Top Site Research Articles

Density Functional Theory Study on the Influence of Cation and Anion Elements Doping on the Surface of Ti3C2 on the Adsorption Performance of Formaldehyde

Based on the generalized gradient approximation of density functional theory, the geometric structure and electronic properties of the intrinsic Ti3C2 and Cu-, Pt-, Co-, Si-, F-, Cl- or Br-doped Ti3C2 are optimized, and the adsorption process of HCHO on the surface of the intrinsic Ti3C2 and doped Ti3C2 is calculated. The effects of adsorption energy, stability, DOS and doping on bond length were discussed. The results show that the adsorption energy of the intrinsic Ti3C2 crystal plane at the top site is the strongest, at −7.58 eV. The optimal adsorption sites of HCHO on various doping systems are Cu-Top, Pt-Top, Co-Top, Si-Hollow, Cl-Hollow, F-Bridge and Br-Hollow, respectively. Among the doped elements, anion (F, Cl, Br) doping at each adsorption site generally reduces the formaldehyde adsorption activity of the substrate; cationic doping (Cu, Pt, Co, Si) enhances the adsorption activity of the substrate for formaldehyde at most of the adsorption sites, indicating that the modification effect of anions on Ti3C2 is not as good as that of cations. The adsorption capacity of Si-doped Ti3C2 for formaldehyde was significantly improved. Compared with the intrinsic Ti3C2 crystal plane at the same adsorption site, the adsorption activity of HCHO was improved, and the highest adsorption energy was −8.09 eV.

ReaxFF Molecular Dynamics Simulations of Large Gold Nanocrystals.

A systematic study of gold nanocrystals is carried out using molecular dynamics simulations with reactive force fields. The nanocrystal size is varied between 2 and 10 nm with methane and butane thiolate as ligands. The reactive force fields allow investigation of the formation of staples. The simulations explain several experimental observations such as the number of staples per thiolate of about 40% and the occupation of the top adsorption sites on the facets. They also show that the frequency of staples is increased on the edges, which leads to a desorption of gold atoms from the nanocrystal edges. In contrast to previous nonreactive simulations, no difference between the distances of the ligands on the nanocrystal edges and facets is observed. Except for the 2 nm particles, the nanocrystal size and the alkane chain length of the ligands have only a small influence on the nanocrystal properties. The occupation of adsorption sites and staple frequencies are very slowly converging properties, taking more than ns.

Ab initio investigation of the role of the d-states on the adsorption and activation properties of CO2 on 3d, 4d, and 5d transition-metal clusters.

We report a theoretical investigation of the adsorption and activation properties of CO2 on eight-atom 3d, 4d, and 5d transition-metal (TM) clusters based on density functional theory calculations. From our results and analyses, in the lowest energy configurations, CO2 binds via a chemisorption mechanism on Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt (adsorption energy from -0.49eV on Pt up to -1.40eV on Os), where CO2 breaks its linearity and adopts an angular configuration due to the charge transfer from the clusters toward the C atom in the adsorbed CO2. In contrast, it binds via physisorption on Cu, Ag, and Au and maintains its linearity due to a negligible charge transfer toward CO2 and has a small adsorption energy (from -0.17eV on Cu up to -0.18eV on Ag). There is an energetic preference for twofold bridge TM sites, which favors binding of C with two TM atoms, which enhances the charge transfer ten times than on the top TM sites (onefold). We identified that the strength of the CO2-TM8 interaction increases when the energy values of the highest occupied molecular orbital (HOMO) of the TM8 are closer to the energy values of the lowest unoccupied molecular orbital of CO2, which contributes to maximize the charge transfer toward the molecule. Beyond the energy position of the HOMO states, the delocalization of 5d orbitals plays an important role in the adsorption strength in TM, especially for the iron group, e.g., the adsorption energies are -1.08eV (Fe, 3d), -1.19eV (Ru, 4d), and -1.40eV (Os, 5d).

Is Scoliosis Associated with Dance Injury in Young Recreational Dancers? A Large-Scale Cross-Sectional Epidemiological Study.

Some studies suggested that adolescent scoliotic dancers were more likely to sustain dance injuries than non-scoliotic dancers. This study aimed to investigate the association between scoliosis and dance injury among children and adolescent recreational dancers. Identical web-based and paper-based questionnaires were distributed to children and adolescent recreational dancers to collect demographic information, dance experiences, history and location of dance injuries, as well as the frequency of dance injury in the last 12 months. The prevalence rates of the top three dance injury sites (lower back, knee, and ankles) were estimated. Associations between the presence of scoliosis and various dance injuries in the last 12 months were evaluated by multivariate logistic regression. Data from 704 respondents (644 females, 13.3 ± 2.4 years) was analyzed. Ninety-one respondents (12.9%) reported scoliosis and 11 respondents (1.6%) were wearing scoliosis braces. The 12-month prevalence rates of lumbar, knee, and ankle injuries in scoliotic dancers (24.2%, 22.2%, and 28.5%, respectively) were significantly higher than those of non-scoliotic dancers (10.4%, 14.9%, and 14.8%, respectively). Scoliosis was an independent risk factor for lumbar spine injury (Odds ratio, OR = 2.7), knee injury (OR = 2.6), and multi-site dance-related injury (OR = 1.9). Given the observed strong associations between scoliosis and lumbar or knee dance injuries in the current study, future studies are warranted to investigate the underlying causes.

Site Logistics Factors Impacting Resource Use on Construction Sites: A Delphi Study

Over 48% of the world’s energy is consumed by buildings in their construction and operation alone, which add to over 39% of global carbon emissions. In addition, the building sector generates over 569 million tons of waste every year within just the United States. Reducing the environmental impacts and construction waste generated by buildings has, therefore, become a concerning global issue. Very few studies have addressed how site logistics planning may impact construction resource use on a site and how it may affect a project’s embodied energy. Site logistics plans control the sequencing of labor, materials, and equipment. Inefficient plans may lead to rework, material damage, and waste generation, requiring additional materials to complete the same task, which eventually increases the embodied energy of a project. In this study, we investigated, identified, and ranked site logistics-related factors that may affect the amount of resources used in a construction project. The Delphi Method is applied to determine, verify, and rank these factors to help improve existing methods of site logistics planning from an embodied energy perspective. Results show that the installer’s skill, technology/equipment, prefabrication, planning and forecasting, and material movement are among the top influential site logistics-related factors that may help reduce construction waste. Considering these factors while developing the site logistics plan will help lower the energy and carbon footprint of a construction project.

Adsorption of Transition-Metal Clusters on Graphene and N-Doped Graphene: A DFT Study.

Using the dispersion-corrected density functional theory (DFT-D3) method, we systematically studied the adsorption of 15 kinds of transition-metal (TM) clusters on pristine graphene (Gr) and N-doped graphene (N-Gr). It has been found that TMn (n = 1-4) clusters adsorbed on the N-Gr surface are much stronger than those on the pristine Gr surface, while 3d series clusters present similar geometries on Gr and N-Gr surfaces. The most preferred sites of TMs migrate from hollow to bridge to the top site on the Gr surface along the d series in the periodic table, while the preferred sites of TMs migrate in a much more complex manner on the N-Gr surface. It has also been found that charge transfer decreases along the d series for adsorbed clusters on both surfaces, but adsorbed clusters present less charge transfer on the N-Gr surface than on the Gr surface. What is more interesting is that some TM (Tc, Ru, and Re) clusters change the growth mechanism from the three-dimensional (3D) growth mode on the Gr surface to the two-dimensional (2D) growth mode on the N-Gr surface. At last, it has been found that adsorbed clusters are more dispersed on the N-Gr surface than on the pristine Gr surface due to growth and average aggregation energies.

Fundamental invariant-neural network potential energy surface and dissociative chemisorption dynamics of N2 on rigid Ni(1 1 1)

We constructed a new full-dimensional potential energy surface (PES) for the dissociative chemisorption of N2 on rigid Ni(111). The PES was fitted using the fundamental invariant-neural network method based on DFT energy points. The resulting PES is accurately fitted with very small fitting error of about 4.5 meV, which reproduces well the minimum energy path and energies of stationary points. Based on the new PES, the effects of incidence energy, incidence angle as well as the vibrational excitations of impinging molecules on dissociation probability were investigated by quasi-classical trajectory calculations. The vibrational excitation enhances the reactivity more effectively than the same amount of translational energy, which is consistent with the very “product-like” transition state for this system. The dissociation occurs close to the bridge site, presumably due to the extremely tight and high-energy barriers of PES at top and hollow sites.

Enhanced adsorption performance of subordinate magnesium sites in pinhole magnesium oxide nanosheets with rich oxygen vacancies

Phosphorus recovery from wastewater is important for protecting the aquatic environment and achieving sustainable development. However, as a typical phosphorus adsorbent, nanoscale magnesium oxide (MgO) exhibits aggregation and limited adsorption ability. Herein, melamine foam (MF) was selected as a self-sacrifice template to prepare an oxygen-vacancy-rich MgO/MF phosphate adsorbent with high dispersion and a multistage pore structure. Density-functional theory calculations reveal that the phosphate preferentially adsorbed on the hollow sites rather than top sites of MgO when there were oxygen vacancies, which improved the intrinsic adsorption ability of MgO/MF. The MgO/MF adsorbent exhibited excellent phosphorus removal from water within a wide pH range of 2–12; the maximum adsorption capacity of phosphate was as high as 1226 ​mg/g. The adsorption capacity of the MgO/MF adsorbent after phosphate adsorption was reactivated to ca. 100%. After six adsorption cycles, MgO/MF with a high phosphate content of 117.5 ​mg ​P/g is a potential high-quality fertilizer. This work provides a promising strategy for constructing an efficient adsorbent for wastewater treatment and resource recovery.

Theoretical investigation of the hydrogen production by adsorption of methanol on bimetallic Pd-Ge (1 1 0) surface as future green combustible using DFT-D method: Energetic and structural aspect of interaction pathways of metal with methanol

Dehydrogenation and adsorption mechanism of methanol on PdGe (110) surface was undertaken using self-consistent periodic DFT-D. Different kinds of adsorption modes of relevant intermediates on the surface were identified. It was found that methanol and CHO prefer to adsorb on top site(tPd), CH3O, CH2OH adsorb on top(tGe), while CHOH, COH, CO, and H adsorb on bridge(bPdPd) and CH2O on top(tPd; tGe) sites. The four-way reactions indicated that the initial OH bond scission of methanol seems to be more favorable than CH bond cleavage on PdGe (110) from the perspective of activation barriers. It is also shown that (CH3OH → CH3O → CH2O → CHO → CO) is the predominant pathway on PdGe (110). Ge Insertion in Pd(110) shows that the predominant path is different from those of Pd(100), Pd(111), also the activation barrier of PdGe (110) is lower than those of Pd(100), Pd(111).

The vibrational and thermodynamic properties of hydrogen adsorbed on the Pt(100) surface: a theoretical study

The adsorption of hydrogen on the Pt(100) surface is investigated theoretically within the conventional ultrahigh vacuum (UHV) surface modeling. Both density functional theory (DFT) and Monte Carlo (MC) simulation are implemented to determine the stability, the vibrational properties of the adsorbed hydrogen atom, and the H-H pair interactions. From the converged data, it is found that the H adsorbed on the bridge sites (B sites) have the strongest binding energy. Meanwhile, the H adsorbed on the top sites (T sites) have the highest vertical stretching frequency. In the increment of H coverage (), up to 1 ML, only the H on the B sites are counted. The shape of the g-value curve obtained by MC simulation shows a good agreement with the result of the cyclic voltammetry (CV) measurement. Reducing the pair interaction parameters by about 30%, the g-value is also decreased. From 0.3 to 0.6 with respect to the g-value is extremely fitted to the experimental data. This indicates that the interactions of H-H on the Pt(100) surface within the range of are mainly attributed to those hydrogen atoms adsorbed on the B sites.

Near‐Surface Geomechanical Properties and Weathering Characteristics Across a Tectonic and Climatic Gradient in the Central Nepal Himalaya

AbstractShallow bedrock strength controls both landslide hazard and the rate and form of erosion, yet regional patterns in near‐surface mechanical properties are rarely known quantitatively due to the challenge in collecting in situ measurements. Here we present seismic and geomechanical characterizations of the shallow subsurface across the central Himalayan Range in Nepal. By pairing widely distributed 1D shear wave velocity surveys and engineering outcrop descriptions per the Geological Strength Index classification system, we evaluate landscape‐scale patterns in near‐surface mechanical characteristics and their relation to environmental factors known to affect rock strength. We find that shallow bedrock strength is more dependent on the degree of chemical and physical weathering, rather than the mineral and textural differences between the metamorphic lithologies found in the central Himalaya. Furthermore, weathering varies systematically with topography. Bedrock ridge top sites are highly weathered and have S‐wave seismic velocities and shear strength characteristics that are more typical of soils, whereas sites near valley bottoms tend to be less weathered and characterized by high S‐wave velocities and shear strength estimates typical of rock. Weathering on hillslopes is significantly more variable, resulting in S‐wave velocities that range between the ridge and channel endmembers. We speculate that variability in the hillslope environment may be partly explained by the episodic nature of mass wasting, which clears away weathered material where landslide scars are recent. These results underscore the mechanical heterogeneity in the shallow subsurface and highlight the need to account for variable bedrock weathering when estimating strength parameters for regional landslide hazard analysis.

Zinc-Blende GeC Stabilized on GaN (001): An Ab Initio Study

First-principle calculations have been performed to explore the initial stages of the zinc blende-like germanium carbide epitaxial growth on the gallium nitride (001)-(2 × 2) surface. First, we studied the Ge/C monolayer adsorption and incorporation at high symmetry sites. Results show that the adsorptions at the top and hcp1 sites are the most stable structures of C and Ge, respectively. Different terminated surfaces were used on the GeC epitaxial growth. According to the surface formation energies, only the first two bilayers are stable; therefore, the GeC epitaxial growth is favorable only under N-rich conditions on a Ge-terminated surface and with Ge bilayers terminated. In addition, it is demonstrated that GeC bilayers on the C-terminated surfaces are unstable and preclude the epitaxial growth. Electronic properties have been investigated by calculating the density of states (DOS) and the projected density of states (PDOS) of the most favorable structures.

The Evolving Role of Social Media in Pediatric Orthopaedics.

Social media has grown significantly and its application in health care has been dramatically accentuated by the COVID-19 pandemic. It is often considered as a "new dimension" of health care, particularly in its ability to provide health information. In 2017, the top social media sites utilized by pediatric orthopaedic surgeons included Facebook, LinkedIn, and Twitter. In our study, we analyze the current social media usage, trends in Instagram and TikTok content, and the perceptions on social media usage among pediatric orthopaedic surgeons. The Pediatric Orthopaedic Society of North America (POSNA) membership directory was searched for the presence of social media. A review of all Instagram and TikTok posts made by the POSNA members were reviewed. A survey regarding the perception of social media networks and content was distributed to all POSNA members. A total of 1231 POSNA members actively practicing in the United States were included in our study. In all, 327 (26.6%) had a LinkedIn profile, 34 (2.8%) had a professional Facebook profile, 15 (1.2%) had a public Instagram account, 0 (0%) had TikTok, and 72 (5.8%) had a professional Twitter account. Fifteen POSNA members with public Instagram accounts had 10,878 followers. A total of 907 Instagram posts were made, 134 (14.8%) of which were education and 462 (50.9%) of which were personal or political. The perception of various social media networks such as Instagram (3.02), Facebook (3.16), and LinkedIn (3.51) were positive on a 5-point Likert scale, while perceptions of TikTok (2.36) and Twitter (2.99) were negative. Educational posts on Instagram (3.19) and Facebook (3.37) were positive. We provide an update to the utilization of social media by pediatric orthopaedists. Use of Instagram and TikTok accounts remain rare. Educational posts, when hosted on an appropriate social media platform, are perceived positively among pediatric orthopaedists. Level IV.

Amorphous-crystalline cobalt phosphide hollow nanocubes induced by dual ligand environment for highly efficient hydrogen evolution

CoP is one of the most promising catalysts for catalyzing hydrogen evolution reaction. The foremost issue is how to improve intrinsic activity by regulating electronic structure at the molecular level. Herein, utilizing selective combination of EDTA and Co2+, an amorphous-crystalline CoP with lower valence cobalt and hollow porous structure which induced by dual ligand environment is successfully synthesized via microwave heating and following phosphating process. Synthesize CoPBA from EDTA3+ and Co3+ in a ratio of 1:1 and followed by phosphating (ECP-1) exhibits excellent performance for HER in alkaline media, requiring 173 mV to achieve 10 mA cm−2. The enhanced catalytic activity may be ascribed to the amorphous-crystalline crystal structure with enlarged exposure of active sites and the hollow porous framework induced by EDTA, as well as the homogeneously distribution of (111) plane, on which the change of free energy on both Co bridge sites and P top sites is close to zero when adsorbing hydrogen. Besides, its great catalytic stability has been evaluated via 1000 cycles of CV measurement. The possible mechanism of valence state regulation of cobalt ions in CoP is discussed in detail. Furthermore, the optimal ratio of EDTA to Co2+ and different precursor states are explored reasonably.

Methanol decomposition on Ni(111) and O/Ni(111).

Methanol decomposition on Ni(111) surfaces has been studied in the presence and absence of oxygen using temperature-programmed desorption and temperature-dependent sum frequency generation spectroscopy. Under both conditions the C-H and O-H bonds break, forming carbon monoxide and atomic hydrogen on the surface. No C-O bond scission was observed, limiting the number of reaction pathways. The O-H bonds break first (>150K), forming surface methoxy, followed by C-H bond breakage (>250K). All atomic hydrogen desorbs from the surface as H2 through H+H recombinative desorption. H2 desorbs at a higher temperature in the presence of oxygen (>300K) than the absence of oxygen (>250K) as the oxygen on the surface stabilizes the H atoms, forming surface hydroxide (OH). The surface oxygen also appears to stabilize the O-H and C-H bonds, leading to slightly higher dissociation temperatures. The CO molecules occupy both the bridge sites and the top sites of the Ni atoms as surface H appears to force the CO molecules to the top sites. There is a slight blueshift in the C-O bond vibration for both the O covered and O free surfaces due to CO being more mobile. On the O free surface, the C-O peak width broadens as low-frequency modes are activated. Finally, CO desorbs between 350 and 400K.

Decreased DNA Methylation of RGMA is Associated with Intracranial Hypertension After Severe Traumatic Brain Injury: An Exploratory Epigenome-Wide Association Study.

Cerebral edema and intracranial hypertension are major contributors to unfavorable prognosis in traumatic brain injury (TBI). Local epigenetic changes, particularly in DNA methylation, may influence gene expression and thus host response/secondary injury after TBI. It remains unknown whether DNA methylation in the central nervous system is associated with cerebral edema severity or intracranial hypertension post TBI. We sought to identify epigenome-wide DNA methylation patterns associated with these forms of secondary injury after TBI. We obtained genome-wide DNA methylation profiles of DNA extracted from ventricular cerebrospinal fluid samples at three different postinjury time points from a prospective cohort of patients with severe TBI (n = 89 patients, 254 samples). Cerebral edema and intracranial pressure (ICP) measures were clustered to generate composite end points of cerebral edema and ICP severity. We performed an unbiased epigenome-wide association study (EWAS) to test associations between DNA methylation at 419,895 cytosine-phosphate-guanine (CpG) sites and cerebral edema/ICP severity categories. Given inflated p values, we conducted permutation tests for top CpG sites to filter out potential false discoveries. Our data-driven hierarchical clustering across six cerebral edema and ICP measures identified two groups differing significantly in ICP based on the EWAS-identified CpG site cg22111818 in RGMA (Repulsive guidance molecule A, permutation p = 4.20 × 10-8). At 3-4days post TBI, patients with severe intracranial hypertension had significantly lower levels of methylation at cg22111818. We report a novel potential relationship between intracranial hypertension after TBI and an acute, nonsustained reduction in DNA methylation at cg22111818 in the RGMA gene. To our knowledge, this is the largest EWAS in severe TBI. Our findings are further strengthened by previous findingsthat RGMA modulates axonal repair in other central nervous system disorders, but a role in intracranial hypertension or TBI has not been previously identified. Additional work is warranted to validate and extend these findings, including assessment of its possible role in risk stratification, identification of novel druggable targets, and ultimately our ability to personalize therapy in TBI.

Investigation of the Adhesion Strength, Fracture Toughness, and Stability of M/Cr2N and M/V2N (M = Ti, Ru, Ni, Pd, Al, Ag, and Cu) Interfaces Based on First-Principles Calculations

Obtaining detailed information regarding the interfacial characteristics of metal/hexagonal-TMN composites is imperative for developing these materials with optimal mechanical properties. To this end, we systematically investigate the work of adhesion, fracture toughness, and interfacial stability of M/Cr2N and M/V2N interfaces using first-principles calculations. The orientation (0001) of hexagonal phases and (111) of fcc phases are selected as the interface orientations. Accordingly, we construct M/Cr2N interface models by considering 1N, 2N, and Cr terminations of Cr2N(0001), as well as two stacking sequences (top and hollow sites) for the 1N- and 2N-terminated interface models, respectively. The M/V2N interface models are constructed in the same way. The V-terminated Ni/V2N interface is demonstrated to provide a good combination of the work of adhesion, fracture toughness, and interfacial stability. Therefore, the Ni/V2N interface model can be regarded as the preferred configuration among the metal/hexagonal-TMN interface models considered. The present results offer a practical perspective for tailoring the interfaces in metal/hexagonal-TMN composite materials to obtain improved mechanical properties.

Most Attractive Scenic Sites of the Bulgarian Black Sea Coast: Characterization and Sensitivity to Natural and Human Factors

Beach management is a complex process that demands a multidisciplinary approach, as beaches display a large variety of functions, e.g., protection, recreation and associated biodiversity conservation. Frequently, conflicts of interest arise, since management approaches are usually focused on recreation, preferring short-term benefits over sustainable development strategies; meanwhile, coastal areas have to adapt and face a changing environment under the effects of long-term climate change. Based on a “Sea, Sun and Sand (3S)” market, coastal tourism has become a major economic sector that depends completely on the coastal ecosystem quality, whilst strongly contributing to its deterioration by putting at risk its sustainability. Among beach users’ preferences, five parameters stand out: safety, facilities, water quality, litter and scenery (the “Big Five”), and the latter is the focus of this paper. Bulgaria has impressive scenic diversity and uniqueness, presenting real challenges and opportunities as an emerging tourist destination in terms of sustainable development. However, most developing countries tend to ignore mistakes made previously by developed ones. In this paper, scenic beauty at 16 coastal sites was field-tested by using a well-known methodology, i.e., the Coastal Scenic Evaluation System (CSES), which enables the calculation of an Evaluation Index “D” based on 26 physical and human parameters, utilizing fuzzy logic matrices. An assessment was made of these high-quality sites located in Burgas (8), Varna (3) and Dobrich (4) provinces. Their sensitivity to natural processes (in a climate change context) and human pressure (considering tourist trends and population increases at the municipality scale) were quantified via the Coastal Scenic Sensitivity Indexes (CSSIs) method. The CSES and CSSI methods allowed us to conduct site classification within different scenic categories, reflecting their attractiveness (Classes I–V; CSES) and level of sensitivity (Groups I–III; CSSI). Their relationship made it possible to identify management priorities: the main scenic impacts and sensitivity issues were analyzed in detail and characterized, and judicious measures were proposed for the scenic preservation and enhancement of the investigated sites. Seven sites were classified as extremely attractive (Class I; CSES), but with slight management efforts; several Class II sites could be upgraded as top scenic sites, e.g., by cleaning and monitoring beach litter. This paper also reveals that investigated sectors were more sensitive to environmental impacts than human pressure; for example, eight were categorized as being very sensitive to natural processes (Group III; CSSI).

First principle study of adsorption and desorption behaviors of NH<sub>3</sub> molecule on the TaC (0001) surface

The adsorption and desorption behaviors of ammonia on TaC(0001) surface are studied by employing spin-polarized density function theory calculations. The surface energy calculation results show that the TaC (0001) terminating with Ta is the most stable surface. According to the optimized structural and energetic properties, it is found that NH<sub>3</sub> prefers to adsorb on the top site, whereas NH<sub>2</sub>, H prefer to adsorb on the triple hcp site and NH, N prefer to stay on the triple fcc site. In addition, three transition states are found for analyzing the mechanism of dehydrogenation of NH<sub>3</sub>, and the N recombination reaction is also considered. The results show that the desorption of nitrogen atoms is the rate-determining step in the overall reaction. Finally, in order to further elucidate the mechanism of NH<sub>3</sub> adsorption and dissociation on the surface of Ta-TaC, the electronic structure of the most stable adsorption position is analyzed from the perspective of charge density distribution and electron density of states. The results of electronic structure calculation show that NH<sub>3</sub> molecule is adsorbed on the surface through the mixture of 2p<i><sub>z</sub></i> orbital of N atom and <inline-formula><tex-math id="Z-20211229103116-1">\begin{document}$ 5{\rm d}_{z^2} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20210400_Z-20211229103116-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20210400_Z-20211229103116-1.png"/></alternatives></inline-formula> orbital of substrate Ta. With the progress of dehydrogenation, the charge transfer phenomenon becomes more and more serious. The charge transfer between adsorbate and substrate plays an important role in accelerating NH<sub>3</sub> dehydrogenation catalytic process.

Activation of single atom alloys towards alkyl C–H bond: A theoretical study

Single atom alloys (SAAs), composed of active metal dopants atomically dispersed on the Cu, Ag, or Au host metals, have recently become a “rising star” in single atom catalysis research. SAAs usually display unique catalytic behavior, mainly due to the anomalous electronic structure of isolated active sites, distinguishing from that of the parentmetals. As the consequence, there is lack of robust and reliable descriptor of catalytic properties of SAAs. In this work, we present a systematically theoretical study on the first C–H bond activation of methane, propane and ethylbenzene over 15 SAAs comprising of Rh, Ir, Ni, Pd, and Pt doping Cu(111), Ag(111), and Au(111) surfaces. Our DFT calculations demonstrate that not only the d-band centers but also the H atom adsorption energies can not correlate well with the activation barriers of alkyl C–H bond, while enhanced performance is achieved when using the reaction energy as a descriptor. We find that there exists orbital interaction similarity between C atom adsorption on top site and the transition states of C–H activation because both of them involve not only σ donation with dz, orbital but also the π back-donation from dxy/dyz orbital(s). As a consequence, the C adsorption energies and C–H bond activation energies are very strongly correlated (R2>0.9), not only for methane but also for propane and ethylbenzene.