Bimetallic PtNi/CeO2 catalysts were successfully synthesized via a mechanochemical approach, specifically ball milling, and evaluated for methane steam reforming (MSR). A fractional factorial design of experiments was employed to systematically explore the effects of key milling parametersmilling frequency, milling time, and ball-to-powder ratioon the catalysts' structural properties and catalytic performance. The catalysts were characterized by X-ray diffraction, H2 temperature-programmed reduction, transmission electron microscopy, and Raman spectroscopy. Catalytic activity tests were performed in a plug flow reactor under a high gas hourly space velocity (200,000 mL gcat -1 h-1) at a steam-to-carbon ratio of 2 between 700 and 950 °C. The mechanochemically synthesized catalysts were benchmarked against those prepared via incipient wetness impregnation. The most active milled catalysts achieved a methane conversion rate of ca. 22 mol CH4 gNi -1 h-1 at 700 °C (83.5% methane conversion for a PtNi/CeO2 mechanochemically synthesized), outperforming the impregnated counterpart (64% methane conversion under the same reaction conditions). Notably, increasing the milling intensity resulted in enhanced catalytic activity, with milling frequency emerging as the most influential factorcorrelating with the formation of smaller NiO particles. To elucidate the role of Pt addition, in situ X-ray absorption near-edge structure (XANES) and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) measurements were conducted on the most active milled catalysts under MSR conditions. NAP-XPS revealed surface segregation of Pt during MSR, alongside an inhibitory effect on solid carbon deposition, suggesting the potential for a coke-resistant catalyst. These findings highlight the power of mechanochemical synthesis in tuning catalyst properties, offering a scalable and efficient route to high-performance catalysts for methane reforming and hydrogen production.

This study explores the impact of electron beam irradiation (EBI) on the structural and catalytic properties of cerium dioxide (CeO2) and palladium supported on ceria (PdO x /CeO2) catalysts synthesized by incipient wetness impregnation and vibratory ball milling. All materials were subjected to controlled electron beam irradiation (10 MeV) for different absorption doses (from 2.5 to 10 MGy) and subsequently characterized using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron microscopy (SEM and HRTEM). Catalytic performance was assessed through CO oxidation as a model reaction. The results reveal significant irradiation-induced modifications in surface chemistry, crystallinity, and Pd speciation depending on the synthesis method. Notably, EBI enhanced catalytic activity across both catalyst systems, primarily through the appearance of structural defects and the formation of PdO x -Ce interfacial sites and metallic Pd species.

Cu-based catalysts are highly attractive for CO2 hydrogenation to methanol due to their efficiency, selectivity, and cost-effectiveness. To further accelerate methanol synthesis, dual-site activation mechanisms are particularly effective. In this direction, solid solutions serve as effective supports, enhancing methanol production through improved hydrogenation, though the exact nature of the active sites in CuGa-based solid solutions remains unclear. In this study, we examine the synergistic interactions between Ga and Cu nanoparticles/clusters deposited on Ce0.9Zr0.1O2 for CO2-to-methanol hydrogenation. Through in situ diffuse reflectance infrared Fourier transform spectroscopy and temperature-programmed (TPR/TPD), we analyze the nature of the active sites and elucidate the reaction pathway. The results demonstrate that CO2 adsorption and activation are favored by the appropriate Cu/Ga ratio, while Ga sites, in addition to Cu, play a critical role in promoting H2 dissociation under methanol synthesis conditions. Furthermore, the oxygen vacancies in the CuGa/Ce0.9Zr0.1O2 catalyst play a crucial role in stabilizing the key *HCOO intermediate, facilitating its further hydrogenation to methanol via the formate pathway. This synergy between Ga and Cu optimizes both CO2 activation and hydrogenation steps, emphasizing Ga as an active site alongside Cu and highlighting the catalyst’s potential for efficient methanol production from CO2.

Copper-based catalysts are highly promising for carbon dioxide (CO2) reduction to carbon monoxide (CO) via the reverse water-gas shift (RWGS) reaction, owing to their efficiency, copper abundance, sustainability and costeffectiveness. However, enhancing CO2 conversion and CO selectivity requires achieving high copper dispersion through a scalable and economical synthesis method. In this study, Cu was combined with CeO2 rods via a mechanochemical ball-milling approach to optimize performance in the RWGS reaction. Comprehensive characterization and kinetic analysis revealed how metal content influences catalyst architecture and activity. Additionally, in situ diffuse reflectance infrared Fourier transform spectroscopy was used to investigate the nature of copper species at different dispersion levels and elucidate the reaction pathway. Notably, the Cu/CeO2 catalyst with a high Cu loading (similar to 5 wt%) and well-dispersed active sites achieved an activity (R-Cu(CO2)) of 4.8 lozenge 10(-5) mol(CO2) m(Cu)(- 2) s(-1) with over 99% CO selectivity at 450 degrees C. These findings provide a robust strategy for developing high-performance Cu-based catalysts for the RWGS reaction.

The positive effect of Eu3+ doping on the stability of the Ru/ceria catalyst during the methane steam reforming (MSR) reaction, which was used for H2 production, was observed. The effect is attributed to a significant inhibition of coking-induced deactivation of the catalyst by Eu doping, which we explain by three hypotheses. The first one is an increase in basicity with Eu doping, which inhibits carbon deposition on the working catalyst during the MSR reaction. The second one is that Eu addition introduces strain into the ceria lattice, which could facilitate oxygen diffusion and, as a consequence, prevents catalyst's coking. The third one is related to the presence of an additional high-temperature pathway for supplying lattice oxygen based on Eu3+ → Eu2+ reduction on the surface of the Eu-doped ceria support.

Dry reforming of methane (DRM) offers a promising route to convert biogas into syngas while capturing CO2. However, the harsh reaction conditions (>= 700 degrees C) lead to rapid deactivation of conventional Ni-based catalysts due to carbon deposition and sintering. In this work, we explore the catalytic behavior of commercial Raney-Ni for DRM and introduce electrochemically synthesized CoNi microparticles as co-catalysts to enhance stability and performance. Catalyst screening was performed in a fixed-bed reactor using a CH4:CO2:N-2 = 3:2:10 feed mixture under atmospheric pressure. Raney-Ni showed high activity (CH4 conversion >92 % at 700 degrees C), but suffered from coke accumulation and deactivation after 5 h of continuous operation. CoNi-Raney-Ni composites were prepared via physical blending of CoNi and Raney-Ni powders, and tested at various compositions. The best-performing among the tested compositions (25 wt% CoNi) maintained high conversion (>90 %) and stable syngas production (H-2/CO approximate to 1.0) over extended periods. Post-reaction analysis revealed extensive filamentous carbon on pure Raney-Ni, while CoNi-containing catalysts exhibited smoother surfaces and suppressed graphitic carbon, as confirmed by FE-SEM and Raman spectroscopy. Notably, CoNi alone showed minimal CH4 activation but enhanced CO2 dissociation and limited carbon formation. These results demonstrate a synergistic effect, where CoNi promotes carbon gasification while Raney-Ni provides high CH4 reactivity. This composite approach enables scalable, low-cost catalysts with improved coke tolerance for biogas reforming applications.

Additive manufacturing (AM) technologies are revolutionizing the production of ceramic components, particularly in fields like catalysis, where complex shapes offer remarkable advantages in performance. AM also minimizes material waste while reducing the number of fabrication steps. This work is focused on the fabrication of Ni/gamma-Al2O3 monoliths for CO2 methanation in one step by using Direct-Ink Writing (DIW) of Ni-enriched hydrogel-based gamma-Al2O3 inks, and the debinding and sintering in a single thermal treatment. For this purpose, the influence of Ni precursor amount (2.5-5.0 wt% Ni) on the rheological properties of inks and the catalytic activity is investigated. Monoliths with woodpile architecture and 50 % infill are sintered at 450 degrees C and 600 degrees C to determine the effect of the sintering temperature on the Ni distribution in the catalyst. Results evidence successful incorporation of the metallic active phase into the monolithic structures. Both the Ni amount and sintering temperature are key factors to enhance the CO2 methanation performance. The 5.0 wt% Ni monolith sintered at 450 degrees C presents both the highest CO2 conversion and methane selectivity at 350-500 degrees C, due to better reduction degree, dispersion, and smaller size of Ni nanoparticles at the maximum metal loading. These remarkable results demonstrate the potential of DIW for the fabrication of fully 3D-printed monolithic catalysts with well-dispersed metal particles, all while minimizing production steps.

Additive manufacturing enhances the catalyst performance via hierarchical design. To address environmental and resource concerns, this work aims to fabricate directly recycled 3D-printed monoliths using Direct-Ink Writing (DIW) from 100 % recovered cobalt-zirconia powders. Virgin cobalt-zirconia monoliths were firstly fabricated by DIW of 3.0-7.0 wt% Co-enriched hydrogel-based ceramic inks, followed by calcination at 600 degrees C in a single thermal treatment. After testing the catalytic performance of monoliths in ethanol steam reforming, 3Dprinted cobalt-zirconia monoliths were fragmented and subjected to subsequent milling and sieving steps to recover composite cobalt-zirconia powders with the appropriate properties for reuse in DIW. The recovered powders, inks and monoliths were microstructurally, rheologically and catalytically characterized, and then compared to catalysts constituted by virgin materials. The rheology properties of inks for the recycled and virgin monoliths presented an appropriate printability. Furthermore, the catalytic performance of recycled monoliths was close to that exhibited by virgin catalysts. This study demonstrates the feasibility of directly recycling fully 3D-printed catalysts, potentially reducing the environmental impact with a circular production model to enhance sustainability in the catalyst industry.

Amorphous metallic alloys, with their liquid‐like atomic‐scale structure, are promising candidates for developing unprecedented heterogeneous catalysts due to their non‐equilibrium, highly disordered state. This study explores the combination of copper‐based metallic glasses with crystalline ceria as catalysts for CO oxidation and preferential CO oxidation. The amorphous/crystalline interfaces are synthesized mechanochemically, offering a cost‐effective alternative to the use of precious metals while maintaining high catalytic activity. Key parameters of the ball milling process are optimized, namely milling time and frequency, to enhance the interaction between the disordered metal and crystalline ceria, and the new catalysts are thoroughly characterized using ex situ techniques (XRD, DSC, HAADF‐STEM‐EDX, H 2 ‐TPR, Raman spectroscopy, and XPS), and under operando conditions (XAFS and NEXAFS). These analyses reveal that the amorphous/crystalline architectures play a crucial role in catalytic performance. The results show that combining amorphous Cu‐based metallic glasses with crystalline CeO 2 delivers remarkable catalytic activity in preferential CO oxidation ( T 50 = 115 °C; 43.1 ± 0.4 mol CO 2 min −1 g catalyst −1 ), pointing to a sustainable and efficient design strategy of catalysts. This approach reduces reliance on noble metals while leveraging the synergy between structural disorder and crystallinity, thereby opening new directions for next‐generation catalyst development.

Developing active and stable catalysts for carbon-free hydrogen production is crucial to mitigate the effects of climate change. Ammonia is a promising carbon-free hydrogen source, as it has a high hydrogen content and is liquid at low pressure, which allows its easy storage and transportation. We have recently developed a nickel-based catalyst with a small content of ruthenium supported on cerium oxide which exhibits high activity and stability in ammonia decomposition. Here we investigate mechanochemical milling for its synthesis, a faster and less energy-consuming technique than conventional ones. Results indicate that mechanochemical synthesis increases catalytic activity compared to the conventional incipient wetness impregnation method. The interaction between the metal precursors and the support is key in fine-tuning catalytic activity, which increases linearly with oxygen vacancies in the support. Moreover, the mechanochemical method modifies the oxidation state of Ni and Ru species, with a variation depending on the precursors.

Ni-Fe nanocatalysts supported on CeO2 have been prepared for the catalysis of methane steam reforming (MSR) aiming for coke-resistant noble metal-free catalysts. The catalysts have been synthesized by traditional incipient wetness impregnation as well as dry ball milling, a green and more sustainable preparation method. The impact of the synthesis method on the catalytic performance and the catalysts' nanostructure has been investigated. The influence of Fe addition has been addressed as well. The reducibility and the electronic and crystalline structure of Ni and Ni-Fe mono- and bimetallic catalysts have been characterized by temperature programmed reduction (H2-TPR), in situ synchrotron X-ray diffraction (SXRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Their catalytic activity was tested between 700 and 950 °C at 108 L gcat-1 h-1 and with the reactant flow varying between 54 and 415 L gcat-1 h-1 at 700 °C. Hydrogen production rates of 67 mol gmet-1 h-1 have been achieved. The performance of the ball-milled Fe0.1Ni0.9/CeO2 catalyst was similar to that of Ni/CeO2 at high temperatures, but Raman spectroscopy revealed a higher amount of highly defective carbon on the surface of Ni-Fe nanocatalysts. The reorganization of the surface under MSR of the ball-milled NiFe/CeO2 has been monitored by in situ near-ambient pressure XPS experiments, where a strong reorganization of the Ni-Fe nanoparticles with segregation of Fe toward the surface has been observed. Despite the catalytic activity being lower in the low-temperature regime, Fe addition for the milled nanocatalyst increased the coke resistance and could be an efficient alternative to industrial Ni/Al2O3 catalysts.

A mechanochemical synthesis method has been used to synthesize CoRu nanoparticles supported on CeO2 for methane dry reforming. In this work, we study the effect of Ru addition to Co/CeO2-based catalysts and of the synthesis method by screening their catalytic activity, using synchrotron X-ray diffraction (XRD), and operando near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). Ruthenium addition directly impacts the reducibility of cobalt species and results in smaller particle sizes, as demonstrated by H-2-temperature programmed reduction and XRD. NAP-XPS shows that Ru modifies the metal-support interaction, as evidenced by the higher Ce3+/Ce ratios for the bimetallic samples and tuning the oxidation state of Ru. The synthesis method also influences the dispersion of Co and Ru on the surface. Mechanochemically-prepared samples (mono- and bimetallic) outperformed the conventionally-synthesized counterparts by reaching higher CH4 and CO2 conversions, resulting in a stable CoRu/CeO2 catalyst for 24 h at 700 degrees C and yielding an H-2/CO ratio close to 1.

A stable Pd0/Pd2+ arrangement generated on Pd/CeO2 prepared by mechanochemistry enables high methane activation rates in the absence of excess oxygen being available.

Supported Pd/CeO2 catalytic systems have been widely investigated in the low-temperature oxidation of CO (LTO CO) due to the unique oxygen storage capacity and redox properties of the ceria support, which highly influence the structural, chemical and electronic state of Pd species. Herein, operando near-ambient pressure XPS (NAP-XPS) technique has allowed the study of a conventional Pd/CeO2 catalyst surface during the CO oxidation reaction under experimental conditions closer to the actual catalytic reaction, unfeasible with other surface science techniques that demand UHV conditions. SEM, HRTEM and XRD analyses of the powder catalyst, prepared by conventional incipient wetness impregnation, reveal uniformly CeO2-loaded Pd NPs of less than 2 nm size, which generated an increase in oxygen vacancies with concomitant ceria reduction, as indicated by H2-TPR and Raman measurements. Adsorbed peroxide (O22−) species on the catalyst surface could also be detected by Raman spectra. Operando NAP-XPS results obtained at the ALBA Synchrotron Light Source revealed two kinds of Pd species under reaction conditions, namely PdOx and PdII ions in a PdxCe1−xO2−δ solution, the latter one appearing to be crucial for the CO oxidation. By means of a non-destructive depth profile analysis using variable synchrotron excitation energies, the location and the role of these palladium species in the CO oxidation reaction could be clarified: PdOx was found to prevail on the upper surface layers of the metallic Pd supported NPs under CO, while under reaction mixture it was rapidly depleted from the surface, leaving a greater amount in the subsurface layers (7% vs. 12%, respectively). On the contrary, the PdxCe1−xO2−δ phase, which was created at the Pd–CeO2 interface in contact with the gas environment, appeared to be predominant on the surface of the catalyst. Its presence was crucial for CO oxidation evolution, acting as a route through which active oxygen species could be transferred from ceria to Pd species for CO oxidation.

Photocatalysts based on TiO2 and its modification have become popular as promising materials for the sus-tainable photoproduction of hydrogen. In this work, novel Pt -Cu -TiO2 composites with different TiO2 nano -shapes and modified with biomass-derived reduced graphene oxide (rGO) are reported as promising photocatalysts for the generation of hydrogen from water-alcohol mixtures. The developed photocatalyst has been characterized by X-ray diffraction, X-ray fluorescence spectroscopy, Raman and Fourier-transform infrared spectroscopies, scanning electron microscopy and Brunauer-Emmett-Teller surface area analysis. The partial replacement of platinum with copper definitely lowered the cost of hydrogen photoproduction still keeping its high efficiency. Furthermore, the additional modification of the composite with rGO successfully boosted the amount of generated H2, which was ca. 27 mmol h-1 g-1.

Efficiently treating methane emissions in transportation remains a challenge. Here, we investigate palladium and platinum mono- and bimetallic ceria-supported catalysts synthesized by mechanical milling and by traditional impregnation for methane total oxidation under dry and wet conditions, reproducing those present in the exhaust of natural gas vehicles. By applying a toolkit of in situ synchrotron techniques (X-ray diffraction, X-ray absorption and ambient pressure photoelectron spectroscopies), together with transmission electron microscopy, we show that the synthesis method greatly influences the interaction and structure at the nanoscale. Our results reveal that the components of milled catalysts have a higher ability to transform metallic Pd into Pd oxide species strongly interacting with the support, and achieve a modulated PdO/Pd ratio than traditionally-synthesized catalysts. We demonstrate that the unique structures attained by milling are key for the catalytic activity and correlate with higher methane conversion and longer stability in the wet feed.

3D-printed ceria structures have been prepared by robocasting, without using any additive, and impregnated with different amounts of Ni and Ru, characterized and tested for the catalytic decomposition of ammonia in a fixed bed reactor. The best catalytic performance has been achieved with an active phase of 0.5Ni0.1Ru (w/w%). A kinetic expression has been obtained using a crushed catalytic structure, which has been employed in a 1D model to simulate the behaviour of the Ni-Ru impregnated 3D-printed ceria structures. The results have been compared with the experimental data to validate the proposed model. A series of simulations have been performed to determine the relationship between the geometric parameters of the 3D-printed structures and their catalytic performance in the ammonia decomposition, in order to optimize the catalytic structure with the aim of supplying the hydrogen produced to a PEM-type fuel cell.

Ceria-supported Ni-Ru bimetallic catalysts with different metal loadings have been prepared by co-impregnation, characterized and tested in the production of hydrogen from the catalytic decomposition of ammonia. The bimetallic catalysts showed an excellent catalytic performance in long-term stability tests with respect to monometallic Ru/CeO2 and Ni/CeO2 and in multicycle tests under pure ammonia. The best catalytic performance has been obtained over catalysts with 2.4-5 wt.% Ni, 0.4-0.6 wt.% Ru, and a Ni/Ru wt.% ratio of ca. 7. TOFH2 values exceeding 2 s(-1) have been obtained, which are among the highest reported for ammonia decomposition at 400 degrees C. Raman spectroscopy, XRD, HRTEM, XPS, TPR and H-2 chemisorption have revealed the existence of an intimate contact between Ni and Ru and CeO2, which is considered the reason of the excellent catalytic activity and stability observed. A kinetic model has been developed using the Langmuir-Hinshelwood-Hougen-Watson approach for the decomposition of ammonia in a fixed bed reactor. The reaction rate expression of the ammonia decomposition on Ni-Ru bimetallics supported on ceria suggests that the dehydrogenation of the ammonia adsorbed on the surface of the catalyst is the limiting step of the reaction and that ammonia decomposition is inhibited by the presence of H-2.

The development of better catalysts is a passionate topic at the forefront of modern science, where operando techniques are necessary to identify the nature of the active sites. The surface of a solid catalyst is dynamic and dependent on the reaction environment and, therefore, the catalytic active sites may only be formed under specific reaction conditions and may not be stable either in air or under high vacuum conditions. The identification of the active sites and the understanding of their behaviour are essential information towards a rational catalyst design. One of the most powerful operando techniques for the study of active sites is near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), which is particularly sensitive to the surface and sub-surface of solids. Here we review the use of NAP-XPS for the study of ceria-based catalysts, widely used in a large number of industrial processes due to their excellent oxygen storage capacity and well-established redox properties.