In this article, we describe the development of a new aerobic C−H oxidation methodology catalyzed by a precious metal-free LaMnO 3 perovskite catalyst. Molecular oxygen is used as the sole oxidant in this approach, obviating the need for other expensive and/or environmentally hazardous stoichiometric oxidants. The electronic and structural properties of the LaMnO 3 catalysts were systematically optimized, and a reductive pretreatment protocol was proved to be essential for acquiring the observed high catalytic activities. It is demonstrated that this newly developed method was extremely effective for the oxidation of alkylarenes to ketones as well as for the oxidative dimerization of 2-naphthol to 1,1-binaphthyl-2,2-diol (BINOL), a particularly important scaffold for asymmetric catalysis. Detailed spectroscopic and mechanistic studies provided valuable insights into the structural aspects of the active catalyst and the reaction mechanism.
Copper nanowires (Cu NWs) hold promise as they possess equivalent intrinsic electrical conductivity and optical transparency to silver nanowires (Ag NWs) and cost substantially less. However, poor resistance to oxidation is the historical challenge that has prevented the large-scale industrial utilization of Cu NWs. Here, we use benzotriazole (BTA), an organic corrosion inhibitor, to passivate Cu NW networks. The stability of BTApassivated networks under various environmental conditions was monitored and compared to that of bare Cu NW control samples. BTA passivation greatly enhanced the stability of networks without deteriorating their optoelectronic performance. Moreover, to demonstrate their potential, BTA-passivated networks were successfully utilized in the fabrication of a flexible capacitive tactile sensor. This passivation strategy has a strong potential to pave the way for large-scale utilization of Cu NW networks in optoelectronic devices.
Fundamental understanding
of catalytic deactivation phenomena such
as sulfur poisoning occurring on metal/metal-oxide interfaces is essential
for the development of high-performance heterogeneous catalysts with
extended lifetimes. Unambiguous identification of catalytic poisoning
species requires experimental methods simultaneously delivering accurate
information regarding adsorption sites and adsorption geometries of
adsorbates with nanometer-scale spatial resolution, as well as their
detailed chemical structure and surface functional groups. However,
to date, it has not been possible to study catalytic sulfur poisoning
of metal/metal-oxide interfaces at the nanometer scale without sacrificing
chemical definition. Here, we demonstrate that near-field nano-infrared
spectroscopy can effectively identify the chemical nature, adsorption
sites, and adsorption geometries of sulfur-based catalytic poisons
on a Pd(nanodisk)/Al2O3 (thin-film) planar model
catalyst surface at the nanometer scale. The current results reveal
striking variations in the nature of sulfate species from one nanoparticle
to another, vast alterations of sulfur poisoning on a single Pd nanoparticle
as well as at the assortment of sulfate species at the active metal–metal-oxide
support interfacial sites. These findings provide critical molecular-level
insights crucial for the development of long-lifetime precious metal
catalysts resistant toward deactivation by sulfur.
SO x uptake and release properties of LaMnO 3 , Pd/LaMnO 3 , LaCoO 3 and Pd/LaCoO 3 perovskites were investigated via in situ Fourier transform infrared (FTIR) spectroscopy, temperature programmed desorption and X-ray photoelectron spectroscopy. Sulfation of the perovskite leads to the formation of surface sulfite/sulfate and bulk-like sulfate species. Pd addition to LaMnO 3 and LaCoO 3 significantly increases the sulfur adsorption capacity. Pd/LaMnO 3 sample accumulates significantly more sulfur than LaMnO 3 ; however it can also release a larger fraction of the accumulated SO x species in a reversible fashion at elevated temperatures in vacuum. This is not the case for Co-based materials, where thermal regeneration of bulk sulfates on poisoned LaCoO 3 and Pd/ LaCoO 3 is extremely ineffective under similar conditions. However, in the presence of an external reducing agent such as H 2 (g), Pd/LaMnO 3 requires much lower temperature (873 K) for complete sulfur regeneration as compared to that of Pd/LaCoO 3 (973 K). Sequential CO and SO x adsorption experiments performed via in situ FTIR indicate that in the presence of carbonyls and/or carbonates, Pd adsorption sites may have a stronger affinity for SO x as compared to that of the perovskite surface, particularly in the early stages of sulfur poisoning.
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