Single-atom catalysts have recently been applied in many applications such as CO oxidation. Experimental in situ investigations into this reaction, however, are limited. Hereby, we present a suite of ...operando/in situ spectroscopic experiments for structurally well-defined atomically dispersed Rh on phosphotungstic acid during CO oxidation. The identification of several key intermediates and the steady-state catalyst structure indicate that the reactions follow an unconventional Mars-van Krevelen mechanism and that the activation of O
is rate-limiting. In situ XPS confirms the contribution of the heteropoly acid support while in situ DRIFT spectroscopy consolidates the oxidation state and CO adsorption of Rh. As such, direct observation of three key components, i.e., metal center, support and substrate, is achieved, providing a clearer picture on CO oxidation on atomically dispersed Rh sites. The obtained information are used to engineer structurally similar catalysts that exhibit T
values up to 130 °C below the previously reported Rh
/NPTA.
In coordination chemistry, catalytically active metal complexes in a zero‐ or low‐valent state often adopt four‐coordinate square‐planar or tetrahedral geometry. By applying this principle, we have ...developed a stable Pt1 single‐atom catalyst with a high Pt loading (close to 1 wt %) on phosphomolybdic acid(PMA)‐modified active carbon. This was achieved by anchoring Pt on the four‐fold hollow sites on PMA. Each Pt atom is stabilized by four oxygen atoms in a distorted square‐planar geometry, with Pt slightly protruding from the oxygen planar surface. Pt is positively charged, absorbs hydrogen easily, and exhibits excellent performance in the hydrogenation of nitrobenzene and cyclohexanone. It is likely that the system described here can be extended to a number of stable SACs with superior catalytic activities.
An atomically dispersed Pt1 catalyst has been developed with a high catalyst loading where each Pt atom is anchored on supported phosphomolybdic acid with distorted square‐planar coordination geometry. The catalyst is highly active for nitrobenzene and cyclohexanone hydrogenation.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Unlike nanostructured metal catalysts, supported single-atom catalysts (SACs) contain only atomically dispersed metal atoms, hinting at much more pronounced metal–support effects. Herein, we take a ...series of polyoxometalate-supported Pt catalysts as examples to quantitatively investigate the stability of Pt atoms on oxide supports and how the Pt–support interaction influences the catalytic performance. For this entire series, we show that the Pt atoms prefer to stay at a 4-fold hollow site of one polyoxometalate molecule and that the least adsorption energy to obtain sintering-resistant Pt SACs is 5.50 eV, which exactly matches the cohesive energy of bulk Pt metal. Further, we compared their catalytic performance in several hydrogenation reactions and simulated the reaction pathways of propene hydrogenation by density functional theory (DFT) calculations. Both experimental and theoretical approaches suggest that despite the Pt1–support interactions being different, the reaction pathways of various Pt1–polyoxometalate catalysts are very similar and their effective reaction barriers are close to each other and as low as 24 kJ/mol, indicating the possibility of obtaining SACs with improved stability without compromising activity. DFT calculations show that all reaction elementary steps take place only on the Pt atom without involving neighboring O atoms and that hydrogenation proceeds from the molecularly adsorbed H2 species. Pt SACs give a weaker H2 adsorption energy than Pt clusters or surfaces, resulting in small adsorption equilibrium constants and small apparent activation barriers, which agree between experiment and theory.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Chemical synthesis of amino acids directly from biomass feedstock is rare. Reported here is a one‐step protocol to convert crude glycerol, from the biodiesel industry, into 43 % alanine over a ...Ru1Ni7/MgO catalyst. The multifunctional catalytic system promotes glycerol conversion into lactic acid, and then into alanine. X‐ray absorption spectroscopy and scanning transmission electron microscopy revealed the existence of bimetallic RuNi species, whereas density‐functional theory calculations suggested Ni‐doped Ru substantially decreased the Ea of C−H bond dissociation of lactate alkoxide to form pyruvate, which is the rate‐determining step. The catalytic route established in this work creates new opportunities for glycerol utilization and enriches the substrate scope of renewable feedstock to access value‐added amino acids.
Direct conversion: 43 % alanine was achieved from crude glycerol over a Ru1Ni7/MgO catalyst. Ni‐doped Ru remarkably promoted lactic acid amination, a key step in the reaction. The catalytic route creates new opportunities for glycerol utilization and enriches the substrate scope of renewable feedstock to access value‐added amino acids.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
In this paper, NiRu, NiRh, and NiPd catalysts were synthesized and evaluated in the hydrogenolysis of lignin C–O bonds, which is proved to be superior over single-component catalysts. The optimized ...NiRu catalyst contains 85% Ni and 15% Ru, composed of Ni surface-enriched, Ru–Ni atomically mixed, ultrasmall nanoparticles. The Ni85Ru15 catalyst showed high activity under low temperature (100 °C), low H2 pressure (1 bar) in β-O-4 type C–O bond hydrogenolysis. It also exhibited significantly higher activity over Ni and Ru catalysts in the direct conversion of lignin into monomeric aromatic chemicals. Mechanistic investigation indicates that the synergistic effect of NiRu can be attributed to three factors: (1) increased fraction of surface atoms (compared with Ni), (2) enhanced H2 and substrate activation (compared with Ni), and (3) inhibited benzene ring hydrogenation (compared with Ru). Similarly, NiRh and NiPd catalysts were more active and selective than their single-component counterparts in the hydrogenolysis of lignin model compounds and real lignin.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Abstract
Single-atom metal catalysts offer a promising way to utilize precious noble metal elements more effectively, provided that they are catalytically active and sufficiently stable. Herein, we ...report a synthetic strategy for Pt single-atom catalysts with outstanding stability in several reactions under demanding conditions. The Pt atoms are firmly anchored in the internal surface of mesoporous Al
2
O
3
, likely stabilized by coordinatively unsaturated pentahedral Al
3+
centres. The catalyst keeps its structural integrity and excellent performance for the selective hydrogenation of 1,3-butadiene after exposure to a reductive atmosphere at 200 °C for 24 h. Compared to commercial Pt nanoparticle catalyst on Al
2
O
3
and control samples, this system exhibits significantly enhanced stability and performance for
n
-hexane hydro-reforming at 550 °C for 48 h, although agglomeration of Pt single-atoms into clusters is observed after reaction. In CO oxidation, the Pt single-atom identity was fully maintained after 60 cycles between 100 and 400 °C over a one-month period.
The emergence of the Omicron variant of SARS-CoV-2 is an urgent global health concern
. In this study, our statistical modelling suggests that Omicron has spread more rapidly than the Delta variant ...in several countries including South Africa. Cell culture experiments showed Omicron to be less fusogenic than Delta and than an ancestral strain of SARS-CoV-2. Although the spike (S) protein of Delta is efficiently cleaved into two subunits, which facilitates cell-cell fusion
, the Omicron S protein was less efficiently cleaved compared to the S proteins of Delta and ancestral SARS-CoV-2. Furthermore, in a hamster model, Omicron showed decreased lung infectivity and was less pathogenic compared to Delta and ancestral SARS-CoV-2. Our multiscale investigations reveal the virological characteristics of Omicron, including rapid growth in the human population, lower fusogenicity and attenuated pathogenicity.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Propane dehydrogenation has been a promising propylene production process that can compensate for the increasing global demand for propylene. However, Pt-based catalysts with high stability at ≥600 ...°C have barely been reported because the catalysts typically result in short catalyst life owing to side reactions and coke formation. Herein, we report a new class of heterogeneous catalysts using high-entropy intermetallics (HEIs). Pt–Pt ensembles, which cause side reactions, are entirely diluted by the component inert metals in PtGe-type HEIs. The resultant HEI (PtCoCu) (GeGaSn)/Ca–SiO2 exhibited an outstandingly high catalytic stability, even at 600 °C (k d –1 = τ = 4146 h = 173 d), and almost no deactivation of the catalyst was observed for 2 months for the first time. Detailed experimental studies and theoretical calculations demonstrated that the combination of the site-isolation and entropy effects upon multi-metallization of PtGe drastically enhanced the desorption of propylene and the thermal stability, eventually suppressing the side reactions even at high reaction temperatures.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
A CO2‐mediated hydrogen storage energy cycle is a promising way to implement a hydrogen economy, but the exploration of efficient catalysts to achieve this process remains challenging. Herein, ...sub‐nanometer Pd–Mn clusters were encaged within silicalite‐1 (S‐1) zeolites by a ligand‐protected method under direct hydrothermal conditions. The obtained zeolite‐encaged metallic nanocatalysts exhibited extraordinary catalytic activity and durability in both CO2 hydrogenation into formate and formic acid (FA) dehydrogenation back to CO2 and hydrogen. Thanks to the formation of ultrasmall metal clusters and the synergic effect of bimetallic components, the PdMn0.6@S‐1 catalyst afforded a formate generation rate of 2151 molformate molPd−1 h−1 at 353 K, and an initial turnover frequency of 6860 molH2
molPd−1 h−1 for CO‐free FA decomposition at 333 K without any additive. Both values represent the top levels among state‐of‐the‐art heterogeneous catalysts under similar conditions. This work demonstrates that zeolite‐encaged metallic catalysts hold great promise to realize CO2‐mediated hydrogen energy cycles in the future that feature fast charge and release kinetics.
Sub‐nanometer Pd–Mn clusters were encaged within silicalite‐1 zeolites by a ligand‐protected method under direct hydrothermal conditions. The obtained zeolite‐encaged metallic nanocatalysts exhibited a record formate generation rate of 2151 molformate molPd−1 h−1 at 353 K, and an excellent initial turnover frequency of 6860 molH2
molPd−1 h−1 for CO‐free formic acid decomposition at 333 K without any additive.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
PDF
