One of the biggest challenges in catalysis is efficiently delivering thermal energy to reaction sites without unnecessary heat loss. Traditional catalytic reactors rely on steady-state heating, which often leads to inefficient energy use, catalyst degradation, and suboptimal reaction rates.

In our lab, we break away from the limitations of steady-state operation by using pulsed photothermal catalysis, where ultrafast laser pulses generate rapid and highly localized temperature spikes on catalytic surfaces. Using plasmonic nanomaterials as light absorbers and pulsed lasers to excite them, we can fine-tune the intensity, duration, and repetition rate of thermal pulses to optimize different catalytic reactions.

There are several advantages to this approach. First, these pulses drive chemical reactions at unprecedented rates. Theoretically, our research has shown that we can achieve at least 100× faster reaction rates compared to steady-state reaction conditions. Secondly, we reduce energy consumption. Instead of heating the entire reactor, we only apply heat where it is required, thereby improving energy efficiency.

A further key component of this strategy is that the chemistry occurs under non-steady state conditions, where there is an ever-changing availability of energy on the catalyst surface. Our research indicates that by choosing a pulse “rhythm” that mathces the underlying transport phenomena and catalytic cycles, we can control the distribution of adsorbed species when the next pulse hits. This can have great benefits for enhancing the selectivity of catalytic reactions and manipulation of reaction pathways, which we’re eager to explore in our lab’s experiments.

Finally, rapid heat-pulsing also has the power to improve catalyst lifetime. Since the catalyst is not kept at a continuous high temperature and only transiently heated, slow processes that lead to catalyst degradation (sintering, migration) are avoided. Therefore, in our lab we explore how intense heat-pulses can improve long-term stability.

Key Publications: Baldi & Askes, ACS Catalysis 2023: Pulsed Photothermal Heterogeneous Catalysis

Nanoscale thermometry and heat localization: precision temperature mapping for catalysis

Accurately measuring and controlling nanoscale localized temperatures is crucial in a broad range of technologies, such as heat management of computer chips, quantum computers, and optimization of catalyst nanomaterials. However, traditional temperature measurements, such as thermocouples or infrared thermometry, lack the spatial resolution required to detect nanoscale temperature variations.

Together with the groups of Andrea Baldi and Charusheela Ramanan, our lab specializes in nanoscale thermometry, where we use Raman spectroscopy combined with Copper Phthalocyanine (CuPc) thin films as temperature-sensitive probes. This technique allows us to quantify localized temperature changes down to the nanometer scale.

Specifically, using CuPc as thermometer, we have developed a very robust thermometer that is able to reliably tell us the local temperature up to 300 °C. In the future we’re applying this technique to single nanoparticle studies (and beyond). Stay tuned for more!

Key Publications: Li et al., J. Phys. Chem. C 2023: Nanoscale Thermometry of Plasmonic Structures

Breaking the limit of nanoscale optical heating

One of the most exciting frontiers in photothermal catalysis is the ability to generate and control at a sub nanoparticle level. Such “thermal hotspots”, where heat is strongly confined in space, would offer us unprecedented control over reaction dynamics and enable us to drive chemical transformations with minimal energy input. We are actively working on an innovative way to generate such thermal hotspots, which could exist for hundreds of ps under pulsed illumination, thereby giving acces to extreme temperatures at “ultrafast thermal hotspots” with only mild illumination.

Ordinarily, the high thermal conductivity of metallic nanoparticles prevents nanostructures to have large internal thermal gradients. Therefore, in our lab we use unconventional materials that are much more suited for this approach: we design and fabricate plasmonic metal nitride nanostructures (HfN, TiN) as highly robust light-to-heat converters that can fully convert light energy to heat within a mere 100 fs.

Our research has shown that we can achieve precise temporal and spatial control of heat deposition and 3× higher temperatures than their gold analogues, which we will apply in the future to catalytic conversion. By controlling the intensity, frequency, and duration of light pulses, we will fine-tune heat transfer at the nm level, opening new pathways for light-driven chemical synthesis, catalysis, and materials transformations.

Key Publications: Askes and Garnett, Advanced Materials: Ultrafast thermal imprinting of plasmonic hotspots

Metal nitride plasmonics: advancing high-temperature and ultrafast catalysis with robust materials

Traditional plasmonic materials like gold (Au) and silver (Ag) have long been used in photothermal applications due to their strong light absorption properties. However, they suffer from thermal instability: at high temperatures, they melt, deform, and lose function.

To overcome these limitations, we investigate transition metal nitrides (such as hafnium nitride (HfN) and titanium nitride (TiN)) as alternative plasmonic materials for high-temperature applications. These materials offer: (1) Exceptional thermal stability, because they can withstand temperatures above 1000°C without degradation; (2) Broad optical absorption across visible and infrared wavelengths, making them highly efficient for a broad range of optical applications; and (3) Chemical robustness, as they are highly resistant to oxidation and corrosion

To explore the fabrication of HfN nanostructures, we have use focussed ion beam milling and electron-beam lithography to fabricate them and used cathodoluminesnce to map their plasmonic modes.

We also employed a colloidal synthesis to obtain HfN nanocrystals and explored their photophysical dynamics using transient absorption in combination with optical and heat-transfer FEM modelling using comsol. We discovered that such nanocrystals convert all absorbed light energy to heat within 100 fs due to very strong electron-phonon interactions in this material.

Key Publications:

O’Neill et al., Adv. Optical Mater. 2021: Ultrafast Photoinduced Heat Generation by Plasmonic HfN 

Askes et al., Nanoscale 2019: Tunable plasmonic HfN nanoparticles and arrays.

Simulating photothermal reactors and mapping thermal gradients to understand light-driven chemistry

In photothermal catalysis, understanding how light interacts with catalysts to generate heat is crucial for optimizing reaction efficiency. In light-driven reactions, temperature is rarely uniform, which can lead to large experimental errors.

While experimental measurements provide crucial insights, computational simulations are just as valuable because they allow us to predict temperature distributions, reaction kinetics, and energy transfer mechanisms with high precision.

In our lab, we develop multiscale simulation models that integrate:

Electromagnetic modeling (Lumerical FDTD, COMSOL) to study light absorption and heat generation in plasmonic nanostructures.

Heat transfer simulations (COMSOL) to track how heat propagates and dissipates at the nanoscale.

Microkinetic modeling to understand how temperature fluctuations influence reaction rates and selectivity.

Heat and fluid dynamics on the macroscale (COMSOL) to understand, design and engineer lab-scale photothermal reactors and simulate the whole system under illuminated conditions.

Key Publications: Szalad et al., ACS Catalysis 2025: Solving the Conundrum of the Influence of Irradiation Power on Photothermal CO2 Hydrogenation

Why our research matters

Our work in photothermal catalysis, nanoscale thermometry, and advanced materials provides fundamental breakthroughs in nanoscale heat management, catalysis, and sustainable chemistry. These discoveries pave the way for (1) More energy-efficient chemical reactors that use light instead of fossil fuels for heating; (2) Highly selective catalytic reactions that minimize unwanted byproducts; and (3) New nanomaterials that are stable under extreme conditions, expanding the possibilities of photothermal applications.

Want to collaborate on any of our topics? Contact us or further explore all our publications.