As the global urgency intensifies to combat climate change and drastically reduce greenhouse gas emissions, hydrogen has rapidly risen to the forefront as an exemplary clean energy carrier. When produced sustainably, particularly from renewable feedstocks, hydrogen offers a versatile solution: it can fuel transportation, serve as a critical raw material for various chemical industries, and function as an efficient medium for energy storage capable of balancing the intermittent nature of renewable power sources. In this evolving landscape, the pursuit of green hydrogen technologies tailored to regional resources has garnered significant attention worldwide.
In Brazil, a country globally recognized for its vast production of ethanol derived from sugarcane biomass, a particularly promising avenue emerges—using ethanol as a feedstock for hydrogen production. Brazil’s well-established bioethanol infrastructure, encompassing robust production, distribution, and consumption systems, creates an ideal platform to upscale technological innovations that valorize ethanol beyond conventional fuel applications. This strategy not only capitalizes on domestically abundant bioresources but also aligns with the country’s commitment to sustainable energy pathways.
Breaking new ground in this area, a research team led by Fabio Coral Fonseca, a senior scientist at the Institute of Energy and Nuclear Research (IPEN), has revealed crucial insights into the catalytic conversion of ethanol into hydrogen. Their findings underscore the importance of meticulously tuning the synthesis parameters of perovskite-type ceramic catalysts to optimize ethanol steam reforming—a reaction whereby ethanol and steam interact at elevated temperatures to produce hydrogen and carbon dioxide. This work, recently published in the International Journal of Hydrogen Energy, heralds a major advance by demonstrating enhanced catalyst stability and performance while eliminating the reliance on expensive noble metals typically used in such catalytic systems.
The fundamental chemistry of ethanol steam reforming (ESR) can be expressed by the reaction: C₂H₅OH + 3 H₂O → 2 CO₂ + 6 H₂. Achieving this reaction efficiently, however, entails navigating a complex reaction network with multiple intermediate species and competing side reactions. Catalysts play a pivotal role by dictating reaction pathways, enhancing hydrogen yield, and suppressing deleterious phenomena such as coke formation—carbonaceous deposits that deteriorate catalyst activity and longevity. The quest, therefore, is to engineer catalyst surface properties at the nanoscale to sustain long-term, high-performance ESR.
Conventional catalysts typically involve depositing metal nanoparticles on supports, but such systems suffer from particle sintering and agglomeration under high-temperature ESR conditions, impairing catalytic activity over time. By contrast, the IPEN research team adopts a transformative approach by incorporating the catalytic metal, nickel (Ni), directly into the crystalline lattice of perovskite oxides during synthesis. This lattice incorporation enables a phenomenon known as exsolution, where nickel atoms migrate from the bulk perovskite matrix to the surface, forming finely dispersed, metallic Ni nanoparticles that remain strongly anchored and resist sintering and coke accumulation.
This inside-out emergence of catalytically active nanoparticles distinguishes exsolved perovskites from traditional impregnation methods. The strongly tethered nickel species boast pronounced thermal stability, overcoming one of the most persistent challenges in ethanol steam reforming catalysts. Maintaining nanoscale dispersion ensures a high density of active sites, which is essential for sustaining catalytic efficiency during prolonged operation at the needed severe conditions.
A pivotal innovation highlighted in the study involves controlling the calcination temperature of the perovskite precursor oxide during the catalyst preparation. Researchers examined calcination at 650 °C, 800 °C, and 1200 °C, observing that this seemingly simple parameter critically influences the microstructural evolution of the catalyst. Lower calcination temperatures preserve finer ceramic particles and larger surface areas, which facilitate efficient nickel exsolution and nanoparticle formation. In contrast, higher temperatures promote particle growth and grain coalescence, severely reducing surface area and impeding exsolution.
The material calcined at 650 °C exhibited superior catalytic activity, delivering complete ethanol conversion and producing over four moles of hydrogen per mole of ethanol—remarkable efficiency that remained stable over extended operation periods exceeding 85 hours with minimal coke deposition. Conversely, catalysts subjected to higher calcination temperatures showed diminished nickel exsolution, lowered overall conversion, and a dominant reaction pathway favoring simple ethanol dehydrogenation instead of the desired steam reforming, resulting in reduced hydrogen yield.
This evidence emphasizes that catalyst design extends beyond elemental selection to encompass precise processing controls that define particle size distributions and surface characteristics foundational to catalytic performance. Substrate particle size emerges as a critical parameter regulating metal exsolution dynamics and ultimately dictates the catalytic outcome during ESR.
Fonseca situates this breakthrough within a broader technological context, underscoring that while ethanol-to-hydrogen conversion is promising, direct utilization of ethanol in energy devices such as fuel cells may offer greater overall energy efficiency. Recognizing this, his research group is concurrently exploring perovskite materials tailored for direct ethanol fuel cells, which convert ethanol straight into electricity without intermediate hydrogen production. The flexibility of perovskites, defined by their distinctive ABO₃ crystal framework, enables such multifaceted applications through strategic elemental substitutions at the A and B lattice sites, offering tailored electronic, ionic, magnetic, and catalytic functionalities.
Beyond nickel-based systems, the research team has also probed exsolution phenomena with ruthenium embedded within lanthanum chromite (LaCrO₃) perovskites. Ruthenium, a metal with exceptional catalytic properties in reforming reactions, similarly exsolves as nanoparticles during ESR, strongly anchored within the perovskite matrix to yield enhanced reactivity and stability. This complementary work, conducted in collaboration with U.S. institutions and supported by FAPESP and NSF, further validates the promise of exsolved metal nanoparticles in perovskites as a general strategy to reduce reliance on scarce noble metals without compromising catalytic efficiency.
Looking forward, the IPEN team is transitioning toward more precise, atomically engineered materials by fabricating epitaxial thin films of these perovskites through pulsed laser deposition techniques. This state-of-the-art approach entails transforming polycrystalline powders into ceramic wafers, which are then vaporized and redeposited onto single-crystal substrates, producing near-perfect crystalline films. Such model systems enable the elucidation of exsolution mechanisms and catalytic behavior at the atomic scale, leveraging powerful characterization tools available at Sirius, Brazil’s cutting-edge synchrotron light source.
This rigorous investigation into material synthesis-structure-performance relationships signals a clear route to producing highly active, robust, and economically viable catalysts for sustainable hydrogen production from bioethanol. The ability to harness earth-abundant metals and stabilize them via exsolution elevates perovskite catalysts as vital players in advancing the global energy transition. Brazil’s rich ethanol resources combined with these innovative catalysts may well position the country at the forefront of renewable hydrogen technologies, contributing decisively to decarbonizing industrial processes and transportation mediums.
Ultimately, these advances illustrate how meticulous control over fundamental material processing parameters can unlock new frontiers in catalysis, fostering scalable, cost-effective solutions essential for a low-carbon, circular economy.
Subject of Research: Catalytic conversion of ethanol to hydrogen using perovskite-type oxide catalysts
Article Title: Calcination temperature of the perovskite parent compound controls active metal exsolution and catalytic performance for ethanol steam reforming
News Publication Date: 31-Dec-2025
Web References: https://doi.org/10.1016/j.ijhydene.2025.153326
References: Fonseca, F. C. et al., International Journal of Hydrogen Energy, 2025
Image Credits: Fabio Coral Fonseca / Institute of Energy and Nuclear Research (IPEN)
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