The transition from fossil fuels to renewable energy sources is hindered by the intermittent nature of renewables, necessitating efficient energy storage solutions. H2, a carbon-free energy carrier with the highest mass-energy density (33.3 kWh.kg-1), is a promising option. However, its direct use is limited by safety concerns, including a wide flammability range (4-75 vol%) in air, high flame speed, elevated flame temperature (over 2100 °C), and, consequently, NOx emissions. Therefore, in all the H2 applications, maintaining its concentration below the lower flammability limit in air is crucial. Catalytic H2 combustion (CHC), therefore, emerges as a promising alternative to overcome these challenges. State-of-the-art CHC catalysts are based on Pt and Pd, which can initiate the reaction at room temperature. However, at high H2 concentrations, the rapid water formation rate will extinguish the reaction. This operational drawback, combined with cost and resource scarcity, underscores the need for alternative catalysts based on earth-abundant transition metals (TMs). Replacing Pt and Pd while addressing their limitations remains a central challenge, necessitating a deeper understanding of reaction kinetics, catalytic mechanisms, and nanoscale engineering of metal particles.
To ensure reliable catalytic activity comparisons, we developed a method to calculate metal dispersion that considers nanoparticles' (NP) geometry and crystal structure. It is demonstrated that an incorrect geometry assumption (such as spherical nanoparticles) would introduce errors in dispersion and turnover frequency (TOF) calculations, ultimately leading to unreliable assessments of catalytic activity.
We then synthesised a series of TM-Al2O3 catalysts (TM = Pt, Ru, Co, Ni, Mo) and evaluated their CHC activity. Owing to the high activity of the Pt-Al2O3 catalyst, a new low-temperature plug-flow reactor is designed and built. By integrating the multi-ion detection mode of a quadrupole mass spectrometer (QMS) with an analogue inputted thermocouple, a high data acquisition rate is achieved, which is essential for reliably determining the kinetic parameters. Moreover, it is found that the Ru-Al2O3 and Co-Al2O3 catalysts exhibited similar CHC activity with long-term stability.
To optimise Ru utilisation and maximise the H2 conversion rate, we tuned the Ru NPs' size to modulate the metal-support interaction (MSI). Advanced spectroscopic and microscopy methods revealed that NP's size influences Ru dispersion, MSI and the ratio between Ru-O and Ru0, which plays a critical role in the CHC activity. Furthermore, using in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), the role of OH groups in the CHC reaction mechanism is identified, a finding further validated by density functional theory (DFT) calculations.
Lastly, we investigate the effect of operational parameters on the CHC stability of the Pt-Al2O3 catalyst to control the water-induced deactivation. Usin
