scholarly journals Crucial impact of exchange between layers on temperature programmed desorption

2021 ◽  
Author(s):  
Tobias Dickbreder ◽  
Ralf Bechstein ◽  
Angelika Kühnle
Keyword(s):  
Kinetic Modelling ◽  
Leading Edge ◽  
Temperature Programmed Desorption ◽  
Desorption Peak ◽  
Adsorbate Layer ◽  
Temperature Programmed

Kinetic modelling shows that layer exchange between the 1st and 2nd adsorbate layer on a surface alters the appearance of desorption spectra considerably. Especially, a rapid layer exchange causes a broader desorption peak and a flatter leading edge.

The acidity of trivalent cation-exchanged montmorillonite. Temperature-Programmed desorption and infrared studies of pyridine and n-butylamine

Clay Minerals ◽  
1987 ◽  
Vol 22 (2) ◽  
pp. 169-178 ◽  
Author(s):  
C. Breen ◽  
A. T. Deane ◽  
J. J. Flynn
Keyword(s):  
Variable Temperature ◽  
Temperature Programmed Desorption ◽  
Acid Sites ◽  
Trivalent Cation ◽  
Desorption Peak ◽  
Lewis Acid Sites ◽  
Ir Studies ◽  
Infrared Studies ◽  
Interlamellar Space ◽  
Temperature Programmed

AbstractTemperature-programmed desorption (TPD) and IR spectroscopy were used to characterize the number and strength of acid sites in Al3+-, Cr3+- and Fe3+-exchanged montmorillonite. The bases pyridine and n-butylamine occupied three different sites in the interlamellar space: (i) physisorbed base, (ii) base bound to Lewis acid sites, and (iii) protonated base. TPD profiles for pyridine were characterized by maxima at 40°, 150° and 340°C, whilst those for n-butylamine occurred at 30°, 200° and 410°C. The Al3+- and Cr3+-exchanged forms were stable up to pretreatment temperatures of 300°C, but the Fe3+-form required > 3 day exposure to base vapour to re-establish the high-temperature desorption peak. Variable-temperature IR studies showed that the number of Brönsted-bound pyridine molecules increased with increased outgassing temperature.

scholarly journals Aktive Zentren in CaNaX und NiNaX-Zeolithen / Active Sites in CaNaX and NiNaX Zeolites

1977 ◽  
Vol 32 (7) ◽  
pp. 790-794 ◽  
Author(s):  
Johannes Latzel ◽  
Heinrich Noller
Keyword(s):  
Active Sites ◽  
Temperature Programmed Desorption ◽  
Desorption Peak ◽  
Pyridine Adsorption ◽  
Desorption Temperature ◽  
Temperature Programmed ◽  
Special Case

Temperature programmed desorption of pyridine and benzene was carried out on NaX-13, CaNaX and NiNaX. This was correlated with IR investigation of pyridine adsorption according to WARD3 and with microcatalytic investigations of 2-butanol dehydration and butene isomerisation. Pyridine showed three definite desorption maxima for each of the three zeolites. While the catalytically inactive NaX-13 desorbed pyridine up to 385 °C, the comparable desorption maxima of the active CaNaX and NiNaX were situated at 490 and 470 °C, respectively. IR investigations showed zeolitic cations for these adsorption centres (bands at 1443-1444,1443-1445,1447-1448 cm-1). The lower desorption temperature of the system pyridine/NiNaX, compared with CaNaX, is incompatible with the higher acidity of Ni2+ and the higher IR band level, while the desorption temperature on NaX-13 and CaNaX is conform with the acidity of the ions and the IR band. Benzene on NiNaX behaves in the same way as on NaX-13 (highest desorption temperature 160 °C) while a desorption peak still occurs at 375 °C on CaNaX. The special case of NiNaX is explained by migration of the Ni2+ into the sodalite cave.

Chemisorption of CO on Au/TiOx/Pt(111) Model Catalysts with Different Stoichiometry and Defectivity

2008 ◽  
Vol 8 (7) ◽  
pp. 3595-3602 ◽  
Author(s):  
Luca Artiglia ◽  
Gian Andrea Rizzi ◽  
Francesco Sedona ◽  
Stefano Agnoli ◽  
Gaetano Granozzi
Keyword(s):  
Ultrathin Films ◽  
Au Nanoparticles ◽  
Temperature Programmed Desorption ◽  
Model Catalysts ◽  
Desorption Peak ◽  
Adsorption Sites ◽  
Ordered Array ◽  
Temperature Programmed ◽  
A Minor ◽  
Minor Extent

Au/TiOx/Pt(111) model catalysts were prepared starting from well characterized TiOx/Pt(111) ultrathin films, according to an established procedure consisting in a reactive evaporation of Ti, subsequent thermal treatment in O2 or in UHV, and final deposition of submonolayer quantities of Au. Temperature Programmed Desorption measurements were performed to compare the interaction of CO in the case of two reduced TiOx/Pt(111) substrates (indicated as w-TiOx and w′-TiOx, being the former characterized by an ordered array of defects that can act as template for the deposition of a stable array of Au nanoparticles), with the case of a stoichiometric rect′-TiO2/Pt(111) substrate. It was found that in all cases CO is molecularly adsorbed and two different desorption peaks are detected: one at ≈140 K corresponding to CO desorption from less active adsorption sites (terraces) of the Au nanoparticles and one at ≈200 K corresponding to CO desorption from Au nanoparticles step sites. After annealing at 770 K, the high temperature CO desorption peak is still present in the case of the defective reduced w-TiOx phase, supporting the good templating and stabilizing effect of such phase. On the rect′-TiO2 stoichiometric phase, the CO uptake decreases after annealing but only to a minor extent.

scholarly journals Micro-Kinetic Modelling of CO-TPD from Fe(100)—Incorporating Lateral Interactions

Catalysts ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 310 ◽  
Author(s):  
Thobani Gambu ◽  
R. Abrahams ◽  
Eric van Steen
Keyword(s):  
Monte Carlo ◽  
Kinetic Modelling ◽  
Kinetic Monte Carlo ◽  
Mean Field ◽  
Temperature Programmed Desorption ◽  
Lateral Interactions ◽  
Field Techniques ◽  
Co Dissociation ◽  
The Mean ◽  
Temperature Programmed

The experimentally determined temperature programmed desorption profile of CO from Fe(100) is characterized by four maxima, i.e., α1-CO, α2-CO, α3-CO, and β-CO (see e.g., Moon et al., Surf. Sci. 1985, 163, 215). The CO-TPD profile is modeled using mean-field techniques and kinetic Monte Carlo to show the importance of lateral interactions in the appearance of the CO-TPD-profile. The inclusion of lateral interactions results in the appearance of a new maximum in the simulated CO-TPD profile if modeled using the mean-field, quasi-chemical approach or kinetic Monte Carlo. It is argued that α2-CO may thus originate from lateral interactions rather than a differently bound CO on Fe(100). A detailed sensitivity analysis of the effect of the strength of the lateral interactions between the species involved (CO, C, and O), and the choice of the transition state, which affects the activation energy for CO dissociation, and the energy barrier for diffusion on the CO-TPD profile is presented.

Surface Chemistry of Dimethylaluminum Hydride and Trimethylaluminum on Aluminum

1989 ◽  
Vol 158 ◽  
Author(s):  
Daniel R. Strongin ◽  
Paul B. Comita
Keyword(s):  
Surface Chemistry ◽  
Auger Electron Spectroscopy ◽  
Electron Spectroscopy ◽  
Auger Electron ◽  
Temperature Programmed Desorption ◽  
Aluminum Surface ◽  
Desorption Peak ◽  
Carbonaceous Species ◽  
Temperature Programmed ◽  
Dimethylaluminum Hydride

ABSTRACTThe surface chemistry of dimethylaluminum hydride (DMAH) and trimethylaluminum (TMA) on aluminum has been investigated with temperature programmed desorption (TPD), and Auger electron spectroscopy (AES). The TPD spectra of TMA shows a single desorption peak with a peak maximum which shifts from 190 to 200 K for surface coverages of 0.5 and 2.0 monolayers (ML) respectively. DMAH desorbs from an aluminum surface between 198 and 236 K at surface coverages ranging from 0.1 to 4.0 ML. A second DMAH desorption peak is observed at about 200 K (2.0 ML) when the aluminum surface is contaminated with carbonaceous species, resulting from the decomposition of DMAH. Both DMAH and TMA yield methane as a reaction product on the aluminum surface. The surface reactions of DMAH on aluminum also yield TMA as a reaction product.

Electron Stimulated Desorption of Deuterium from GaN (0001) Surface

2002 ◽  
Vol 743 ◽  
Author(s):  
Y. Yang ◽  
J. Lee ◽  
B. D. Thoms
Keyword(s):  
Temperature Programmed Desorption ◽  
Desorption Peak ◽  
First Order ◽  
Desorption Temperature ◽  
Temperature Programmed ◽  
Electron Stimulated Desorption

AbstractTemperature programmed desorption (TPD) was performed on deuterated GaN(0001) surfaces which had been exposed to various doses of 90-eV electrons. TPD of the deuterated surface without electron exposure shows a broad D2 desorption feature with a peak desorption temperature at ∼400 °C. Electron exposure results in a decrease in intensity of the desorption peak which is attributed to removal of surface deuterium by electron stimulated desorption (ESD). This removal of deuterium by ESD produces no change in the peak desorption temperature indicating that recombinative desorption is first order in deuterium coverage.

Interactions of Ge Atoms with High- ê Oxide Dielectric Surfaces

2005 ◽  
Vol 879 ◽  
Author(s):  
Scott K. Stanley ◽  
John G. Ekerdt
Keyword(s):  
Oxide Layer ◽  
Photoelectron Spectroscopy ◽  
Chemical Vapor ◽  
Temperature Programmed Desorption ◽  
Tungsten Filament ◽  
X Ray ◽  
Dielectric Surfaces ◽  
Temperature Programmed ◽  
The Stability ◽  
Ge Nanocrystals

AbstractGe is deposited on HfO2 surfaces by chemical vapor deposition (CVD) with GeH4. 0.7-1.0 ML GeHx (x = 0-3) is deposited by thermally cracking GeH4 on a hot tungsten filament. Ge oxidation and bonding are studied at 300-1000 K with X-ray photoelectron spectroscopy (XPS). Ge, GeH, GeO, and GeO2 desorption are measured with temperature programmed desorption (TPD) at 400-1000 K. Ge initially reacts with the dielectric forming an oxide layer followed by Ge deposition and formation of nanocrystals in CVD at 870 K. 0.7-1.0 ML GeHx deposited by cracking rapidly forms a contacting oxide layer on HfO2 that is stable from 300-800 K. Ge is fully removed from the HfO2 surface after annealing to 1000 K. These results help explain the stability of Ge nanocrystals in contact with HfO2.

scholarly journals Nanosheet-Like Ho2O3 and Sr-Ho2O3 Catalysts for Oxidative Coupling of Methane

Catalysts ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 388
Author(s):  
Yuqiao Fan ◽  
Changxi Miao ◽  
Yinghong Yue ◽  
Weiming Hua ◽  
Zi Gao
Keyword(s):  
Oxidative Coupling ◽  
Temperature Programmed Desorption ◽  
Oxidative Coupling Of Methane ◽  
Molar Ratio ◽  
Impregnation Method ◽  
Oxygen Species ◽  
N2 Adsorption ◽  
Basic Sites ◽  
Chemisorbed Oxygen ◽  
Temperature Programmed

In this work, Ho2O3 nanosheets were synthesized by a hydrothermal method. A series of Sr-modified Ho2O3 nanosheets (Sr-Ho2O3-NS) with a Sr/Ho molar ratio between 0.02 and 0.06 were prepared via an impregnation method. These catalysts were characterized by several techniques such as XRD, N2 adsorption, SEM, TEM, XPS, O2-TPD (temperature-programmed desorption), and CO2-TPD, and they were studied with respect to their performances in the oxidative coupling of methane (OCM). In contrast to Ho2O3 nanoparticles, Ho2O3 nanosheets display greater CH4 conversion and C2-C3 selectivity, which could be related to the preferentially exposed (222) facet on the surface of the latter catalyst. The incorporation of small amounts of Sr into Ho2O3 nanosheets leads to a higher ratio of (O− + O2−)/O2− as well as an enhanced amount of chemisorbed oxygen species and moderate basic sites, which in turn improves the OCM performance. The optimal catalytic behavior is achievable on the 0.04Sr-Ho2O3-NS catalyst with a Sr/Ho molar ratio of 0.04, which gives a 24.0% conversion of CH4 with 56.7% selectivity to C2-C3 at 650 °C. The C2-C3 yield is well correlated with the amount of moderate basic sites present on the catalysts.

scholarly journals The interaction of size-selected Ru3 clusters with RF-deposited TiO2: probing Ru-CO binding sites with CO-Temperature Programmed Desorption

2021 ◽  
Author(s):  
Liam Howard-Fabretto ◽  
Timothy Gorey ◽  
Guangjing Li ◽  
Siriluck Tesana ◽  
Gregory F Metha ◽  
...  
Keyword(s):  
Radio Frequency ◽  
Chemical Reactions ◽  
Binding Sites ◽  
Co Hydrogenation ◽  
Temperature Programmed Desorption ◽  
Temperature Programmed

Small Ru clusters are efficient catalysts for chemical reactions such as CO hydrogenation. In this study 3-atom Ru3 clusters were deposited onto radio frequency (RF)-deposited TiO2 which is an inexpensive,...

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