Temperature Programmed Surface Reaction using

In this work, an attempt is made to show the role of the different metal species present in Co and Co/Pd based FER zeolites, using UV-Vis and H2-TPR experiments, coupled with Temperature Programmed Surface Reaction (TPSR) tests. 

Catalytic runs were carried out in a U-type quartz reactor, under Temperature Programmed Surface Reaction (TPSR) conditions (GHSV= 45000 h"1). The sample was pre-treated in flowing argon from room temperature (RT) to 500 °C, using a heating rate of 5 °C min"1, and kept at 500 °C for lh. Further details are also given elsewhere [19]. 

Using a temperature-programmed surface reaction (TPSR) technique, Li et al. (154) showed that this complete oxidation of methane took place on the NiO catalyst during the CHfOi reaction. Weng et al. (145) used in situ microprobe Raman and in situ time-resolved IR spectroscopies to obtain a relationship between the state of the catalyst and the reaction mechanism. These authors showed that RuC>2 in the Ru/SiC>2 catalyst formed easily at 873 K in the presence of a CH4/02/Ar (2/1/45, molar) mixture and that the dominant pathway to synthesis gas was by the sequence of total oxidation of CH4 followed by reforming of the unconverted CH4 by C02 and H20. Thus, these results indicate that the oxidation of methane takes place principally by the combustion mechanism on the oxidized form of this catalyst. 

Temperature-programmed surface reaction (TPSR). Measurements were performed in a flow apparatus with a BALZERS quadrupolar mass spectrometer to monitor effluent products versus temperature. Samples of 300 mg were used in each measurement. The gases employed were He (99.9%) and mixtures 4% NH3/He, 1% NO/He and 5% 02/He. TPSR measurements were obtained after NH3 adsorption at 70°C under continuous flow until base line stabilization. The reactor was heated to 500°C at 20°C/min and kept at this... 

In a previous study (9 ) we used temperature-programmed surface reaction (TPSR) with 1 atm hydrogen to determine the... 

Fastrup et al. [9] presented a detailed experimental study of the hydrogenation of an iron-based surface precovered with atomic nitrogen using the temperature-programmed surface reaction (TPSR) method. Their modeling results clearly demonstrate the effect of the initial coverage of N- and the effect of the H2 partial pressure. The kinetic mechanism of the TPSR experiment can be written as depicted below. 

Degradation of 7/-nitrosodimethylamine (NDMA) and A -nitrosopyrrolidine (NPYR) on zeolites was investigated by use of temperature programmed surface reaction and GC-MS. Activation of zeolite had almost no effect on TPSR of NPYR, because zeolite could selectively adsorb A-nitrosamines. Cyano derivative appeared as the main product on NaZSM-5 or NaY zeolites similar to that in pyrolysis while DNA became the dominant one on HZSM-5 or HY. On the latter the Bronsted acid sites probably play the role of main catalytic sites, hence N-nitrosamines degrades to amines on Bronsted acid sites while on the former A-nitrosamines might decompose through radical reaction process, similar as pyrolysis. No desorption of the A -nitrosamines occurs on zeolites even at elevated temperature, and protonation of zeolite... 

The temperature-programmed surface reaction (TPSR) experiment was carried out in a quartz-made microreactor connected to a thermal conductivity detector (TCD) equipped with active charcoal column using 0.2 g passivated catalysts. The passivated catalysts were reduced by hydrogen at 673 K for 1 h, and then... 

Previous investigations demonstrated for the first time in the literature that in situ isopropanol chemisorption and quantitative temperature programmed surface reaction are suitable to be used to determine the nature, number, and acid strength of the surface/bulk active sites of tungsten oxide-based catalysts and particularly of the heteropoly compounds [15]. 

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]. 

Special features Includes a large array of temperature-programed cycles. Main use is to smdy chemisorption and catalysis. Analyses include TPR (reduction), TPD (desorption), TPO (oxidation), TPRx (reaction) as well as surface area measurements. 

Characterization and analysis are performed using the following surface science techniques temperature programmed desorption/reaction (TPD/TPR), pulsed molecular beam reactive scattering (pMBRS) (IRRAS), metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS) and auger electron spectroscopy (AES). First the experimental setup is briefly described, followed by the support preparation and characterization as well procedures utilized in this work. These descriptions include a concise introduction to the underlying physical principles of the applied techniques (including experimental details). 

TEM observation and elemental analysis of the catalysts were performed by means of a transmission electron microscope (JEOL, JEM-201 OF) with energy dispersion spectrometer (EDS). The surface property of catalysts was analyzed by an X-ray photoelectron spectrometer (JEOL, JPS-90SX) using an A1 Ka radiation (1486.6 eV, 120 W). Carbon Is peak at binding energy of 284.6 eV due to adventitious carbon was used as an internal reference. Temperature programmed oxidation (TPO) with 5 vol.% 02/He was also performed on the catalyst after reaction, and the consumption of O2 was detected by thermal conductivity detector. The temperature was ramped at 10 K min to 1273 K. 

Several spectroscopic, microscopic and diffraction techniques are used to investigate catalysts. As Fig. 4.2 illustrates, such techniques are based on some type of excitation (in-going arrows in Fig. 4.2) to which the catalyst responds (symbolized by the outgoing arrows). For example, irradiating a catalyst with X-ray photons generates photoelectrons, which are employed in X-ray photoelectron spectroscopy (XPS) -one of the most useful characterization tools. One can also heat a spent catalyst and look at what temperatures reaction intermediates and products desorb from the surface (temperature-programmed desorption, TPD). 

Desorption is important both because it represents the last step in a catalytic cycle and because it is also the basis of temperature-programmed desorption (TPD), a powerful tool used to investigate the adsorption, decomposition and reaction of species on surfaces. This method is also called thermal desorption spectroscopy (TDS), or sometimes temperature programmed reaction spectroscopy, TPRS (although strictly speaking the method has nothing to do with spectroscopy). 

Finally, although both temperature-programmed desorption and reaction are indispensable techniques in catalysis and surface chemistry, they do have limitations. First, TPD experiments are not performed at equilibrium, since the temperature increases constantly. Secondly, the kinetic parameters change during TPD, due to changes in both temperature and coverage. Thirdly, temperature-dependent surface processes such as diffusion or surface reconstruction may accompany desorption and exert an influence. Hence, the technique should be used judiciously and the derived kinetic data should be treated with care ... 

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