Temperature-programmed desorption-mass

Interaction of nanomaterials with native cells is an important problem in modem life science. Recent progress in mass spectrometry provides a vital tool to study this problem. Advances in applications of mass spectrometry for investigating the interaction of nanoparticles with cell membranes and biomacromolecules are based on at least two methods. The first is matrix-assisted laser desorption ionization (MALDI),1 and the second is temperature-programmed desorption mass spectrometry (TPD MS), newly developed to study the interaction of nanoparticles with a cell surface.2 ... 

V. A. Pokrovskiy. Temperature-programmed desorption mass spectrometry of biomolecules, Rapid Commun. Mass Spectrom. 9, 588-591 (1995). 

Figure 1.11. A plot of the number of catalytically produced CO2 molecules against the nuclearity of Pt clusters. The CO2 molecules produced by oxidation of CO are studied by means of temperature-programmed desorption mass spectrometry. (Reproduced with permission from reference 77.)...

FIGURE 4.11 TPD mass spectra for heated carbosil prepared by phenylethanol carbonization at a silica gel surface. (Adapted from Carbon, 37, Pokrovskiy, V.A., Leboda, R., Turov, V.V., Charmas, B., and Ryczkowski, J., Temperature programmed desorption mass spectrometry of carbonized silica surface, 1039-1047, 1999, Copyright 1999, with permission from Elsevier.)... 

Danilchenko, S.N., Pokrovskiy, V.A., Bogatyrov, V.M., Sukhodub, L.R, and SuUdo-Cleff, B. 2005. Carbonate location in bone tissue mineral by X-ray diffraction and temperature-programmed desorption mass spectrometry. Cryst. Res. Technol. 40 692-697. 

TPD-MS temperature-programmed desorption-mass spectrometry TPR temperature-programmed reduction TREF temperature rising elution fractionation... 

Concerning the activation by ethylene monomer, Liu et al. reported an extensive investigation on reduction of the hexavalent chromate by means of XPS, temperature-programmed desorption-mass spectrometry (TPD-MS) methods and found that surface chromium species might exist in three oxidation states (1) surface chromate Cr(VI)Ox,surf species, (2) surface-stabihzed trivalent Cr(III) species, and (3) surface-stabilized Cr(II) species (Liu et al., 2002). Some short alkenes including propylene and butylene as well as the reduction by-product of formaldehyde were confirmed based on TPD-MS characterizations (Liu et al., 2003). 

Elementary steps in which a bond is broken form a particularly important class of reactions in catalysis. The essence of catalytic action is often that the catalyst activates a strong bond that cannot be broken in a direct reaction, but which is effectively weakened in the interaction with the surface, as we explained in Chapter 6. To monitor a dissociation reaction we need special techniques. Temperature-programmed desorption is an excellent tool for monitoring reactions in which products desorb. However, when the reaction products remain on the surface, one needs to employ different methods such as infrared spectroscopy or secondary-ion mass spectrometry (SIMS). 

The scanning transmission electron microscope (STEM) was used to directly observe nm size crystallites of supported platinum, palladium and first row transition metals. The objective of these studies was to determine the uniformity of size and mass of these crystallites and when feasible structural features. STEM analysis and temperature programmed desorption (TPD) of hydrogen Indicate that the 2 nm platinum crystallites supported on alumina are uniform In size and mass while platinum crystallites 3 to 4 nm in size vary by a factor of three-fold In mass. Analysis by STEM of platinum-palladium dn alumina established the segregation of platinum and palladium for the majority of crystallites analyzed even after exposure to elevated temperatures. Direct observation of nickel, cobalt, or iron crystallites on alumina was very difficult, however, the use of direct elemental analysis of 4-6 nm areas and real time Imaging capabilities of up to 20 Mx enabled direct analyses of these transition metals to be made. Additional analyses by TPD of hydrogen and photoacoustic spectroscopy (PAS) were made to support the STEM observations. 

Specific surface areas of the catalysts used were determined by nitrogen adsorption (77.4 K) employing BET method via Sorptomatic 1900 (Carlo-Erba). X-ray difiraction (XRD) patterns of powdered catalysts were carried out on a Siemens D500 (0 / 20) dififactometer with Cu K monochromatic radiation. For the temperature-programmed desorption (TPD) experiments the catalyst (0.3 g) was pre-treated at diflferent temperatures (100-700 °C) under helium flow (5-20 Nml min ) in a micro-catalytic tubular reactor for 3 hours. The treated sample was exposed to methanol vapor (0.01-0.10 kPa) for 2 hours at 260 °C. The system was cooled at room temperature under helium for 30 minutes and then heated at the rate of 4 °C min . Effluents were continuously analyzed using a quadruple mass spectrometer (type QMG420, Balzers AG). 

This study presents kinetic data obtained with a microreactor set-up both at atmospheric pressure and at high pressures up to 50 bar as a function of temperature and of the partial pressures from which power-law expressions and apparent activation energies are derived. An additional microreactor set-up equipped with a calibrated mass spectrometer was used for the isotopic exchange reaction (DER) N2 + N2 = 2 N2 and the transient kinetic experiments. The transient experiments comprised the temperature-programmed desorption (TPD) of N2 and H2. Furthermore, the interaction of N2 with Ru surfaces was monitored by means of temperature-programmed adsorption (TPA) using a dilute mixture of N2 in He. The kinetic data set is intended to serve as basis for a detailed microkinetic analysis of NH3 synthesis kinetics [10] following the concepts by Dumesic et al. [11]. 

Accessibility to Cu sites was determined by temperature programmed desorption of NO (NO TPD), using an experimental setup similar to that used for TPR, except the detector was a quadrupole mass spectrometer (Balzers QMS421) calibrated on standard mixtures. The samples were first activated in air at 673 K, cooled to room temperature in air, and saturated with NO (NO/He 1/99, vol/vol). They were then flushed with He until no NO could be detected in the effluent, and TPD was started up to 873 K at a heating rate of 10 K/min with an helium flow of 50 cm min. The amount of NO held on the surface was determined from the peak area of the TPD curves. 

Temperature programmed desorption (TPD) of NH3 adsorbed on the samples was carried out on an Altamira TPD apparatus. NH3 adsorption was performed at 50°C on the sample that had been heat-treated at 120°C in a helium flow. After flushing with helium, the sample was subjected to TPD from 50 to 600°C (AT = 10°C min 1). The evolved NH3, H20 and N2 were monitored by mass spectroscopy by recording the mass signals of m/e = 16, 18 and 28, respectively using a VG Trio-1 mass spectrometer. 

After the catalyst was saturated with carbon dioxide, a temperature programmed desorption (TPD) was carried out by heating the sample in helium (40 cm3min 1) from room temperature to 873 K (10 Kmin 1). The mass spectrometer was used to follow water (mass 18), carbon monoxide (mass 28), carbon dioxide (mass 44) and oxygen (mass 32). 

Fig. 4 (a) Stepwise dehydrocyclization of -hexane (21, 62). (b) Temperature programmed desorption of benzene originating from various adsorbates over Pt-AljOs. Temperature of adsorption 25°C. Rate of heating 23°C per minute. Detector monopolar mass spectrometer, the ordinate corresponds to the I intensity of mass number 78, in arbitrary units. For clarity, the thermodesorption curves for other compounds (starting hydrocarbon) hexene from hexa-dienes and hydrogen have not been shown (62c). 

The term 1 or h indicates low or high coverage of adsorbed ethene, as inferred from ethene exposures.h TPD, temperature-programmed desorption LITD, laser-induced thermal desorption 1 FT-MS, Fourier-transform mass spectrometry SIMS, secondary-ion mass spectrometry MS, mass spectrometry T-NEXAFS, transient near-edge X-ray absorption fine structure spectroscopy RAIRS, reflection-absorption infrared spectroscopy. d Data for perdeut-erio species.1 Estimated value. 

Fig. 2.8 Experimental set-up for temperature-programmed desorption studies in ultra-high vacuum. The heat dissipated in the tantalum wires resistively heats the crystal the temperature is measured by a thermocouple which is spot-welded to the back of the crystal. Desorption of gases is followed using mass spectrometry.

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