Plasmonic two-dimensional materials have emerged as a promising platform for photothermal catalysis, offering unique advantages over conventional thermal approaches. Materials such as doped transition metal dichalcogenides (TMDCs) and graphene exhibit strong light-matter interactions due to their confined electronic states and tunable plasmonic resonances. These properties enable efficient light absorption, localized heating, and hot carrier generation, which are critical for driving chemical reactions such as methane dry reforming (CH₄ + CO₂ → 2H₂ + 2CO).

A key mechanism in plasmonic 2D materials is the generation of localized surface plasmon resonances (LSPRs) under light irradiation. When photons with energy matching the plasmon frequency are absorbed, collective oscillations of free electrons create intense electromagnetic fields near the material surface. In doped TMDCs, such as MoS₂ with sulfur vacancies or substitutional dopants, plasmon resonances can be tuned across the visible to near-infrared spectrum. Graphene plasmons, on the other hand, are highly confined in the mid-infrared range and can be adjusted via electrostatic gating or chemical doping. These resonances lead to highly localized heating, with temperature gradients confined to nanoscale regions near catalytic sites.

The photothermal effect in plasmonic 2D materials differs fundamentally from conventional thermal catalysis. In traditional thermal processes, heat is supplied globally, often requiring high furnace temperatures (600–1000°C) to activate methane dry reforming. This results in energy inefficiency, thermal stress on catalysts, and unwanted side reactions. In contrast, plasmonic materials convert light directly into heat at the reaction sites, enabling precise spatial and temporal control. Experimental studies have demonstrated that illuminated plasmonic nanostructures can achieve local temperatures exceeding 300°C under moderate light intensities, even while the bulk environment remains near ambient conditions. This selective heating minimizes energy waste and reduces catalyst degradation.

Hot electron transfer is another critical aspect of plasmon-enhanced catalysis. Upon plasmon decay, high-energy electrons are generated with sufficient energy to populate antibonding orbitals of adsorbed reactants. For example, in methane dry reforming, hot electrons can weaken C–H bonds in CH₄ and facilitate CO₂ activation. Graphene’s high carrier mobility allows these electrons to travel rapidly to reaction sites before thermalizing, enhancing catalytic turnover. Doped TMDCs exhibit similar effects, with sulfur vacancies acting as trapping sites for hot electrons, further promoting reactant dissociation. Spectroscopic measurements have shown that plasmon-driven reactions exhibit different intermediate species compared to thermally driven pathways, suggesting distinct mechanistic routes.

Wavelength-dependent activity is a hallmark of plasmonic catalysis. The reaction rate in plasmon-enhanced systems correlates strongly with the overlap between the incident light spectrum and the material’s plasmon resonance. For instance, graphene-based catalysts show higher methane conversion rates under infrared illumination matching their plasmon peak, while doped MoS₂ performs optimally under visible light. This tunability allows for solar-driven reactions with minimal reliance on broad-spectrum heating. Studies have reported methane conversion efficiencies of up to 20% under simulated sunlight using plasmonic 2D catalysts, compared to less than 5% for conventional catalysts under similar conditions.

The synergy between plasmonic heating and catalytic active sites further enhances performance. In hybrid systems where 2D materials are coupled with metal nanoparticles (e.g., Au or Pt), the plasmonic field concentrates around the metal-semiconductor interface, creating hotspots for reaction initiation. The 2D material acts as both a light absorber and a charge mediator, while the metal nanoparticles provide additional catalytic centers. This configuration has been shown to improve syngas selectivity in dry reforming by suppressing coke formation, a common issue in thermal catalysis.

A comparison between plasmonic and conventional thermal catalysis reveals several advantages of the former.
- Energy efficiency: Plasmonic systems require lower total energy input since heating is localized.
- Reaction control: Light intensity and wavelength can be adjusted in real time to modulate reaction rates.
- Catalyst stability: Reduced bulk heating mitigates sintering and deactivation.
- Selectivity: Plasmon-driven pathways often favor different products due to non-thermal electron effects.

However, challenges remain in scaling plasmonic 2D catalysts for industrial applications. Uniform large-area synthesis of doped TMDCs and graphene with consistent plasmonic properties is still under development. Long-term stability under continuous illumination and reactive gas environments requires further optimization. Additionally, the design of photoreactors that maximize light utilization while maintaining efficient mass transport is an ongoing area of research.

Future advancements may involve stacking multiple 2D materials to broaden plasmonic absorption bands or engineering defects to create additional active sites. Computational studies suggest that alloyed TMDCs or graphene heterostructures could further enhance hot electron lifetimes and catalytic activity. As understanding of plasmon-exciton interactions deepens, new strategies for coupling light harvesting with chemical conversion will likely emerge.

In summary, plasmonic 2D materials represent a paradigm shift in catalytic methane reforming, leveraging nanoscale heating and electronic effects to overcome limitations of conventional thermal methods. Their ability to harness light energy with precision offers a sustainable pathway for industrial chemistry, aligning with the growing demand for carbon-neutral processes. Continued research into material design and reactor engineering will be essential to unlock their full potential.