Temperature-programmed desorption linear heating rate

Figure 16 Simulated and experimental temperature-programmed desorption spectra for OlPt(lll). The solid lines are experimental spectra. The crosses indicate simulated spectra for a model of the lateral interactions with nearest and next-nearest pair interactions, and also a linear 3-particle interaction. The O2 is formed from two atoms at next-nearest-neighbor positions. The kinetic parameters are — 206.4 kj/mol, v = 2.5 x 10 s a = 0.773, cpxN — 19.9 kjjmol, tp NN = 5.5 kjjmol, and (punear = 6.1 kJImol. In each plot the curves from top to bottom are for initial oxygen coverage of 0.194, 0.164, 0.093, and 0.073 ML, respectively. The heating rate is 8 Kjs ...

Temperature programmed desorption (TPD) of NH3 was performed in a quartz micro-reactor. 0.10 g of sample was firstly heated in helium at 600°C for 2 h. NH3 was introduced to the sample after it was cooled down to room temperature. To remove the weakly adsorbed NH3, the sample was swept using helium at 100°C for 1 h. The TPD experiments were then carried out with a carrier-gas flow rate of 40 ml/min helium from 100 to 600°C using a linear heating rate of 10°C/min. The desorption of NH3 was detected by Shimadzu GC-8A equipped with a TCD detector. 

Heats of adsorption can be experimentally measured by calorimetry, temperature programmed desorption (TPD), and adsorption isotherms taken at different temperatures. Calorimetry involves the direct measmement of temperature rise caused by the adsorption of a known amount of gas on to a well-characterized surface. TPD is the most coimnon method of determining the heats of adsorption. In this procedure, molecules are adsorbed on to a clean well-characterized substrate at a fixed temperature. The sample is then heated in a linear fashion while the pressure of the desorbing species is monitored with a mass spectrometer. The desorption rate E (t ) is given by... 

The supported catalysts were characterized for their basicity distribution by temperature programmed desorption (TPD) of CO2 from 50 to 950 C at a linear heating rate of 20°C.min in a flow of helium(40cm. min ). The surface area of the catalysts was determined by the single-point BET method, using a Monosorb surface-area analyser (Quanta Chrome Corp. USA). 

The activation energies and entropies of activation of desorption of gases adsorbed on the surfaces of solids can be determined by measuring the rates of desorption at several constant temperatures. In the temperature-programmed desorption the temperature is usually continuously varied and the rates of desorption are simultaneously influenced by the manner in which the process depends both on time and on temperature. In general, an analysis of the process can be carried out only if the variation of the temperature with time, the heating schedule, is of a simple functional form. At least for simpler systems, two heating schedules fulfill this requirement (1) a linear temperature increase with time, i.e.,... 

The sample pre-treatment as well as adsorption and desorption experiments were performed with a flow rate of 100 cm rnin-i that was passed through a quartz reactor (U-type) containing 1 g of bentonite meshes. The sample was first pre-treated under N2 flow at 473 K for 30 minutes than adsorption was carried out using the model mixture flow until saturation was reached in order to obtain breakthrough curves. The gas mixture was switched again to pure N2 flow, to proceed with isothermal desorption xmtil o-xylene concentration at the reactor outlet reached zero. This step was followed by a subsequent linear heating in order to perform Temperature Programmed Desorption (TPD) experiment. 

Fig. 3. Profile of the variation of o-xylene concentration in the gas flow at reactor outlet, represented as relative values (Cout/Qn), during a cycle of successive steps adsorption performed with a mixture of 0.36% xylene in N2 at 300K until saturation followed by isothermal desorption than Temperature Programmed Desorption carried out with a linear heating rate of 5K/ min...

Temperature-programmed desorption (TPD) can be described as the measurement of the rate of desorption of preadsorbed molecules as a function of temperature. It involves heating of sample while contained in a sample holder—as the temperature rises, certain absorbed species will have enough energy to desorb and will be detected simultaneously by means of specific detector (for example, mass spectrometer). In TPD experiments, temperature increases linearly and the concentration of desorbed gas is recorded as a function of temperature. Therefore, TPD profile is traced as desorption rate versus time (or temperature). If detector signal is properly calibrated, concentration of desorbed gas can be plotted as a function of temperature. 

The surface acidity of the ceria-doped SBA-15 samples was studied by a temperature-programmed desorption of ammonia (NH3-TPD). The measiuements were performed with a Micromeritics Autochem 2910 apparatus equipped with a thermal conductivity detector (TCD) and a mass quadmpole spectrometer (Thermostar, Balzers). Prior to the ammonia sorption, the samples ( 100 mg) were outgassed in a flow of O2 (5% in He) at 500°C for Ih, then, cooled to room temperature under He and saturated in a flow of NH3 (5% in He, 30 mL/min) for Ih. Subsequently, the catalysts were purged in a He flow at lOO C for Ih until a constant baseline level was reached. The ammonia desorption was carried out with a linear heating rate (10°C/min) up to 1050°C under a flow of He (30 mL/min). Cahbration of the TCD were carried out in order to evaluate the ammonia desorption peaks. 

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