Acid-Catalyzed Liquid ALD Growth of Lanthanum Aluminate Thin Films Using Stoichiometric Injections

Atomic-level control in catalyst synthesis is critical for optimizing the catalytic performance. Here, we have developed a generalizable and scalable liquid atomic layer deposition (L-ALD) technique using stoichiometric injections of metal alkoxide precursors to deposit lanthanum on Al₂O₃ nanoparticles, with precise control over surface chemistry and catalyst properties. Quantitative gas chromatography revealed distinct stoichiometric reaction stages during lanthanum deposition, showing initial ligand exchange with surface hydroxyl groups and transition to sterically hindered saturation due to limited hydroxyl utilization. Optimized acidic hydrolysis conditions (1 mM HNO₃, 40 °C) ensured a nearly complete counter-reaction with unreacted ligands, regenerating hydroxyl sites effectively and promoting consistent deposition cycles. Cyclic L-ALD systematically modulated the surface acidic and basic sites, influencing the catalytic behavior. As a model reaction, an La thin-film coating of Al₂O₃ was demonstrated for enhanced and selective catalytic performance in oxidative coupling of methane (OCM), with a C₂₊ hydrocarbon selectivity of 32% with a stable (90 h) CH₄ conversion (∼35 to 40%) after five deposition cycles. Structural and spectroscopic characterizations (X-ray diffraction (XRD), TEM, X-ray photoelectron spectroscopy (XPS), and CO₂/NH₃TPD) confirmed the formation of uniform, conformal lanthanum aluminate layers, controlled lanthanum dispersion, and optimized electronic interactions at the catalyst surface. This work demonstrates how atomic-scale deposition techniques can precisely tune surface and electronic properties, enabling enhanced catalytic selectivity and stability for complex environmentally and energy-related reactions such as OCM.