Subsequent Desorption Research Articles

Mechanistic investigations of the promoting role of Rh on the NSR performance of NOx storage BaO-based catalysts

To determine the promoting effect of Rh on the overall NOx storage and reduction (NSR) performance, the studies in the current work were directed toward investigating the storage and release ability over Rh NOx storage BaO-based catalysts compared to Pt. In terms of the metal surface dispersion and the ability of the noble metals to release oxygen at lower temperatures, the synthesized catalysts were characterized by means of dynamic CO chemisorption (RT) and N2O dissociation (RT - 773K). The NOx storage capacity and the thermal stability of the NOx adsorbed species formed on the surface were analyzed via NOx storage tests and temperature programmed desorption (TPD) without and in the presence of CO2 and H2O. In addition, experiments with lean and rich cycling were conducted at 473, 573 and 673K. The results from the N2O dissociation experiments showed the superior ability of Rh/Al and Rh/Ba/Al catalysts compared to Pt toward O2 release from the catalytic surface at lower temperatures. In this work, we show that the presence of Rh into the BaO/γ-Al2O3 system has a considerable effect on the spill-over process of NOx to the precious metal, controlling the subsequent desorption of NOx to occur at lower temperatures in comparison with that of the Pt catalysts. It is suggested a mechanism of NOx desorption where the lower temperature of O2 release from the surface of Rh catalysts could leave a significant number of noble metal sites accessible for adsorption. Thus this could facilitate the rate of spill-over of NOx from the storage site (the surface sites on γ-Al2O3 and those on BaO) to the noble metal and their desorption at lower temperatures. The limited NOx storage ability of the Rh-based BaO/γ-Al2O3 catalysts under lean-burn conditions was found to originate from both low NO oxidation activity and NOx reduction activity, while the main limiting factor for the low NSR performance of the Pt-based catalysts was the limited regeneration ability during rich period.

MC simulation of desorption–recombination reaction and grain growth of nano-structured disproportionated NdFeB alloy

The process of mechanically activated disproportionation by ball milling in hydrogen and subsequent desorption–recombination has been proved to be a promising method to produce nanocrystalline NdFeB-type magnets. To ensure a fully recombinated microstructure with homogeneous nano-sized Nd2Fe14B grains, the desorption–recombination processing temperature and time should be properly selected or optimized. Thus, Monte Carlo (MC) simulation was performed to elucidate the effect of processing temperature on the kinetics of the recombination reaction to form Nd2Fe14B phase as well as the growth of the recombinated Nd2Fe14B grains. Based on the recombination reaction and grain growth mechanism of the disproportionated NdFeB alloy, a modified Monte Carlo (MC) model was introduced to simulate the kinetics of the reaction and grain growth behavior under various desorption–recombination processing conditions. The results show that the kinetics of both the recombination reaction and the growth of the newly formed Nd2Fe14B grains accelerate with increasing temperature. In particular, the recombination reaction of the disproportionated stoichiometrical Nd2Fe14B (atomic ratio) alloy can be completed in 30min at 800°C, with the grain size of the recombinated Nd2Fe14B phase being 35nm in average. After the finish of the recombination reaction, the growth of the Nd2Fe14B grains will proceed, with the growth rate or kinetics depending on the processing temperature. This paper presents an effective way to simulate the reaction progress and the grain growth during the desorption–recombination processing of nano-structured as-disproportionated NdFeB alloy, which is useful for process control and optimization.

Diffusion of H2 and Ne impurities in fullerite C60. Quantum effects

The kinetics of sorption and subsequent desorption of normal H2 and Ne gases in C60 powder has been investigated in the temperature range 12–292 K using the method of direct pressure measurement. The measured characteristic times for filling the octahedral interstitial sites of fullerite with gas molecules were used to obtain the temperature dependences of the diffusion coefficients in fullerite for H2 and Ne. Upon cooling down below room temperature the diffusion coefficients of the impurities were found to initially decrease in both solid state solutions and then rise steeply below 90 K (H2) or 100 K (Ne). At the lowest temperatures reached in the experiments, the temperature dependence of the diffusion leveled. The features revealed are attributed to the competition between the thermally activated diffusion, which is dominant at comparatively high temperatures, and the quantum diffusion, which prevails at low temperatures.

Switching the electronic properties of Co-octaethylporphyrin molecules on oxygen-covered Ni films by NO adsorption

Using x-ray absorption spectroscopy, we demonstrate that the electronic properties of Co-octaethylporphyrin (CoOEP) molecules on oxygen-covered ultrathin Ni films can be reversibly manipulated by a chemical stimulus. This is achieved by adsorption of nitrogen monoxide (NO), leading to the formation of a NO–CoOEP nitrosyl complex, and subsequent thermal desorption of the NO from the Co ions. The integration of the absorption spectra of the Co L2,3 edges reveals a partial oxidation of the Co ions after dosing with NO compared to the pristine sample, for which a valency of 2 + and a low-spin state of the Co ions can be deduced from the Co L2,3 XAS line shape. By means of x-ray magnetic circular dichroism the magnetic moments of the Co ions were found to be coupled parallel to the magnetization of the Ni films across the intermediate layer of atomic oxygen, before and after NO uptake.

Tryptophan-containing milk protein-derived dipeptides inhibit xanthine oxidase

Of twelve dipeptides tested, only the Trp containing peptides Val-Trp and its reverse peptide Trp-Val showed a xanthine oxidase (XO) inhibitory activity. Studies with Val and Trp revealed that XO inhibition was mainly attributed to the Trp residue. No significant difference (P≥0.05) was found for the XO inhibitory potency (IC50) values for Trp, Val-Trp and Trp-Val, which were about 200 times higher than that for Allopurinol. Lineweaver and Burke analysis demonstrated that Trp, Val-Trp and Trp-Val were non-competitive inhibitors while Allopurinol was a competitive inhibitor. Of the different milk-protein substrates hydrolyzed with gastro-intestinal enzyme activities, only lactoferrin (LF) hydrolyzates displayed XO inhibition. Peptides present in a LF hydrolyzate (GLF-240min) were adsorbed onto activated carbon followed by subsequent desorption with stepwise elution using acetonitrile (ACN). Separation and detection of Trp containing peptides within the different fractions were achieved using RP-HPLC coupled with fluorescence detection. The desorbed fractions displayed different XO inhibitory properties, with no inhibition in the unbound fraction and highest inhibition in fractions eluted with 30, 40 and 70% ACN. The fraction eluting at 40% ACN was significantly more potent (19.1±2.3% inhibition at 1.25mgmL−1) than the GLF-240min hydrolyzate (13.4±0.4% inhibition at 1.25mgmL−1), showing the potential for enrichment of the bioactive peptides on fractionation with activated carbon.

Adsorption and Desorption Behavior of Lithium Ion in Spherical PVC–MnO2 Ion Sieve

A spherical PVC–MnO2 ion sieve of 2.0–3.5 mm diameter was prepared by the antisolvent method using synthesized Li4Mn5O12 ultrafine powder as the precursor, poly(vinyl chloride) as the binder, and N-methyl-2-pyrrolidone as solvent. Batch experiments of the adsorption capacity (isotherm) and adsorption rate of Li+ on the spherical PVC–MnO2 ion sieve were studied. Spherical PVC–MnO2 had a high adsorption capacity for Li+, and the isotherm data were well fitted by the Langmuir model; the adsorption kinetics were well described by the Lagergren equation. Furthermore, a mathematical model was set up to calculate the film mass transfer coefficient (kf) and pore diffusivity (Dp) of the adsorbent. Continuous flow experiments for study of Li+ adsorption breakthrough and the subsequent desorption (elution) in a PVC–MnO2 packed column were carried out employing six feed solutions of various pH values and concentrations of Li+, Na+, K+, and Mg2+ for simulating brine samples of various salt lakes and/or seawaters. Afte...

Infrared study of triruthenium dodecacarbonyl interactions with gold

We present here a study of the interaction of triruthenium dodecacarbonyl Ru3(CO)12 with gold surfaces using time-evolved and temperature-programmed infrared reflection absorption spectroscopy (IRAS) and STM. Ru3(CO)12 exhibits drastically different adsorption/desorption behavior on high-index surfaces of gold in comparison to the smooth Au(111) surface. On the smooth Au(111) surface, the adsorption of Ru3(CO)12 at 200K is observed to be molecular and reversible with the molecule's Ru3-plane oriented essentially perpendicular to the surface in the first and second layer. In the multilayer (>3ML), the molecule is oriented parallel (or moderately inclined) to the surface. On high-index gold surfaces, prepared by partial annealing of rough gold films, the molecules dissociate. Vibrational spectra reveal dissociation of carbonyl to Ru and CO at elevated temperature (>250K) with the formation of CO covered Ru-islands and the subsequent desorption of CO from Ru-islands. Increasing amounts of CO observed with increasing surface roughness demonstrate that the rate of Ru3(CO)12 dissociation is related directly to the surface roughness of the gold surface. STM images reveal at low coverage the formation of 2-D islands of carbonyl fragments with lateral sizes of 1 to 1.5nm and at higher coverage the formation of larger 3-D islands of 1 to 3 layers and lateral sizes above 10nm.

Ultra-fine grained Nd–Fe–B by high pressure reactive milling and desorption

This paper reports on the grain refinement in dynamic hydrogenation disproportionation desorption and recombination (d-HDDR) processed Nd-rich Nd2Fe14B and stoichiometric Nd2Fe14B powders using high pressure reactive milling (HPRM) followed by a subsequent desorption and recombination. In contrast to the dynamic-HDDR processed anisotropic powder with a grain size of the Nd2Fe14B phase of 300nm, the new approach yields a further reduction of the Nd2Fe14B1 grain size to less than 70nm. Nd-rich Nd2Fe14B powder produced by HPRM and subsequent desorption exhibits a coercivity μ0iHc=1.35T and a remanence of 0.80T. In the stoichiometric material, the reduction of the Nd-content leads to an increase in remanence to 0.85T. Additionally, it is demonstrated that highly anisotropic powders can also be obtained by dynamic-HDDR processing of stoichiometric Nd2Fe14B powders.

Controlled Fabrication of Gold Nanoparticle and Fluorescent Protein Conjugates

The unique optical properties of gold nanopar- ticles make them attractive for a wide range of applications which require optical detection and manipulation techni- ques. Here, we experimentally demonstrate the use of single femtosecond pulses at resonance wavelength for a con- trolled conjugation of gold nanoparticles and fluorescent proteins. This optically driven reaction is rigorously studied and analyzed using a variety of experimental techniques, and a detailed model is proposed which describes the ad- sorption of the proteins onto the nanoparticles' surface, as well as their subsequent desorption by a reducing agent. Potential applications of the resulting nanoparticle-protein conjugates include controlled delivery of fluorescent markers and local sensing of biochemical processes.

Surface oxygen generated upon N2O activation on iron containing ZSM-5 type zeolites with different elemental composition

Various ZSM-5 zeolites with iron contents ranging from of 0.86 to 4.98 and Si/Al ratios of 11.5–140 were prepared by solid-state ion exchange with FeCl2. The catalysts were characterised by XRD, H2-TPR and NH3-TPD. The formation and stability of surface oxygen over these zeolites were investigated with a transient multipulse technique combined with subsequent temperature-programmed desorption (TPD). Higher iron contents enhance the formation of surface oxygen. However, when a critical iron content is reached, larger iron oxide clusters and particles are formed and these larger clusters do not contribute significantly to surface oxygen formation. Moreover, the amount of desorbed oxygen is more than that formed from N2O due to the additional desorption of oxygen present in the lattice of such oxide clusters. TPD studies indicate the presence of different surface oxygen species depends on both the zeolite iron content and Si/Al ratio.

Comparison of New Ampac Bags and FireDebrisPAK® Bags as Packaging for Fire Debris Analysis

The FireDebrisPAK(®) bags that were produced by Kapak were considered to be one of the best containers for fire debris. Kapak bags were discontinued; however, from July 2010, Ampac is offering a new packaging material. The aim of the presented research was to compare the properties (durability, background interferences, and permeability) of Kapak bags and packaging material offered by Ampac. The analysis was conducted by passive adsorption from the headspace with subsequent thermal desorption and analysis by GC-MS. The results proved that the properties of the compared materials are similar. Their greatest advantage is that they are impermeable for components of flammable liquids, so there is no danger of losing analytes or cross-contamination. Their one significant drawback is that they should not be exposed to temperatures above 80°C. At this temperature, they become soft, their inner layer is compromised (becomes sticky), and they emit some volatile organic compounds. Among them, there are compounds that constitute the components of some of flammable liquids.

Evaluating a direct swabbing method for screening pesticides on fruit and vegetable surfaces using direct analysis in real time (DART) coupled to an Exactive benchtop orbitrap mass spectrometer

Rapid screening of pesticides present on the surfaces of fruits and vegetables has been facilitated by using a Direct Analysis in Real Time (DART(®)) open air surface desorption ionization source coupled to an Exactive(®) high-resolution accurate mass benchtop orbitrap mass spectrometer. The use of cotton and polyester cleaning swabs to collect and retain pesticides for subsequent open air desorption ionization is demonstrated by sampling the surface of various produce to which solutions of pesticides have been applied at levels 10 and 100 times below the tolerance levels established by the United States Environmental Protection Agency (US EPA). Samples analyzed include cherry tomatoes, oranges, peaches and carrots each chosen for their surface characteristics which include: smooth, pitted, fuzzy, and rough respectively. Results from the direct analysis of fungicides on store-bought oranges are also described. In all cases, the swabs were introduced directly into the heated ionizing gas of the DART source resulting in production of protonated pesticide molecules within seconds of sampling. Operation of the orbitrap mass spectrometer at 25,000 full-width half maximum resolution was sufficient to generate high-quality accurate mass data. Stable external mass calibration eliminated the need for addition of standards typically required for mass calibration, thus allowing multiple analyses to be completed without instrument recalibration.

Theoretical study on the possibility of using silicon carbide nanotubes as dehydrogenation catalysts for ammonia–borane

The adsorption and decomposition of ammonia–borane (AB) on the surface of silicon carbide nanotubes (SiCNTs) was investigated using density functional theory. Five adsorption types and four reaction channels were identified. The most favorable reaction channel that generates a H2 molecule is slightly endothermic; furthermore, the energy barrier for the decomposition of the AB molecule is only 9.6 kcal mol−1. The side reactions that generate NH3 or BH3 are highly endothermic; therefore, the generation of side products can be depressed by decreasing the temperature. However, desorption of hydrogen atoms from the surface appears to be a more difficult step. The energy-barrier height for generation of a H2 molecule and its subsequent desorption from the surface is approximately 34.2 kcal mol−1. The migration of hydrogen atoms on the surface of SiCNTs involves lower energy than the desorption process, indicating that the desorption of H2 molecules from the surface may be more complicated.

Surface-aligned femtochemistry: Photoinduced reaction dynamics of CH3I and CH3Br on MgO(100)

Methyl iodide and methyl bromide molecules were adsorbed at submonolayer coverages on an ultrathin MgO(100) film on Mo(100) and photoexcited by 266 nm femtosecond-laser irradiation. The subsequent photodissociation and desorption dynamics were probed by time delayed multi photon ionization mass spectrometric detection of the emerging reaction products. The pronounced difference in the appearance times of the methyl radical fragments from methyl iodide and bromide is discussed on the basis of the different molecular adsorption geometries on magnesia. The surface adsorption structure also defines the alignment of the encounter complex for the observed bimolecular formation of the halogen molecules I2 and Br2 within about 1 and 2 ps, respectively. Finally, photoexcitation of co-adsorption layers of CH3I and CH3Br resulted in a heteronuclear bi-molecular reaction yielding IBr molecules.

Phytochemical Study of the North Caucasian Rosa Spinossima L. Fruit

Qualitative composition and content of anthocyanins in the Rosa spinossima L. fruit were studied. The anthocyanin sum was isolated by talc adsorption with subsequent desorption. The presence of anthocyanins in the resultant fraction was confirmed by thin layer chromatography. Three spots corresponding to anthocyanins were found. Anthocyanins were identified by mass spectrometry. Ion peaks corresponding to glycoside cyanidin and delphinidin were found. Position of sugar in the glycoside structure was determined by UV spectrophotometry with aluminum chloride. The content of anthocyanins was measured by direct UV spectrophotometry by the anthocyanins absorption. Anthocyanin content in raw material in conversion to cyanidin-3-glucoside was 1.46±0.03%.

Coating and release of an anti‐inflammatory hormone from PLGA microspheres for tissue engineering

Many biomaterials used in tissue engineering cause a foreign body response in vivo, which left untreated can severely reduce the effectiveness of tissue regeneration. In this study, an anti-inflammatory hormone α-melanocyte stimulating hormone (α-MSH) was physically adsorbed to the surface of biodegradable poly (lactic-co-glycolic) acid (PLGA) microspheres to reduce inflammatory responses to this material. The stability and adsorption isotherm of peptide binding were characterized. The peptide secondary structure was not perturbed by the adsorption and subsequent desorption process. The α-MSH payload was released over 72 h and reduced the expression of the inflammatory cytokine, Tumor necrosis factor-α (TNF-α) in lipopolysaccharide activated RAW 264.7 macrophage cells, indicating that the biological activity of α-MSH was preserved. α-MSH coated PLGA microspheres also appeared to reduce the influx of inflammatory cells in a subcutaneous implantation model in rats. This study demonstrates the potential of α-MSH coatings for anti-inflammatory delivery and this approach may be applied to other tissue engineering applications.

Ca‐Rich Ca–Al‐Oxide, High‐Temperature‐Stable Sorbents Prepared from Hydrotalcite Precursors: Synthesis, Characterization, and CO2 Capture Capacity

We present the design and synthesis of Ca-rich Ca-Al-O oxides, with Ca(2+)/Al(3+) ratios of 1:1, 3:1, 5:1, and 7:1, which were prepared by hydrothermal decomposition of coprecipitated hydrotalcite-like Ca-Al-CO(3) precursors, for high-temperature CO(2) adsorption at 500-700 °C. In situ X-ray diffraction measurements indicate that the coprecipitated, Ca-rich, hydrotalcite-like powders with Ca(2+)/Al(3+) ratios of 5:1 and 7:1 contained Ca(OH)(2) and layered double hydroxide (LDH) phases. Upon annealing, LDH was first destroyed at approximately 200 °C to form an amorphous matrix, and then at 450-550 °C, the Ca(OH)(2) phase was converted into a CaO matrix with incorporated Al(3+) to form a homogeneous solid solution without a disrupted lattice structure. CaO nanocrystals were grown by thermal treatment of the weakly crystalline Ca-Al-O oxide matrix. Thermogravimetric analysis indicates that a CO(2) adsorption capacity of approximately 51 wt. % can be obtained from Ca-rich Ca-Al-O oxides prepared by calcination of 7:1 Ca-Al-CO(3) LDH phases at 600-700 °C. Furthermore, a relatively high CO(2) capture capability can be achieved, even with gas flows containing very low CO(2) concentrations (CO(2)/N(2) = 10 %). Approximately 95.6 % of the initial CO(2) adsorption capacity of the adsorbent is retained after 30 cycles of carbonation-calcination. TEM analysis indicates that carbonation-promoted CaCO(3) formation in the Ca-Al-O oxide matrix at 600 °C, but a subsequent desorption in N(2) at 700 °C, caused the formation CaO nanocrystals of approximately 10 nm. The CaO nanocrystals are widely distributed in the weakly crystalline Ca-Al-O oxide matrix and are present during the carbonation-calcination cycles. This demonstrates that Ca-Al-O sorbents that developed through the synthesis and calcination of Ca-rich Ca-Al LDH phases are suitable for long-term cyclic operation in severe temperature environments.

Revisiting the effects of organic solvents on the thermal reduction of graphite oxide

Treatment of graphite oxide (GO) with organic solvents via sorption from either liquid or gas phase, and subsequent desorption, induces profound changes in the layered GO structure: loss of stacking order, retention of trace amounts of solvents and decreasing decomposition temperature. This study presents new evidences of the effect of organic solvents on the thermal reduction of GO by means of thermogravimetric analysis, X-ray diffraction and X-ray photoelectron spectroscopy. The results reveal a relative higher decrease of the oxygen amounts in solvent-treated GO as compared to untreated GO and the restacking inhibition of the thermally reduced GO sheets upon slow heating. The kinetic experiments evidence changes occurring in the reduction mechanisms of the solvent-treated GO, which support the close link between GO structure and thermal properties.

Molecular sieve carbons for CO2 capture

With the current interest in controlling greenhouse gases, there is a new focus on materials that can discriminate between gas molecules by capturing those gases which must be curtailed and releasing those which pose no adverse effects to the atmosphere. Although zeolites can be applied to such tasks, molecular sieve (MS) carbons have an additional advantage in their ability to both adsorb and desorb molecules cyclically with comparatively little energy demand.This paper describes studies of commercial ATMI carbons obtained from polyvinylidene chloride pyrolysis that have experienced different levels of activation and additives to modify the sizes of pore ‘portals’ (i.e., those pores which orchestrate movement of molecules from the gas phase into the inner structure of the carbon). The structures are probed using molecules in the 0.3–0.68nm size range. One significant feature of these materials is that total pore volume for smaller molecules is maintained during the ‘tailoring’ of the portal pore size. These carbons have additional benefits such as high strength and high density, becoming ideal candidates for capturing CO2. Data for select carbons indicate capacities at ambient conditions for CO2 of >140v/v (∼20wt.%) and, in simulated power plant exhaust, Henry’s Law Separation Factors >6. Through collaboration with SRI International, ATMI has developed carbons that exhibit >97% capture of CO2 in such streams with subsequent desorption of 98% purity CO2 in the stripper section of a pilot-scale unit. In this application, these carbons outperform the claims made for MOFs and other similar materials.

Influence of graphite surface properties on the first electrochemical lithium intercalation

The electrochemical insertion of lithium ions into graphite materials having different surface chemistry and defect concentration was studied during the first cycle in half-cell containing 1 M LiPF 6 in an electrolytic solvent mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC). The graphite surface properties were varied by thermal treatments in either hydrogen, oxygen, or nitrogen oxide or chemical treatment in boiling nitric acid. The influence of the surface modifications on the course of the first electrolyte reduction was investigated. The surface group chemistry was analyzed by temperature-programmed desorption coupled with mass spectrometry. The surface defect concentration was determined in terms of the active surface area (ASA) measured by oxygen chemisorption and a subsequent temperature-programmed desorption. The experimental results showed that the ASA parameter governs the exfoliation tendency of the graphite negative electrode material with the existence of a critical value below which the graphite systematically exfoliates. The specific charge loss during the first electrochemical insertion of lithium and the exfoliation behavior of the graphite negative electrode material are not influenced by the type and amount of oxygen surface groups. But hydrogen present on the graphite surface increased the graphite exfoliation tendency even for graphite materials with an ASA above the critical value.