EID study on the system platinum-hydrogen

Electron induced desorption of hydrogen on polycrystalline platinum has been studied in continuation of former work. The results remain consistent with a supposed adsorption model implying that electron induced H⁺ emission is restricted to hydrogen adsorbed only at particular sites occupying not more than 1 per cent coverage. These sites are ascribed to characteristic and stable surface impurities which are not influenced by the improved target treatment applied. Depletion of sites by sputter cleaning is cancelled by recovery during annealing. The highest observed H⁺ yield (all available sites filled with hydrogen) is 2 · 10⁻⁵ ions per electron. The total cross section for desorption by electron impact is 2 · 10⁻¹⁷ cm². Complex interaction phenomena between the electrons and the hydrogen covered platinum surface have been observed.     

A rat brain protein expression map including cytosolic and enriched mitochondrial and microsomal fractions

Proteomics is a powerful tool to screen brain protein expression but the methodology is hampered by low abundance of proteins or compartmentalization or overload of high-abundance proteins. It was therefore the aim of the study to determine the expression of brain proteins by using enriched cellular subfractions and pre-electrophoretic chromatographical separation of brain homogenates. We used two-dimensional electrophoresis with subsequent matrix-assisted laser desorption/ionization (MALDI) detection and characterization of brain proteins. Subfractionation into cytosolic, mitochondrial and microsomal compartments was performed by ultracentrifugation. Pre-electrophoretic fractionation of the cytosolic fractions was carried out by ion exchange column chromatography. We detected and identified a large series of 437 proteins in rat brain and have shown proteins specific for the individual subcellular compartments. These proteins included housekeeping, signaling, cytoskeletal, intermediary metabolism, antioxidant proteins on the one and neuron and synaptosomal specific proteins on the other hand. Using fractionations of brain homogenates we were able to improve the power of the method on forming the basis for brain protein expressional studies and providing a reference map as a powerful tool for the neuroscientist.     

碳纳米纤维吸附储氢性能分析

文中综合碳纳米纤维微观结构的表征结果以及氢吸脱附等温线的实验测量结果,对碳纳米纤维的吸附储氢性能进行了综合分析,分析发现:比表面积和中孔容积均与氢吸附量成线性关系;微孔容积对材料吸附性能影响较大,微孔容积与氢吸附量成抛物线关系;氢在常温左右以及77K下的吸附等温线呈现超临界气体的吸附特征,氢在273K和353K下的吸脱附等温线也基本重合,呈现的是物理吸附的特征。实验结果还说明:常温左右,甚至是77K下,碳纳米纤维均不适合于氢的吸附储存。     

Adsorption kinetics of alkanes on TiO2 nanotubesarray - structure-activity relationship

Presented are thermal desorption spectroscopy (TDS) measurements of iso-/n-butane adsorption on a variety of TiO₂ nanotubes (TiNTs) samples which are characterized by different crystal structures. The results are compared with a prior study on anatase(0 0 1) thin films grown on SrTiO₃(0 0 1). A distinct kinetic structure-activity relationship was present, i.e., the binding energies of the alkanes depend on the polymorph (anatase vs. mixed anatase/rutile) of TiO₂. A direct-fitting procedure of the TDS data has been applied to extract the kinetics parameters. The binding energies in the limit of zero coverage decrease as anatase thin film > amorphous-TiNTs ∼ polycrystalline anatase TiNTs > polycrystalline mixed anatase/rutile TiNTs.     

Methods for calculating the desorption rate of an isolated molecule from a surface: Water on MgO(0 0 1)

We present two types of Molecular Dynamics (MD) simulation for calculating the desorption rate of molecules from a surface. In the first, the molecules move freely between two surfaces, and the desorption rate is obtained either by counting the number of desorption events in a given time, or by looking at the average density of the molecules as a function of distance from the surface and then applying transition state theory (TST). In the second, the potential of mean force (PMF) for a molecule is determined as a function of distance from the surface and the desorption rate is obtained by means of TST. The methods are applied to water on the MgO(0 0 1) surface at low coverage. Classical potentials are used so that long simulations can be performed, to minimise statistical errors. The two sets of MD simulations agree well at high temperatures. The PMF method reproduces the 0 K adsorption energy of the molecule to within 5 meV, and finds that the well depth of the PMF is not linear with temperature. This implies the prefactor frequency f in the Polanyi-Wigner equation is a function of temperature, increasing at lower temperatures due to the reduction of the available configuration space associated with an adsorbed molecule compared with a free molecule.     

Adsorption and reactions of ethanol on Mo2C/Mo(1 0 0)

The adsorption, desorption and dissociation of ethanol have been investigated by work function, thermal desorption (TPD) and high resolution electron energy loss (HREELS) spectroscopic measurements on Mo₂C/Mo(1 0 0). Adsorption of ethanol on this sample at 100 K led to a work function decrease suggesting that the adsorbed layer has a positive outward dipole moment By means of TPD we distinguished three adsorption states, condensed layer with a Tp = 162 K, chemisorbed ethanol with Tp = 346 K and irreversibly bonded species which decomposes to different compounds. These are hydrogen, acetaldehyde, methane, ethylene and CO. From the comparison of the Tp values with those obtained following their adsorption on Mo₂C it was inferred that the desorption of methane and ethylene is reaction limited, while that of hydrogen is desorption limited process. HREEL spectra obtained at 100 K indicated that at lower exposure ethanol undergoes dissociation to give ethoxy species, whereas at high exposure molecularly adsorbed ethanol also exists on the surface. Analysis of the spectral changes in HREELS observed for annealed surface assisted to ascertain the reaction pathways of the decomposition of adsorbed ethanol.     

On the use of elastic peak electron spectroscopy (EPES) to measure the H content of hydrogenated amorphous carbon films

Quasi‐elastic scattering of 1–2 keV electrons is considered with respect to measuring the H content in hydrogenated amorphous carbon (a‐C:H) materials. Interest in the technique lies in the fact that H cannot be typically detected by electron spectroscopic means (AES or XPS for instance). The feasibility of the approach is demonstrated and a quantification procedure is proposed. At the same time however, limitations of the technique (electron stimulated H desorption, low intensity of the H related signal and its spectral interference with the π‐plasmon peak) are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Analysis of NH3-TPD Profiles for CuSSZ-13 SCR Catalyst of Controlled Al Distribution – Complexity Resolved by First Principles Thermodynamics of NH3 Desorption,IR and EPR Insight into Cu Speciation**

NH₃ temperature-programmed desorption (NH₃-TPD) is frequently used for probing the nature of the active sites in CuSSZ-13 zeolite for selective catalytic reduction (SCR) of NO_x. Herein, we propose an interpretation of NH₃-TPD results, which takes into account the temperature-induced dynamics of NH₃ interaction with the active centers. It is based on a comprehensive DFT/GGA+D and first-principles thermodynamic (FPT) modeling of NH₃ adsorption on single Cu²⁺, Cu⁺, [CuOH]⁺ centers, dimeric [Cu-O-Cu]²⁺, [Cu-O₂²⁻-Cu]² species, segregated CuO nanocrystals and Brønsted acid sites (BAS). Theoretical TPD profiles are compared with the experimental data measured for samples of various Si/Al ratios and distribution of Al within the zeolite framework. Copper reduction, its relocation, followed by the intrazeolite olation/oxolation processes, which are concomitant with NH₃ desorption, were revealed by electron paramagnetic resonance (EPR) and IR. DFT/FPT results show that the peaks in the desorption profiles cannot be assigned univocally to the particular Cu and BAS centers, since the observed low-, medium- and high-temperature desorption bands have contributions coming from several species, which dynamically change their speciation and redox states during NH₃-TPD experiment. Thus, a rigorous interpretation of the NH₃-TPD profiles of CuSSZ-13 in terms of the strength and concentration of the active centers of a particular type is problematic. Nonetheless, useful connections for molecular interpretation of TPD profiles can be established between the individual component peaks and the corresponding ensembles of the adsorption centers.     

Application of nanodiamonds in human body fluid analysis by matrix-assisted laser desorption/ionization mass spectrometry

Direct mass spectrometric analysis of complex biological samples is very important and challenging. In this paper, nanodiamonds have been successfully used in matrix-assisted laser desorption/ionization mass spectrometric analysis of human serum and urine. As a practical tool and platform, it can be widely used in the field of humoral proteomics, and it plays a very promising role in clinical diagnosis, including identification of novel disease-associated biomarkers.