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The scalable and facile preparation of single-atom catalysts remains a critical challenge. Here, we introduce Diluted Atomic Layer Deposition (DALD), a unique approach for synthesizing supported metal catalysts with precisely tunable loadings. Unlike conventional metal deposition by ALD which uses pure metal precursors, DALD employs a diluted precursor mixture, combining organometallic precursors with the corresponding free ligand in controlled ratios. The method enables precise control over metal loadings, allowing the synthesis of structures ranging from nanoparticles to isolated single atoms, as exemplified by Ir, Rh, and Pt on high-surface-area γ-Al2O3. With its inherent simplicity and exceptional efficiency in metal precursor utilization, DALD represents a highly scalable strategy, unlocking opportunities for integrating single-atom catalysts into industrial processes. 

H2 activation is fundamental in catalysis. Single-atom catalysts (SACs) can be highly selective hydrogenation catalysts due to their tunable geometric and electronic properties. In this work, H2 activation (adsorption, splitting, and diffusion) on the anatase TiO2-supported SAC has been modeled in detail. The stable configurations of 14 transition metals from 3d to 5d (Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Os, Ir, Pt, and Au) and Sn have been screened. We compared H and H2 adsorption and H2 heterolytic and homolytic splitting on SA/TiO2. H on the SAC in neutral, hydridic, and proton forms and the preferred H2 dissociation paths are revealed. We found that the metal adatoms strengthen the Brønsted acids via forming the SA-O bonds and promote the H adsorption on Ti sites via forming the Ti3+ sites. The electronic descriptor using the energy level of the frontier d orbital, referenced to vacuum, can predict the single H and H2 dissociative adsorption energies on the metal site. As the SA-Hδ- interaction is stronger than Ti-Hδ-, the activation barriers for heterolytic paths over SA-O sites are lower than over Ti-O sites. H2 adsorption is activated on Au, Ru, Rh, Pd, and Ir in a dihydrogen complex structure with an elongated H-H bond. Homolytic splitting over SA sites is favored thermodynamically and kinetically on Rh, Pd, Os, Ir, and Pt. In contrast, for the remaining SA/TiO2, H-H splitting at the SA-O is kinetically favored compared to the Ti-O sites, but the products are less thermodynamically favored.