CO Shift Research Articles

Direct magnetic-field dependence of NMR chemical shift.

Nuclear shielding and chemical shift are considered independent of the magnetic-field strength. Ramsey proposed on theoretical grounds in 1970 that this may not be valid for heavy nuclei. Here we present experimental evidence for the direct field dependence of shielding, using 59Co shielding in Co(acac)3 [tris(acetylacetonate)cobalt(iii)] as an example. We carry out NMR experiments in four field strengths for this low-spin diamagnetic Co(iii) complex, which features a very large and negative nuclear shielding constant of the central Co nucleus. This is due to a magnetically accessible, low-energy eg ← t2g orbital excitation of the d6 system. The experiments result in temperature-dependent magnetic-field dependence of -5.7 to -5.2 ppb T-2 of the 59Co shielding constant, arising from the direct modification of the electron cloud of the complex by the field. First-principles multiconfigurational non-linear response theory calculations verify the sign and order of magnitude of the experimental results.

Hydrogen bonds leading nanodiamonds performing different thermal conductance enhancement in different MWCNTs epoxy-based nanocomposites

The lack of thermal conductance (TC) remains to be a challenge for epoxy resin. Fortunately, the thermal conductance of epoxy resin can be effectively improved by filler incorporation. Recently, compositing epoxy resin with hybrid filler system has been the direction for the development of next-generation thermal conductive functional materials. In this paper, epoxy-based nanocomposites containing nanodiamonds (DNDs)/pristine multi-walled carbon nanotubes (p-MWCNTs) and DNDs/KH550 functionalized MWCNTs (MWCNTs-KH) as the hybrid filler system were prepared respectively, and the thermal conductance of the nanocomposites was compared. The addition of DNDs was found to play a dominating role in the MWCNTs-KH filler systems (0.2 g, from 0.30 W/mK to 0.34 W/mK), but hardly has any effect on the p-MWCNTs filler system (0.2 g, from 0.24 to 0.26 W/mK only). Furthermore, the TC of the DNDs/MWCNTs-KH (2 g) epoxy-based nanocomposite increased to 0.45 W/mK, displaying an enhancement of 114.2 %. A shift of 5 cm-1 recorded by FTIR and the shift of CO revealed by XPS for DNDs/MWCNTs-KH strongly confirmed the existence of hydrogen bonds. Associating with the characterization results of SEM, TEM and dispersion qualitative experiment, the significant improvement in the TC of DNDs/MWCNTs-KH (2 g) epoxy-based nanocomposite was attributed to the hydrogen bond attachment between DNDs and MWCNTs-KH. The mechanism is that the attachment improves the dispersion of the fillers in epoxy, leading to the formation of a more effective thermal conductive network, thus, the enhanced TC. This work may inspire future studies in hybrid filler recognition and self-assemble technology via hydrogen bonds.

Using a multiway chemometric tool in the evaluation of methanol electro-oxidation mechanism

In the present work, an innovative methodology is used to contribute in the elucidation of methanol electro-oxidation reaction on polycrystalline Pt surface. We coupled infrared spectroscopy to linear voltammetry and evaluate the data using parallel factor analysis (PARAFAC) to extract hidden information concerning the oxidation reaction. Five adsorbed species were simultaneously extracted and quantified at different applied potentials corresponding to: formate, sulfate, water, total CO and COL shift. It was observed that the CO adsorbed content starts at maximum on low potentials and gradually decreases up to 1.0 V. Meanwhile, the interfacial water content on the surface of the CO-free Pt increases, which causes the shift on the COL band, resulting in a further decrease of the interfacial water content. The water content increases again until up to 0.8 V, which it reaches a constant value, due to formate production and subsequent adsorption of sulfate. Using this technique, it was possible to determine the potential window where each chemical species is adsorbed on the surface, as well as the effect of methanol concentration and scan rate on the mechanism.

Validation and Application of a Kinetic Model for Downdraft Biomass Gasification Simulation

AbstractBiomass gasification is widely recognized as an effective method to obtain renewable energy. To accurately predict the syngas and tar compositions is a challenge. A chemical reaction kinetics model based on comprehensive gasification kinetics is proposed to simulate downdraft biomass gasification. The kinetic model is validated by direct comparison to experimental results of two downdraft gasifiers available in the literature and is found to be more accurate than the widely used Gibbs energy‐minimizing model (GEM model). The kinetic model is then applied to investigate the effects of equivalence ratio (ER), gasification temperature, biomass moisture content, and biomass composition on syngas and tar production. Accurate water‐gas shift and CO shift reaction kinetics are found critical to achieve good agreement with experimental results.

First-principle investigation on multiferroicity and interfacial coupling of nonstoichiometric tetragonal La2/3Sr1/3MnO3/BiCoO3 interface

The energetically stable tetragonal nonstoichiometric La2/3Sr1/3MnO3/BiCoO3 (LSMO/BCO) interface, whose chemical formula is (BiO)3(CoO2)4/(LaO)3(SrO)1(MnO2)3, was investigated by using first-principle calculations. A magnetoelectric coupling effect, i.e., an electric control of the magnetism, was approved by a maximum variation of 17.9% in magnetic moments tuned by the electric polarization reversal. The interfacial coupling was controlled by the polar shifts of the interfacial Co and/or O atoms. A huge variation in spin-polarization from 6.3% to 72.7% was achieved upon switching the electric polarization. These findings are useful for magnetoelectric coupled spintronic device applications.

How oxides affect the stretching modes of carbon monoxide adsorbed on Ni catalyst?

Testing the stretching frequency shift of adsorbed CO has been a popular tool to evaluate the chemical property change of catalysts. We demonstrated first-principles models to reveal the mechanism of oxides effect on the frequency shift of CO on the Ni catalysts. Our calculations show that higher coverage of CO molecules leads to blue frequency shift, and there is negligible frequency shift when co-adsorbed with Al2O3 species and red frequency shift when co-adsorbed with ZrO2 or CeO2 species, which are consistent with the experimental literatures. The frequency shift is conformed to be proportional to the charge transfer amount of the π back-donation from Ni to the π⁎ orbital of CO molecule. The frequency shift direction is not determined by whether the oxide species is an electron acceptor or donor when adsorbed on Ni surface, but by how the oxide species affects the electrons on t2g and eg orbitals of the Ni atom under the CO molecule. The redistribution between t2g and eg orbitals induces the decreasing or increasing back-donation when a CO molecule co-adsorbed with the CO molecules or CeO2 species.

Chemical shift assignments of the catalytic and ATP-binding domain of HK853 from Thermotoga maritime.

HK853 is a transmembrane protein from Thermotoga maritime, which belongs to HK853/RR468 two-component signal transduction system (TCS) and acts as a sensor histidine kinase. HK853 is mainly composed of a transmembrane domain, dimerization and histidine-containing phosphotransfer domain (HK853DHp), catalytic and ATP-binding domain (HK853CA) and several linkers. HK853 can be completely autophosphorylated, which is the first step for signal transduction of TCS. HK853CA is an essential domain for its kinase function, since HK853CA could bind with ATP and convert it to ADP. Here, we report the backbone and part of side chain assignments of HK853CA. By analyzing the chemical shifts of HN, N, CO, Cα and Cβ, the secondary structure was predicted and contrasted with the published crystal structure of HK853CA. The result showed that our predicted structure could basically fit into the crystal structure. Thus, the chemical shift assignments of HK853CA are the starting point for further structural and dynamics study.

Unravelling the structure-performance relationship over iron-based Fischer-Tropsch synthesis by depositing the iron carbonyl in syngas on SiO2 in a fixed-bed reactor

A new process, in situ deposition method, was developed to unveil Fe phase evolution behavior in iron-based Fischer-Tropsch synthesis (FTS). In detail, Fe(CO)x-containing syngas (CO/H2) was fed into a fixed-bed reactor where Fe(CO)x directly decomposes to metallic Fe with subsequent favorable carburization to form active χ-Fe5C2 on SiO2 under FTS reaction conditions. This facile process gives a high χ-Fe5C2 content (80–90%) without Fe3O4 phase in spent catalyst. In contrast, the 5.3Fe/SiO2 prepared by the conventional impregnation method results in very low χ-Fe5C2 content (14.5%) and high Fe3O4 content (47%) in spent catalyst, which is ascribed to the strong Fe oxide-SiO2 interaction hindering its deep reduction into metallic Fe but terminating as FeO. The reduced FeO could not be efficiently carburized into χ-Fe5C2 and tends to oxidize into Fe3O4 during the FTS reaction. Furthermore, the factors determining CO2 selectivity are systematically investigated based on abundant experiments. Results show that CO2 selectivity is closely related to CO conversion, Fe phase composition, reaction conditions, and the presence of K promoter. In brief, when the factor enhances H*/C* ratio on χ-Fe5C2, the reaction of dissociative O* from CO shifts towards hydrogenation to H2O despite that its reaction with CO* to form CO2via Boudouard mechanism is kinetically favorable. In addition, CO2 selectivity could be reduced via reverse water-gas shift (RWGS) reaction on Fe3O4 with H2O generation.

Novel, multifunctional mucilage composite films incorporated with cellulose nanofibers

In the current study, mucilage composite films were produced by incorporating the cellulose nanofibrils (CNF) at different concentrations i.e.,3 and 6% to chia mucilage matrix by solution casting method. To evaluate the effect of CNF incorporation into mucilage matrix, the obtained composite films were characterized extensively using both physicochemical and biological tools. FT-IR spectra confirmed the composite formation by broader OH bond peaks than in the spectrum of mucilage control film and shift of CO stretching vibration peak lower wave number and widen in the mucilage films including cellulose nanofibers. Cellulose nanofibers did not reveal a significant effect on the thermal properties of the all three composite films and dynamic thermogravimetric values were recorded as ≃287 °C. Atomic force microscopy revealed a homogenous distribution of cellulose nanofibers across the mucilage matrix. Dynamic mechanical analysis revealed that the inclusion of cellulose nanofibers in mucilage film led to an enhancement of the tensile modulus as well as the tensile strength, but without reducing the strain at break of the film. Cellulose nanofibers incorporation significantly enhanced the hydrophobic properties of the composite films. The cytotoxicity assay results demonstrated mucilage composite films were nontoxic and have anticancer properties; reducing the viability of cancer cell line by ≃ 20% and retaining the cell viability of epithelial cell line by ≃ 90%. Cellulose nanofibers incorporation also significantly enhanced the antioxidant and antimicrobial attributes of the mucilage composite films. Overall, the current study provided an idea regarding the biocompatible, non-toxic, highly antioxidative and antimicrobial biodegradable nature of mucilage-CNF composite films, making it a suitable candidate for food and pharmaceutical industry.

Living on borrowed time - Amazonian trees use decade-old storage carbon to survive for months after complete stem girdling.

Summary Nonstructural carbon (NSC) reserves act as buffers to sustain tree activity during periods when carbon (C) assimilation does not meet C demand, but little is known about their age and accessibility; we designed a controlled girdling experiment in the Amazon to study tree survival on NSC reserves.We used bomb‐radiocarbon (14C) to monitor the time elapsed between C fixation and release (‘age’ of substrates). We simultaneously monitored how the mobilization of reserve C affected δ13 CO 2.Six ungirdled control trees relied almost exclusively on recent assimilates throughout the 17 months of measurement. The Δ14C of CO 2 emitted from the six girdled stems increased significantly over time after girdling, indicating substantial remobilization of storage NSC fixed up to 13–14 yr previously. This remobilization was not accompanied by a consistent change in observed δ13 CO 2.These trees have access to storage pools integrating C accumulated over more than a decade. Remobilization follows a very clear reverse chronological mobilization with younger reserve pools being mobilized first. The lack of a shift in the δ13 CO 2 might indicate a constant contribution of starch hydrolysis to the soluble sugar pool even outside pronounced stress periods (regular mixing).

Coupled-cluster treatment of molecular strong-field ionization.

Ionization rates and Stark shifts of H2, CO, O2, H2O, and CH4 in static electric fields have been computed with coupled-cluster methods in a basis set of atom-centered Gaussian functions with a complex-scaled exponent. Consideration of electron correlation is found to be of great importance even for a qualitatively correct description of the dependence of ionization rates and Stark shifts on the strength and orientation of the external field. The analysis of the second moments of the molecular charge distribution suggests a simple criterion for distinguishing tunnel and barrier suppression ionization in polyatomic molecules.

Ligand Effect on Bonding in Gold(III) Carbonyl Complexes.

We quantitatively assess the Dewar-Chatt-Duncanson (DCD) components of the Au(III)-CO bond and the charge density polarization at the CO, in a series of neutral, cationic, and dicationic bis- and monocyclometalated gold(III) complexes via charge-displacement (CD) analysis. A striking feature concerns the very small net electron charge flux from CO to the metal fragment which is unexpectedly stable toward both the charge of the complex and the oxidation state of gold (I, III). All systems exhibit a similar trend for the σ charge rearrangement in the region of the carbonyl bond, where, by contrast, the π back-donation trend variation is large, which is strictly correlated to the change in CO bond distance and the shift in CO stretching frequencies, in close analogy with the gold(I) carbonyl complexes. In the whole series of gold(III) compounds, a large Au(III) ← CO σ donation is measured (from 0.19 to 0.31 electrons), as well as a significant Au(III) → CO π back-donation (from -0.09 to -0.22 electrons), which however is not generally able to completely balance the polarization of the CO π electrons in the direction from oxygen to carbon (C ← O) induced by the presence of the metal fragment [LAu(III)]0/+1/+2. Surprisingly, all the gold(III) complexes in the series are characterized by a very small anisotropy in the Au(III) → CO in-plane and out-of-plane π back-donation components, in sharp contrast with the marked anisotropy found before for the experimentally characterized [(C^N^C)Au(III)CO]+ complex. A first attempt to figure out a rationale on the bonding/reactivity relationship for Au(III)-CO is made by performing a comparative study with an isostructural [(N^N^C)Pt(II)CO]+ complex in a model water-gas shift (WGS) reaction.

Improvement of Performance of Selective CO2 Facilitated Transport Membrane in Hydrogen Station

The cost reduction of hydrogen stations is a must in order to spread fuel cell vehicles. Generally, the PSA device in the hydrogen station occupies 30% of the construction cost. We have already proposed the cost reduction by replacing the PSA and CO shift converter with a membrane reactor to which CO2 selective facilitated transport membrane is built in 2011. Although the CO2 facilitated transport membrane achieved the CO2/H2 selectivity of 100 or more even if the operation temperature was 160°C, the durability was poor. Therefore, it is necessary to improve the heat resistance and the rate of reaction between carrier and CO2 furthermore so that it can be adopted for the membrane reactor. In order to improve the membrane performance at 160°C by keeping high water content of membrane, graphite rubbish was added to the membrane as it was expected to function as grain for water absorption. As a result, the CO2 selectivity of the membrane improved more than that of the previous membrane by 3 times.

Temperature dependent polymorphism of pyrazinamide: An in situ Raman and DFT study

The α and γ polymorphs of drug pyrazinamide have been detected with the help of temperature dependent Raman spectroscopic technique. Pyrazinamide is a very useful drug used for the treatment of tuberculosis (TB) and plays a significant role in destroying the dormant tubercle bacilli which are not destroyed by other common TB drugs. Temperature dependent Raman spectra suggest polymorphic phase change from α→γ form of pyrazinamide between 145 and 146°C. In situ Raman spectra of pyrazinamide between 145 and 146°C show the conversion of α→γ form by the shift in CO stretching vibration accompanied by several other changes. The phase change is characterized by the breaking of two linear NH⋯O type hydrogen bonds associated with CO stretching vibration in α dimer and formation of one linear NH⋯N type hydrogen bond along with a weak intramolecular CH⋯O type hydrogen bond in the γ dimer.

Synthesis, characterization, crystal structure and theoretical studies of 4-[(E)-(3-chloro-4-hydroxyphenyl) diazenyl]-1, 5-dimethyl-2-phenyl-1, 2-dihydro-3H-pyrazol-3-one

Crystals of new heterocyclic azo compound of 4-aminoantipyrine, 4-[(E)-(3-chloro-4-hydroxyphenyl)diazenyl]-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one have been grown by slow evaporation method at room temperature and its structural characterization was performed by X- ray diffraction method. The spectroscopic characterization was also performed by FT-IR, UV–Vis, 13C and 1H NMR techniques. The compound crystallizes in the monoclinic CC space group with cell dimensions a = 12.4842 (13), b = 16.4492 (16), c = 8.3389 (8) and β = 102.698 (3)°. The phenyl ring attached to the pyrazolone moiety is disordered over two positions with an occupancy ratio 52:48. The components of the disorder were refined. DFT calculations have been performed by using B3LYP/6-311G (d,p) level basis set. The calculated vibrational frequency showed a red shift for CO and OH stretching. The natural bond orbital analysis of monomer, dimer and trimer structures reveals the absence of intramolecular hydrogen bonding; however intermolecular hydrogen bonding is observed. The cationic and anionic reactive sites of compound have been visualized on MEP surface.

Hydrogen production from biomass: The behavior of impurities over a CO shift unit and a biodiesel scrubber used as a gas treatment stage

Most of the hydrogen produced is derived from fossil fuels. Bioenergy2020+ and TU Wien have been working on hydrogen production from biomass since 2009. A pilot plant for hydrogen production from lignocellulosic feedstock was installed onsite using a fluidized bed biomass gasifier in Gussing, Austria. In this work, the behavior of impurities over the gas conditioning stage was investigated. Stable CO conversion and hydration of sulfur components could be observed. Ammonia, benzene, toluene, xylene (BTX) and sulfur reduction could be measured after the biodiesel scrubber. The results show the possibility of using a commercial Fe/Cr-based CO shift catalyst in impurity-rich gas applications. In addition to hydrogen production, the gas treatment setup seems to also be a promising method for adjusting the H2 to CO ratio for synthesis gas applications.

Co-oxidation of CO and propylene on Pd/CeO2-ZrO2 and Pd/Al2O3 monolith catalysts: A light-off, kinetics, and mechanistic study

The light-off (ignition) and steady-state behavior for individual oxidation and co-oxidation of CO and propylene under near-stoichiometric conditions was studied using Pd/Al2O3 and Pd/CeO2-ZrO2 monolith catalysts. CO and propylene are shown to be self- and mutually-inhibiting, with inhibition mitigated by the promotional effect of CeO2-ZrO2. Oxidation is enhanced at low temperatures for CO, and at intermediate and high temperatures for propylene. Light-off behavior during CO and propylene co-oxidation is similarly improved at low and high temperatures. Steady-state differential kinetics measurements using Pd/Al2O3 show reaction orders of ∼−1 with respect to CO and propylene. Using Pd/CeO2-ZrO2, the reaction order with respect to CO shifts towards zero and the activation energy decreases, suggesting an alternate reaction mechanism for CO oxidation when enough ceria is present. Mechanisms for CO and propylene oxidation that are consistent with the kinetics and inhibition trends are presented.

First-Principles Investigation of Adsorbate–Adsorbate Interactions on Ni(111), Ni(211), and Ni(100) Surfaces

Periodic density functional theory calculations were employed to investigate the coadsorption patterns between CO and key water gas shift reaction (WGSR) intermediates, i.e., H2O, H, OH, O, and COOH, on Ni(111), Ni(100), and Ni(211) single-crystal surfaces. It has been shown that although the nature of these adsorbate pair interactions are predominantly repulsive, as commonly assumed in the literature, the interaction pattern for each adsorbate pair can be complicated by facet lattice structures and potential intermolecular hydrogen bonds, which play an unsubtle role in influencing the WGSR redox and carboxyl pathways. This investigation can enrich our descriptions of the adsorbate lateral interactions for surface chemistry modeling and will also provide theoretical insights into tuning the properties of nanoscale nickel catalysts by manipulating the surface structure and morphology for hydrogen fuel production.

Sorption-enhanced steam reforming of glycerol over Ni[sbnd]Cu[sbnd]Ca[sbnd]Al catalysts for producing fuel-cell grade hydrogen

The concentration of CO in the high-purity hydrogen from sorption-enhanced steam reforming (SESR) processes is usually too high to be directly used in fuel cells. Herein, we report a production of fuel-cell grade H2 with <30 ppm CO through SESR of glycerol (SESRG), a by-product of biodiesel manufacture. High purity H2 can be produced by employing a catalyst-sorbent hybrid material composed of Ni as catalyst, CaO as CO2 sorbent and Ca12Al14O33 as spacer. By introducing copper as promoter, the performance of the bi-functional catalyst could be modified to produce a 97.15 vol% purity of H2 with 28 ppm CO. With an optimized Ni/Cu ratio, the 7.5Ni–7.5Cu catalyst shows the excellent stability for producing about 97% H2 with <30 ppm CO for ten cycles. The characterizations and model reaction tests indicate that copper can affect CO, CO2 hydrogenation and water gas shift reaction to adjust the performance of SESRG reaction. The results presented here show the promise of tuning the catalyst composition for achieving high quality H2 through SESR processes.

Catalytic ash free coal gasification in a fluidized bed thermogravimetric analyzer

Catalytic ash free coal gasification was investigated in the newly developed fluidized bed thermogravimetric analyzer. The total yield obtained from the fluidized bed TGA showed good agreement with the total gas product. For char gasification, the values of activation energy and pre-exponential factor were similar to those obtained from coal gasification in our previous work. The activation energy for the CO shift reaction decreased by 56% and 37% from the value reported in our previous work for coal gasification and in literature for catalytic coal gasification respectively. For the methane reforming reaction, the value of the activation energy was reduced by 33% from the one observed previously in our work, in the absence of a catalyst and decreased by 42% from the one reported in literature for catalytic gasification. The carbon conversion for the catalytic ash free coal gasification was 69% higher than the value obtained from the coal gasification for the same experimental conditions. This value was found to be 44.5% for the ash free coal gasification. The heating value of the gas product by using the catalyst for temperatures below 520°C was also higher than without catalyst. However, at higher temperature, using the catalyst had no effect on the heating value of the gas product.