85 mol%) and CH4 selectivity (close to 100%) under mild conditions. The results place the obtained Ni–CeO2 catalysts among the most effective systems reported to date for CO2 methanation with strong potential for integration in sustainable catalytic technologies.

Mesostructured aluminosilicates, namely Al-MCM-41, Al-SBA-15, and Al-SBA-16, with distinct pore architectures (hexagonal vs. cubic) and Si/Al molar ratios of 10, 15, and 20 were investigated as acidic components in the one-pot CO2-to-dimethyl ether (DME) reaction. The materials were prepared through different synthesis routes, including conventional sol–gel, hydrothermal sol–gel, and evaporation-induced self-assembly (EISA), allowing the combined effects of synthesis method, aluminum incorporation, mesostructural organization, and textural properties to be examined. Catalytic tests demonstrate that the DME selectivity follows the trend Al-MCM-41 < Al-SBA-15 < Al-SBA-16, and also increases with decreasing Si/Al ratio within each material series. Solid-state NMR spectroscopy provides evidence for framework Al incorporation, while also revealing the co-presence of a fraction of extra-framework Al species. In particular, 27Al MAS NMR shows the coexistence of tetrahedrally coordinated Al, associated in part with framework Al sites, and extra-framework five- and six-coordinated Al species. High Al content leads to partial segregation into amorphous Al2O3, a phenomenon strongly influenced by the synthesis route and the mesostructure. Pyridine-adsorption FTIR reveals that total acidity follows the trend Al-MCM-41 > Al-SBA-15 > Al-SBA-16. However, when normalized per unit surface area, the acid site surface density follows the opposite trend, with Al-SBA-16 exhibiting the highest values. The Brønsted/Lewis ratio also increases from Al-MCM-41 to Al-SBA-16, indicating a progressively higher relative abundance of Brønsted acid sites, the key species for methanol dehydration. These results suggest that the enhanced DME selectivity of Al-SBA-16 arises from the combined effects of low surface area, higher Brønsted acid-site surface density, and favorable Al incorporation/speciation. Ultimately, this systematic study strengthens the hypothesis that the spatial proximity of Brønsted acid sites, rather than their absolute concentration, governs DME selectivity by facilitating the bimolecular methanol dehydration pathway.​

This work deals with the design of nanocomposite hydrogenation-dehydration bifunctional catalysts for the one-pot conversion of CO2 to dimethyl ether (DME), focusing on obtaining a high and homogeneous dispersion of a Cu-based CO2 hydrogenation phase into the pores of mesostructured supports. Particularly, three aluminosilicate mesostructured acid catalysts with catalytic activity towards methanol dehydration and featuring different porous structures (Al-MCM-41, Al-SBA-15, Al-SBA-16) were synthesized and used as supports to host a CuO/ZnO/ZrO2 (CZZ) CO2 hydrogenation catalyst for methanol synthesis. The use of a mesostructured support allows to maximize the exposed surface of the CO2 reduction function by nanostructuring it through its confinement within the mesochannels, thus obtaining nanocomposite bifunctional catalysts with an ultra-small hydrogenation nanophase. The nanocomposites were obtained using an impregnation strategy combined with a self-combustion reaction, allowing to incorporate the CO2 reduction phase inside the mesopores. In all cases, the characterization shows that the hydrogenation phase species are highly and homogeneously dispersed into the supports as either small nanoparticles or as a nanolayer. The as-obtained nanocomposites were tested for their catalytic activity and the results discussed taking into account the structural, textural, and acidic properties of the supports and nanocomposites.

Mesostructured aluminosilicates (Al-SBA-16) with Si/Al molar ratios of 10, 15, and 20 were synthesized and evaluated as methanol dehydration catalysts for the one-pot conversion of CO2 to dimethyl ether (DME). Increasing the Al content was expected to enhance activity by generating additional acid sites. Although catalytic tests confirmed higher DME selectivity at lower Si/Al (higher Al content), the gain was modest relative to the nominal increase in Al amount, motivating a closer examination of Al incorporation and its contribution to Bro̷nsted acidity. To address this, 27Al and 29Si solid-state NMR were combined with pyridine adsorption FT-IR. 27Al NMR resolved framework tetrahedral Al alongside extra-framework penta- and octa-coordinated species. Higher Si/Al ratios favored framework incorporation, whereas increased Al loading promoted segregation as amorphous Al2O3. 29Si MAS/CP-MAS supported partial framework substitution (subtle Q4 shift) together with a slight increase in Q3/Q2 (silanol/Si-O-Al) contributions. FTIR corroborated these findings, showing only a moderate increase in the amount of Bro̷nsted sites with decreasing Si/Al and a greater persistence of Lewis sites at high temperature. This work demonstrates that catalytic performance in CO2-to-DME conversion is controlled not only by the nominal Al content of Al-SBA-16 but also by the coordination and distribution of Al species between framework and extra-framework environments, establishing a direct structure-acidity-activity relationship that guides the design of more efficient aluminosilicate catalysts.

In this work, non-ordered and ordered CeO2-based catalysts are proposed for CO2 conversion to dimethyl carbonate (DMC). Particularly, non-ordered mesoporous CeO2, consisting of small nanoparticles of about 8 nm, is compared with two highly porous (635–722 m2/g) ordered CeO2@SBA-15 nanocomposites obtained by two different impregnation strategies (a two-solvent impregnation method (TS) and a self-combustion (SC) method), with a final CeO2 loading of 10 wt%. Rietveld analyses on XRD data combined with TEM imaging evidence the influence of the impregnation strategy on the dispersion of the active phase as follows: nanoparticles of 8 nm for the TS composite vs. 3 nm for the SC composite. The catalytic results show comparable activities for the mesoporous ceria and the CeO2@SBA-15_SC nanocomposite, while a lower DMC yield is found for the CeO2@SBA-15_TS nanocomposite. This finding can presumably be ascribed to a partial obstruction of the pores by the CeO2 nanoparticles in the case of the TS composite, leading to a reduced accessibility of the active phase. On the other hand, in the case of the SC composite, where the CeO2 particle size is much lower than the pore size, there is an improved accessibility of the active phase to the molecules of the reactants.

Cubic bi-magnetic hard-soft core-shell nanoarchitectures were prepared starting from cobalt ferrite nanoparticles, prevalently with cubic shape, as seeds to grow a manganese ferrite shell. The combined use of direct (nanoscale chemical mapping via STEM-EDX) and indirect (DC magnetometry) tools was adopted to verify the formation of the heterostructures at the nanoscale and bulk level, respectively. The results showed the obtainment of core-shell NPs (CoFe2O4@MnFe2O4) with a thin shell (heterogenous nucleation). In addition, manganese ferrite was found to homogeneously nucleate to form a secondary nanoparticle population (homogenous nucleation). This study shed light on the competitive formation mechanism of homogenous and heterogenous nucleation, suggesting the existence of a critical size, beyond which, phase separation occurs and seeds are no longer available in the reaction medium for heterogenous nucleation. These findings may allow one to tailor the synthesis process in order to achieve better control of the materials' features affecting the magnetic behaviour, and consequently, the performances as heat mediators or components for data storage devices.

In this work, we propose two bifunctional nanocomposite catalysts based on acidic mesostructured γ-Al2O3 and a Cu/ZnO/ZrO2 redox phase. γ-Al2O3 was synthesized by an Evaporation-Induced Self-Assembly (EISA) method using two different templating agents (block copolymers Pluronic P123 and F127) and subsequently functionalized with the redox phase using an impregnation method modified with a self-combustion reaction. These nanocomposite catalysts and their corresponding mesostructured supports were characterized in terms of structural, textural, and morphological features as well as their acidic properties. The bifunctional catalysts were tested for the CO2-to-DME process, and their performances were compared with a physical mixture consisting of the most promising support as a dehydration catalyst together with the most common Cu-based commercial redox catalyst (CZA). The results highlight that the most appropriate Pluronic for the synthesis of γ-Al2O3 is P123; the use of this templating agent allows us to obtain a mesostructure with a smaller pore size and a higher number of acid sites. Furthermore, the corresponding composite catalyst shows a better dispersion of the redox phase and, consequently, a higher CO2 conversion. However, the incorporation of the redox phase into the porous structure of the acidic support (chemical mixing), favoring an intimate contact between the two phases, has detrimental effects on the dehydration performances due to the coverage of the acid sites with the redox nanophase. On the other hand, the strategy involving the physical mixing of the two phases, distinctly preserving the two catalytic functions, assures better performances.

The catalytic performance in the direct CO2 methanation of a model biogas is investigated on NiO-CeO2 nanostructured mixed oxides synthesized by the soft-template procedure with different Ni/Ce molar ratios. The samples are thoroughly characterized by means of ICP-AES, XRD, TEM and HR-TEM, N2 physisorption at -196 & DEG;C, and H2-TPR. They result to be constituted of CeO2 rounded nanocrystals and of polycrystalline needle-like NiO particles. After a H2-treatment at 400 & DEG;C for 1 h, the surface basic properties and the metal surface area are also assessed using CO2 adsorption microcalorimetry and H2-pulse chemisorption measurements, respectively. At increasing Ni content the Ni0 surface area increases, while the opposite occurs for the number of basic sites. Using a CO2/CH4/H2 feed, at 11,000 cm3 h-1 gcat-1, CO2 conversions in the 83-89 mol% range and methane selectivities >99.5 mol% are reached at 275 & DEG;C and atmospheric pressure, highlighting the very good performances of the investigated catalysts.& COPY; 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

In this work, we designed four different mesostructured acidic materials to be used as methanol dehydration catalysts for the one-pot CO2-to-DME process, in the form of physical mixtures with a Cu/ZnO/Al2O3-based commercial redox catalyst (CZA). The studied systems consist in a mesostructured gamma-Al2O3 and three mesostructured aluminosilicates (namely Al-MCM-41, Al-SBA-15, and Al-SBA-16) with the same Si/Al ratio (= 15) but significantly different textural properties. The main goal of this work is to understand how the textural features can influence the acidic properties (typology, amount, strength, surface density) and, consequently, how catalytic performances can be correlated with acidic features. On this note, we found that the systems presenting both Bronsted and Lewis sites (namely the three aluminosilicates) show much better catalytic performances than gamma-Al2O3, that only features Lewis sites, thus implying that Bronsted sites are more active towards methanol dehydration than Lewis sites. The three aluminosilicates, despite presenting comparable amounts of Bronsted sites, show significantly different performances in terms of selectivity to DME; particularly, Al-SBA-16, the system with the lowest surface area, proved to be the most efficient catalyst. This finding led us to infer that, besides Bronsted acidity, a high surface density of acid sites is a key factor to obtain a high dehydration activity; being methanol dehydration a bi-molecular reaction, the close proximity of two acid sites would indeed favor the kinetics of the process.

Iron oxides/oxyhydroxides, namely maghemite, iron oxide-silica composite, akaganeite, and ferrihydrite, are studied for AsV and AsIII removal from water in the pH range 2–8. All sorbents were characterized for their structural, morphological, textural, and surface charge properties. The same experimental conditions for the batch tests permitted a direct comparison among the sorbents, particularly between the oxyhydroxides, known to be among the most promising As-removers but hardly compared in the literature. The tests revealed akaganeite to perform better in the whole pH range for AsV (max 89 mg g−1 at pH0 3) but to be also efficient toward AsIII (max 91 mg g−1 at pH0 3–8), for which the best sorbent was ferrihydrite (max 144 mg g−1 at pH0 8). Moreover, the study of the sorbents’ surface chemistry under contact with arsenic and arsenic-free solutions allowed the understanding of its role in the arsenic uptake through electrophoretic light scattering and pH measurements. Indeed, the sorbent’s ability to modify the starting pH was a crucial step in determining the removal of performances. The AsV initial concentration, contact time, ionic strength, and presence of competitors were also studied for akaganeite, the most promising remover, at pH0 3 and 8 to deepen the uptake mechanism.

Dimethyl ether (DME) production from hydrogenation of CO2 based on two-function (redox and acidic) catalysts is receiving increasing attention due to the high demand for alternative and green fuels. In this work, we propose different mesostructured acidic metal oxides as methanol dehydration catalysts to be used as physical mixtures in combination with a commercial Cu-based redox catalyst (CZA) for the CO2-to-DME one-pot production. Al-MCM-41, TiO2 and TiO2-ZrO2 mixed oxides, obtained through Sol-Gel methods, either in a conventional or Evaporation-Induced Self-Assembly approach were selected as mesostructured acidic systems and compared with a commercial zeolite (ferrierite). The regular mesoporous structure should render the active sites of the acidic catalyst easily accessible for CO2 and H2 and allow a homogeneous dispersion of the redox phase inside the mesopores in view of a possible development of bifunctional catalysts (redox + acidic). With the aim of understanding how the textural and acidic properties can be correlated with the performances and eventually design efficient dehydration catalysts, a careful study on the acidic sites was performed by both adsorption microcalorimetry with ammonia and FTIR-monitored adsorption of pyridine. The results of the performances highlighted a higher activity toward methanol dehydration for catalysts featured by Brønsted sites (zeolite and Al-MCM-41); as for catalysts with Lewis sites only (TiO2, Ti0.77Zr0.23O2) better performances were shown in case of systems presenting sites of moderate strength (Ti0.77Zr0.23O2). In the light of the above, Al-MCM-41 and TiO2-ZrO2 demonstrated to be the most promising mesostructured dehydration catalysts in terms of selectivity to DME.

Nanostructured spinel cobalt ferrite samples having crystallite size ranging between 5.6 and 14.1 nm were characterized by X-ray photoelectron spectroscopy and X-ray induced Auger electron spectroscopy in order to determine the chemical state of the elements, the iron/cobalt ratio and the cation distribution within tetrahedral and octahedral sites. The presence of size-dependent trends in the binding energy of the main photoelectron peaks and in the kinetic energy of the X-ray induced O KLL signal was also investigated. The results showed that iron is present as Fe-III and cobalt is present as Co-II. The iron/cobalt ratio determined by XPS ranges between 1.8 and 1.9 and it is in very good agreement, within experimental uncertainty, with the expected 2 : 1 ratio. The percentage of Fe in octahedral sites ranges between 62% and 64% for all samples. The kinetic energy of the O KLL signals increases with crystallite size. These results are explained in terms of changes in the ionicity of the metal-oxygen bonds. The results of this investigation highlight how the XPS technique represents a powerful tool to investigate the composition, the chemical state and inversion degree of cobalt spinel ferrites, contributing to the comprehension of their properties.