📄 chemistry

Dynamic Light Regulation of Surface CO Coverage Enables Efficient Low-Temperature RWGS on Electron-Rich Pt

This study demonstrates that light irradiation dynamically regulates surface CO coverage on electron-rich Pt-MoO $_{3-x}$ catalysts by inducing interfacial charge redistribution and weakening Pt-CO interactions, thereby mitigating CO poisoning and enabling efficient low-temperature reverse water-gas shift reactions.

Original authors: Zhaoke Zheng, Guo Qingzheng, Haopeng Ge, Guangyao Zhai, Zeyan Wang, Yuanyuan Liu, Peng Wang, Hefeng Cheng, Ying Dai, Baibiao Huang

Published 2026-08-05

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Zhaoke Zheng, Guo Qingzheng, Haopeng Ge, Guangyao Zhai, Zeyan Wang, Yuanyuan Liu, Peng Wang, Hefeng Cheng, Ying Dai, Baibiao Huang

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Great Chemical Traffic Jam

Imagine a busy highway where cars (chemical molecules) are trying to get from one city to another to build something new. In the world of chemistry, this highway is a catalyst—a special material that speeds up reactions without getting used up itself. But sometimes, the road gets clogged. A specific type of car, let's call it the "CO monster," is so sticky and clingy that it parks itself right in the middle of the most important lanes, blocking everyone else from passing. This is called "poisoning," and it stops the whole process dead in its tracks.

One of the most important jobs for these chemical highways is the Reverse Water-Gas Shift (RWGS) reaction. Think of this as a recycling plant that takes carbon dioxide (CO2), a greenhouse gas, and turns it into carbon monoxide (CO), a useful building block for making fuels and plastics. The problem is that this recycling plant usually needs to be super hot to work, which wastes a lot of energy. Plus, the "CO monster" loves to stick to the workers (the metal catalysts) and stop them from doing their job. Scientists have been trying to find a way to clear this traffic jam without just turning up the heat, hoping to make the process faster, cheaper, and cleaner.

The Light Switch Solution

In this study, researchers from Shandong University discovered a clever way to clear that traffic jam using light. They built a special catalyst made of platinum (a shiny metal) sitting on a support material called molybdenum oxide that is missing some oxygen atoms. When they shined a full-spectrum light on this setup, something magical happened: the "CO monsters" started letting go of the platinum workers much faster than they did in the dark.

Usually, when you shine a light on a material, it just gets warm, like a rock baking in the sun. This is called a "photothermal" effect. But the team was very careful to prove that this wasn't just about heat. They measured the temperature of the catalyst with extreme precision and showed that even when the catalyst was at the exact same temperature in the dark and under the light, the light version was working nearly three times faster. It wasn't just a hot rock; the light was doing something else entirely.

The secret lies in the electrons. The researchers found that when light hits the catalyst, it pushes extra electrons onto the platinum atoms, making them "electron-rich." Imagine the platinum atoms as magnets. In the dark, they are super strong magnets that grab the CO monsters tightly. But when the light hits them, the extra electrons change the magnet's strength, making it much weaker. Suddenly, the CO monsters aren't so sticky anymore; they let go and float away, freeing up the platinum workers to grab new CO2 molecules and keep the recycling plant running.

The Evidence and the "Why"

To prove this wasn't just a lucky guess, the scientists used some high-tech tools to watch the reaction happen in real-time. They used a technique called DRIFTS, which is like a super-sensitive camera that can "see" the CO molecules stuck to the surface. When they turned on the light, the camera showed a dramatic drop in the number of CO molecules hanging around. Even more interestingly, they tested different colors of light and found that blue light (450 nm) was the most effective at clearing the traffic, suggesting that the energy of the light particles (photons) was the key, not just the warmth.

They also compared their platinum catalyst to a similar one made with palladium (another metal). The palladium version didn't react to the light at all; it just got warm and stayed slow. This proved that the effect was specific to the unique electronic structure of the platinum in this specific setup.

Using computer simulations, the team modeled what was happening at the atomic level. They confirmed that the "electron-rich" state of the platinum fundamentally changed how it interacted with CO. The simulations showed that the bond between the platinum and the CO became much weaker, making it easier for the CO to leave. This is crucial because if the CO stays stuck, it blocks the hydrogen (H2) from getting in, which is the other half of the recipe needed to make the reaction work. By clearing the CO, the light allowed the hydrogen to do its job, speeding up the whole process.

The Big Picture

The result is a catalyst that can turn CO2 into useful CO at much lower temperatures than before, with a production rate of 1246 mmol per gram of catalyst per hour under light, and over 99% of the product being the desired CO. The catalyst also proved to be very stable, lasting for over 200 hours without falling apart.

This study suggests that we don't always need to crank up the heat to fix a clogged chemical reaction. Instead, we can use light to gently nudge the electronic structure of the catalyst, making it "repel" the sticky byproducts that usually slow things down. It's like having a traffic cop who doesn't just yell at the cars to move, but actually changes the road rules so the cars naturally want to keep moving. This approach could open the door to more efficient and energy-saving ways to recycle carbon and create new chemicals in the future.

Technical Summary: Dynamic Light Regulation of Surface CO Coverage Enables Efficient Low-Temperature RWGS on Electron-Rich Pt

Problem Statement
Heterogeneous catalysis is frequently hindered by the strong adsorption and accumulation of surface intermediates, which block active sites and suppress catalytic activity. A representative challenge is the reverse water–gas shift (RWGS) reaction ( $CO_2 + H_2 \rightarrow CO + H_2O$ ), a critical pathway for sustainable carbon utilization. While Pt-based catalysts are effective for $H_2$ activation, their intrinsic strong affinity for CO leads to severe surface poisoning. This "CO poisoning" blocks Pt sites, impedes reactant activation, and suppresses performance. Existing mitigation strategies, such as tuning metal–support interactions or engineering single-atom structures, rely on static structural modifications. These static approaches fail to dynamically balance the continuous generation and replenishment of CO during the RWGS reaction, leading to progressive site blocking. Furthermore, the endothermic nature of RWGS typically necessitates high operating temperatures, resulting in significant energy consumption and catalyst sintering. There is a critical need for strategies that can dynamically regulate steady-state adsorbate coverage under milder reaction conditions.

Methodology
The study employs a Pt-MoO $_{3-x}$ catalyst system, where oxygen-deficient MoO $_{3-x}$ supports act as electron donors to create electron-rich Pt nanoparticles. The research integrates experimental characterization with theoretical modeling to investigate the effects of light irradiation on catalytic performance and surface chemistry.

Catalyst Synthesis and Characterization: Oxygen-deficient MoO $_{3-x}$ was synthesized via a hydrothermal method, followed by Pt loading using an ice-template method. Structural properties were analyzed using XRD, Raman spectroscopy, STEM, HRTEM, EDS, XPS, and EPR.
Catalytic Testing: RWGS performance was evaluated under full-spectrum illumination (2.8 W cm $^{-2}$ , 350–1200 nm) and dark conditions. Rigorous temperature monitoring was conducted using both infrared thermography and an internal thermocouple embedded in the catalyst bed to decouple photothermal heating from non-thermal photo-effects.
In Situ Spectroscopy:
- In Situ XPS: Performed under dark and illumination conditions to probe electronic state changes at the Pt–O–Mo interface.
- Continuous-Flow CO-DRIFTS: Conducted under a steady feed of 10% CO/Ar to simulate a CO-supplemented environment relevant to RWGS, measuring steady-state surface CO coverage at identical temperatures in light and dark.
- Adsorption–Purge DRIFTS: Used to isolate chemisorbed CO species from gas-phase contributions, confirming the light-induced removal of adsorbed CO.
- Transient DRIFTS & KIE: Used to elucidate the reaction pathway (redox vs. associative) and identify rate-limiting steps via kinetic isotope effects ( $H_2$ vs. $D_2$ , $C^{16}O_2$ vs. $C^{18}O_2$ ).
Theoretical Calculations: Density Functional Theory (DFT) calculations were performed using Pt $_4$ and Pt $_{10}$ cluster models on MoO $_{3-x}$ surfaces. These models simulated electron-rich (oxygen-deficient support) and electron-deficient (pristine support) states to analyze Pt–CO binding energies, projected density of states (PDOS), and crystal orbital Hamilton population (COHP). Free-energy profiles were calculated to assess the impact of varying CO coverage on reaction energetics.

Key Results

Enhanced Catalytic Performance: Under full-spectrum illumination without external heating, the Pt-MoO $_{3-x}$ catalyst achieved a catalyst temperature of ~350°C and a CO production rate of 1246 mmol g $_{cat}^{-1}$ h $^{-1}$ with >99% selectivity. Crucially, at an identical catalyst temperature of 350°C, the activity under illumination was nearly three times higher than under dark (thermal) conditions. The apparent activation energy decreased from 45.5 kJ mol $^{-1}$ (dark) to 34.3 kJ mol $^{-1}$ (light).
Electronic Modulation: In situ XPS revealed that illumination induces electron enrichment at Pt sites (negative shift in Pt 4f by 0.32 eV) and electron depletion in the MoO $_{3-x}$ support, indicating interfacial charge redistribution across the Pt–O–Mo interface.
Dynamic Regulation of CO Coverage: Continuous-flow CO-DRIFTS experiments demonstrated that illumination significantly reduces steady-state surface CO coverage compared to dark conditions at the same temperature. At 420°C, the normalized CO signal decreased by ~50% under illumination versus ~36% in the dark. Adsorption–purge DRIFTS confirmed that this effect applies specifically to chemisorbed CO species, not gas-phase CO.
Selectivity and Stability: Under illumination, the catalyst maintained high CO selectivity (>99%) even at low temperatures (50°C), whereas dark conditions at 100°C resulted in dominant methane production (86.4%) due to CO over-hydrogenation. The catalyst exhibited high stability over 200 hours, retaining structural integrity and oxygen vacancies, whereas high-temperature thermal operation (700°C) caused severe Pt sintering.
Mechanistic Insights:
- Reaction Pathway: Transient DRIFTS and KIE studies confirmed a redox mechanism where CO $_2$ dissociates directly on oxygen-deficient MoO $_{3-x}$ sites, followed by hydrogenation. Hydrogen activation/migration is the kinetically relevant step.
- Poisoning Mechanism: DFT calculations showed that high CO coverage blocks Pt sites, thermodynamically suppressing H $_2$ dissociation (free energy shift from -2.23 eV to -0.65 eV) and increasing the energy barrier for CO $_2$ dissociation and H $_2$ O formation.
- Light Effect: DFT revealed that the illumination-induced electron-rich state of Pt weakens the Pt–CO interaction (adsorption energy reduced from -2.53 eV to -2.11 eV for linear CO), facilitating CO desorption and maintaining active sites for H $_2$ activation.
Specificity: The effect is metal-dependent; Pd-MoO $_{3-x}$ did not show similar activity enhancement or CO coverage regulation under illumination, confirming that the phenomenon relies on the unique electronic structure of Pt.

Significance and Claims
The paper claims to establish light-mediated dynamic regulation of surface adsorbate coverage as an effective strategy for mitigating catalyst poisoning. The core contribution is demonstrating that illumination can actively manipulate the electronic states of metal active sites under operando conditions to weaken the binding of strongly adsorbed intermediates (CO). This dynamic regulation overcomes the limitations of static catalyst designs, allowing for efficient RWGS performance at lower temperatures and preventing the progressive site blocking that typically degrades catalysts. The work decouples this electronic effect from simple photothermal heating, highlighting a non-thermal mechanism where charge redistribution fundamentally alters adsorption thermodynamics. The authors suggest this concept of dynamically controlling surface intermediates via electronic structure modulation could be a general strategy for enhancing the activity and stability of various heterogeneous catalytic systems beyond the specific RWGS reaction studied.

The Great Chemical Traffic Jam

The Light Switch Solution

The Evidence and the "Why"

The Big Picture

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