Estimation of activation energy for desorption of low-volatility dioxins on zeolites by TPD technique
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Thermal desorption spectroscopy
Thermal desorption spectroscopy
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The temperature programmed desorption (TPD) spectra of Bi from Ni(100) are characteized by a large shift of the desorption maximum to lower temperatures with increasing coverage. Similar behavior is observed for the desorption of Bi from other metal substrates. Analysis of the desorption of Bi from Ni(100) was performed to determine the kinetic order of desorption and the energetics of the Bi–Ni interaction. We find that Bi desorption is described well by first‐order kinetics with a strong coverage dependence of the activation energy of desorption Ed. The value of Ed varies from 70 kcal mol−1 at low Bi coverage to 57 kcal mol−1 for monolayer Bi coverage. We discuss the possible role of Bi2 in the desorption process and also report the effect of coadsorbed oxygen on the Bi TPD spectrum and the Bi–Ni interaction.
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The kinetic model for desorption activation energy of solid acids was determined.A new simulation method for determination of desorption activation energy over solid acid catalysts from temperature programmed desorption(TPD) results was established.The results showed that the TPD process fits well with second-order desorption mechanism,and the activation energy for the desorption(acidity) first increased and then declined with activation temperature of the catalyst.The same adsorption order and trends in desorption activation energy over different catalysts were seen between kinetic model from single group of TPD data and multi-groups of TPD data.The kinetic model from single group of TPD data is simpler and more reliable.
Thermal desorption spectroscopy
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D301 weakly basic resin was used as an adsorbent for Cr(Ⅵ)adsorption and desorption.The effect of the adsorption time,adsorption tempreture and pH on adsorption capacity were discussed.The adding amount and time of desorption agent on adsorption capacity were analyzed.The experimental results indicated that it facilitated to adsorb for Cr(Ⅵ)in acid medium at pH=2,the equilibrium time of adsorption was achieved within 6 h,the adsorption isotherm could be fitted by the Langmuir equation.The desorption showed better performance with 3% NaOH and desorption time was 30 min,the desorption rate could be reached 97.59%,three times adsorption desorption proved its excellent adsorption for Cr(Ⅵ).
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Temperature-programmed desorption (TPD) has been used to investigate the adsorption of NO on Pt{211} at 300 K and 120 K. Results show that NO dissociation occurs readily on Pt{211}, as evidenced by the observation of N2 and N2O in the TPD spectrum. Following adsorption at 120 K three NO TPD peaks at 338, 416, and 503 K are observed, in agreement with previous observations. In combination with data acquired in a recent reflection absorption infrared spectroscopy and density functional theory investigation of NO/Pt{211}, these peaks are assigned to the desorption of NO from an O–NO complex, the recombinative desorption of N and O atoms, and to desorption of a step-bridged NO species, respectively. These assignments are in disagreement with previous work, where the high-temperature NO peak was assigned to the desorption of step bound NO and the two low-temperature peaks were assigned to the desorption of NO from terrace sites. TPD spectra recorded following adsorption at 300 K, with a heating rate of 1 K s−1, show similar features to those recorded following 120 K adsorption. This is also in disagreement with previous observations, where only two NO TPD peaks were observed following adsorption at room temperature. This disagreement can be accounted for by the different heating rates used in the two experiments.
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Adsorption and desorption of hydrogen by gas-phase Pd clusters, Pdn(+), were investigated by thermal desorption spectroscopy (TDS) experiments and density functional theory (DFT) calculations. The desorption processes were examined by heating the clusters that had adsorbed hydrogen at room temperature. The clusters remaining after heating were monitored by mass spectrometry as a function of temperature up to 1000 K, and the temperature-programmed desorption (TPD) curve was obtained for each Pdn(+). It was found that hydrogen molecules were released from the clusters into the gas phase with increasing temperature until bare Pdn(+) was formed. The threshold energy for desorption, estimated from the TPD curve, was compared to the desorption energy calculated by using DFT, indicating that smaller Pdn(+) clusters (n ≤ 6) tended to have weakly adsorbed hydrogen molecules, whereas larger Pdn(+) clusters (n ≥ 7) had dissociatively adsorbed hydrogen atoms on the surface. Highly likely, the nonmetallic nature of the small Pd clusters prevents hydrogen molecule from adsorbing dissociatively on the surface.
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The effective desorption kinetic parameters of CO on the Pd(111) surface have been studied by thermal desorption spectroscopy. The zero coverage effective desorption activation energy and the preexponential factor were found to be 35.5 kcal/mol and 1013.5 s−1, respectively. As a function of CO coverage, a four-stage correlation between Ed(θ) and the development of stable low-energy electron desorption (LEED) structures was observed for the first time at Tads= 200 K. Ed and ν1 showed a strong compensation effect with Tc=519 K. The adsorption temperature dependence of Ed from Tads=87 to 200 K was observed and interpreted qualitatively by a model involving the production of different domain structures at various adsorption temperatures and the preservation of domain structures at higher coverages during temperature programmed desorption.
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