Adsorption of PTCDI induces a bandgap opening on graphene, due to the specific electronic structure of PTCDI, characterized by a LUMO energetically located in the vicinity of the Dirac point. The ...approach is highly versatile for bandgap engineering, tuning the bandgap by modifying the adsorption geometry, the active adsorbate coverage, or by chemical modifications of the adsorbate.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
Metal promotion is the most widely adopted strategy for enhancing the hydrogenation functionality of an oxide catalyst. Typically, metal nanoparticles or dopants are located directly on the ...catalyst surface to create interfacial synergy with active sites on the oxide, but the enhancement effect may be compromised by insufficient hydrogen delivery to these sites. Here, we introduce a strategy to promote a ZnZrO
x
methanol synthesis catalyst by incorporating hydrogen activation and delivery functions through optimized integration of ZnZrO
x
and Pd supported on carbon nanotube (Pd/CNT). The CNT in the Pd/CNT + ZnZrO
x
system delivers hydrogen activated on Pd to a broad area on the ZnZrO
x
surface, with an enhancement factor of 10 compared to the conventional Pd-promoted ZnZrO
x
catalyst, which only transfers hydrogen to Pd-adjacent sites. In CO
2
hydrogenation to methanol, Pd/CNT + ZnZrO
x
exhibits drastically boosted activity—the highest among reported ZnZrO
x
-based catalysts—and excellent stability over 600 h on stream test, showing potential for practical implementation.
The adsorption and diffusion of benzene, hexafluorinated benzene, perylene, perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI) and perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) on ...graphene has been studied by density functional means on a generalized gradient approximation level, including a semi-empirical correction to account for dispersive forces. It is shown that for all considered molecules the adsorption strength is mainly due to the latter, with the electronic interaction being relatively small and repulsive. As a rule-of-thumb, the strength of the adsorption interaction is 11–13kJmol−1 per C atom. The adsorption energies are large enough to avoid desorption at room temperature. The estimated diffusion and rotation barriers are remarkably small, thus allowing a rapid diffusion and self-arrangement even at cryogenic temperatures. Finally, the adsorption of benzene or perylene derivatives may act, depending on the molecule and nature of the substituents, as a source for n- or p-doping, achieving up to 0.2 electrons(holes)/molecule. The lowest unoccupied molecular orbitals of PTCDI and PTCDA are close in energy to the Dirac point of graphene and induce a conduction gap of ∼210–240meV in the graphene band structure. Thus, they can be used for graphene band gap engineering and doping by the non-aggressive method of molecular adsorption.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Beyond the catalytic activity of nanocatalysts, the support with architectural design and explicit boundary could also promote the overall performance through improving the diffusion process, ...highlighting additional support for the morphology‐dependent activity. To delineate this, herein, a novel mazelike‐reactor framework, namely multi‐voids mesoporous silica sphere (MVmSiO2), is carved through a top‐down approach by endowing core‐shell porosity premade Stöber SiO2 spheres. The precisely‐engineered MVmSiO2 with peripheral one‐dimensional pores in the shell and interconnecting compartmented voids in the core region is simulated to prove combined hierarchical and structural superiority over its analogous counterparts. Supported with CuZn‐based alloys, mazelike MVmSiO2 nanoreactor experimentally demonstrated its expected workability in model gas‐phase CO2 hydrogenation reaction where enhanced CO2 activity, good methanol yield, and more importantly, a prolonged stable performance are realized. While tuning the nanoreactor composition besides morphology optimization could further increase the catalytic performance, it is accentuated that the morphological architecture of support further boosts the reaction performance apart from comprehensive compositional optimization. In addition to the found morphological restraints and size‐confinement effects imposed by MVmSiO2, active sites of catalysts are also investigated by exploring the size difference of the confined CuZn alloy nanoparticles in CO2 hydrogenation employing both in‐situ experimental characterizations and density functional theory calculations.
Through endowing core‐shell porosity to premade Stöber SiO2 spheres, a novel mazelike reactor configuration with complex hierarchical porosity is realized. Such mazelike nanoreactors offer peripheral 1D channels in shell and interconnecting compartmented voids in the core region, boost catalysis performance, and improve utilization of metals supported by the silica phase.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Oxide overlayers covering metal supports find applications in sensors, catalysis, microelectronics, and optical devices. For example, depending on the choice of metal support, ZnO films may serve as ...sensors for hydrogen or ethanol and exhibit catalytic activity in CO oxidation or methanol synthesis, which is catalyzed in the chemical industry by intensely studied Cu-ZnO catalysts. Here, we apply density functional (DFT) calculations to characterize the properties of periodic ZnO monolayers supported on close-packed surfaces of various metals (Mo, Ru, Pd, Pt, Cu, Ag, Au, Sn, and Pb) under oxidative, ambient, and hydrogenation conditions. Thermodynamic analysis revealed high stability of the films on most metals, except highly reactive Mo and insufficiently reactive Sn and Pb. Metal-oxide interactions are found to have a significant and locally uneven effect on the electronic structure of ZnO. Compared to pristine ZnO, the supported ZnO films show a higher propensity for H adsorption and O vacancy formation, whose energies may be tuned by more than 1 eV depending on the choice of metal support. As a result, under hydrogenation conditions supported ZnO films are calculated to adsorb significant quantities of H or develop O vacancies, unlike pristine ZnO. The calculations reveal how the composition, stability and reactivity of ZnO films are affected by the metal support and provide guidelines for the rational design of ZnO-metal interfaces.
The composition, electronic structure, and chemical properties of ZnO
x
H
y
films can be engineered by the choice of underlying metal support.
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•Bimetallic CuNi nanoparticles on ZrO2 were characterized by FTIR, NAP-XPS and DFT.•After reduction, Cu rich surfaces were observed even for Ni rich nanoparticles.•Methane ...decomposition at 425°C induced Ni segregation on the surface.•DFT indicated that adsorbed CHx provided the major driving force.•An “ideal” CuNi nanoparticle is suggested.
Bimetallic CuNi nanoparticles of various nominal compositions (1:3, 1:1, 3:1) supported on ZrO2 were employed for operando spectroscopy and theoretical studies of stable surface compositions under reaction conditions of catalytic methane decomposition up to 500°C. The addition of Cu was intended to increase the coke resistance of the catalyst. After synthesis and (in situ) reduction the CuNi nanoparticles were characterized by HR-TEM/EDX, XRD, FTIR (using CO as probe molecule) and NAP-XPS, all indicating a Cu rich surface, even when the overall nanoparticle composition was rich in Ni. Density functional (DF) theory modelling, applying a recently developed computational protocol based on the construction of topological energy expressions, confirmed that in any studied composition Cu segregation on surface positions is an energetically favourable process, with Cu preferentially occupying corner and edge sites. Ni is present on terraces only when not enough Cu atoms are available to occupy all surface sites.
When the catalysts were applied for methane decomposition they were inactive at low temperature but became active above 425°C. Synchrotron-based operando NAP-XPS indicated segregation of Ni on the nanoparticle surface when reactivity set in for CuNi-ZrO2. Under these conditions C 1s core level spectra revealed the presence of various carbonaceous species at the surface. DF calculations indicated that both the increase in temperature and especially the adsorption of CHx groups (x=0-3) induce the segregation of Ni atoms on the surface, with CH3 providing the lowest and C the highest driving force.
Combined operando and theoretical studies clearly indicate that, independent of the initial surface composition after synthesis and reduction, the CuNi-ZrO2 catalyst adopts a specific Ni rich surface under reaction conditions. Based on these findings we provide an explanation why Cu rich bimetallic systems show improved coke resistance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We have studied the interaction of water with stoichiometric CeO2(111)/Cu(111), partially reduced CeO2–x /Cu(111), and Pt/CeO2/Cu(111) model catalysts by means of synchrotron–radiation photoelectron ...spectroscopy (SRPES), resonant photoemission spectroscopy (RPES) at the Ce 4d edge, infrared reflection absorption spectroscopy (IRAS), and density functional (DF) calculations. The principal species formed during adsorption of water at 160 K on CeO2(111) films is chemisorbed molecular water. On the surface of CeO2–x water partially dissociates yielding hydroxyl groups. By use of core-level PES, differentiation between chemisorbed water and hydroxyl groups is complicated by the overlap of the corresponding spectral features. Nevertheless, we determined three characteristic indicators for OH groups on ceria: (i) the presence of 1π and 3σ states in valence band (VB) PES; (ii) an increase of the binding energy (BE) separation between the O 1s spectral components of lattice oxygen and OH/H2O; (iii) an increase of the amplitude of the Ce3+ resonance in RPES. Chemisorbed water desorbs below 400 K and hydroxyl groups vanish at 500 K. The most favorable configurations of chemisorbed water and hydroxyl groups have been investigated by DF calculations. Both CeO2(111) and CeO2–x involve strongly tilted H2O and OH species which complicate their detection by IRAS. On Pt/CeO2, water adsorbs molecularly at 160 K but undergoes partial dissociation during annealing. The dissociation of water is accompanied by spillover of hydrogen to ceria and formation of hydroxyl groups between 180 and 250 K. Above 250 K, decomposition of hydroxyl groups and reverse spillover of hydrogen from ceria to Pt occurs, followed by desorption of molecular water.
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The product of ozonolysis, glycero-(9,10-trioxolane)-trioleate (ozonide of oleic acid triglyceride, OTOA), was incorporated into polylactic acid/polycaprolactone (PLA/PCL) blend films in the amount ...of 1, 5, 10, 20, 30 and 40%
/
. The morphological, mechanical, thermal and antibacterial properties of the biodegradable PLA/PCL films after the OTOA addition were studied. According to DSC and XRD data, the degree of crystallinity of the PLA/PCL + OTOA films showed a general decreasing trend with an increase in OTOA content. Thus, a significant decrease from 34.0% for the reference PLA/PCL film to 15.7% for the PLA/PCL + 40% OTOA film was established using DSC. Observed results could be explained by the plasticizing effect of OTOA. On the other hand, the PLA/PCL film with 20% OTOA does not follow this trend, showing an increase in crystallinity both via DSC (20.3%) and XRD (34.6%). OTOA molecules, acting as a plasticizer, reduce the entropic barrier for nuclei formation, leading to large number of PLA spherulites in the plasticized PLA/PCL matrix. In addition, OTOA molecules could decrease the local melt viscosity at the vicinity of the growing lamellae, leading to faster crystal growth. Morphological analysis showed that the structure of the films with an OTOA concentration above 20% drastically changed. Specifically, an interface between the PLA/PCL matrix and OTOA was formed, thereby forming a capsule with the embedded antibacterial agent. The moisture permeability of the resulting PLA/PCL + OTOA films decreased due to the formation of uniformly distributed hydrophobic amorphous zones that prevented water penetration. This architecture affects the tensile characteristics of the films: strength decreases to 5.6 MPa, elastic modulus E by 40%. The behavior of film elasticity is associated with the redistribution of amorphous regions in the matrix. Additionally, PLA/PCL + OTOA films with 20, 30 and 40% of OTOA showed good antibacterial properties on
,
(
) and
, making the developed films potentially promising materials for wound-dressing applications.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Cerium dioxide is a compound important for heterogeneous catalysis, energy technologies, biomedical applications,
etc.
One of its most remarkable properties is low O vacancy (O
vac
) formation energy
...E
f
. Nanostructuring of ceria was shown to decrease
E
f
and to make the oxide material more active in oxidative reactions. Here we investigate computationally formation of O
vac
on CeO
2
(111) surfaces nanostructured by steps with experimentally observed structures. To facilitate the search for O
vac
+ 2Ce
3+
configurations that yield the lowest
E
f
values we proposed and employed an efficient computational scheme where DFT +
U
calculations were preceded by a pre-screening procedure based on the results of plain DFT calculations.
E
f
values on the steps were calculated to be up to 0.7 eV lower than on a regular CeO
2
(111) surface. Some energetically stable O
vac
+ 2Ce
3+
configurations were found to include subsurface Ce
3+
ions. The present results quantify to what extent the roughness of the CeO
2
(111) surface affects its reducibility.
Oxygen vacancies (O
vac
) are by 0.5-0.7 eV more stable on steps than on CeO
2
(111) terraces. An efficient procedure has been proposed to search for the most stable O
vac
+ 2Ce
3+
configurations.
Oxidative addition (OA) is a necessary step in mechanisms of widely used synthetic methodologies such as the Heck reaction, cross-coupling reactions, and the Buchwald-Hartwig amination. This study ...pioneers the exploration of OA of aryl halide to palladium nanoparticles (NPs), a process previously unaddressed in contrast to the activity of well-studied Pd(0) complexes. Employing DFT modeling and semi-empirical metadynamics simulations, the oxidative addition of phenyl bromide to Pd nanoparticles was investigated in detail. Energy profiles of oxidative addition to Pd NPs were analyzed and compared to those involving Pd(0) complexes forming under both ligand-stabilized (phosphines) and ligandless (amine base) conditions. Metadynamics simulations highlighted the edges of the (1 1 1) facets of Pd NPs as the key element of oxidative addition activity. We demonstrate that OA to Pd NPs is not only kinetically facile at ambient temperatures but also thermodynamically favorable. This finding accentuates the necessity of incorporating OA to Pd NPs in future investigations, thus providing a more realistic view of the involved catalytic mechanisms. These results enhance the understanding of aryl halide (cross-)coupling reactions, reinforcing the concept of a catalytic "cocktail". This concept posits dynamic interconversions between diverse active and inactive centers, collectively affecting the outcome of the reaction. High activity of Pd NPs in direct C-X activation paves the way for novel approaches in catalysis, potentially enhancing the field and offering new catalytic pathways to consider.
A computational elucidation of the mechanism of R-X oxidative addition to Pd nanoparticles revealed high activity at the edges of nanoparticles and identified key intermediates before and after oxidative addition.
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