First-Principles Study of Oxygen-Induced Disintegration and Ripening of Late Transition Metal Nanoparticles on Rutile-TiO₂(110)

Abstract

Under an industry-related high-temperature oxidation atmosphere, the structure and chemical states of metal nanocatalysts meeting sustainable development challenges change dramatically, deteriorating the activity and/or lowering the yield. Theoretically revealing the mechanisms of oxygen-induced structure evolution and establishing a framework to distinguish them are vital to improving the operando stability and rational design of metal nanocatalysts. Here, we studied the oxygen-induced disintegration and Ostwald ripening of Ni, Cu, Pt, Pd, and Ag nanoparticles on TiO2(110) using first-principles-based thermodynamic and kinetic simulations. It was found that oxygen promotes Ostwald ripening via the formation of Ag/Ag–O and Pd intermediates on the support and volatile gaseous PtO2 complexes, induces disintegration of Ni nanoparticles to Ni–O complexes, and leads to the formation of copper oxide. These differences in the deactivation pathways can be attributed to the dependence of the ripening activation energies and disintegration free energies on the interaction between metal atoms/complexes and TiO2(110). Revealed knowledge and corresponding models provide valuable insights into the general mechanisms governing the structural evolution of supported nanocatalysts under reaction conditions.

Oxidative Redispersion-Derived Single-Site Ru/CeO2 Catalysts with Mobile Ru Complexes Trapped by Surface Hydroxyls Instead of Oxygen Vacancies

“…Equation indicated that when migrating across the support surface, the mobile Ru(CO) n complexes could be “trapped” at the cost of isolated hydroxyls. According to Li and co-workers, − both CO and O 2 were typical adsorbents that gave rise to adatom complexes with low diffusion barrierprecursors of the disintegration of supported metal nanoparticles (i.e., Δ G NP dis < 0 with X = CO or O 2 in eq ). By replacing the adsorbed CO atoms in eq with O atoms, the OH-Ru–O x interactions over CeO 2 could be presented in eq : Ru − O x + Ce 3 + − OH − → Ce 4 + − O lattice 2 − − Ru − O x + 1 / 2 H 2 ↑ …”

“…The relatively high Ru dispersion of the as-received catalyst was evidenced by CO chemisorption (Table ) and was reconfirmed by the absence of Ru-related phases in the XRD pattern (Figure S3). To launch “oxidative redispersion” of the supported Ru nanoparticles, the as-received catalyst was calcined in an air flow (200 mL/min) at 300 °C for 1 ha proven strategy to produce single-site Ru species over CeO 2 . ,,, The thus-obtained sample (O300) did show a 1.6 times increased Ru dispersion (Table ), indicating that the disintegration of Ru nanoparticles occurred during the oxidation treatment. − As illustrated in Table , such treatment did not lead to detectable Ru loss. Therefore, the redispersion process was more likely induced by Ru particle disintegration and surface atom migration rather than trapping of gaseous species like RuO 4 , which was in consistent with the results obtained by Liu et al Nevertheless, small Ru nanoparticles (with an average diameter of 1.3 nm) could still be found on the surface of O300 (Figure C), some of which were covered with oxide overlayers (see Figure D and Figure S4, probably corresponding to the Ru@RuO 2 core–shell structure , ).…”

“…After exposing the H 2 -prtreated Ru/CeO 2 to air, the adsorption of O atoms on Ru sites gave rise to mobile Ru− O x complexes (e.g., Ru−O or O−Ru−O) within 1 min, which detached from the Ru nanoparticles and migrated across the CeO 2 surface. 22 When encountering the hydrogenated (type II or III) steps over CeO 2 (111), these complexes could be trapped as Ce 4+ −O lattice 2− −Ru−O x at the cost of OH (II) groups and give rise to single-site Ru species (see discussion about Figure 5). As a piece of evidence for such stabilization, some atomically dispersed Ru species could be indeed observed on sufficiently thin parts of CeO 2 step edges (see Figure S24).…”

“…Specifically, as a necessary reactant for catalytic combustion, gaseous O 2 may interact with the supported metal nanoparticles and lead to “oxidative redispersion”. Based on the model proposed by Li and co-workers, − such redispersion falls under the broad umbrella of Ostwald ripening and can be launched only when the Gibbs free energy of disintegration, Δ G NP dis , of the supported metal nanoparticles (with radius of curvature R ) into the metal–reactant complexes is negative, i.e., normalΔ G NP dis false( R , T , P X false) = E X f − normalΔ E̅ NP false( R false) − n normalΔ μ X false( T , P X false) − T ΔS < 0 where X refers to reactants (e.g., CO, NO, and O 2 ). According to eq , at given catalysts (constant R ) and reaction conditions (constant T and P X ), an exothermic adatom complex formation energy ( E X f ) is crucial for the disintegration of metal nanoparticles.…”

Growth inhibition of bacterial pathogens by photo-catalyst process of nano-alloys FeCuNi doped TiO2 under ultraviolet irradiation

“…TiO 2 has three crystal structures namely brookite, rutile, and anatase. The last two crystal structures are thermodynamically more stable [ 9 ] with the band gap energy (Eg) of ±3.0–3.2 eV. When compared to the rutile structure, the anatase TiO 2 phase structure has more excellent photo-catalytic properties including electron transfer rate that is 89 times greater, chemically and biologically inert, mechanical toughness, low cost and non-toxic [ 10 , 11 , 12 , 13 , 14 ].…”