How Subsurface Catalysis Is Revolutionizing Chemical Reactions
The secret to cleaner, more efficient chemical manufacturing lies not on the surface of catalysts, but deep within their hidden layers.
Imagine a grand theater where the most critical drama unfolds not on the stage but in the hidden spaces beneath it. Similarly, in catalysis—the science of speeding up chemical reactions—the most pivotal action often occurs not on the catalyst's surface but in its subsurface layers, a realm once considered merely passive support. For decades, chemists focused almost exclusively on surface interactions, but recent discoveries have revealed that the subsurface region plays a decisive role in directing chemical transformations, particularly in dehydrogenation reactions essential for producing everyday materials. This article explores how this paradigm shift is enabling more selective, efficient, and stable industrial processes.
In simple terms, catalysis works by providing a surface where reactant molecules meet and rearrange into desired products more easily. Traditional analysis focused squarely on these surface atomic layers. However, subsurface catalysis refers to the phenomenon where atoms or molecules residing several layers beneath the catalyst's surface significantly influence the reaction's speed and selectivity.
Atoms beneath the surface influence reactions
The catalyst's subsurface can be modified by the incorporation of foreign atoms—a process called doping—or by the dissolution of reaction intermediates like carbon, hydrogen, or oxygen. These subsurface occupants are far from silent; they exert powerful electronic effects that ripple up to the surface, changing how strongly reactants, intermediates, and products bind there. This subtle tuning can make the difference between a highly selective process that creates valuable chemicals and an unselective one that wastes resources through unwanted side reactions.
This understanding has been pivotal for dehydrogenation reactions, where hydrogen atoms are stripped away from larger molecules. These reactions are fundamental for converting cheap, abundant alkanes from natural gas into valuable alkenes—the building blocks for plastics, fibers, and other essential materials. The challenge has always been to prevent the catalyst from breaking the desired product down further. Subsurface engineering provides a powerful solution.
A pivotal 2018 study, "Subsurface catalysis-mediated selectivity of dehydrogenation reaction," provided a clear demonstration of this principle. The research team set out to systematically investigate how different metals hidden beneath a platinum surface would affect the selectivity of propane dehydrogenation to propylene.
The experiment was a masterclass in precision catalyst design9 :
The researchers first created nanoparticles containing both platinum and a second 3d transition metal (3dTM), specifically iron (Fe), cobalt (Co), or nickel (Ni). In these initial catalysts, the second metal was present on the surface.
The critical step was selectively removing the Fe, Co, or Ni atoms only from the surface. This was achieved through a controlled chemical process that preferentially leached the more reactive second metal from the surface layers, leaving behind a pure platinum "skin" surface.
The resulting catalysts, denoted as PtFe@Pt, PtCo@Pt, and PtNi@Pt, featured a pure platinum surface but retained the secondary metal atoms in the subsurface layers. This created an ideal system to isolate the effect of the subsurface composition.
The team then tested the catalytic performance of these subsurface-alloy catalysts. The initial bimetallic catalysts with exposed Co and Ni sites showed poor selectivity because these metals readily facilitated C-C bond breaking, a side reaction that degrades propylene. However, once these metals were confined to the subsurface and covered by a platinum skin, the selectivity trend reversed dramatically9 .
The table below shows how the propylene selectivity changed after engineering the subsurface layer.
Table 1: Propylene Selectivity of Platinum-Based Catalysts9
| Catalyst Type | Key Feature | Propylene Selectivity |
|---|---|---|
| Pure Pt | Baseline catalyst | Low |
| PtNi | Both metals on surface | Low |
| PtCo | Both metals on surface | Low |
| PtFe | Both metals on surface | High |
| PtNi@Pt | Ni in subsurface only | High |
| PtCo@Pt | Co in subsurface only | Higher |
| PtFe@Pt | Fe in subsurface only | Highest |
The data revealed a clear and exciting trend: the selectivity increased markedly in the sequence Pt < PtNi@Pt < PtCo@Pt < PtFe@Pt. This demonstrated unequivocally that the chemical identity of the subsurface metal directly governed the reaction's selectivity, even though the reacting molecules never directly touched it.
What invisible force was at work? The answer lies in the world of quantum chemistry. The researchers used theoretical calculations to determine the "d-band center" of the different Pt-skin surfaces. The d-band center is an electronic descriptor that indicates how tightly a surface will bind reaction intermediates. A lower d-band center generally leads to weaker binding, which is often beneficial for releasing the desired product before it undergoes further unwanted reactions9 .
Electronic descriptor for binding strength
The calculations showed that the subsurface metals shifted the d-band center of the surface platinum atoms in a predictable way: Fe caused the largest downward shift, followed by Co, then Ni. This perfectly matched the experimental selectivity trend. A lower d-band center weakened the binding of the propylene intermediate, preventing it from being over-decomposed. This established a direct electronic link between the hidden subsurface layer and the catalytic outcome on the surface.
Unraveling the mysteries of the subsurface requires a sophisticated array of tools. Today's scientists use both experimental and computational techniques to design and analyze these complex catalysts.
Table 2: The Scientist's Subsurface Catalysis Toolkit
Primary Function: XPS performed under reaction-like conditions.
Role in Subsurface Analysis: Allows real-time (operando) tracking of carbon and other species moving between the surface and subsurface during reaction6 .
Primary Function: Determines the structure and environment of specific nuclei.
Role in Subsurface Analysis: Can unambiguously characterize the coordination environment of atoms like tin (Sn) in zeolite frameworks, identifying true incorporation into the subsurface structure1 .
Primary Function: Mathematical modeling of the reaction's elementary steps.
Role in Subsurface Analysis: Uses data from DFT to simulate overall reaction rates and selectivity, enabling the rapid computational screening of promising subsurface alloys4 .
The concept of subsurface control extends beyond metal alloys. A groundbreaking 2025 study on a Pt@Sn-MFI zeolite catalyst for propane dehydrogenation revealed a similar principle at work, though in a different guise. Here, the "subsurface" framework of the zeolite, doped with tin (Sn) atoms, created unique anchoring sites for platinum clusters. This architecture, complemented by abundant structural defects (silanol groups, Si-OH), resulted in a catalyst with exceptional selectivity (≥98.5%) and remarkable stability for over 120 hours1 .
Subsurface structure with unique anchoring sites
This system operates through a "hydroxy-assisted" reaction pathway, where the synergy between surface platinum sites and nearby subsurface hydroxyl groups in the zeolite framework significantly lowers the energy barrier for a key step in the reaction1 . This highlights that the subsurface influence is not limited to electronic effects in metals but can also involve strategic positioning of active sites in the support material itself.
Furthermore, the impact of mobile subsurface species is a universal theme. A 2025 study on palladium-catalyzed methane oxidation used advanced operando spectroscopy to show that a "carbon traffic jam" in the catalyst's subsurface directly controlled the overall reaction rate and shifted selectivity between hydrogen (H₂) and water (H₂O) formation6 . This demonstrates the dynamic and often decisive role of dissolved species in the catalyst's bulk.
The exploration of the catalyst's subsurface is more than an academic curiosity; it is a powerful strategy for rationally designing the next generation of high-performance catalysts. By moving beyond the surface, scientists are learning to control chemistry with unprecedented precision. This knowledge paves the way for more energy-efficient chemical processes, reduced waste, and enhanced sustainability across the multi-trillion-dollar chemical industry. The hidden world beneath the surface, once ignored, is now proving to be the key to a more efficient and selective future in catalysis.
More efficient chemical processes
This article is based on scientific studies from peer-reviewed journals including Science Advances, Nature Communications, and Journal of Catalysis. For further reading, explore the cited research papers.