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.

The lanthanum ferrite perovskite (La_0.8FO) was synthesized using a citric combustion route and then modified with a porous graphitic nitride nanosheet via the wet impregnation-assisted ultrasonic method to produce La₀.₈FO@PgNS. Various techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet diffuse reflectance spectroscopy (UV-DRS), and Tauc plot analysis were employed to confirm the functional moieties, crystallinity, phase change, morphology, composition, and bandgap of La._0.8FO and La₀.₈FO@PgNS. La_0.8FO and La₀.₈FO@PgNS were used for the sonophotocatalytic oxidative degradation of sulfamethoxazole (SMX) under low energy and ultrasound wave frequency in the presence of visible light. La_0.8FO and La₀.₈FO@PgNS exhibited a sonophotocatalytic degradation capacity of 52.06 and 99.60%, respectively. Furthermore, the rate constant at the optimum condition of pH 7 and 5 mg L⁻¹ concentration was 0.01343 and 0.01494 min⁻¹ for La_0.8FO and La₀.₈FO@PgNS, respectively. The integration of sonolysis and photocatalysis in the remediation process of SMX resulted in a synergy of 2.5-fold. Ultrasonic waves and hydroxyl and superoxide radicals are the main species governing the degradation process while La₀.₈FO@PgNS was stable over 8 cycles, proving to be a sustainable material for environmental remediation.

Coking poses a significant challenge to the longevity and efficacy of catalysts in dry reforming of methane (DRM), particularly for nickel-based catalysts, which are widely used for their affordability and high catalytic activity. This study explores a recent approach integrating DRM with NO reduction to address coking-related deactivation, aiming to gasify carbon deposits and reduce NO simultaneously. Therefore, herein, NO conversion is achieved using the carbon undesired by-product of the DRM reaction, avoiding the use of valuable resources for NO conversion (such as NH₃), via an approach “from waste to value” that enhances the sustainability of the process. Four nickel-impregnated oxide supports (γ-Al₂O₃, MgAl₂O₄ coated γ-Al₂O₃, CaZrO₃, and LaFeO₃) were compared to understand the key properties of catalyst design. The best performances were obtained for supports with a high surface area and high interaction with metal particles (95% reactant conversion for Ni/γ-Al₂O₃) as they allowed stable activity and protection from NO oxidation. Supports with a lower surface area suffered from coke blockage of active sites, whereas no protection from oxidation led to complete deactivation of the active phase. The LaFeO₃ support stood out for its ability to protect Ni from NO oxidation by reducing NO. Overall, this study showed the importance of balancing NO oxidative power and coking issues, emphasizing the relevance of catalyst design in both protecting Ni from NO oxidation and avoiding coke blockage of the active sites via high surface area supports.

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.

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.