Thermal Programmed Desorption Research Articles

Step Site-Specific Semihydrogenation of Acetylene on the Au Surface.

Supported Au catalysts are highly selective and size-sensitive in catalytic hydrogenation of alkynes under mild conditions. Using thermal-programmed desorption and density functional theory calculations, we study the hydrogenation reactions of C2 hydrocarbons with atomic H and clarify the site-specific selective hydrogenation of C2H2 on Au(997) at low temperatures. On atomic H(a) covered Au(997), hydrogenation of C2H2 goes with 100% selectivity to C2H4 at steps, yet no hydrogenation occurs at terraces; adsorbed C2H4 on neither steps nor terraces reacts with H(a). DFT calculations suggest that the increased adsorption free energies and appropriate reaction barriers of C2 species at steps lead to the step-site specific semihydrogenation of C2H2. These results elucidate the elementary surface reactions between C2 hydrocarbons and atomic H on Au surfaces at the molecular level and significantly deepen the fundamental understanding of the unique selectivity of Au catalysts.

Adsorption Behavior of 9-Anthracenecarboxylic Acid on (110) Rutile TiO2

The adsorption behavior of 9-anthracenecarboxylic acid (AnCA) on a rutile TiO2 (110) surface has been investigated with scanning tunneling microscopy (STM) at room temperature. Upon deposition, the molecules adsorb, resulting in a commensurate herringbone c-(2 × 2) structure, as confirmed by low-energy electron diffraction (LEED). Annealing of the sample below the desorption point causes irreversible superstructure derangement. Thermally programmed desorption (TPD) reveals that, after prior decomposition on the surface, AnCA molecules desorb into anthracenes and carboxyl acid derivatives.

Tritium release and retention in beryllium and titanium beryllide after neutron irradiation up to damage doses of 23-38 dpa

• For the first time, beryllium and titanium beryllide as massive pellets were irradiated in a nuclear reactor at temperatures of 710−1040 K up to production of 430–653 appm tritium and 4144–5992 appm helium, respectively. • The tritium retention in irradiated Be-7at.%Ti pellets is much lower than that in Be pellets, for example, 1 and 0.5 % to 48 and 34 % at 940 and 1040 K, respectively. • Open channels along grain and sub-grain boundaries are formed under neutron irradiation in beryllium, essentially contributing to the enhanced tritium release. Titanium beryllide is considered as an advanced neutron multiplier in the Helium Cooled Pebble Bed (HCPB) blanket of DEMO. Neutron irradiation of titanium beryllide together with beryllium as a reference material in material testing nuclear reactors can give essential data for the DEMO blanket design. Be-7at.%Ti (Be-7Ti) as well as Be were irradiated in the HFR, Petten, the Netherlands, at four temperatures of 710, 800, 940, 1040 K up to 23, 31, 36, 38 dpa, respectively. The post-irradiation examination (PIE) included thermal-programmed desorption (TPD) and Vickers hardness tests as well as microstructure study by optical metallography. Be and Be-7Ti pellets maintained their integrity after irradiation. Microstructure of Be-7Ti contains two phases, mainly, TiBe 12 , and also small amount of Be. Under irradiation, gas bubbles were formed in Be samples as well as in Be-phase in Be-7Ti samples. These bubbles contain helium and tritium produced in Be under irradiation. TPD tests showed a much lower tritium retention in Be-7Ti than in Be for all four irradiation temperatures. Vickers hardness of TiBe 12 phase is much higher than that of Be-phase. According to the obtained data, Be-7Ti could be considered more preferred than Be as a neutron multiplier material in future fusion reactors due to the enhanced radiation damage resistance.

Desorption of N2, CO, CH4, and CO2 from interstellar carbonaceous dust analogues

ABSTRACTThe interaction of volatile species with carbonaceous interstellar dust analogues is of relevance in the chemistry and physics of dense clouds in the interstellar medium. Two deposits of hydrogenated amorphous carbon (HAC), with different morphologies and aromatic versus aliphatic ratio in their structure, have been grown to model interstellar dust. The interaction of N2, CO, CH4, and CO2 with these two surfaces has been investigated using thermal programmed desorption (TPD). Desorption energy distributions were obtained by analysing TPD spectra for one monolayer coverage with the Polanyi–Wigner equation. The desorption energies found in this work for N2, CO, and CH4 are larger by 10–20 per cent than those reported in the literature for siliceous or amorphous solid water surfaces. Moreover, the experiments suggest that the interaction of the volatiles with the aromatic substructure of HAC is stronger than that with the aliphatic part. Desorption of CO2 from the HAC surfaces follows zero-order kinetics, reflecting the predominance of CO2–CO2 interactions. A model simulation of the heating of cold cloud cores shows that the volatiles considered in this work would desorb sequentially from carbonaceous dust surfaces with desorption times ranging from hundreds to tens of thousands of years, depending on the molecule and on the mass of the core.

Numerical simulation by finite element modelling of diffusion and transient hydrogen trapping processes in plasma facing components

In order to simulate hydrogen charging and discharging cycles of mechanically loaded structures full 3D Macroscopic Rate Equation (MRE) modelling is proposed based on a finite element method (FEM). The model, implemented in the 3DS Abaqus software, uses a generalized transport equation, which accounts for mechanical fields, hydrogen transport and trapping, and their evolution with time. The influence of a-priori known thermal field has also been included. To ensure the solution convergence and the numerical stability, the trapping kinetic is introduced by using an approximation of the analytical solution the McNabb and Foster equation. Comparisons with a relevant 1D MRE code and with thermal programmed desorption (TPD) experimental results are performed on a 1D configuration to validate the model. Next, the model is used to simulate the tritium diffusion and trapping in a 2D geometry of interest in the upper plug of ITER tokamak, and results of tritium inventory are compared with an equivalent 1D calculation.

Hydrogenolysis of glycerol to 1,2‐propanediol in a continuous flow trickle bed reactor

AbstractBACKGROUNDHydrogenolysis of glycerol to glycols in continuous flow three phase reactors is of practical importance due to the need to give value to huge amounts of surplus glycerol. Thermodynamic and kinetic aspects must be revised for a proper design. The system was studied in a trickle‐bed reactor using copper chromite and Cu/Al2O3as catalysts.RESULTSPhase equilibrium and flow pattern were verified. Solid, liquid and gas phases were present, with the liquid phase in ‘trickling’ flow. Catalysts were characterized by inductively coupled plasma (ICP), nitrogen sortometry, X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), temperature programmed reduction (TPR) and pyridine thermal programmed desorption (TPD). The average reaction rate was found to be practically constant under different process conditions. A theoretical analysis indicated that the resistance to the transfer of hydrogen from the gas to the liquid phase dominated the overall kinetics. Selectivity to 1,2‐propanediol varied with temperature, with a maximum at 230 °C (97%). Selectivity was a function of the catalyst acidity. When the pressure was increased the selectivity to 1,2‐propanediol was increased, up to 97% at 14 bar. Higher pressures did not modify this value.CONCLUSIONSOptimum reaction conditions for maximum selectivity to 1,2‐propanediol with Cu‐based catalysts are 230 °C and 14 bar. System kinetics are, however, dominated by the gas–liquid mass transfer resistance. © 2017 Society of Chemical Industry

(Invited) Impact of Carbon Surface Functionalities on the Electrochemical Detection of Hemoglobin

The electrochemical biosensing of hemoglobin (Hb) may provide a relatively fast method of detection with the possibility of developing point-of-care diagnostics or at-home monitoring; however, obtaining a Hb electrochemical signal is often slow and difficult because the four redox active heme groups are buried in the interior hydrophobic regions of the protein. Ideally, the biosensor electrode would be inexpensive and formed from environmentally sustainable materials, such as carbon. However, the electroactivity of Hb is inconsistent on different carbon electrode materials. Additionally, Hb electroactivity is strongly dependent on whether the Hb is immobilized on the electrode surface or is in a solution-based sample. Clearly, for a point-of-care diagnostic, it would be useful to be able to measure the Hb concentrations within a liquid phase, and therefore a carbon material which evidences Hb-electroactivity is required. Until this work, there was little understanding of the role that carbon-oxygen surface functional groups (from the carbon electrode) played in Hb electroactivity. We examine Hb electroactivity of several carbons are examined through cyclic voltammetry and differential pulse voltammetry in a neutral phosphate buffered electrolyte. Carbon-oxygen surface functionalities were characterized using X-ray photoelectron spectroscopy (XPS), thermal programmed desorption (TPD) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Our findings show that Hb electroactivity is inhibited by ether and carbonyl surface groups present on the carbon electrode. Using this information, a Hb-inactive carbon (Vulcan XC-72) was made active for Hb detection by removal of these surface groups (see figure). Ultrasonication removed the ether functionalities, resulting in a significant increase in the Hb electroreduction. The amount of reduction was increased further if the ultrasonication was followed by a relatively simple 15 minute electroreduction at -1.95 V vs. Hg/Hg2SO4 (saturated K2SO4) in stirred 10 mM phosphate electrolyte (pH 5.03) purged with N2. The electroreduction was shown to selectively remove the carbonyl and quinone functionalities, resulting in the increase Hb electroactivity. The knowledge of carbon-oxygen surface functionalities is essential to better understand hemoglobin’s electroactivity on carbon and influences the choice of carbon electrode materials for further development of hemoglobin electrochemical biosensors. Figure: Representative CVs (a) and DPVs (b) of glassy carbon (dotted green curve), ultrasonicated Vulcan XC-72 on glassy carbon (dashed purple curve) and ultrasonication+electrochemically reduced Vulcan XC-72 on glassy carbon (solid purple curve) in 0.1 M PB containing 0.2 g L-1 BHb from at least three replicate trials. Figure 1

Enhanced hydrogen release of metal borohydrides M(BH4)n (M = Li, Na, Mg, Ca) mixed with reduced graphene oxide

Mixtures of light metal borohydrides M(BH4)n, M = Li, Na, Mg, Ca and reduced graphene oxide (rGO) or graphite with molar ratio 70:30 were prepared by high energy ball milling. Samples were investigated with thermal programmed desorption (TPD) volumetric analysis to test their gas release profiles.The presence of rGO led to a lower decomposition temperature for every mixture and to a different gas-release profile compared to pristine borohydrides and mixtures with graphite. The onset of decomposition temperature was reduced by 200 °C for LiBH4, 360 °C for NaBH4, 130 °C for Mg(BH4)2 and 50 °C for Ca(BH4)2.The comparison of XRD profiles of decomposed samples showed a different pattern for each metal cation, confirming an interaction of the decomposition products with rGO sheets and suggesting a different pathway for the decomposition reaction.Reduced graphene oxide was prepared by clean thermal treatment in H2 atmosphere from graphene oxide obtained by modified wet chemical synthesis, and its presence significantly affected the gas release performance.

Toward a Delaminated Organotalc: The Use of Polyamidoamine Dendrons.

A sequence of generations of the polyamideamine dendron, PAMAM-talc-Gn (n = 1-7), was constructed on the surfaces of ethylenediaminepropyl-functionalized magnesium phyllosilicate lamellas by using a modified microwave-assisted synthesis. The successful functionalization of the inorganic layers by the organic dendrimer was confirmed by FTIR and (13)C NMR spectroscopies, elemental analyses, and thermogravimetric analysis (TGA). The solid materials presented an increase in their interlamellar space and disorganization of lamella packing with the growth of the dendrons. Thermal-programmed desorption analysis showed that the lower dendron generation, PAMAM-talc-G1, adsorbed 1.30 mmol of CO2/g of sorbent at 30 °C. PAMAM-talc-G5 adsorbed the double of PAMAM-talc-G3, probably due to the higher amount of the primary amine group; however, PAMAM-talc-G5 adsorbed more CO2 than PAMAM-talc-G7 probably because in the delaminated seventh generation intradendron N-H interactions were more prevalent than in the fifth generation and blocked CO2 interaction sites.

Physisorption and desorption of H2, HD and D2 on amorphous solid water ice. Effect on mixing isotopologue on statistical population of adsorption sites.

We study the adsorption and desorption of three isotopologues of molecular hydrogen mixed on 10 ML of porous amorphous water ice (ASW) deposited at 10 K. Thermally programmed desorption (TPD) of H2, D2 and HD adsorbed at 10 K have been performed with different mixings. Various coverages of H2, HD and D2 have been explored and a model taking into account all species adsorbed on the surface is presented in detail. The model we propose allows to extract the parameters required to fully reproduce the desorption of H2, HD and D2 for various coverages and mixtures in the sub-monolayer regime. The model is based on a statistical description of the process in a grand-canonical ensemble where adsorbed molecules are described following a Fermi-Dirac distribution.

TPD and DSC insights in the basicity of MCM-48-like silica and modified counterparts

The basicity of MCM-48-like silica and modified counterparts was investigated by CO2 thermal programmed desorption (TPD) and differential scanning calorimetry (DSC). Post-synthesis modifications were achieved through: (i) incorporation of dihexylamine (DHA); (ii) DHA removal by ethanol; (iii) calcination at 550°C in air stream and (iv) incorporation of Boltorn H-20 dendrimer. After DHA incorporation, the specific surface area dropped from 953 down to 74m2g−1, and the pore volume decreased from 0.41 to 0.13cm3g−1. The surface basicity, expressed in terms of retained CO2 amount decreased markedly after template removal, but was slightly revived after dendrimer loading. CO2 was found to adsorb via physical or chemical interactions on two types of sites, according to the post-synthesis treatment. Correlating TPD and DSC measurements allows assessing the extent of the acidity attenuation and basicity adjustment for a wide variety of catalysts and adsorbents through suitable post-synthesis modifications.

Cold-surface photochemistry of selected organic nitrates.

Reflection-absorption infrared (RAIR) spectroscopy has been used to explore the low temperature condensed-phase photochemistry of atmospherically relevant organic nitrates for the first time. Three alkyl nitrates, methyl, isopropyl, and isobutyl nitrate together with a peroxyacyl nitrate, peroxyacetyl nitrate (PAN), were examined. For the alkyl nitrates, similar photolysis products were observed whether they were deposited neat to the gold substrate or codeposited with water. In addition to peaks associated with the formation of an aldehyde/ketone and NO, a peak near 2230 cm(-1) was found to emerge in the RAIR spectra upon UV photolysis of the thin films. Together with evidence obtained by thermal programmed desorption (TPD), the peak is attributed to the formation of nitrous oxide, N2O, generated as a product during the photolysis. On the basis of the known gas-phase photochemistry for the alkyl nitrates, an intermediate pathway involving the formation of nitroxyl (HNO) is proposed to lead to the observed N2O photoproduct. For peroxyacetyl nitrate, CO2 was observed as a predominant product upon photolytic decomposition. In addition, RAIR absorptions attributable to the formation of methyl nitrate were also found to appear upon photolysis. By analogy to the known gas-phase and matrix-isolated-phase photochemistry of PAN, the formation of methyl nitrate is shown to likely result from the combination of alkoxy radicals and nitrogen dioxide generated inside the thin films during photolysis.

Preparation of MgO-templated carbons from waste polymeric fibres

Mesoporous carbons with a high surface area were produced using reinforcing fibres from scrap tyres, polyester Dacron®, polyamide Nylon6 and a bituminous waste as carbon precursor by two different procedures: physical activation and MgO-template synthesis. Moreover, MgO-template synthesis was carried out by means of two different mixing methods: powder- and solution-mixing procedures. The maximum surface area, highest pore volume and mesopore ratio were obtained for MgO-templated carbons. Nanocarbons with narrow pore size distributions showing maxima at 4.5–5nm in the case of powder-mixed MgO templated carbons and at 7nm for solution-mixed MgO templated carbons were obtained. The mesopore size of the carbon-coated materials was in agreement with their crystallite size as determined by X-ray diffraction (XRD). The surface chemistry of the materials was also studied by thermal programmed desorption (TPD), infrared spectroscopy and by determining the pHPZC. The MgO-templated carbons had acid surface groups, whereas activated carbons had basic surface groups. The adsorption of a reactive dye by two nanocarbons prepared by two different mixing procedures was tested.

Zinc/Lanthanum Mixed-Oxide Catalyst for the Synthesis of Glycerol Carbonate by Transesterification of Glycerol

ZnO/La2O3 mixed oxides are prepared by a coprecipitation method at different molar ratios and used as catalysts for the synthesis of glycerol carbonate by transesterification of glycerol with dimethyl carbonate (DMC). X-ray diffraction, N2 adsorption, transmission electron microscopy, scanning electron microscopy, and thermal-programmed desorption methods were used for characterization of the catalysts. The surface area and porosity of the catalysts prepared by the precipitation method proved to be better than those prepared by combustion and modified-citrate methods. Zn4La1 and Zn2La1 (mole ratio Zn:La of 4:1 and 2:1, respectively) were found to be the best proportions in view of both higher activity and higher selectivity. The rates offered by these catalysts were substantially high compared to reported Mg/La and other catalysts. The effects of parameters such as the temperature, catalyst loading, and mole ratio of DMC to glycerol were examined, and a suitable kinetic model was proposed for the Zn4La1 catalyst.

Inhibition of hydrogen absorption in bulk Pd by the formation of Ru–Pd surface alloy

Thermal programmed desorption (TPD) of hydrogen was performed in Pd and 5% Ru–Pd foils. The foils were inspected with Auger Electron Spectroscopy and Ar ion-sputter cleaned. Hydrogen dosage was 1000L at 10−3Pa. Hydrogen evolving from Pd (TPD curves) was 12 times larger than for the 5% Ru–Pd foil. A 1.8μm thick Ru–Pd surface alloy was grown on the surface of Pd and the TPD curves were very similar to those of the 5% Ru–Pd bulk alloy. The lattice parameter of the Pd fcc crystal structure decreased by 2.8%, when alloying with 5% Ru. The lattice parameter of the fcc cell of Pd increased by 2.3% when absorbing hydrogen. Hydrogen saturation amount at 4655Pa was obtained using a quartz crystal microbalance in a 24nm Pd film and in a 5% Ru–Pd film. A hydrogen–metal ratio (x=H/Pd) was calculated from these measurements yielding a ratio of xPd=0.68 for Pd and xRuPd=0.27 for ~2% Ru–Pd film.

Electron-induced chemistry of methyl chloride caged within amorphous solid water

The interaction of low energy electrons (1.0-25 eV) with methyl-chloride (CD3Cl) molecules, caged within Amorphous Solid Water (ASW) films, 10-120 monolayer (ML) thick, has been studied on top of a Ru(0001) substrate under Ultra High Vacuum (UHV) conditions. While exposing the ASW film to 3 eV electrons a static electric field up to 8 × 10(8) V∕m is developed inside the ASW film due to the accumulation of trapped electrons that produce a plate capacitor voltage of exactly 3 V. At the same time while the electrons continuously strike the ASW surface, they are transmitted through the ASW film at currents of ca. 3 × 10(-7) A. These electrons transiently attach to the caged CD3Cl molecules leading to C-Cl bond scission via Dissociative Electron Attachment (DEA) process. The electron induced dissociation cross sections and product formation rate constants at 3.0 eV incident electrons at ASW film thicknesses of 10 ML and 40 ML were derived from model simulations supported by Thermal Programmed Desorption (TPD) experimental data. For 3.0 eV electrons the CD3Cl dissociation cross section is 3.5 × 10(-16) cm(2), regardless of ASW film thickness. TPD measurements reveal that the primary product is deuterated methane (D3CH) and the minor one is deuterated ethane (C2D6).

Conversion of zeolite—A in to various ion-exchanged catalytic forms and their catalytic efficiency for the synthesis of benzimidazole

Zeolite-A was synthesized and converted into various ion-exchanged catalytic forms successfully. These catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer Emmett Teller (BET) surface area measurement and thermal programmed desorption (TPD). Their catalytic activity was tested on the synthesis of benzimidazole using o-phenylenediamine (OPDA) and aldehyde at room temperature. The reaction proceeds efficiently under ambient conditions. The catalysts gave a high isolated yield of benzimidazole in a shorter reaction time at room temperature and were recycled several times.

Investigation of hydrogen occlusion by molybdenum carbide

The incorporation of hydrogen in the bulk of molybdenum carbide is studied by experimental and theoretical methods. The motivation for this study is to explain the features of the deactivation of Mo2C catalyst during the hydrogenation of benzene when the reaction is performed at atmospheric pressure. In this condition, deactivation occurs for different reaction times depending on reaction temperature. By means of thermal-programmed desorption it was observed that there is an evolution of hydrogen for the deactivated catalyst at temperatures higher than 923K. In order to verify if during the carburization of MoO3 to Mo2C there is hydrogen occlusion in the interior of the carbidic phase, a systematic thermodynamic analysis was performed based on density functional theory (DFT) and the harmonic oscillator-rigid rotor approach to calculate partition functions. Possible diffusion paths of hydrogen atoms in molybdenum carbide were calculated by the nudged-elastic bands method at DFT level. The results of calculations are totally consistent with experimental findings confirming that there is indeed hydrogen occlusion during the synthesis of molybdenum carbide.

Synthesis and characterization of various zeolites and study of dynamic adsorption of dimethyl methyl phosphate over them

Zeolite-A, MCM-22, Zeolite-X and Erionite were synthesized successfully under hydrothermal conditions and were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Brunauer–Emmett–Teller (BET) surface area analysis and thermal programmed desorption (TPD). Dynamic adsorption of dimethyl methyl phosphate (DMMP) was carried out on these zeolites. Zeolite-X having high surface area among all four zeolites shows highest adsorption capacity followed by Erionite and MCM-22 where as Zeolite-A shows the least. For all zeolites adsorption was found to be high initially and it then decreases with increase in injected volume. Then desorption pattern was analyzed which shows two types of peaks, sharp peak representing desorption of physisorbed DMMP and a broad peak representing desorption of strongly chemisorbed DMMP.

Nanoconfined mixed Li and Mg borohydrides as materials for solid state hydrogen storage

Several mixtures of LiBH4 and Mg(BH4)2 borohydrides in different stoichiometric ratios (1:0, 2:1, 1:1, 1:2, 0:1), prepared by high energy ball milling, have been investigated with X-ray powder diffraction and thermal programmed desorption (TPD) volumetric analysis to test the dehydrogenation kinetics in correlation with the physical mixture composition. Afterwards mixed and unmixed borohydrides were dispersed on high specific surface area ball milled graphite by means of the solvent infiltration technique. BET and statistical thickness methods were used to characterize the support surface properties, and SEM micrographs gave a better understanding of the preparation techniques. It has been observed by TPD volumetric measurements that the confinement of the reactive borohydrides on the nanoporous supports leads to a lower dehydrogenation temperature compared to unsupported borohydrides. Moreover, a further decrease of the dehydrogenation temperature has been observed by increasing the specific surface area of the support and the pores volume and by using the prepared mixtures instead of pure materials. The dehydrogenation process seems to be favoured by the heterogeneous nucleation on the graphite surface of decomposition products or intermediate phases from melted liquid borohydrides.