Development of novel catalysts for ammonia synthesis and decomposition under mild conditions

Thesis

Ammonia has recently been regarded as a promising energy vector for on-board hydrogen generation purposes thanks to the breakthrough in renewable powers. The intermittent nature of these energies mean that both the generation and utilisation of ammonia need to be carried out at mild temperatures and pressures to afford frequent ramping. Under such conditions, catalysts are easily prone to hydrogen poisoning where the surface active sites are extensively blocked by H atoms originated from the competitive reaction between dihydrogen and other gaseous reactants. In such context, this thesis explores the use of a metal-doped electrostatically polar refractory oxide catalyst for efficient thermal catalytic ammonia synthesis and decomposition reactions with the primary aim to alleviate hydrogen poisoning. In-depth catalytic activity and kinetic order studies were examined for both the forward and backward N-cycle reaction. A thorough round of surface characterisations combined with a series of spectroscopic, imaging and computational techniques were conducted to investigate the relationship between the activity and the structural and electronic properties of the catalyst.

In the second part of the thesis, the polar oxide catalyst was aptly modified to construct a well-defined frustrated Lewis pair to decipher the elemental pathway for which H atoms are transferred from the metal active site to the catalytic support. Atom probe tomography in conjunction with in-situ x-ray photoelectron spectroscopy were employed to reconstruct the 3D environment of the spillover effect and the surface changes were monitored in real-time.

Authors: Wu, S

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Catalyst design; ammonia synthesis; ammonia decomposition; nanotechnology; hydrogen storage; green energy utilisation; polar material
• Subjects: Chemistry; Nanotechnology