Temperature programmed desorption experiment

NO is now chemisorbed on the Rh particles at a temperature where it does not adsorb on the AI2O3. The saturation coverage of NO on Rh(lOO) corresponds to one NO molecule per two rhodium surface atoms, with NO sitting in a c(2x2) surface structure. After having saturated the catalyst with NO, a temperature-programmed desorption experiment (TPD) is performed with a heating rate of 2 K min". NO is seen to desorb with a maximal rate at 460 K. The total NO gas that desorbs amounts to 18.5 mL per gram catalyst (P = 1 bar and T = 300 K). It can be assumed that NO does not dissociate on the Rh(lOO) surface. 

All of the Au/metal oxide catalysts deactivate quickly, under the conditions shown in Figure 4. In addition, the deactivation of the Au/metal oxide catalysts appears to be enhanced in the presence of COj. In support of the theory that increased basicity of the metal oxides leads to lower stability, we carried out COj temperature programmed desorption experiments on the various catalysts. The COj TPD data also confirmed that an increase in the basicity of the metal oxides leads to an increase in the amount of COj adsorption on the catalysts. 

Figure 3 Sketch of an example of the evolution of a system during a temperature-programmed desorption experiment in the system s phase diagram. The fat line indicates the change of the temperature and coverage during the experiment, and the thin lines indicate the phase transitions (see text). The snapshots below the order-disorder transition line are taken during a simulation of the experiment. The coverages are 0.3, 0.5, and 0.7 ML. The snapshots above the order-disorder transition line show adlayers of 0.3 and 0.7 ML at high temperatures...

The production of butadiene from butene involves at least three surface intermediates adsorbed butene, 7t-allyl, and butadiene. One or more of these may be particularly vulnerable to attack by gas-phase oxygen on a-Fe203. From the temperature programmed desorption experiments, it was found that the products of isomerization, selective oxidation, and combustion... 

Tsuchiya et al.36 performed temperature-programmed desorption experiments of H2 chemisorbed on platinum. This gave rise to several desorption maxima. To explain different... 

Temperature programmed desorption experiments have been used to examine the photochemical properties of MoCCO) adsorbed on Si(lOO). At 150 K, KrF laser radiation (248 run) partially decomposes the adsorbed Mo(CO) releasing gas-phase CO. MoL, (HL.=monothiodibenzoylmethaune) has been synthesised by UV induced oxidative decarbonylation of Mo(CO) in the presence of HL in THF. Similarly, M(CO), Sn[N(SiMe,) and... 

In this study, suboxides of vanadia catalysts were used in pentane, pentene, dicyclopentadiene and cyclopentane oxidation reactions. In the previous phase of the work [12,13], the role of alkali promoters on the catalyst selectivity was examined. The catalysts were reduced in situ at different temperatures and the effect of pre-reduction temperature was investigated. Controlled-atmosphere characterization of pre-reduction, post-reduction, and post-reaction catalysts were performed using X-ray diffraction. X-ray photoelectron spectroscopy, laser Raman spectroscopy and temperature-programmed desorption experiments. The objectives of this study were to determine the activity and selectivity of different suboxides of vanadia in... 

Further infonnatioii on the catalytic properties of stoichiometric and nonstoichiometric CaHAp may be obtained from studies on the adsorption and dehydrogenation of methanol. WiA stoichiometric CaHAp methanol decomposes at 600°C to produce predominantly carbon monoxide (Table 1) whose selectivity diminishes as the Ca/P ratio decreases while those to formaldehyde and dimethyl ether increase. Infrared spectra show that methoxy groups are formed on the surface of both the stoichiometric and nonstoichiometric catalysts. The results from temperature-programmed desorption experiments together with those from infrared spectroscopy suggest that the acidic sites found on the nonstoichiometric CaHAp catalyze the dissociative adsorption whereas the basic sites on the stoichiometric analogue catalyze the C-H bond scission and formation of CO and H. ... 

Observations from the temperature-programmed desorption experiments suggest that molecules, e.g. water, may be transported through the bulk structure of the heteropoly oxometalates. Further evidence for such a possibility as well as for the thermal stability of the heteropoly oxometalates may be obtained from photoacoustic (PAS) FTIR spectroscopy... 

Figure 2 Temperature programmed desorption experiment after acetic acid adsorption on Pd(llO) a) on the clean surface and b) on the surface predosed with half a monolayer of C atoms in the c(2x2) structure...

In temperature programmed desorption experiments this carbonate species desorbs as CO2 at a peak maximum temperature of 333 K. The desorption/decomposition activation energy, E, ... 

Fig. 8. A [ N]-NH3 pulse was adsorbed on the pre-oxidised platinum sponge kept under He flow (40 cm /min) at 373 K followed after 170 s by a temperature programmed desorption experiment (a) TPD spectrum (b) PEP image, the colour intensity represents the concentration of (c) normalised concentration as function of time...

Fig. 17. Formation of N2, N2O, and H2O measured by oniine mass spectrometry in a temperature programmed desorption experiment after ammonia oxidation at 323 K (lOK/min, He flow of 40cm /min).

Unfortunately, the position of the 6as(NH4) modes of the ammonium ion strongly depends on the adsorption geometry and does not permit any definite conclusions on the acid strength. To determine the acid strength, one needs to combine IR spectroscopy with temperature-programmed desorption experiments. In conclusion, ammonia as a probe gives information on the number of acidic hydroxyls (that are able to pro-tonate it) and, by combination with other techniques, on the strength of these sites. 

Joly, J.P. and Perrard, A. (2000) Determination of the heat of adsorption of ammonia on zeolites from temperature-programmed desorption experiments. Langmuir 1538-42. 

Foeth, F., et al.. Equilibrium adsorption data from temperature-programmed desorption experiments. Adsorption, 2(4), 279-286(1996). 

Another ZSM-5 sample (Si/Al = 34) was studied by Sharma et al. [168] both by microcalorimetric measurements at 473 K and temperature-programmed desorption experiments. This zeolite possessed a relatively homogeneous distribution of acid strengths with occurrence of a plateau of adsorption heats of ammonia around ISOkJmoH. For pyridine adsorption on the... 

Boszo reported the temperature programmed desorption spectroscopy, indicating that the temperature of maximum desorption rate on Fe (111) is at the range of 850 K-890 K. The prediction temperatures by analysis of three microkinetic models are 820 K-870K, 790 K 830 K and 760 K 820K, respectively. The value predicted by model III seems too low, but close to the temperatures with maximmn desorp>-tion rate in the nitrogen temperature programmed desorption experiments carried out by authors on Fe obtained after reduction of Fei xO-basis catalyst. Possibly, it relates to the catalytic activity. 

Kinetic Monte Carlo simulations can be parameterized from DFT calculations and used to model surface processes. We shall demonstrate how they can be used to predict the rate at which NH3 molecules desorb from a surface during a temperature programmed desorption experiment, assuming there is no readsorption of molecules to the surface. 

Third possibility to obtain the adsorption heats is to extract them from the data acquired from temperature-programmed desorption experiments. This possibility will be exposed in detail later, in the Sect.4.5.2. However, for that purpose, it is obligatory to know some basic postulates about the kinetics of adsorption and desorption what is given in the following section. 

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