Search

Despite the extensive study of the Fe-based Fischer–Tropsch synthesis (FTS) over the past 90 years, its active phases and reaction mechanisms are still unclear due to the coexistence of metals, oxi...

Ruthenium (Ru) serves as a promising catalyst for ammonia synthesis via the Haber-Bosch process, identification of the structure sensitivity to improve the activity of Ru is important but not fully explored yet. We present here density functional theory calculations combined with micro-kinetic simulations on nitrogen molecule activation, a crucial step in ammonia synthesis, over a variety of hexagonal close-packed (hcp) and face-center cubic (fcc) Ru facets. Hcp {213¯0} facet exhibits the highest activity toward N2 dissociation in hcp Ru, followed by the (0001) monatomic step sites. The other hcp Ru facets have N2 dissociation rates at least three orders lower. Fcc {211} facet shows the best performance for N2 activation in fcc Ru, followed by {311}, which indicates stepped surfaces make great contributions to the overall reactivity. Although hcp Ru {213¯0} facet and (0001) monatomic step sites have lower or comparable activation barriers compared with fcc Ru {211} facet, fcc Ru is proposed to be more active than hcp Ru for N2 conversion due to the exposure of the more favorable active sites over step surfaces in fcc Ru. This work provides new insights into the crystal structure sensitivity of N2 activation for mechanistic understanding and rational design of ammonia synthesis over Ru catalysts.

Strong metal-support interactions (SMSI) is an important concept in heterogeneous catalysis. Herein, we demonstrate that the Au-TiO2 SMSI of Au/TiO2 catalysts sensitively depends on both Au nanoparticle (NP) sizes and TiO2 facets. Au NPs of ca. 5 nm are more facile undergo Au-TiO2 SMSI than those of ca. 2 nm, while TiO2 {001} and {100} facets are more facile than TiO2 {101} facets. The resulting capsulating TiO2-x overlayers on Au NPs exhibit an average oxidation state between +3 and +4 and a Au-to-TiO2-x charge transfer, which, combined with calculations, determines the Ti:O ratio as ca. 6:11. Both TiO2-x overlayers and TiO2-x -Au interface exhibit easier lattice oxygen activation and higher intrinsic activity in catalyzing low-temperature CO oxidation than the starting Au-TiO2 interface. These results advance fundamental understanding of SMSI and demonstrate engineering of metal NP size and oxide facet as an effective strategy to tune the SMSI for efficient catalysis.

Atomically dispersed metal catalysts with high atomic utilization and selectivity have been widely studied for acetylene semi-hydrogenation in excess ethylene among others. Further improvements of activity and selectivity, in addition to stability and loading, remain elusive due to competitive adsorption and desorption between reactants and products, hydrogen activation, partial hydrogenation etc. on limited site available. Herein, comprehensive density functional theory calculations have been used to explore the new strategy by introducing an appropriate ligand to stabilize the active single atom, improving the activity and selectivity on oxide supports. We find that the hydroxyl group can stabilize Ni single atoms significantly by forming Ni1(OH)2 complexes on anatase TiO2(101), whose unique electronic and geometric properties enable high performance in acetylene semi-hydrogenation. Specifically, Ni1(OH)2/TiO2(101) shows favorable acetylene adsorption and promotes the heterolytic dissociation of H2 achieving high catalytic activity, and it simultaneously weakens the ethylene bonding to facilitate subsequent desorption showing high ethylene selectivity. Hydroxyl stabilization of single metal atoms on oxide supports and promotion of the catalytic activity are sensitive to transition metal and the oxide supports. Compared to Co, Rh, Ir, Pd, Pt, Cu, Ag and Au, and anatase ZrO2, IrO2 and NbO2 surfaces, the optimum interactions between Ni, O and Ti and resulted high activity, selectivity and stability make Ni1(OH)2/TiO2(101) a promising catalyst in acetylene hydrogenation. Our work provides valuable guidelines for utilization of ligands in the rational design of stable and efficient atomically dispersed catalysts., Hydroxyl group can stabilize significantly Ni single atom by forming Ni1(OH)2 complexes on anatase TiO2(101), which displays high catalytic performance in acetylene semi-hydrogenation.

An active and stable bi-functional catalyst for the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) is highly desirable for clean energy conversion devices, such as anion exchange membrane fuel cells (AEMFCs) and magnesium (Mg)–seawater batteries. Herein, DFT analysis predicates that the amine-ligand modulation manipulates the d-band center of ruthenium (Ru) downshift from the Fermi level, resulting in optimized hydrogen and hydroxide bonding energies (HBE and OHBE), and thus lowering the limiting energy of the HOR/HER. We elaborately fabricate NH2-ligand modulated Ru nanoclusters (Ru/PEI-XC), taking advantage of the abundant –NH2 groups of polyethylene imine (PEI). The optimal Ru/PEI-XC catalyst exhibits a superior HOR activity of 423.3 A gmetal−1 at an overpotential (η) of 50 mV and a specific exchange current density of 687.1 μA cmmetal−2, which are about 1.7 and 3.6 fold those of the commercial Pt/C catalyst. Ru/PEI-XC presents an overwhelming advantage for the HER in a wide pH range, especially in alkaline electrolyte, with η = 13 mV at −10 mA cm−2, which is 20 mV lower than that of Pt/C. Both the potentiostatic and accelerated degradation tests manifest the excellent long-term stability of Ru/PEI-XC in catalyzing the HOR and HER. Furthermore, Ru/PEI-XC as the anode of an AEMFC delivers a peak power density of 1.4 W mgPGM−1, comparable with that of its Pt/C-based counterpart. A proof-of-concept rechargeable Mg–seawater battery could also be driven by the Ru/PEI-XC cathode, delivering a maximum discharging power density of 18.9 mW cm−2, with low charging voltage and good cycling properties. This study reveals that ligand modulation is an effective strategy to manipulate the d-band center of metals and tune the reactivity, which paves an avenue for designing advanced hydrogen electrocatalysts.

Fischer–Tropsch synthesis, the conversion of CO and H2 to long-chain hydrocarbons, is performed at relatively low temperatures and high pressures over the most commonly encountered iron-, ruthenium...

CO methanation is an industrially important reaction for the removal of trace amounts of CO from the hydrogen feed for ammonia production and in proton exchange membrane fuel cells. Although the H-assisted CO dissociation mechanism has been extensively elucidated, discrepancies exist in determining through which C1-oxygenate intermediates the C–O bonds are broken. Using density functional theory calculations and microkinetic studies, we show that theoretical studies can reach agreement in C–O bond scission via the CHO intermediate on Co(0001) at a low coverage regime, and this mainly controls the CO methanation rate. This mechanism is independent of the functionals considered and the presence of graphitic carbon, and likely also pertains to other Co surface structures, including some open facets and step sites. The work provides fundamental insights into the mechanistic discrepancies relating to CO activation and methanation on hexagonal close-packed Co catalysts, which can potentially be used to design improved CO hydrogenation catalysts.

Gastric cancer (GC) is one of the leading causes of cancer-related deaths in our country. Circular RNAs (circRNAs) are being found to have relevance to human cancers, including GC. The purpose of this study was to investigate the functional role of circRNA BTG3 associated nuclear protein (circBANP) in GC and underlying mechanisms governing it. CircBANP was identified using RNase R assay and polymerase chain reaction (PCR) with specific primers. The levels of circBANP, let-7a and Frizzled-5 (FZD5) mRNA were assessed by quantitative real-time PCR (qRT-PCR). Cell proliferation, colony formation ability, apoptosis, and migration and invasion were determined by Cell Counting Kit-8 (CCK-8) assay, colony formation assay, flow cytometry, transwell assay, respectively. The targeted interaction between let-7a and circBANP or FZD5 was confirmed by dual-luciferase reporter assay or RNA pull-down assay. Western blot analysis was performed to detect the indicated protein expression. A xenograft model assay was established to observe the role of circBANP in vivo. We found that circBANP was up-regulated in GC tissues and cell lines, and associated with clinicopathologic features of GC patients. CircBANP knockdown repressed the proliferation, migration, invasion, and promoted the apoptosis in GC cells. CircBANP sequestered let-7a by acting as a molecular sponge of let-7a. Moreover, the regulatory effect of circBANP on GC cell progression in vitro was mediated by let-7a. CircBANP protected against FZD5 repression by sponging let-7a in GC cells. Wnt/β-catenin signaling was involved in the regulatory network of the circBANP/let-7a axis in GC cell progression. Additionally, circBANP depletion retarded tumor growth in vivo. In conclusion, our study suggested that the knockdown of circBANP suppressed GC cell progression in vitro and in vivo at least partially through sponging let-7a and regulating FZD5/Wnt/β-catenin signaling, providing a novel mechanism for understanding the pathogenesis of GC.

Purpose Long non-coding RNA (lncRNA) HOX transcript antisense RNA (HOTAIR) has been reported to dysregulate in many tumors. However, the mechanism of HOTAIR was rarely reported in GC. Methods The levels of HOTAIR, microRNA-618 (miR-618) and Krueppel-like factor 12 (KLF12) in GC tissues and cells were detected by quantitative real-time polymerase chain reaction (qRT-PCR). The cell viability and apoptotic rate were assessed via cell counting kit-8 (CCK-8) assay and flow cytometry, respectively. The migrating and invading abilities were tested by Transwell assay. The protein levels of KLF12, p-PI3K, PI3K, p-ATK and ATK were measured by Western blot assay. These interactions between miR-618 and HOTAIR or KLF12 were predicted by DIANA tools, and then, dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay were conducted to validate these interactions. Besides, the xenograft tumor experiment was performed to further verify the roles of HOTAIR in GC. Results The levels of HOTAIR and KLF12 were significantly upregulated and the level of miR-618 was strikingly downregulated in GC tissues and cells. miR-618 was verified as a direct target of HOTAIR or KLF12. HOTAIR silencing blocked GC progression and PI3K/ATK signaling pathway by sponging miR-618 and also restrained xenograft tumor growth in vivo. miR-618 inhibited GC progression and PI3K/ATK signaling pathway by targeting KLF12. Mechanistically, HOTAIR modulated KLF12 expression by sponging miR-618 in GC cells. Conclusion These data unraveled that HOTAIR promoted GC progression through PI3K/ATK signaling pathway via miR-618/KLF12 axis.

Nitrogen-doped graphene is a promising non-precious metal electrocatalyst for the oxygen reduction reaction (ORR). We report that distorted nitrogen-doped graphene layers encapsulating Fe3Co nanoparticles supported on carbon (Fe3Co@NG-C) display excellent activity toward ORR in alkaline media. Compared with a commercial Pt/C electrocatalyst at a loading of 80 μgPt/cm2 on a rotating disk electrode, the Fe3Co@NG-C exhibits an onset potential positively shifted by 50 mV at 0.1 mA/cm2 and a nearly identical half-wave potential. The Fe3Co@NG-C has minimal activity degradation during accelerated durability testing and superior tolerance to methanol than commercial Pt/C. Density functional theory calculations combined with poisoning experiments reveal that the high activity of the Fe3Co@NG-C mainly arises from strain in nitrogen-doped graphene induced by encapsulation of Fe3Co nanoparticles with exposed (1 1 0) planes, which promotes stabilization of the key OOH* intermediate involved in ORR. Our study shows the rational design of improved carbon-based electrocatalysts for ORR can be achieved by using strain engineering.

Despite the maximized metal dispersion offered by single-atom catalysts, further improvement of intrinsic activity can be hindered by the lack of neighboring metal atoms in these systems. Here we report the use of isolated Pt1 atoms on ceria as “seeds” to develop a Pt-O-Pt ensemble, which is well-represented by a Pt8O14 model cluster that retains 100% metal dispersion. The Pt atom in the ensemble is 100–1000 times more active than their single-atom Pt1/CeO2 parent in catalyzing the low-temperature CO oxidation under oxygen-rich conditions. Rather than the Pt-O-Ce interfacial catalysis, the stable catalytic unit is the Pt-O-Pt site itself without participation of oxygen from the 10–30 nm-size ceria support. Similar Pt-O-Pt sites can be built on various ceria and even alumina, distinguishable by facile activation of oxygen through the paired Pt-O-Pt atoms. Extending this design to other reaction systems is a likely outcome of the findings reported here.

Cobalt carbide based catalyst shows a promising activity and selectivity in the direct conversion of syngas (a mixture of carbon monoxide and hydrogen molecules) toward oxygenates and lower olefin....

Electrocatalytic reduction is a promising approach to remediate nitrate (NO3–), one of the world’s most widespread water pollutants. In the present work, we elucidate activity and selectivity trend...

Non-oxidative direct methane conversion provides a potentially economic and environmental friendly route for the use of natural gas and shale gas, but this process suffers the disadvantages of low ...

Identification of the structure sensitivity of nitrogen molecule (N2) activation and ammonia synthesis on metal surfaces is important for the mechanistic understanding and rational design of more efficient catalysts. In the present work, density functional theory calculations together with microkinetic simulations were performed to study the influence of cobalt crystal structures including hexagonal close-packed (HCP) and face-centered cubic (FCC) on nitrogen molecule dissociation and ammonia synthesis. Molecular and dissociative adsorption energies of N2 as well as dissociation barriers are calculated for a total of ten cobalt surfaces. It is found that molecular adsorption energies on Co surfaces vary modestly on the order of 0.25 eV, whereas dissociative adsorption energies and the corresponding barriers vary considerably in magnitude by about 0.80 eV. First-principles microkinetic simulations show that HCP Co displays higher activity than FCC cobalt for nitrogen molecule dissociation and ammonia synth...

Transmissible spongiform encephalopathies (TSEs) are epidemic neurodegenerative diseases caused by prion proteins, in particular, they are induced by misfolded prion proteins (PrPSc). PrPSc tend to aggregate into insoluble amyloid prion fibrils (fPrPWT), resulting in apoptosis of neuron cells and sequential neurodegeneration. Previous studies indicate that microglia cells play an important role in the innate immune system, and that these cells have good neuroprotection and delay the onset of TSEs. However, microglia can be a double-sided blade. For example, both Cu2+ and Mn2+ can induce microglia activation and secrete many inflammatory cytokines that are fatal to neuron cells. Unfortunately, PrP have cation binding sites at the N-terminus. When PrPSc accumulate during microglial phagocytosis, microglia may change the phenotype to secrete pro-inflammation cytokines, which increases the severity of the disease. Some studies have revealed an increase in the concentration of Mn2+ in the brains of patients. In this study, we treated microglia with fPrPWT and cations and determined I&kappa, B&alpha, and IL-1&beta, expression by Western blotting and quantitative polymerase chain reaction. The results showed that Mn&ndash, fPrPWT decreased I&kappa, levels and dramatically increased IL-1&beta, mRNA expression. In addition, competing binding between Cu2+ and Mn2+ can decrease the effect of Mn&ndash, fPrPWT on I&kappa, The effects of divalent cations and fPrPWT in microglia inflammation are also discussed.

Synthesis of atomically dispersed catalysts with high metal loading and thermal stability is challenging but particularly valuable for industrial application in heterogeneous catalysis. Here, we report a facile synthesis of a thermally stable atomically dispersed Ir/α-MoC catalyst with metal loading as high as 4 wt%, an unusually high value for carbide supported metal catalysts. The strong interaction between Ir and the α-MoC substrate enables high dispersion of Ir on the α-MoC surface, and modulates the electronic structure of the supported Ir species. Using quinoline hydrogenation as a model reaction, we demonstrate that this atomically dispersed Ir/α-MoC catalyst exhibits remarkable reactivity, selectivity and stability, for which the presence of high-density isolated Ir atoms is the key to achieving high metal-normalized activity and mass-specific activity. We also show that the water-promoted quinoline hydrogenation mechanism is preferred over the Ir/α-MoC, and contributes to high selectivity towards 1,2,3,4-tetrahydroquinoline. The present work demonstrates a new strategy in constructing a high-loading atomically dispersed catalyst for the hydrogenation reaction., Atomically dispersed Ir/α-MoC catalyst with high metal loading exhibits remarkable activity, selectivity and stability for quinoline hydrogenation reaction through water-promoted hydrogenation mechanism.

Developing advanced Fischer-Tropsch synthesis (FTS) technology to acquire fuel and valuable chemicals from non-petroleum sources more efficiently is one of the important tasks in heterogeneous catalysis and chemical engineering research. With the purpose of improving iron-based FTS catalyst, we explored the modification effect of boron on the χ-Fe5C2 catalyst by density functional theory (DFT) calculations. Boron atom adsorption on χ-Fe5C2 surfaces is considered to modulate the stability as well as the activity of CO activation on FTS process. Anti-coking can be observed when boron atom adsorbs on χ-Fe5C2 catalyst due to the competitive adsorption and repulsive interactions between carbon and boron atoms. More open and active planes, such as (311), (021), and (31 2 ) facets, can expose in the morphology of χ-Fe5C2 when boron atom adsorbs on χ-Fe5C2. It is found that co-adsorbed boron atoms have little effect on the barrier of CO direct dissociation in most cases, while there is also particular situation that CO is adsorbed and activated on boron with carbon termination. Our work shed light on the promoting effects of boron adsorption on CO activation, which can provide useful guide for the design of novel iron-based FTS catalysts.

A simplified method is presented to fabricate polymer composite electrodes for electrocardiograph (ECG) measurements. The composite electrode was fabricated by loading a high content of carbon nanotubes (CNTs) and silver nanoparticles (Ag NPs) in polydimethylsiloxane (PDMS). The conductive polymer mixture was prepared by ultrasonically stirring and heat-stirring. Polymer electrodes were fabricated by the doctor blade technique. Two-dimensional electrodes were fabricated to evaluate the effect of thickness on signal quality. Three polymer electrodes were combined into the ECG electrode patch. The polymer electrodes were successfully applied in ECG measurements. Continuous measurements for 14 days indicated the polymer electrodes are suitable for long-term monitoring. Wearable electrodes were fabricated with a layer of gauze embedded by the CNT/Ag-PDMS mixtures. Conductive wires were sewed in the gauze as connectors for the measurement circuit. Three wearable electrodes were sewed into a vest as a measurement module. The ECG measurement results demonstrated that the wearable electrodes are qualified for such medical devices. The CNT-based polymer electrodes are flexible, washable, and suitable for long-term wear, possessing great promise in practical applications in wearable medical instruments.

Fischer-Tropsch synthesis (FTS) is an increasingly important approach for producing liquid fuels and chemicals via syngas—that is, synthesis gas, a mixture of carbon monoxide and hydrogen—generated from coal, natural gas, or biomass. In FTS, dispersed transition metal nanoparticles are used to catalyze the reactions underlying the formation of carbon-carbon bonds. Catalytic activity and selectivity are strongly correlated with the electronic and geometric structure of the nanoparticles, which depend on the particle size, morphology, and crystallographic phase of the nanoparticles. In this article, we review recent works dealing with the aspects of bulk and surface sensitivity of the FTS reaction. Understanding the different catalytic behavior in more detail as a function of these parameters may guide the design of more active, selective, and stable FTS catalysts.

Exploring the unique catalytic properties of gold clusters associated with specific nano-architectures is essential for designing improved catalysts with a high mass-specific activity. We investigate the geometric and electronic structure of hexadecagold clusters in which Rh was doped. Density functional theory calculations demonstrate that the resulting neutral and negatively charged Rh-doped Au16 clusters are stable and bind CO and O2 stronger than Au16. Consequently, activation barriers for CO oxidation are lowered. Microkinetics simulations predict especially negatively charged Rh-doped Au16 clusters to exhibit very high CO oxidation activity, already at sub-ambient temperature. Our findings highlight the promise of alloying gold clusters with more reactive transition metals and the importance of charge transfer from the support in heterogeneous gold systems in catalyzing CO oxidation.

Structure sensitivity on chain growth and selectivity in cobalt catalyzed Fischer–Tropsch synthesis (FTS) were studied by density functional theory (DFT) calculations. It is found that at a lower CO coverage, chain growth tends to proceed via a CO insertion mechanism on close-packed Co (0001) and stepped Co, with CH4 as the main product. However, a carbide mechanism is preferable on more open Co (101) accompanied with higher selectivity to C2 hydrocarbons than CH4. The origin is identified from the structure sensitive adsorption of the key intermediates, specifically the least “saturated” C/CH species, which exhibit a relatively strong dependence on the structure evolution. With increasing CO coverage, the CO insertion mechanism becomes more favorable, and both FTS activity and C2 hydrocarbon selectivity increase on Co (0001). This work highlights the intrinsic structure and coverage effects, achieving fundamental insight that can potentially be used to design and develop improved catalysts for FTS and other important reactions in syngas conversion.

Exploring the dependence of the structure–activity relationship of catalysts is important for improving the activity and selectivity in heterogeneous catalysis. Among other factors, the influence of the crystal phases, face-centered cubic (FCC) and hexagonal close-packed (HCP), of Ni catalysts on CO dissociation is studied by density functional theory (DFT). Surface energies of numerous FCC and HCP facets are calculated to construct the corresponding morphologies, and the exposed facets (six facets for FCC Ni and five facets for HCP Ni) are used to investigate the CO dissociation. For FCC Ni, (311) is the most active facet with the least barrier of 1.58 eV, followed by (100) and (211) with barriers of 1.63 and 1.75 eV, respectively. For HCP Ni, (1012) is the most active facet with the least barrier of 1.73 eV, followed by (1011) with a barrier of 1.86 eV. On both FCC and HCP Ni, CO dissociation shows a dramatic structural sensitivity irrespective of direct or H-assisted pathway. Compared to the direct d...

In this study, the concept of polymer electrodes integrated with a wireless electrocardiogram (ECG) system was described. Polymer electrodes for long-term ECG measurements were fabricated by loading high content of carbon nanotubes (CNTs) in polydimethylsiloxane. Silver nanoparticles (Ag NPs) were added to increase the flexibility of the polymer and the conductivity of the electrode. An ECG electrode patch was fabricated by integrating the electrodes with an adhesive polydimethylsiloxane (aPDMS) layer. Holes in the electrode filled with aPDMS can enable robust contact between the electrode and skin, reducing motion artifacts. A wireless ECG measurement system was developed and adapted to the polymer electrodes. The polymer electrodes combined with the measurement system were successfully applied in wireless, long-term recording of ECG signals. An eleven-day continuous test showed that the ECG signal did not degrade over time. The results of attach/detach tests demonstrated that the ECG signal was affected by motion artifacts after six attach/detach cycles. The electrodes produced are flexible and exhibit good ECG performance, and therefore can be used in wearable medical monitoring systems. The approach proposed in this study holds significant promise for commercial application in medical fields.

First-principles calculations have been performed to explore the charge transport process over defective CeO2(111). Charge transport can proceed either by direct migration of the oxygen anion (i.e., vacancy diffusion) or by a polaron-hopping-assisted mechanism. On the basis of DFT+U calculations, we found that the latter process is significantly more favorable than the former. The overall barrier for charge transport involving polaron migration, followed by oxygen diffusion, is determined by the barrier for polaron hopping, which amounts to 0.18 eV. This computed value is in good agreement with the experimental barrier for ceria with a low defect density. We have shown by a careful analysis of the magnetization density, the density of states, and the reaction pathway trajectory that this process is phonon induced. Our results provide valuable insights into carrier drift processes over defective metal oxide surfaces.

Composite electrodes are fabricated for long-term electrocardiogram (ECG) measurements. The electrode consists of a polydimethylsiloxane base, silver nanowire layer, and adhesive layer. The adhesive layer is fabricated by loading carbon nanotubes into adhesive polydimethylsiloxane. An electrode patch consisting of three composite electrodes and an adhesive polydimethylsiloxane layer is fabricated and combined with a wireless acquisition system to obtain ECG measurements. The composite electrode patch is self-adhesive and can conform to the skin, achieving robust contact between electrode and skin and thus decreasing motion artifacts. The composite electrodes combined with the measurement system are successfully used for wireless long-term recording of ECG signals. Continuous testing for 8 days shows that the ECG signal amplitude decreases slightly after wearing for 6 days and can be largely recovered by cleaning with ethanol. The composite electrodes are flexible and exhibit good ECG performance, and therefore can be used in wearable medical monitoring systems.

Methane (CH 4) combustion is an increasingly important reaction for environmental protection, for which Pd/CeO 2 has emerged as the preferred catalyst. There is a lack of understanding of the nature of the active site in these catalysts. Here, we use density functional theory to understand the role of doping of Pd in the ceria surface for generating sites highly active toward the C-H bonds in CH 4. Specifically, we demonstrate that two Pd 2+ ions can substitute one Ce 4+ ion, resulting in a very stable structure containing a highly coordinated unsaturated Pd cation that can strongly adsorb CH 4 and dissociate the first C-H bond with a low energy barrier. An important aspect of the high activity of the stabilized isolated Pd cation is its ability to form a strong σ-complex with CH 4, which leads to effective activation of CH 4. We show that also other transition metals like Pt, Rh, and Ni can give rise to similar structures with high activity toward C-H bond dissociation. These insights provide us with a novel structural view of solid solutions of transition metals such as Pt, Pd, Ni, and Rh in CeO 2, known to exhibit high activity in CH 4 combustion.

Controllable synthesis of metallic nanocrystals (NCs) with tunable phase, uniform shape, and size is of multidisciplinary interests but has still remained challenging. Herein, a robust phase control strategy is developed, in which seeds with a given phase are added to guide the epitaxial growth of the target metal to inherit the seeds’ phase. Through this strategy, M@Ru (M = Pt, Pd) NCs in the face-centered cubic (fcc) phase, a metastable phase for Ru under ambient conditions, were synthesized with the hydrothermal method. The Pt@Ru NCs showed not only the pure fcc phase but also high morphology selectivity to tetrahedrons surrounded by {111} facets. As revealed by density function theory (DFT) calculations, the preferentially epitaxial growth of Ru atom layers on the nonclosest-packed facets of hetero fcc metal seeds led to the formation of fcc Ru shells. Furthermore, the fcc Pt@Ru tetrahedrons/C showed electrocatalytic activity enhancement with more than an order of magnitude toward hydrogen oxidation r...

Utilization of nonprecious transition metals for high alcohols synthesis is of a great importance in heterogeneous catalysis. We synthesized successfully cobalt metal-carbide (Co–Co2C) catalysts, which present remarkable activity and selectivity for high alpha-alcohols via the Fischer–Tropsch reaction. The formation of the stable cobalt carbide and the Co–Co2C interface are found to be essential for the observed reactivity. Density functional theory calculations show that Co2C is highly efficient for CO nondissociative adsorption, behaving as noble-metal-like, whereas the Co metal is highly active for CO dissociative adsorption and the subsequent carbon-chain growth. The interface between the cobalt metal and its carbide phase, as well as the dual sites available at the interface for facile CO insertion to hydrocarbon, could be used to rationalize the design of the nonprecious transition metal catalysts for the oxygenates in syngas conversion.

Doping CeO 2 with Pd atoms has been associated with catalytic CO oxidation, but current surface models do not allow CO adsorption. Here, we report a new structure of Pd-doped CeO 2(111), in which Pd adopts a square planar configuration instead of the previously assumed octahedral configuration. Oxygen removal from this doped structure is favorable. The resulting defective Pd-doped CeO 2 surface is active for CO oxidation and is also able to cleave the first C-H bond in methane. We show how the moderate CO adsorption energy and dynamic features of the Pd atom upon CO adsorption and CO oxidation contribute to a low-barrier catalytic cycle for CO oxidation. These structures, which are also observed for Ni and Pt, can lead to a more open coordination environment around the doped-transition-metal center. These thermally stable structures are relevant to the development of single-atom catalysts.

The replacement of platinum group metals by non-noble metals has attracted significant attention in the field of three-way catalysis. Here, we use DFT calculations to comprehensively study NO reduction by CO and CO oxidation on Pd(1 1 1) and transition metal doped Pd(1 1 1). Whilst direct NO dissociation is very difficult on metallic Pd(1 1 1), doping with transition metals can substantially lower the reaction barrier for NO dissociation. The lowest barrier is predicted for Ti-doped Pd(1 1 1). An electronic structure analysis shows that the low barrier is due to the strong adsorption of N and O on surface sites involving Ti atoms. It relates to strong hybridization of the N and O orbitals with the half-filled d-band of the metallic surface. At the same time, the anti-bonding states are shifted above the Fermi level, which further strengthens the adsorption of N and O. A Brønsted-Evans-Polanyi relation for NO dissociation on TM-doped Pd(1 1 1) surfaces is identified. The complete reaction pathway for N2, N2O and CO2 formation on Pd(1 1 1) and Ti-doped Pd(1 1 1) was considered. Besides more facile NO dissociation, the energy barrier for CO oxidation is decreased for the Ti-doped surface. Microkinetics simulations confirm that the activity and selectivity for NO reduction and CO oxidation are drastically improved after Ti doping. Our findings indicate that doping of Pd with non-noble metal can further improve the performance of three-way catalysts.

We carried out density functional theory calculations to investigate the ripening of Pd clusters on CeO2(111). Starting from stable Pdn clusters (n=1-21), we compared how these clusters can grow through Ostwald ripening and coalescence. As Pd atoms have a high mobility than Pd¬n clusters on the CeO2(111) surface, Ostwald-ripening is predicted to be the dominant sintering mechanism. Particle coalescence is only possible when very small clusters with less than 5 Pd at-oms are involved. These ripening mechanisms are facilitated by adsorbed CO through lowering barriers for the cluster diffusion, detachment of a Pd atom from clusters, and transformation of initial planar clusters.

Unsupported Co–Co2C catalyst and active carbon supported Co–Co2C (Co–Co2C/AC) catalysts were prepared and have been first proven to be highly active for 1-hexene hydroformylation under low pressure (P = 3.0 MPa and T = 453 K). It is found that the catalytic performances over the Co–Co2C and Co–Co2C/AC catalysts were strongly dependent on the ratio of Co2C to Co. Highly catalytic performances were achieved with the XRD intensity ratio of Co2C to Co ranging from 0.7 to 1.2. Co–Co2C/AC catalyst with carburization for 20 h has a highly catalytic stability for 1-hexene hydroformylation with a time stream of 140 h, indicating that no dissolved cobalt carbonyl species were formed and thus led to no cobalt elusion during hydroformylation under reaction conditions. Density functional theory (DFT) calculations have been conducted to understand the nature of the catalytic performance. We found that the interface between Co and Co2C plays a significant role in ethylene hydroformylation. Metallic Co sites are used for...

step sites over terrace sites have been suggested to be the active sites in many catalytic reactions particularly bond breaking of diatomic molecules. aiming to provide insight into the role of step sites in multiatomic molecules bond breaking reactions and their dependence on catalysts, we present herein a systematic first-principles study of carbon-oxygen bond scission of diatomic co and multiatomic hco and ch3hco on flat and stepped co, rh, and ir surfaces. we find that multiatomic molecules exhibit distinct carbon-oxygen scission activity from diatomic molecules regardless of the metal catalysts (co, rh, and ir) considered: compared to the huge enhancement of step sites for co with a barrier 0.81-1.29 ev lower than that of flat surfaces, the role of step sites for ch3cho is substantially weakened with a barrier 0.11-0.27 ev higher than that of flat surfaces. the reason for this is the change of adsorption configurations on flat surfaces and increase of pauli repulsion on the congested stepped sites for the dissociation of multiatomic molecules.

Due to the advantage of controllability on the mechanical property and the degradation rates, electrospun PCL/PTMC nanofibrous scaffold could be appropriate for vascular tissue engineering. However, the tissue response and degradation of electrospun PCL/PTMC scaffold in vivo have never been evaluated in detail. So, electrospun PCL/PTMC scaffolds with different blend ratios were prepared in this study. Mice subcutaneous implantation showed that the continuous degradation of PCL/PTMC scaffolds induced a lasted macrophage-mediated foreign body reaction, which could be in favor of the tissue regeneration in graft.

Identifying the structure sensitivity of catalysts in reactions, such as Fischer-Tropsch synthesis from CO and H2 over cobalt catalysts, is an important yet challenging issue in heterogeneous catalysis. Based on a first-principles kinetic study, we find for the first time that CO activation on hexagonal close-packed (HCP) Co not only has much higher intrinsic activity than that of face centered-cubic (FCC) Co but also prefers a different reaction route, i.e., direct dissociation with HCP Co but H-assisted dissociation on the FCC Co. The origin is identified from the formation of various denser yet favorable active sites on HCP Co not available for FCC Co, due to their distinct crystallographic structure and morphology. The great dependence of the activity on the crystallographic structure and morphology of the catalysts revealed here may open a new avenue for better, stable catalysts with maximum mass-specific reactivity.

Density functional theory (DFT) calculations have been carried out to investigate the structural sensitivity of the elementary processes in CO methanation at low coverage of 0.25 ML, including CO dissociation via either direct or H-assisted path and CHx (x = 0–3) hydrogenation, on Co (0 0 0 1), ( 1 0 1 2 ) and ( 1 1 2 0 ) surfaces. CO direct dissociation was found to be structurally most sensitive, whereas CHx hydrogenation is structurally least sensitive. Specifically, the barrier of CO direct dissociation, H-assisted dissociation and CHx hydrogenation on different surfaces varies in range of 1.12, 0.54 and 0.34 eV, respectively. Regardless of Co surfaces considered, the CO activation is the rate-limiting step of methanation reactions, which would proceed through the H-assisted pathway on Co (0 0 0 1), whereas through both direct and H-assisted pathways on more active Co ( 1 0 1 2 ) and ( 1 1 2 0 ) surfaces. The structure sensitivity of CO activation leads to methanation reaction structural sensitive.

Various carbonaceous species were controllably deposited on Co/Al2O3 catalysts using ethylene as carbon source during the activation process for Fischer–Tropsch synthesis (FTS). Atomic, polymeric and graphitic carbon were distinguished by Raman spectroscopy, thermoanalysis and temperature programmed hydrogenation. Significant changes occurred in both the catalytic activity and selectivity toward hydrocarbon products after ethylene treatment. The activity decreased along with an increase in CH4 selectivity, at the expense of a remarkable decrease of heavy hydrocarbon production, resulting in enhanced selectivity for the gasoline fraction. In situ XPS experiments show the possible electron transfer from cobalt to carbon and the blockage of metallic cobalt sites, which is responsible for the deactivation of the catalyst. DFT calculations reveal that the activation barrier (Ea) of methane formation decreases by 0.61 eV on the carbon-absorbed Co(111) surface, whereas the Ea of the CH + CH coupling reaction changes unnoticeably. Hydrogenation of CHx to methane becomes the preferable route among the elementary reactions on the Co(111) surface, leading to dramatic changes in the product distribution. Detailed coke-induced deactivation mechanisms of Co-based catalysts during FTS are discussed.

Ruthenium is a promising low-temperature catalyst for Fischer–Tropsch synthesis (FTS). However, its scarcity and modest specific activity limit its widespread industrialization. We demonstrate here a strategy for tuning the crystal phase of catalysts to expose denser and active sites for a higher mass-specific activity. Density functional theory calculations show that upon CO dissociation there are a number of open facets with modest barrier available on the face-centered cubic (fcc) Ru but only a few step edges with a lower barrier on conventional hexagonal-closest packed (hcp) Ru. Guided by theoretical calculations, water-dispersible fcc Ru catalysts containing abundant open facets were synthesized and showed an unprecedented mass-specific activity in the aqueous-phase FTS, 37.8 molCO·molRu–1·h–1 at 433 K. The mass-specific activity of the fcc Ru catalysts with an average size of 6.8 nm is about three times larger than the previous best hcp catalyst with a smaller size of 1.9 nm and a higher specific su...

Density functional theory (DFT) is a powerful tool to study heterogeneous catalysis nowadays. In past decades, numerous DFT calculations have been conducted to investigate the mechanism of catalytic reaction from which the rationale of catalyst design can be revealed. Because the catalyst electronic and geometric structures determine the intrinsic activity, corresponding composition, size, and morphology have been explored extensively to tune the structure–activity relationship for higher activity and selectivity. In this review, we focus on the recent theoretical progress of the crystal phase effect on catalysis. Catalysts with different crystal phases have different symmetries, and could expose very different facets with distinct electronic and geometrical properties, which would have significant influential on the activity and selectivity of the active sites as well as the site density. Exploration of the dependence of catalysis on the crystal phases provides a new rationale of catalysts design toward a high-specific activity. WIREs Comput Mol Sci 2016, 6:571–583. doi: 10.1002/wcms.1267 For further resources related to this article, please visit the WIREs website.

article i nfo Density functional theory calculations have been performed to investigate the structural and electronic prop- erties of bulk Co2C and the stability of low index Co2C surfaces. We found that the formation of Co2C is exo- thermic with the formation energy of �0.81 eV/Co2C with respect to Co under the presence of syngas (mixture of CO and H2). While formed Co2C can be decomposed further to metal Co and graphite carbon with modest energy gain of 0.37 eV/Co2C. This suggests that Co2C is only metastable in Fischer-Tropsch syn- thesis, which agrees well with experimental findings. The density of states (DOSs) reveals that the Co2 Ci s paramagnetic and strong metallic-like. The difference of charge density analysis indicates that the bond of Co2C is of the mixtures of metallic, covalent, and ionic properties. A variety of low index Co2C surfaces with different terminations are studied. We find that the surface energy of low index stoichiometric Co2C highly relies on the surface area, the number of coordination of surface atoms and the surface dipole, with the decreased stability order of (101)>(011)>(010)>(110)>(100)>(001)=(111). Our results indicate that underCo-poor condition,theformation of nonstoichiometric surface(011) and(111) without terminated cobalt is energetically more favorable, whileunderCo-rich condition theformation of nonstoichiometric (111) surface with cobalt overlayer are preferential.

Carbon Chain Growth by Formyl Insertion on Rhodium and Cobalt Catalysts in Syngas Conversion

Polymer-based flexible electrodes are receiving much attention in medical applications due to their good wearing comfort. The current fabrication methods of such electrodes are not widely applied. In this study, polydimethylsiloxane (PDMS) and conductive additives of carbon nanotubes (CNTs) were employed to fabricate composite electrodes for electrocardiography (ECG). A three-step dispersion process consisting of ultrasonication, stirring, and in situ polymerization was developed to yield homogenous CNTs-PDMS mixtures. The CNTs-PDMS mixtures were used to fabricate CNTs-PDMS composite electrodes by replica technology. The influence of ultrasonication time and CNT concentration on polymer electrode performance was evaluated by impedance and ECG measurements. The signal amplitude of the electrodes prepared using an ultrasonication time of 12 h and CNT content of 5 wt% was comparable to that of commercial Ag/AgCl electrodes. The polymer electrodes were easily fabricated by conventional manufacturing techniques, indicating a potential advantage of reduced cost for mass production.

Analogues of coenzyme A (CoA) and of CoA thioesters have been prepared in which the amide bond nearest the thiol group has been modified. An analogue of acetyl-CoA in which this amide bond is replaced with an ester linkage was a good substrate for the enzymes carnitine acetyltransferase, chloramphenicol acetyltransferase, and citrate synthase, with K(m) values 2- to 8-fold higher than those of acetyl-CoA and V(max) values from 14 to >80% those of the natural substrate. An analogue in which an extra methylene group was inserted between the amide bond and the thiol group showed less than 4-fold diminished binding to the three enzymes but exhibited less than 1% activity relative to acetyl-CoA with carnitine acetyltransferase and no measurable activity with the other two enzymes. Analogues of several CoA thioesters in which the amide bond was replaced with a hemithioacetal linkage exhibited no measurable activity with the appropriate enzymes. The results indicate that some aspects of the amide bond and proper distance between this amide and the thiol/thioester moiety are critical for activity of CoA ester-utilizing enzymes.

Fischer–Tropsch synthesis (FTS) is an important catalytic process for liquid fuel generation, which converts coal/shale gas/biomass-derived syngas (a mixture of CO and H2) to oil. While FTS is thermodynamically favored at low temperature, it is desirable to develop a new catalytic system that could allow working at a relatively low reaction temperature. In this article, we present a one-step hydrogenation–reduction route for the synthesis of Pt–Co nanoparticles (NPs) which were found to be excellent catalysts for aqueous-phase FTS at 433 K. Coupling with atomic-resolution scanning transmission electron microscopy (STEM) and theoretical calculations, the outstanding activity is rationalized by the formation of Co overlayer structures on Pt NPs or Pt–Co alloy NPs. The improved energetics and kinetics from the change of the transition states imposed by the lattice mismatch between the two metals are concluded to be the key factors responsible for the dramatically improved FTS performance.

Understanding Ostwald ripening and disintegration of supported metal particles under operating conditions has been of central importance in the study of sintering and dispersion of heterogeneous catalysts for long-term industrial implementation. To achieve a quantitative description of these complicated processes, an atomistic and generic theory taking into account the reaction environment, particle size and morphology, and metal-support interaction is developed. It includes (1) energetics of supported metal particles, (2) formation of monomers (both the metal adatoms and metal-reactant complexes) on supports, and (3) corresponding sintering rate equations and total activation energies, in the presence of reactants at arbitrary temperature and pressure. The thermodynamic criteria for the reactant assisted Ostwald ripening and induced disintegration are formulated, and the influence of reactants on sintering kinetics and redispersion are mapped out. Most energetics and kinetics barriers in the theory can be obtained conveniently by first-principles theory calculations. This allows for the rapid exploration of sintering and disintegration of supported metal particles in huge phase space of structures and compositions under various reaction environments. General strategies of suppressing the sintering of the supported metal particles and facilitating the redispersions of the low surface area catalysts are proposed. The theory is applied to TiO(2)(110) supported Rh particles in the presence of carbon monoxide, and reproduces well the broad temperature, pressure, and particle size range over which the sintering and redispersion occurred in such experiments. The result also highlights the importance of the metal-carbonyl complexes as monomers for Ostwald ripening and disintegration of supported metal catalysts in the presence of CO.

Resolving the structure and composition of supported nanoparticles under reaction conditions remains a challenge in heterogeneous catalysis. Advanced configurational sampling methods at the density functional theory level are used to identify stable structures of a Pd8 cluster on ceria (CeO2) in the absence and presence of O2. A Monte Carlo method in the Gibbs ensemble predicts Pd-oxide particles to be stable on CeO2 during CO oxidation. Computed potential energy diagrams for CO oxidation reaction cycles are used as input for microkinetics simulations. Pd-oxide exhibits a much higher CO oxidation activity than metallic Pd on CeO2. This work presents for the first time a scaling relation for a CeO2-supported metal nanoparticle catalyst in CO oxidation: a higher oxidation degree of the Pd cluster weakens CO binding and facilitates the rate-determining CO oxidation step with a ceria O atom. Our approach provides a new strategy to model supported nanoparticle catalysts.