This work raises a fundamental question about the “real” structure of molecular compounds containing three different metals: whether they consist of genuine hetero tri metallic species or of a mixture of parent hetero bi metallic species. Heterotrimetallic complex Li 2 CoNi(tbaoac) 6 ( 1 , tbaoac = tert -butyl acetoacetate) has been designed based on the model tetranuclear structure featuring two transition metal sites in order to be utilized as a molecular precursor for the low-temperature preparation of the LiCo 0.5 Ni 0.5 O 2 battery cathode material. An investigation of the structure of 1 appeared to be very challenging, since the Co and Ni atoms have very similar atomic numbers, monoisotopic masses, and radii as well as the same oxidation state and coordination number/environment. Using a statistical analysis of heavily overlaid isotope distribution patterns of the [Li 2 MM′L 5 ] + (M/M′ = Co 2 , Ni 2 , and CoNi) ions in DART mass spectra, it was concluded that the reaction product 1 contains both heterotrimetallic and bimetallic species. A structural analogue approach has been applied to obtain Li 2 MMg(tbaoac) 6 (M = Co ( 2 ) and Ni ( 3 )) complexes that contain lighter, diamagnetic magnesium in the place of one of the 3d transition metals. X-ray crystallography, mass spectrometry, and NMR spectroscopy unambiguously confirmed the presence of three types of molecules in the reaction mixture that reaches an equilibrium, Li 2 M 2 L 6 + Li 2 Mg 2 L 6 ↔ 2Li 2 MMgL 6 , upon prolonged reflux in solution. The equilibrium mixture was shown to have a nearly statistical distribution of the three molecules, and this is fully supported by the results of theoretical calculations revealing that the stabilization energies of hetero tri metallic assemblies fall exactly in between those for the parent hetero bi metallic species. The LiCo 0.5 Ni 0.5 O 2 quaternary oxide has been obtained in its phase-pure form by thermal decomposition of heterometallic precursor 1 at temperatures as low as 450 °C. Its chemical composition, structure, morphology, and transition metal distribution have been studied by X-ray and electron diffraction techniques and compositional energy-dispersive X-ray mapping with nanometer resolution. The work clearly illustrates the advantages of heterometallic single-source precursors over the corresponding multi-source precursors.
more »
« less
Fundamental understanding of the synthesis of well-defined supported non-noble metal intermetallic compound nanoparticles
Access to well-defined, model-like, non-noble metal intermetallic compound nanomaterials (<10 nm) with phase pure bulk, bulk-like 1st-atomic-layer surface composition, and unique electronic and surface chemical properties is critical for the fields of catalysis, electronics, and sensor development. Non-noble metal intermetallic compounds are compositionally ordered solid compounds composed of transition metals and semimetals or post-transition metals. Their synthesis as model-like high-surface-area supported nanoparticles is challenging due to the elevated reactivity of the constituent elements and their interaction with the support material. In this study, we have developed a systematic understanding of the fundamental phenomena that control the synthesis of these materials such that phase pure bulk nanoparticles (<10 nm) may be produced with bulk-like surface terminations. The effects of the precursor and support choice, chemical potential of H 2 , reduction temperature, and annealing procedures were investigated to understand the fundamental kinetics of particle formation and interactions that dictate phase purity and stability and 1st-atomic-layer surface composition. The understanding developed may serve as a foundation for further developing advanced synthesis procedures for well-defined nanoparticles with increasing compositional complexity.
more »
« less
- Award ID(s):
- 1752063
- NSF-PAR ID:
- 10332838
- Date Published:
- Journal Name:
- Catalysis Science & Technology
- Volume:
- 12
- Issue:
- 11
- ISSN:
- 2044-4753
- Page Range / eLocation ID:
- 3568 to 3581
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract Phase‐pure [NiO]0.5[Al2O3]0.5spinel nanoparticles (NPs) with limited aggregation were obtained via liquid‐feed flame spray pyrolysis (LF‐FSP) by combusting metalloorganic precursor solutions. Thereafter “chocolate chip‐like” Nix[NiO0.5‐x][Al2O3]0.5nanoparticles consisting of primary [NiO0.5‐x][Al2O3]0.5particles with average particle sizes of 40‐60 nm decorated with Ni metal particles (<10 nm in diameter) dispersed on the surface were synthesized by heat treating the spinel NPs at 800°C/7 h in flowing 5% H2:N2100 mL/min in a fluidized bed reactor. The synthesized materials were characterized using TEM, XRD, FTIR, and TGA/DTA. The Ni depleted areas consist primarily of γ‐Al2O3. The Ni content (800°C) was determined by TGA to be ≈11.3 wt.% based on TGA oxidation behavior. The successful synthesis of such nanocomposites with limited aggregation on a high temperature support provides a facile route to synthesize well‐defined NP catalysts. This work serves as a baseline study for an accompanying paper, wherein thin, flexible, dense films made from these same NPs are used as regenerable catalysts for carbon nanotube syntheses.
-
Metal nanoparticles possessing a high density of atomic steps and edge sites provide an increased population of undercoordinated surface atoms, which can enhance the catalytic activity of these materials compared to low-index faceted or bulk materials. Simply increasing reactivity, however, can lead to a concurrent increase in undesirable, non-selective side products. The incorporation of a second metal at these reactive stepped features provides an ideal avenue for finely attenuating reactivity to increase selectivity. A major challenge in synthesizing bimetallic nanomaterials with tunable surface features that are desirable for fundamental catalytic studies is a need to bridge differences in precursor reduction potentials and metal lattice parameters in structures containing both a noble metal and a non-noble metal. We report the use of low micromolar concentrations of iodide ions as a means of differentially controlling the relative reduction rates of a noble metal (palladium) and a non-noble metal (copper). The iodide in this system increases the rate of reduction of palladium ions while concurrently slowing the rate of copper ion reduction, thus providing a degree of control that is not achievable using most other reported means of tuning metal ion reduction rate. This differential control of metal ion reduction afforded by iodide ions enables access to nanoparticle growth conditions in which control of palladium nanoparticle growth by copper underpotential deposition becomes possible, leading to the generation of unique terraced bimetallic particles. Because of their bimetallic surface composition, these terraced nanoparticles exhibit increased selectivity to acetaldehyde in gas phase ethanol oxidation.more » « less
-
more » « less
Abstract Porous noble metal nanoparticles have received particular attention recently for their unique optical, thermal, and catalytic functions in biomedicine. However, limited progress has been made to synthesize such porous metallic nanostructures with large mesopores (≥25 nm). Here, a green yet facile synthesis strategy using biocompatible liposomes as templates to mediate the formation of mesoporous metallic nanostructures in a controllable fashion is reported. Various monodispersed nanostructures with well‐defined mesoporous shape and large mesopores (≈ 40 nm) are successfully synthesized from mono‐ (Au, Pd, and Pt), bi‐ (AuPd, AuPt, AuRh, PtRh, and PdPt), and tri‐noble metals (AuPdRh, AuPtRh, and AuPdPt). Along with a successful demonstration of its effectiveness in synthesis of various mesoporous nanostructures, the possible mechanism of liposome‐guided formation of such nanostructures via time sectioning of the synthesis process (monitoring time‐resolved growth of mesoporous structures) and computational quantum molecular modeling (analyzing chemical interaction energy between metallic cations and liposomes at the enthalpy level) is also revealed. These mesoporous metallic nanostructures exhibit a strong photothermal effect in the near‐infrared region, effective catalytic activities in hydrogen peroxide decomposition reaction, and high drug loading capacity. Thus, the liposome‐templated method provides an inspiring and robust avenue to synthesize mesoporous noble metal‐based nanostructures for versatile biomedical applications.
-
more » « less
Abstract In addition to the conventional knobs such as composition, size, shape, and defect structure, the crystal structure (or phase) of metal nanocrystals offers a new avenue for engineering their properties. Various strategies have recently been developed for the fabrication of colloidal metal nanocrystals in metastable phases different from their bulk counterparts. With a focus on noble metals, we begin with a brief introduction to their atomic packing, followed by a discussion about five major synthetic approaches to their colloidal nanocrystals in unconventional phases. We then highlight the success of synthesis in terms of mechanistic insights and experimental controls, as well as the enhanced catalytic properties. We end this Minireview with perspectives on the remaining issues and future opportunities.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2CY00183G
