Repetitively Coupled Chemical Reduction and Galvanic Exchange as a Synthesis Strategy for Expanding Applicable Number of Pt Atoms in Dendrimer-Encapsulated Pt Nanoparticles

In this study, we report the controllable synthesis of dendrimer-encapsulated Pt nanoparticles (Pt DENs) utilizing repetitively coupled chemical reduction and galvanic exchange reactions. The synthesis strategy allows the expansion of the applicable number of Pt atoms encapsulated inside dendrimers to more than 1000 without being limited by the fixed number of complexation sites for Pt²⁺ precursor ions in the dendrimers. The synthesis of Pt DENs is achieved in a short period of time (i.e., ∼10 min) simply by the coaddition of appropriate amounts of Cu²⁺ and Pt²⁺ precursors into aqueous dendrimer solution and subsequent addition of reducing agents such as BH₄^–, resulting in fast and selective complexation of Cu²⁺ with the dendrimers and subsequent chemical reduction of the complexed Cu²⁺ while uncomplexed Pt²⁺ precursors remain oxidized. Interestingly, the chemical reduction of Cu²⁺, leading to the formation of Cu nanoparticles encapsulated inside the dendrimers, is coupled with the galvanic exchange of the Cu nanoparticles with the nearby Pt²⁺. This coupling repetitively proceeds until all of the added Pt²⁺ ions form into Pt nanoparticles encapsulated inside the dendrimers. In contrast to the conventional method utilizing direct chemical reduction, this repetitively coupled chemical reduction and galvanic exchange enables a substantial increase in the applicable number of Pt atoms up to 1320 in Pt DENs while maintaining the unique features of DENs

In Situ Analyses of Carbon Dissolution into Ni-YSZ Anode Materials

A combination of in situ analyses, including measurement of both electrical resistance and volumetric expansion, and thermogravimetric analysis (TGA) was employed to elucidate the deactivation process of a nickel-yttria-stabilized zirconia (Ni-YSZ) cermet (60 wt % NiO-YSZ) upon exposure to methane at 750 °C. In conjunction with the aforementioned in situ techniques, a number of ex situ analyses, including scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), and Raman spectroscopy, revealed that carbon deposition initially occurred at the Ni centers, followed by carbon dissolution into the Ni-YSZ cermet after an induction period of 200 min, which then led to three-dimensional expansion. The structural change of the Ni-based cermet induced increases in electrical resistance of the material. The increased electrical resistance likely originated from the breakage of the Ni–Ni conducting network as well as from the formation of microscopic cracks within the Ni-YSZ material, resulting from the observed process of carbon dissolution. Moreover, a combination of TGA involving measurements of electrical resistance was demonstrated to be useful for determining amounts of carbon deposits critical for carbon dissolution. These results strongly suggest that changes in electrical resistance can be utilized to monitor the extent of carbon dissolution into the Ni-YSZ catalysts in situ, which would be helpful for the development of an efficient curing system for solid oxide fuel cells (SOFCs)

Influence of Cation Substitutions Based on ABO₃ Perovskite Materials, Sr_1–<i>x</i>Y_<i>x</i>Ti_1–<i>y</i>Ru_<i>y</i>O_3−δ, on Ammonia Dehydrogenation

In order to screen potential catalytic materials for synthesis and decomposition of ammonia, a series of ABO₃ perovskite materials, Sr_1–<i>x</i>Y_<i>x</i>Ti_1–<i>y</i>Ru_<i>y</i>O_3−δ (<i>x</i> = 0, 0.08, and 0.16; <i>y</i> = 0, 0.04, 0.07, 0.12, 0.17, and 0.26) were synthesized and tested for ammonia dehydrogenation. The influence of A or B site substitution on the catalytic ammonia dehydrogenation activity was determined by varying the quantity of either A or B site cation, producing <b>Sr</b>_{<b>1</b>–<b><i>x</i></b>}<b>Y</b>_{<b><i>x</i></b>}Ti_0.92Ru_0.08O_3−δ and Sr_0.92Y_0.08<b>Ti</b>_{<b>1</b>–<i><b>y</b></i>}<b>Ru</b>_{<b><i>y</i></b>}O_3−δ, respectively. Characterizations of the as-synthesized materials using different analytical techniques indicated that a new perovskite phase of SrRuO₃ was produced upon addition of large amounts of Ru (≥12 mol %), and the surface Ru⁰ species were formed simultaneously to ultimately yield <b>Ru</b>_{<b><i>z</i></b>}(surface)/Sr_0.92Y_0.08<b>Ti</b>_{<b>1</b>–<b><i>y</i></b>}<b>Ru</b>_{<i><b>y</b></i>–<b><i>z</i></b>}O_3−δ and/or <b>Ru</b>_{<b><i>z</i></b>–<b><i>w</i></b>}(surface)/Sr_<i>w</i>Ru_<i>w</i>O₃/Sr_{0.92–<i>w</i>}Y_0.08<b>Ti</b>_{<b>1</b>–<b><i>y</i></b>}<b>Ru</b>_{<b><i>y</i></b>–<b><i>z</i></b>}O_3−δ. The newly generated surface Ru⁰ species at the perovskite surfaces accelerated ammonia dehydrogenation under different conditions, and Sr_0.84Y_0.16Ti_0.92Ru_0.08O_3−δ exhibited a NH₃ conversion of ca. 96% at 500 °C with a gas hourly space velocity (GHSV) of 10 000 mL g_cat^–1 h^–1. In addition, Sr_0.84Y_0.16Ti_0.92Ru_0.08O_3−δ further proved to be highly active and stable toward ammonia decomposition at different reaction temperatures and GHSVs for >275 h

Amine/Hydrido Bifunctional Nanoporous Silica with Small Metal Nanoparticles Made Onsite: Efficient Dehydrogenation Catalyst

Multifunctional catalysts are of great interest in catalysis because their multiple types of catalytic or functional groups can cooperatively promote catalytic transformations better than their constituents do individually. Herein we report a new synthetic route involving the surface functionalization of nanoporous silica with a rationally designed and synthesized dihydrosilane (3-aminopropylmethylsilane) that leads to the introduction of catalytically active grafted organoamine as well as single metal atoms and ultrasmall Pd or Ag-doped Pd nanoparticles via on-site reduction of metal ions. The resulting nanomaterials serve as highly effective bifunctional dehydrogenative catalysts for generation of H₂ from formic acid