Zeolite Cages Could Tame Metal Catalysts for Cleaner Electric Chemistry

Zeolites, the porous aluminosilicate crystals long used in petroleum refining, are emerging as a serious alternative to carbon supports in electrocatalysis, according to a new review published in the journal Catal. The article, authored by Xiaoyang Han, Qiang Zhang, Wenfu Yan, Jia-Nan Zhang and Jihong Yu, surveys the latest research on metal-in-zeolite (MZ) catalysts, materials in which metal atoms, clusters or nanoparticles are deliberately trapped inside the ordered micropores of a zeolite framework, and evaluates their prospects for reactions such as oxygen reduction, carbon monoxide reduction and carbon dioxide reduction.

The core argument of the review rests on the confinement effect. Because zeolites are built from highly ordered frameworks with regular channels and cages, they generate a stable internal electric field within their pores that can significantly alter how reactants and intermediates adsorb. This can change reaction pathways, lower activation barriers and ultimately improve catalytic activity and selectivity. Confining metal species inside the framework also allows microscopic control over their distribution, coordination state and electronic properties, something that conventional carbon carriers, which anchor metals mainly through defects, cannot match.

Carbon materials such as graphite and graphene dominate electrocatalysis because they conduct electrons well and offer large surface areas. But the review highlights their weaknesses: carbonaceous materials can be oxidized under electrochemical conditions, since their standard potentials are moderate to lower than that of water oxidation, and they adsorb nonpolar small molecules poorly, limiting achievable current densities. Zeolites, by contrast, combine high specific surface area, shape-selectivity and excellent thermal and chemical stability. Their clear pore structure facilitates diffusion of reactants and products and enables molecular sieving that improves product selectivity, while the robust framework maintains structural integrity under reaction conditions and electrolyte erosion.

The authors classify MZ catalysts into two main families. The first, metal atom-containing zeolites, holds single atoms in three configurations: framework-substitution, where metal atoms directly replace tetrahedral skeleton sites through metal-oxygen-silicon bonds; framework-coordination, where atoms anchor at defect sites through covalent coordination; and ion-exchange, where metal cations bind within channels and cages through ionic interactions. Each form brings distinct advantages, from high structural stability and clear coordination environments to tunable metal loading and dynamic adjustability of oxidation states.

The second family, metal@zeolite composites, places non-framework metal species inside the crystals, either as clusters within cages or as nanoparticles embedded in the zeolite matrix. The pores suppress migration and aggregation of metal particles during reactions, and shape-selectivity gives researchers leverage over reaction pathways and product distribution. The trade-offs are real, however: it is difficult to guarantee cluster size and distribution during synthesis, and nanoparticles large enough to strain the framework can damage the zeolite matrix, hinder mass transfer and lead to deactivation. The review also notes that metal species often evolve dynamically between structures during reactions, complicating the identification of true active sites.

Synthesis strategies fall into two broad camps. In situ synthesis introduces metals during zeolite crystallization, achieving uniform distribution and high stability, but the type and loading of metals are constrained by the crystallization process itself. Post-synthesis modification treats pre-formed zeolites and fixes metals using pore adsorption, offering greater flexibility and a wider range of introducible species, at the risk of uneven metal distribution and pore blockage. Precise control over these variables, the authors argue, is key to maximizing catalytic efficiency.

Characterization is where much of the recent progress shows. X-ray diffraction, FTIR and Raman spectroscopy reveal crystallinity, framework chemistry and structural changes during catalysis. X-ray absorption spectroscopy resolves the oxidation state and coordination environment of metal centers at the atomic scale, and in operando variants track how these change with applied potential. In one highlighted example, in situ XAS on an InSn@SnY catalyst for carbon dioxide electroreduction revealed gradually increasing electron transfer between indium and tin atoms at different potentials, along with a dynamically enhanced electronic interaction between tin atoms and the Y zeolite. Aberration-corrected scanning transmission electron microscopy now allows direct, non-destructive imaging of atoms within zeolite frameworks, while solid-state NMR, including 129Xe, 1H, 29Si and 27Al variants, maps pore geometry, hydroxyl groups and framework integrity.

The review also confronts the central obstacle: zeolites are electrical insulators or semiconductors, and their alumina units are prone to the hydrogen evolution reaction, which has limited research on zeolites as electrocatalysts. Recent work suggests ways forward. Redox probe experiments found that silicate materials with the smallest pore sizes showed the most efficient internal electron transfer, and hydroxyl groups inside zeolites were shown to boost charge transfer, dissociating into protons under an electric field and stabilizing intermediates. Separately, a microporous platinum-on-carbon electrocatalyst built with zeolite nanocrystal cavities showed strong oxygen reduction activity, with the zeolite’s oxygen-carrying capacity in water measured at two orders of magnitude above pure water, establishing a high-concentration gas layer at the electrode surface.

Concrete electrocatalytic demonstrations are accumulating. Copper species ion-exchanged into ZSM-5 and sintered under hydrogen formed single-atom clusters whose activity arose from synergy between single atoms and clusters, with the framework preventing aggregation and stabilizing active sites for carbon monoxide reduction. A cobalt catalyst embedded in silicalite-1 formed isolated tri-coordinated Co(OSi)3 centers that promoted oxygen adsorption and maintained optimal bonding with intermediates for two-electron oxygen reduction to hydrogen peroxide. And in a carbon dioxide reduction system, zinc ions introduced into Y zeolite enhanced conductivity and suppressed hydrogen evolution, while cadmium oxide nanoclusters in the cages shifted the cadmium d-band center upward, promoting charge transfer and carbon dioxide activation.

The authors close with an outlook that treats zeolite electrocatalysis as a design problem rather than a settled one. Bandgap engineering, through heteroatom doping or conductive additives, could overcome low conductivity; advanced in situ characterization and density functional theory could pin down dynamic active sites and confined water structures that shape local pH; and machine learning on accumulated catalyst databases could predict promising metal-zeolite combinations and optimize synthesis conditions. If those threads converge, the confinement principles that made zeolites indispensable in thermal catalysis may translate into customizable, stable electrocatalysts for energy conversion.

Subject of Research: Metal-in-zeolite catalysts for electrocatalytic reactions such as oxygen and carbon dioxide reduction

Article Title: Challenges and perspectives of metal-in-zeolite catalysts for electrocatalysis

Article References: Han, X., Zhang, Q., Yan, W., Zhang, J.-N., & Yu, J. (2026). Challenges and perspectives of metal-in-zeolite catalysts for electrocatalysis. Catal, 2(1), Article 8. https://doi.org/10.1007/s44422-026-00016-y

Image Credits: AI Generated

DOI: 10.1007/s44422-026-00016-y

Keywords: zeolites, electrocatalysis, confinement effect, single-atom catalysts, carbon dioxide reduction, oxygen reduction reaction, catalyst supports, X-ray absorption spectroscopy, bandgap engineering, carbon supports, Challenges, perspectives