Temperature-programmed desorption/oxidation/reduction

Choisnet, J Abadzhieva, N Stefanov, P Klissurski, D Bassat, JM Rives, V Minehev, L. X-ray photoeleetron spectroscopy, temperature-programmed desorption and temperature-programmed reduction study of LaNiOs and La2Ni04+s catalysts for methanol oxidation. J. Chem. Soc., Faraday Transactions, 1994, Volume 90, 1987-1991. 

The surface structure and acid sites of alumina-supported molybdenum nitride catalysts have been studied using temperature-programed desorption (TPD), and reduction (TPR), diffuse reflectance infrared spectroscopy, and X-ray diffraction (XRD) analysis. The nitride catalysts were prepared by the temperature-programmed reaction of alumina-supported molybdenum oxide (12.5% and 97.1%) with NH3 at temperatures of 773, 973, and 1173 K. TPR and XRD analyses showed that y-Mo2N was already formed at 973 K. On the basis of NH3-TPD measurements and IR spectroscopy, it was found that Lewis acid sites were predominant over Bronsted acid sites on the surface of Mo2N/A1203. 

In order to understand better these interesting systems without complications that might arise due to different preparation procedures, we compared oxygen-treated WC and Mo2C prepared by similar reduction/ carburization procedures from their respective oxides. The effects of pretreatment conditions were also studied. An attempt was made to correlate the kinetic behavior of these catalysts in n-hexane-H2 reactions with their physical properties obtained from X-ray diffraction (XRD), CO chemisorption, temperature-programed reaction (TPR) with flowing H2 or He, temperature programed desorption (TPD) of adsorbed NH3, and X-ray photoelectron spectroscopy (XPS). 

When the system is used in pulse mode, it allows the measurement of heats of adsorption of a gaseous reactant on a solid or interaction heats between a gaseous reactant and pre-adsorbed species. When used as a flow reactor, it allows the kinetic study of catalytic reactions as well as the study of the activation or the aging of the catalyst. This is also a suitable system to perform calorimetric temperature programmed reduction (TPR), temperature programmed oxidation (TPO) or temperature programmed desorption (TPD) experiments. In addition to calorimetry, temperature programmed desorption (TPD) of adsorbed probe molecules can in principle also be used to estimate heats of adsorption [19]. 

The primaiy emphasis in this review article is to showcase the use of LEISS to examine the outermost layers of Pt-Co alloys in order to correlate interfacial composition with electrocatalytic reactivity towards oxygen reduction. In some instances, it is desirable to compare the properties of the outermost layer with those of the (near-surface) bulk an example is when it becomes imperative to explain the unique stability the alloyed Co under anodic-oxidation potentials. In such cases. X-ray photoelectron spectroscopy and temperature-programmed desorption may be employed since both methods are also able to generate information on the electronic (binding-energy shift measurements by XPS) and thermochemical (adsorption enthalpy determinations by TPD) properties at the sub-surface. However, an in-depth discourse on these and related aspects was not intended to be part of this review article. 

One of the most important properties of these OMS and OL systems is their ability to lose and recover oxygen.92, 3,94,95 Temperature programmed desorption, reduction, Oxidation, and studies of lattice oxygen mobility and structural stability studies have been done on a variety of systems. A review of these and similar open framework structures has recently been submitted. 96... 

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... 

We have recently reported that cerium-exchanged mordenite (CeNa-MOR) is a higjily active and selective catalyst for NO reduction witli ammonia in oxygen-rich conditions [23]. We have furtlier found tliat it oxidizes SO2 to a negligible extent [24, 25], and tliat it appears to flilfill the aforementioned requirements for an ideal NH3-SCR catalyst. In the present paper, we will report on these aspeets of eerium-exchanged zeolite catalysts. Furthermore, its surface interaction with two reactants, NO and NH3, is examined with the temperature programmed desorption (TPD) technique. 

The same reaction regenerates the Pt +(NH3)4 complex after reactions (6.32) and (6.35). In the presence of oxygen, hydrogen will be oxidized to form H2O, which drives this reaction thermodynamically. In the overall reaction scheme, N2 and N2O formation compete in the absence of water through reactions (6.32) and (6.36). In the presence of water, N2 formation is promoted because of reactions (6.33) and (6.35). There is ample evidence that the reduction of the zeolitic protons by reduced metal atoms such as Pt is actually an easy reaction stepl . In the temperature-programmed desorption spectra (Fig. 6.28), N2O formation occurs predominantly in the peak in which excess oxygen is consumed. The other two peaks follow N2 formation. In the absence of water, the low-temperature peak that corresponds to the reaction sequence initiated by reaction step (6.33) is suppressed. 

Temperature programmed desorption, reduction, oxidation and flow chemisorption for the characterisation of heterogeneous catalysts. Theoretical aspects, instrumentation and applications... 

As the thermal change at a given temperature depends on many factors such as the nature of the system, the type of gas used, the flow rate, pressure and several kinetics factors, therefore all the experimental aspects should be taken in consideration. The thermal analyses are often used to investigate surface modifications and bulk reactivity by varying the surface composition, the catalyst preparation method, the pre-treatment for catalyst activation and the analytical conditions. The fundamental differences between temperature programmed desorption and temperature programmed reaction (reduction, TPR, and oxidation, TPO), is that the first analysis involves a surface process, while the TPR/0 involve a bulk reaction. 

Oxide Growth Kinetics and Mechanism. Formation of oxide films by potentiostatic polarization and their characterization by CV enables distinction of various oxide states as a function of the polarization conditions, here Ep, tp and T. This method allows precise determination of the thickness of oxide films with accuracy comparable to the most sensitive surface science techniques 4-7J1-20), CV may be considered the electrochemical analog of temperature programmed desorption, TPD, and one may refer to it as potential programmed desorption, PPD. Theoretical treatment of such determined oxide reduction charge densities by fitting of the data into oxide formation theories leads to derivation of important kinetic parameters of the process as a function of the polarization conditions. The kinetics of electro-oxidation of Rh at the ambient temperature were studied and some representative results are reported in ref 24. The present results are an extension of the previous experiments and they involve temperature dependence studies. 

Long R Q, Yang R T (2001) Temperature-programmed desorption/surface reaction (TPD/ TPSR) study of Fe-exchanged ZSM-5 for selective catalytic reduction of nitric oxide by ammonia. J. Catal. 198 20-28. 

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