Surface oxygen species guide hydrogen production from methanol on platinum catalysts

Hydrogen is often described as a clean energy carrier, but its practical use is limited by a stubborn logistical problem: the gas is difficult to store and transport safely and efficiently. Researchers are now exploring methanol as a liquid alternative. It can be handled under ordinary conditions, contains a substantial amount of chemically bound hydrogen, and can be converted into hydrogen when energy is needed. A new study has revealed that the success of this conversion depends heavily on a hidden feature of the catalyst surface: the precise type of oxygen species surrounding platinum atoms.

The research focuses on aqueous phase reforming of methanol, or APRM, a process in which liquid methanol reacts with water to produce hydrogen and carbon dioxide. Unlike conventional steam reforming, which generally requires temperatures above 300 °C and the additional energy needed to vaporize methanol, APRM operates in the liquid phase at approximately 150 to 250 °C. This lower-temperature route could be useful in compact systems designed for local, distributed, or mobile hydrogen generation, provided that catalysts can be made active, selective, and resistant to deactivation.

The team, led by researchers from Tsinghua University, compared platinum catalysts supported on five different oxide materials: aluminum oxide, zirconium oxide, cerium oxide, titanium oxide, and silicon dioxide. Platinum provides the principal sites where methanol-derived molecules are activated, while the oxide support influences how molecules bind, how water dissociates, and which oxygen-containing intermediates form during the reaction. By combining catalytic measurements with spectroscopy and other characterization methods, the researchers tracked the relationship between surface oxygen chemistry and the reaction pathways followed by methanol.

The differences between the catalysts were striking. Platinum supported on aluminum oxide, written as Pt/Al2O3, produced hydrogen at a rate of 846.9 micromoles per gram of platinum per second at 250 °C. It also achieved a methanol reforming selectivity of 97.3 percent, meaning that most of the converted methanol followed the desired route toward hydrogen and carbon dioxide rather than forming unwanted byproducts. Under the same conditions, its activity was nearly 2.5 times higher than that of Pt/CeO2 and approximately 20 times higher than that of Pt/SiO2.

The researchers attribute this performance to hydroxyl groups on the aluminum oxide surface. These groups contain oxygen and hydrogen and can participate directly in surface reactions. During methanol reforming, platinum can break down methanol into smaller adsorbed species, including carbon monoxide. Carbon monoxide must then be removed or transformed through the water gas shift reaction, in which it reacts with water to form carbon dioxide and additional hydrogen. Surface hydroxyl species, often represented in mechanistic descriptions as OH*, can provide the oxygen-containing chemistry needed to accelerate this step.

An important feature of the aluminum oxide catalyst is that its hydroxyl groups can be regenerated. Water molecules can dissociate on the surface, replenishing reactive OH* species and allowing the catalytic cycle to continue. This makes the oxygen environment active without making it excessively aggressive. The result is a surface capable of helping transform reaction intermediates while avoiding the strong binding that can prevent products from leaving and active sites from becoming available again.

The behavior of the cerium oxide catalyst demonstrated why simply increasing oxygen reactivity is not always an advantage. Cerium oxide contains reactive lattice oxygen that can promote the formation of formate intermediates, compounds containing carbon, hydrogen, and oxygen. However, the formate species interacted too strongly with the surface and persisted rather than converting rapidly to downstream products. When such intermediates accumulate, they can occupy catalytic sites and interrupt the sequence of reactions needed for hydrogen production. In this case, a chemically active support created a bottleneck instead of eliminating one.

The catalysts supported on titanium oxide and silicon dioxide showed the opposite limitation. Their relatively weak metal-support interactions allowed methanol to form methoxy species, but the subsequent steps leading to carbon monoxide and hydrogen were less efficient. Without the right balance between platinum and the oxide support, methanol activation could begin without proceeding effectively through the full reforming pathway. These results show that catalyst performance cannot be predicted from platinum loading or particle size alone. The support determines how reactants, intermediates, water, and oxygen species interact at the active interface.

The study identifies surface oxygen species as a potentially powerful descriptor for designing improved APRM catalysts. The most effective catalyst was not the one with the most reactive oxygen or the strongest interaction with reaction intermediates, but the one that balanced several competing requirements. Oxygen species needed to be reactive enough to assist water gas shift chemistry, yet not so reactive that they trapped formates or other intermediates. The platinum-support interface also had to be strong enough to coordinate the reaction without immobilizing molecules on the surface.

These findings could influence the development of liquid hydrogen-carrier technologies and compact reforming devices. The researchers suggest that hydroxyl-rich, amphoteric oxide supports may provide a promising foundation for future platinum-based catalysts. More broadly, the work highlights a principle that extends beyond methanol reforming: in heterogeneous catalysis, the atoms surrounding a metal active site can determine whether a reaction accelerates, stalls, or follows an entirely different pathway. By learning to control those surface oxygen environments, scientists may be able to make hydrogen production from liquid fuels more efficient and more practical.

Web References: https://doi.org/10.48130/een-0026-0013; Energy & Environment Nexus

References: Yang Y, Bie X, Zhu Y, Quan X, Yu B, et al. 2026. “Surface oxygen species dictate reaction pathways in platinum-catalyzed aqueous phase reforming of methanol.” Energy & Environment Nexus 2: e019. DOI: 10.48130/een-0026-0013.

Keywords

Hydrogen production, methanol reforming, aqueous phase reforming, platinum catalysts, surface oxygen species, hydroxyl groups, water gas shift reaction, catalyst supports, aluminum oxide, cerium oxide, green energy, hydrogen carriers