Jonathan Cavazzani

Syngas production via dry reforming of methane (DRM) represents a promising route for the valorization of carbon-based molecules, CH4 and CO2, in the emerging decarbonization era. However, the harsh operating conditions required by DRM demand highly active and robust catalysts to exploit this process for hydrogen production. In this context, the rational design of thermally stable catalysts with enhanced resistance to deactivation becomes essential. Herein, we focus on elucidating the structural and morphological evolution of Ni-, Ni–Co-, and Ni–Fe-doped titanates with a perovskite framework during guest cation incorporation and subsequent exsolution. Structural, compositional, and surface modifications were investigated by XRD, SEM, EDX, XAFS, N2 physisorption, and XPS. The catalytic performance of the exsolved materials was evaluated in DRM. The Ni-doped titanate (LSTNO-H) exhibited higher catalytic activity than Ni/γ-Al2O3 for CO2 conversion, reaching 80% conversion at 708 °C compared to 715 °C under short-term tests. However, the titanates still show room for improvement in long-term activity and durability. To elucidate the mechanisms governing catalyst deactivation, DRM tests were performed under diluted conditions, enabling a comparative assessment of structural and surface changes during reaction. Under such conditions, catalyst deactivation was mainly associated with nanoparticle sintering, with partial metal oxidation potentially contributing to activity loss, while no significant carbon deposition was detected. In contrast, the benchmark Ni/γ-Al2O3 catalyst showed carbon deposition, although no measurable deactivation occurred under the investigated conditions. Overall, this study highlights the potential of exsolution-based titanates for DRM while providing insights into the deactivation behavior of exsolved Ni under the investigated conditions.

We report a comprehensive structural investigation of La _0.45 Sr _0.45 TiO ₃ (LSTO) as a ceramic matrix for exsolution‐based fuel electrodes in solid oxide fuel cells and electrolyzers. Synchrotron radiation powder diffraction reveals an average cubic perovskite structure from room temperature to 900°C, even under the reducing exsolution conditions (5% H ₂ /Ar), where Ti ions occupy centrosymmetric sites. However, pre‐edge features of X‐ray Absorption Spectroscopy spectra at the Ti K‐edge indicate Ti off‐centering. Combined Pair Distribution Function analysis of synchrotron and neutron diffraction uncovers local distortion on the 2–3 nm scale. An a ⁻ a ⁻ c ⁺ octahedral‐tilting, coupled with Sr/La ordering in alternating planes perpendicular to the c axis, reduces the local symmetry to the orthorhombic P 2 ₁ am space group. Ti ions shift away from La ³⁺ ‐rich planes, exerting stronger electrostatic repulsion than Sr ²⁺ ‐rich ones, while oxygen ions are drawn toward them. This asymmetric environment creates the observed Ti off‐centering. Local distortions persist up to 900°C under a reducing atmosphere. Density Functional Theory calculations support this structural model and clarify the material's electronic structure. The highest occupied electronic states are primarily Ti‐derived, consistent with Ti reduction observed by XPS. Excess charge preferentially localizes on two of four Ti ions per orthorhombic cell, exhibiting weak ferromagnetic coupling.

The Dry Reforming of Methane (DRM) is an efficient route to produce syngas (which is the feedstock for the production of synthetic fuels via the Fischer–Tropsch process) or hydrogen from methane and carbon dioxide. This work evaluates several nickel-based perovskite-type mixed oxides (La_xNiO₃, La_0.8Ni_0.9M_0.1O₃ (M = Co, Fe and Mn) and La_0.8Ni_1−yCo_yO₃) as precursors of the active phase (Ni) for the DRM reaction. Although La_0.8NiO₃ yields slightly smaller Ni particles after reduction, it promotes the accumulation of a significant amount of carbonaceous material during DRM. Partial Ni substitution with Co, Fe and Mn improves redox stability, with the La_0.8Ni_0.75Co_0.25O₃ formulation being the most effective for removing the carbonaceous deposits under a 25% CH₄, 25% CO₂ (50% He) reactant atmosphere. However, when this formulation is used as a catalyst precursor for DRM under more realistic conditions (i.e., employing a feed that simulates real biogas), CH₄ conversion and H₂ yield decrease, and the carbon accumulated increases due to the greater influence of the parallel reactions. As a positive sign for future applications or research, under these conditions, the addition of 0.5% O₂ to the feed and the use of a CO₂ regeneration step decreased the amount of carbonaceous material deposited.

The exsolution process has emerged as an attractive synthesis method for supported metal nanoparticles (NPs) that can be applied to a wide variety of (electro/photo/thermo) catalytic reactions, thanks to the well dispersed and socketed nature of the produced NPs, offering high activity and stability in harsh conditions. Perovskite oxides have been the main choice as precursor and support for exsolved NPs, thanks to the ease of metal cation doping in this structure and the subsequent possibility to extract the doped element as metal NPs in reducing conditions (provided the doped metal cation is more reducible than the main perovskite cation). Both noble and non-noble metals can be doped into and exsolved from such oxide lattices. However, a detailed mechanistic understanding of the exsolution process is still largely lacking, concerning both the diffusion of exsolving metals and the changes occurring on the main perovskite cations. In this work, we performed a systematic investigation of the exsolution process from La0.9B0.9B’0.1O3 perovskites, with B = Mn or Fe, and B’ = Ni or Cu, synthesized through the citrate sol-gel method. Alongside the investigation of structural and chemical properties by ex-situ techniques (X-ray Diffraction, XRD; X-ray Photoelectron Spectroscopy, XPS; Temperature Programmed Reduction, H2-TPR), the exsolution process was followed through an in-situ X-ray absorption spectroscopy (XAS) experiment using synchrotron radiation. It was revealed that Cu, being highly reducible, can be easily exsolved from both Mn-based and Fe-based perovskites without structural decomposition. Ni, on the contrary, can still be appreciably exsolved from a LaFeO3-type matrix, but very hardly from a LaMnO3-type oxide: manganite being poorly stable at the temperatures needed to induce a significant Ni exsolution. In

The imperative reduction of carbon dioxide into valuable fuels stands as a crucial step in the transition towards a more sustainable energy system. Perovskite oxides, with their high compositional and property adjustability, emerge as promising catalysts for this purpose, whether employed independently or as a supporting matrix for other active metals. In this study, an A-site-deficient La_0.9FeO₃ perovskite underwent surface decoration with Ni, Cu or Ni + Cu via a citric acid-templated wet impregnation method. Following extensive characterization through XRD, N₂ physisorption, H₂-TPR, SEM-EDX, HAADF STEM-EDX mapping, CO₂-TPD and XPS, the prepared powders underwent reduction under diluted H₂ to yield metallic nanoparticles (NPs). The prepared catalysts were then evaluated for CO₂ reduction in a CO₂/H₂ = 1/4 mixture. The deposition of Ni or Cu NPs on the perovskite support significantly enhanced the conversion of CO₂, achieving a 50% conversion rate at 500 °C, albeit resulting in only CO as the final product. Notably, the catalyst featuring Ni-Cu co-deposition outperformed in the intermediate temperature range, exhibiting high selectivity for CH₄ production around 350 °C. For this latter catalyst, a synergistic effect of the metal–support interaction was evidenced by H₂-TPR and CO₂-TPD experiments as well as a better nanoparticle dispersion. A remarkable stability in a 20 h time-span was also demonstrated for all catalysts, especially the one with Ni-Cu co-deposition.

Carbon dioxide valorisation is one of the most discussed topics amongst researchers; indeed, finding a way to significantly reduce CO₂ concentration in the atmosphere is crucial in order to mitigate climate change effects in the next decades. In this study, SrTiO₃-supported Cu nanoparticles are exploited as Localised Surface Plasmon Resonance (LSPR)-mediated catalysts for CO₂ reduction. The materials were prepared via sol–gel citrate route methodology, inserting Cu as a dopant in the perovskite structure; reducing treatments at different temperatures were performed to promote copper atom exsolution, thus forming nanostructures upon the surface. The perovskitic structure was confirmed via ex situ and operando XRD analysis, while compositional analysis was carried out through XPS and EDS; SEM and TEM images revealed morphological changes with different reducing treatments, and bulk reducibility was analysed with H₂-TPR, revealing different Cu species in the material. Band gap analysis via DRS showed the successful incorporation of copper in the perovskite, affecting the light absorption properties. Finally, catalytic tests showed that copper nanoparticles play a role in CO₂ activation with sunlight, proving that LSPR could be exploited for catalytic means.

LaMnO₃-based perovskites are widely recognized as promising catalysts for several oxidation reactions, but the final physicochemical and catalytic properties can be greatly influenced by the adopted synthesis procedure. In this work, a series of A-site-deficient perovskites of composition La_0.8MnO₃ and La_0.8Mn_0.9B_0.1O₃ (B = Ni, Cu) were prepared through the citrate combustion route with variations in two synthesis parameters: a citric acid/metal cations molar ratio (CA/M) of either 1.1 or 1.5 and either acidic (given by HNO₃ + citric acid) or neutral (after NH₃ addition) pH of the precursor solution. The obtained samples were characterized by XRD, H₂-TPR, O₂-TPD, N₂ physisorption, SEM-EDX and XPS. Acidic pH coupled with a CA/M ratio of 1.1 clearly emerged superior among all the other combinations of the two parameters, resulting in smaller crystallite size, higher surface area and porosity, enhanced Mn⁴⁺ reducibility and the ability to release oxygen species; these features were even further improved by B-site substitution with 10 mol% Ni and Cu cations. The synthesized catalysts were tested in CH₄ oxidation to CO₂ under stoichiometric O₂, confirming the great superiority of samples prepared in acidic pH with a CA/M ratio of 1.1. Ni and Cu doping had a beneficial effect on catalytic activity, which, however, was more evident for less optimized perovskites (acidic pH and CA/M ratio of 1.5), without significance differences among the two dopants.

To promote the diffusion on the market of solid oxide fuel cell (SOFC) devices, the use of fuels other than the most appealing hydrogen and also decreasing the working temperature could show the way forward. In the first part, we concentrated our efforts on cathodes; hereby, we focused on anodes and concentrated our efforts to develop a sustainable multifuel anode. We decided to develop LSGF (La_0.6Sr_0.4Ga_0.3Fe_0.7O₃)-based nanocomposites by depositing manganite oxide to enhance the performance toward propane. MnO_x has been deposited by a wet impregnation method, and the powders have been largely characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction, oxygen temperature-programmed desorption, and N₂ adsorption. Cell performances were first collected in hydrogen as a function of both the temperature and hydrogen content. EIS measurements were studied using Nyquist and Bode plots, and they show two processes at high frequency, assigned to charge transfer at the electrode/electrolyte interface, and at low frequency due to the dissociative adsorption of hydrogen. The Arrhenius plot of area specific resistance suggests two different trends, and the activation energy decreases from 117 kJ/mol at 750 °C to 46 kJ/mol above that temperature. This behavior is often connected to chemical modification of the catalyst or changes in the limiting step processes. Power densities in hydrogen and propane were determined at 744 °C after 1 h of operation, achieving 70 mW/cm² in H₂ and 67 mW/cm² in C₃H₈. The open-circuit voltage increases from 1.10 V in hydrogen to 1.13 V in propane.

From the large plethora of energy – intensive synthetic processes, ammonia production is particularly impacting for the high energy consumption caused by the Haber Bosch process and for the high GHG emission rate. Thus, new and effective ways to activate N₂ and synthetise NH₃ are crucial to reduce production costs and the anthropogenic footprint derived from the current harsh reaction conditions. In this study, two dimensional materials have been employed in the photo activation of nitrogen in an aqueous medium; MI(II)MII(III) (with MI = Cu, CuNi and MII = Cr, Al) layered double hydroxides have been synthetised using a simple, economic and scalable co-precipitation/filtration method. The structural and functional properties were systematically investigated by XRD, SEM, TPR and BET; the results indicate that the prepared LDHs were successfully synthetised, possess high surface area and, in the case of CuAl LDH, the material showed a nanoplates – like structure, thus confirming the two-dimensional nature of this class of catalyst. The N₂ fixation performances were evaluated using a scalable, cost – effective and low consuming setup; from the catalytic tests, a NH₃ production of 99 µmol∙g^-1∙h^-1 was observed, demonstrating LDHs high potential and the scalability of overall process.