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Peng, Bo

Publications and source records attributed to Peng, Bo.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Effect of Ti on Ag catalyst supported on spherical fibrous silica for partial hydrogenation of dimethyl oxalate

A highly efficient Ag catalyst supported on a novel Ti-decorated spherical fibrous silica (Ag/Ti-KCC-1) was synthesized via a facile approach. Characterization of catalysts, including FT-IR, N2 physisorption, TEM, ICP-OES and DRUV-vis was carried out to investigate the physicochemical properties of the catalyst, XPS, H2-TPR, H2-TPD and DMO-TGA were conducted to further elucidate the effect of Ti dopant. It is shown that the Ti additive is able to, 1) inhibit the aggregation of Ag; 2) induce electron transfer from Ti to Ag, which effect the Ag dispersion and the adsorption ability of the reactants on the catalyst surface. Proper amount of Ti additive provided a balanced coverage of both hydrogen and dimethyl oxalate (DMO) on catalyst surface, which is essential in promoting the performance of the catalyst in the hydrogenation of DMO. By using the novel 10Ag/0.02Ti-KCC-1 catalyst, a high MG yield of 93.0% under extremely high WHSV of 1.75 h-1 is achieved.

silver, titanium, dimethyl oxalate, hydrogenation,↗
DOE OSTI2018

The role of Anderson’s rule in determining electronic, optical and transport properties of transition metal dichalcogenide heterostructures

Two-dimensional (2D) transition metal dichalcogenides (TMDs) MX 2 (M = Mo, W; X = S, Se, Te) possess unique properties and novel applications in optoelectronics, valleytronics and quantum computation. In this work, we performed first-principles calculations to investigate the electronic, optical and transport properties of the van der Waals (vdW) stacked MX 2 heterostructures formed by two individual MX 2 monolayers. Here, we found that the so-called Anderson's rule can effectively classify the band structures of heterostructures into three types: straddling, staggered and broken gap. The broken gap is gapless, while the other two types possess direct (straddling, staggered) or indirect (staggered) band gaps. The indirect band gaps are formed by the relatively higher energy level of Te-d orbitals or the interlayer couplings of M or X atoms. For a large part of the formed MX2 heterostructures, the conduction band maximum (CBM) and valence band minimum (VBM) reside in two separate monolayers, thus the electron–hole pairs are spatially separated, which may lead to bound excitons with extended lifetimes. The carrier mobilities, which depend on three competitive factors, i.e. elastic modulus, effective mass and deformation potential constant, show larger values for electrons of MX 2 heterostructures compared to their constituent monolayers. Finally, the calculated optical properties reveal strong absorption in the ultraviolet region.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Green’s function coupled cluster formulations utilizing extended inner excitations

Here, we analyze new approximations of the Green’s function coupled cluster (GFCC) method where locations of poles are improved by extending the excitation level of inner auxiliary operators. These new GFCC approximations can be categorized as the GFCC-i( n, m ) method, where the excitation level of the inner auxiliary operators ( m ) used to describe the ionization potential and electron affinity effects in the N-1 and N+1 particle spaces is higher than the excitation level ( n ) used to correlate the ground-state coupled cluster wave function for the N-electron system. Furthermore, we reveal the so-called “n + 1” rule in this category [or the GFCC-i( n, n + 1) method], which states that in order to maintain size-extensivity of the Green’s function matrix elements, the excitation level of inner auxiliary operators X p (ω) and Y q (ω) cannot exceed n + 1. We also discuss the role of the moments of coupled cluster equations that in a natural way assures these properties. Our implementation in the present study is focused on the first approximation in this GFCC category, i.e., the GFCC-i(2,3) method. As our first practice, we use the GFCC-i(2,3) method to compute the spectral functions for the N 2 and CO molecules in the inner and outer valence regimes. Lastly, in comparison with the Green’s function coupled cluster singles, doubles results, the computed spectral functions from the GFCC-i(2,3) method exhibit better agreement with the experimental results and other theoretical results, particularly in terms of providing higher resolution of satellite peaks and more accurate relative positions of these satellite peaks with respect to the main peak positions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Role of Active Phase in Fischer–Tropsch Synthesis: Experimental Evidence of CO Activation over Single-Phase Cobalt Catalysts

In order to understand the role of Co catalysts with different phases on Fischer-Tropsch synthesis, single-phase face-centered cubic (fcc) and hexagonal close-packed (hcp) Co were synthesized via a two-step approach, involving the formation of single-phase CoO materials followed by reduction in H2. The physicochemical properties of Co catalysts were thoroughly characterized by XRD, SEM, TEM, TPR and H2 chemisorption. It was found that hcp-Co exhibits higher activity on hydrocarbon formation than fcc-Co in Fischer-Tropsch synthesis. For both catalysts, CO dissociation was suggested as the rate determining step, on which hcp-Co presents ca. 40 kJ mol-1 lower activation energy than fcc-Co, in agreement of reported computational study. As a result, hcp-Co is concluded as a preferable phase for rational catalyst design.

Lyu, Shuai↗
DOE OSTI2018

Overcoming Thermodynamic Limitations in Dimethyl Carbonate Synthesis from Methanol and CO2

Shifting the unfavorable equilibrium in the synthesis of dimethyl carbonate from CO2 and methanol via integrated separation opens a feasible and environmentally benign route. The subtle differences in the sorption kinetics of water and methanol on Linde type A zeolites are used to selectively remove water from the methanolic reaction medium with a separation factor of 100. Combining reaction with a low temperature separation enables a 10-time higher DMC yield compared to conventional conversion.

Peng, Bo↗
DOE OSTI2018

Green’s Function Coupled-Cluster Approach: Simulating Photoelectron Spectra for Realistic Molecular Systems

In this paper we present an efficient implementation for the analytical energy- dependent coupled cluster Green’s function with singles and doubles (GFCCSD) approach with our first practice being computing spectral functions of real molecular systems. Due to its algebraic structure, the presented method is highly scalable, and is capable of computing spectral function for a given molecular system in any energy region. Several typical examples have been given to demonstrate its capability of computing spectral functions not only in the valence band, but also in the core-level energy region. Satellite peaks have been observed in the inner valence band and core-level energy region where many-body effect becomes significant and single particle picture of ionization often breaks down. The accuracy test has been carried out by extensively comparing our GFCCSD results with experimental results as well as the theoretical results from other methods. It turns out GFCCSD method is able to provide qualitative or semi-quantitative level of description of ionization processes in both the core and valence regimes. To significantly improve the GFCCSD results for the main states, larger basis set can usually be employed, whereas the improvement of the GFCCSD results for the satellite states needs higher order many-body terms to be included in the GFCC implementation.

electronic structure theory↗
DOE OSTI2018

Vapor-Phase Hydrodeoxygenation of Guaiacol to Aromatics over Pt/HBeta: Identification of the Role of Acid Sites and Metal Sites on the Reaction Pathway

Hydrodeoxygenation of guaiacol, a phenolic compound derived from lignin fraction of biomass, over a Pt/HBeta catalyst at 350 °C and atmospheric pressure produces benzene, toluene, xylenes, and C9+ aromatics with yield of 42%, 29%, 12%, and 5%, respectively. Reaction pathways for conversion of two functional groups (hydroxyl and methoxyl) over the bifunctional catalyst were studied. Both guaiacol and intermediate products (catechol and cyclopentanone) were fed onto zeolite HBeta and Pt/SiO2 to identify the individual role of acid site and metal site. Acid sites (mainly Brønsted acid site, BAS) catalyze transalkylation and dehydroxylation reactions in sequence, producing phenol, cresols and xylenols as the major products at high conversion. Pt sites catalyze demethylation reaction resulting in catechol as the primary product, which can either be deoxygenated to phenol followed by phenol to benzene, or decarbonylated to cyclopentanone and further to butane. The close proximity of Pt and BAS in bifunctional Pt/HBeta enables both transalkylation and deoxygenation reactions with inhibited demethylation and decarbonylation reactions, producing aromatics as major final products with a total yield > 85%. Both activity and stability of bifunctional Pt/HBeta during hydrodeoxygenation of guaiacol is improved compared to HBeta and Pt/SiO2. The addition of water to the feed further improves the activity and stability via hydrolysis of O-CH3 bond of guaiacol on BAS and removing coke around Pt.

Nie, Lei↗
DOE OSTI2018

1D SbSeI, SbSI, and SbSBr With High Stability and Novel Properties for Microelectronic, Optoelectronic, and Thermoelectric Applications

Mechanical exfoliation of 2D materials has triggered an explosive interest in lowdimensional material research. We extend this idea to 1D van derWaals materials. Three 1D semiconductors (SbSeI, SbSI and SbSBr) with high stability and novel electronic properties are discovered using first principles calculations. Both the dynamical and the thermal stability of these 1D materials are examined. We demonstrate that their nanowire thinner than 7 Å can be easily obtained by mechanical exfoliation, hydrothermal method or sonochemical method. The bulk-to-1D transition results in dramatic changes in band gap, effective mass and static dielectric constant due to quantum confinement, making 1D SbSeI a highly promising channel material for transistors with gate length shorter than 1 nm. Under small uniaxial strain, these materials are transformed from indirect into direct band gap semiconductors, paving the way for optoelectronic devices and mechanical sensors. Moreover, the thermoelectric performance of these materials is significantly improved over their bulk counterparts. These highly desirable properties render SbSeI, SbSI and SbSBr promising 1D materials for applications in future microelectronics, optoelectronics, mechanical sensors, and thermoelectrics.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Properties of advanced coupled-cluster Green's function

We present an extension of the analysis previously applied to the retarded part of the coupled cluster (CC) Green's function to its advanced part. In analogy to our earlier studies for the retarded part, we demonstrate that the advanced CC Green's function is expressed in terms of connected diagrams only, which is a direct consequence of algebraic form of equations satisfied by CC amplitudes. We also demonstrate that omega-derivatives of the advanced CC Green's function can be calculated analytically and can be expressed in terms of connected diagrams only. We analyze the structure of connected diagrams and the role of intermediate operators which satisfy electron affinity equation-of-motion CC type conditions.

electronic structure theory↗
DOE OSTI2018

Hydrogenation of Diesters on Copper Catalyst Anchored on Ordered Hierarchical Porous Silica: Pore size effect

An ordered hierarchically porous silica (HPS) with the coexistence of both mesopores and abundant micropores was fabricated and used as support for the preparation of copper-based catalysts (Cu/HPS). The ordered mesoporous structure of the Cu/HPS catalysts was retained. In addition, both Cu0 and Cu+ species are found to be highly dispersed. It might be attributed to the anchoring effect of micropores and the formation of Cu-O-Si species derived from the strong interaction between surface silica and copper precursor. The Cu/HPS catalysts showed excellent performances in the hydrogenation of dimethyl adipate. The catalytic activity in dimethyl oxalate hydrogenation depended on the surface reaction, while the activity in dimethyl adipate hydrogenation will be readily controlled by pore diffusion, which can be improved by tailoring the pore size of HPS. These findings could be meaningful instruction for the rational design of industrial catalysts for the hydrogenation of various diesters.

ester, hydrogenation, higherarchical, copper, diff↗
DOE OSTI2017

First-principles study on the electronic, optical, and transport properties of monolayer α- and β-GeSe

The extraordinary properties and the novel applications of black phosphorene induce the research interest in the monolayer group-IV monochalcogenides. Here using first-principles calculations, we systematically investigate the electronic, transport, and optical properties of monolayer α- and β-GeSe, revealing a direct band gap of 1.61 eV for monolayer α-GeSe and an indirect band gap of 2.47 eV for monolayer β-GeSe. For monolayer β-GeSe, the electronic/hole transport is anisotropic, with an extremely high electron mobility of 2.93×104cm2/Vs along the armchair direction, comparable to that of black phosphorene. However, for β-GeSe, robust band gaps nearly independent of the applied tensile strain along the armchair direction are observed. Both monolayer α- and β-GeSe exhibit anisotropic optical absorption in the visible spectrum.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Activation of surface lattice oxygen in single-atom Pt/CeO 2 for low-temperature CO oxidation

To improve fuel efficiency, advanced combustion engines are being designed to minimize the amount of heat wasted in the exhaust. Hence, future generations of catalysts must perform at temperatures that are 100°C lower than current exhaust-treatment catalysts. Achieving low-temperature activity, while surviving the harsh conditions encountered at high engine loads, remains a formidable challenge. In this study, we demonstrate how atomically dispersed ionic platinum (Pt 2+ ) on ceria (CeO 2 ), which is already thermally stable, can be activated via steam treatment (at 750°C) to simultaneously achieve the goals of low-temperature carbon monoxide (CO) oxidation activity while providing outstanding hydrothermal stability. A new type of active site is created on CeO 2 in the vicinity of Pt 2+ , which provides the improved reactivity. These active sites are stable up to 800°C in oxidizing environments.

Nie, Lei (ORCID:0000000343593451)↗
DOE OSTI2017

Chemical intuition for high thermoelectric performance in monolayer black phosphorus, α-arsenene and aW-antimonene

Identifying materials with intrinsically high thermoelectric performance remains a challenge even with the aid of a high-throughput search. Here, using a chemically intuitive approach based on the bond-orbital theory, three anisotropic 2D group-V materials (monolayer black phosphorus, α-arsenene, and aW-antimonene) are identified as candidates for high thermoelectric energy conversion efficiency. Concepts, such as bond length, bond angle, and bond strength, are used to explain the trends in their electronic properties, such as the band gap and the effective mass. Our first principles calculations confirm that high carrier mobilities and large Seebeck coefficients can be obtained at the same time in these materials, due to complex Fermi surfaces originating from the anisotropic structures. An intuitive understanding of how the bonding character affects phonon transport is also provided with emphasis on the importance of bonding strength and bond anharmonicity. High thermoelectric performance is observed in these materials. In conclusion, our approach provides a powerful tool to identify new thermoelectric materials and evaluate their transport properties.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2017

Mid-infrared Variability of Changing-look AGNs

It is known that some active galactic nuclei (AGNs) transit from Type 1 to Type 2 or vice versa. There are two explanations for the so-called changing-look AGNs: one is the dramatic change of the obscuration along the line of sight, and the other is the variation of accretion rate. In this Letter, we report the detection of large amplitude variations in the mid-infrared luminosity during the transitions in 10 changing-look AGNs using the Wide-field Infrared Survey Explorer ( WISE ) and newly released Near-Earth Object WISE Reactivation data. The mid-infrared light curves of 10 objects echo the variability in the optical band with a time lag expected for dust reprocessing. The large variability amplitude is inconsistent with the scenario of varying obscuration, rather it supports the scheme of dramatic change in the accretion rate.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Highly Efficient and Scalable Compound Decomposition of Two-Electron Integral Tensor and Its Application in Coupled Cluster Calculations

The representation and storage of two-electron integral tensors are vital in large- scale applications of accurate electronic structure methods. Low-rank representation and efficient storage strategy of integral tensors can significantly reduce the numerical overhead and consequently time-to-solution of these methods. In this paper, by combining pivoted incomplete Cholesky decomposition (CD) with a follow-up truncated singular vector decomposition (SVD), we develop a decomposition strategy to approximately represent the two-electron integral tensor in terms of low-rank vectors. A systematic benchmark test on a series of 1-D, 2-D, and 3-D carbon-hydrogen systems demonstrates high efficiency and scalability of the compound two-step decomposition of the two-electron integral tensor in our implementation. For the size of atomic basis set N_b ranging from ~ 100 up to ~ 2, 000, the observed numerical scaling of our implementation shows O(N_b^{2.5~3}) versus O(N_b^{3~4}) of single CD in most of other implementations. More importantly, this decomposition strategy can significantly reduce the storage requirement of the atomic-orbital (AO) two-electron integral tensor from O(N_b^4) to O(N_b^2 log_{10}(N_b)) with moderate decomposition thresholds. The accuracy tests have been performed using ground- and excited-state formulations of coupled- cluster formalism employing single and double excitations (CCSD) on several bench- mark systems including the C_{60} molecule described by nearly 1,400 basis functions. The results show that the decomposition thresholds can be generally set to 10^{-4} to 10^{-3} to give acceptable compromise between efficiency and accuracy.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Discovery of a Mid-infrared Echo from the TDE Candidate in the Nucleus of ULIRG F01004−2237

We present the mid-infrared (MIR) light curves (LCs) of a tidal disruption event candidate in the center of a nearby ultraluminous infrared galaxy F01004−2237 using archival WISE and NEOWISE data from 2010 to 2016. At the peak of the optical flare, F01004−2237 was IR quiescent. About three years later, its MIR fluxes have shown a steady increase, rising by 1.34 and 1.04 mag in 3.4 and 4.6 μ m up to the end of 2016. The host-subtracted MIR peak luminosity is 2–3 × 10{sup 44} erg s{sup −1}. We interpret the MIR LCs as an infrared echo, i.e., dust reprocessed emission of the optical flare. Fitting the MIR LCs using our dust model, we infer a dust torus of the size of a few parsecs at some inclined angle. The derived dust temperatures range from 590–850 K, and the warm dust mass is ∼7 M {sub ⊙}. Such a large mass implies that the dust cannot be newly formed. We also derive the UV luminosity of 4–11 × 10{sup 44} erg s{sup −1}. The inferred total IR energy is 1–2 × 10{sup 52} erg, suggesting a large dust covering factor. Finally, our dust model suggests that the long tail of the optical flare could be due to dust scattering.

79 ASTRONOMY AND ASTROPHYSICS↗