Pathways towards true catalysts: computational modelling and structural transformations of Zn-polyoxotungstates

Ni, Lubin; Güttinger, Robin; Triana, Carlos A.; Spingler, Bernhard; Baldridge, Kim K.; Patzke, Greta R.

doi:10.1039/c9dt03018b

Cited by 4 publications

(1 citation statement)

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“…Relating to the latter class, the classical strategy consists in tuning the particle size and/or morphology of noble metal oxides to maximize surface area and, therefore, the exposure of active centers. − Alternatively, other successful approaches consist of using mixed metal oxides, − depositing oxide nanoparticles ,, or atomically dispersed metal centers , on conductive supports, or doping layered inorganic materials of earth-abundant elements with small amounts of noble metals. ,,− An additional advantage of using mixed metal materials often lies in the possibility of having cooperative effects between redox active and nonactive centers, − similar to what happens with Mn and Ca in the biological oxygen evolving complex.…”

Section: Introductionmentioning

confidence: 99%

Iridium-Doped Nanosized Zn–Al Layered Double Hydroxides as Efficient Water Oxidation Catalysts

Fagiolari

Bini

Costantino

et al. 2020

ACS Appl. Mater. Interfaces

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Layered double hydroxides (LDHs) are an ideal platform to host catalytic metal centers for water oxidation (WO) owing to the high accessibility of water to the interlayer region, which makes all centers potentially reachable and activated. Herein, we report the syntheses of three iridium-doped zinc–aluminum LDHs (Ir-LDHs) nanomaterials ( 1–3 , with about 80 nm of planar size and a thickness of 8 nm as derived by field emission scanning electron microscopy and powder X-ray diffraction studies, respectively), carried out in the confined aqueous environment of reverse micelles, through a very simple and versatile procedure. These materials exhibit excellent catalytic performances in WO driven by NaIO 4 at neutral pH and 25 °C, with an iridium content as low as 0.5 mol % (∼0.8 wt %), leading to quantitative oxygen yields (based on utilized NaIO 4 , turnover number up to ∼10,000). Nanomaterials 1–3 display the highest ever reported turnover frequency values (up to 402 min –1 ) for any heterogeneous and heterogenized catalyst, comparable only to those of the most efficient molecular iridium catalysts, tested under similar reaction conditions. The boost in activity can be traced to the increased surface area and pore volume (>5 times and 1 order of magnitude, respectively, higher than those of micrometric materials of size 0.3–1 μm) estimated for the nanosized particles, which guarantee higher noble metal accessibility. X-ray absorption spectroscopy (XAS) studies suggest that 1–3 nanomaterials, as-prepared and after catalysis, contain a mixture of isolated, single octahedral Ir(III) sites, with no evidence of Ir–Ir scattering from second-nearest neighbors, excluding the presence of IrO 2 nanoparticles. The combination of the results obtained from XAS, elemental analysis, and ionic chromatography strongly suggests that iridium is embedded in the brucite-like structure of LDHs, having four hydroxyls and two chlorides as first neighbors. These results demonstrate that nanometric LDHs can be successfully exploited to engineer efficient WOCs, minimizing the amount of iridium used, consistent with the principle of the noble-metal atom economy.

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