Temperature programmed reduction spectroscopy

Catalysts were characterized using SEM (Hitachi S-4800, operated at 15 keV for secondary electron imaging and energy dispersive spectroscopy (EDS)), XRD (Bruker D4 Endeavor with Cu K radiation operated at 40 kV and 40 mA), TEM (Tecnai S-20, operated at 200 keV) and temperature-programmed reduction (TPR). Table 1 lists BET surface area for the selected catalysts. 

The pros and cons of oxidative dehydrogenation for alkene synthesis using doped cerianites as solid oxygen carriers are studied. The hydrogen oxidation properties of a set of ten doped cerianite catalysts (Ce0.9X0.1Oy, where X = Bi, In, La, Mo, Pb, Sn, V, W, Y, and Zr) are examined under cyclic redox conditions. X-ray diffraction, X-ray photoelectron spectroscopy, adsorption measurements, and temperature programmed reduction are used to try and clarify structure-activity relationships and the different dopant effects. 

One way in which cobalt dispersion can be increased is the addition of an organic compound to the cobalt nitrate prior to calcination. Previous work in this area is summarized in Table 1.1. The data are complex, but there are a number of factors that affect the nature of the catalyst prepared. One of these is the cobalt loading. Preparation of catalysts containing low levels of cobalt tends to lead to high concentrations of cobalt-support compounds. For example, Mochizuki et al. [37] used x-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR) to identify cobalt silicate-like species in their 5% Co/Si02 catalysts modified with nitrilotriacetic acid (NTA). The nature of the support also has... 

The catalysts were characterized by inductively coupled plasma emission spectroscopy (ICP-ES Perkin Elmer Optima 3300RL) to determine cobalt content, x-ray diffraction (XRD Bruker A-500) with crystallite size determination using the Rietveld method, and temperature-programmed reduction (Zeton Altamira AMI-200) using 30 ml/min 10% H2/Ar and a ramp rate of 10°C/min. Surface area... 

Temperature-programmed reduction combined with x-ray absorption fine-structure (XAFS) spectroscopy provided clear evidence that the doping of Fischer-Tropsch synthesis catalysts with Cu and alkali (e.g., K) promotes the carburization rate relative to the undoped catalyst. Since XAFS provides information about the local atomic environment, it can be a powerful tool to aid in catalyst characterization. While XAFS should probably not be used exclusively to characterize the types of iron carbide present in catalysts, it may be, as this example shows, a useful complement to verify results from Mossbauer spectroscopy and other temperature-programmed methods. The EXAFS results suggest that either the Hagg or s-carbides were formed during the reduction process over the cementite form. There appears to be a correlation between the a-value of the product distribution and the carburization rate. 

The aim of this work was to apply combined temperature-programmed reduction (TPR)/x-ray absorption fine-structure (XAFS) spectroscopy to provide clear evidence regarding the manner in which common promoters (e.g., Cu and alkali, like K) operate during the activation of iron-based Fischer-Tropsch synthesis catalysts. In addition, it was of interest to compare results obtained by EXAFS with earlier ones obtained by Mossbauer spectroscopy to shed light on the possible types of iron carbides formed. To that end, model spectra were generated based on the existing crystallography literature for four carbide compounds of... 

Penkova, A., Dzwigaj, S., Kefirov, R., Hadjiivanov, K., and Che, M. (2007) Effed of preparation method on the state of BEA zeolites. A study by Fourier transform Ir spectroscopy of adsorbed CO and NO, temperature programmed reductions, and x-ray... 

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. 

In this paper the origins of the difference in stability of catalysts on different support materials are discussed. Catalysts supported on y-alumina and on titania (anatase) have been tested in the oxidation of 1-butene to butanone. Fresh and spent catalysts have been investigated by means of temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to reveal the causes for deactivation. 

Preservation of the zeolite structure was verified by X-ray powder diffraction (XRD) patterns recorded on a CGR Theta 60 instrument using Cu Kcq filtered radiation. The chemical composition of solids was determined at the Service Central d Analyse CNRS (Solaize, France). Copper in the zeolite was characterised by DR-UV-visible spectroscopy using a Perkin-Elmer Lambda 14 apparatus, equipped with a reflectance sphere, and by temperature programmed reduction (TPR), using a Micromeritics Autochem 2910, equipped with a katharometer (3% H2/Ar gas mixture at 30 mL.min1 and 10 K.min 1). 

Temperature programmed reduction (TPR), oxidation (TPO), desorption (TPD), sulphidation (TPS) and reaction spectroscopy (TPRS) form a class of techniques in which a chemical reaction is monitored while the temperature increases linearly in time. These techniques are applicable to real catalysts and single crystals and have the advantage that they are experimentally simple and inexpensive in comparison to many other spectroscopies. Interpretation on a qualitative base is rather straightforward [13]. 

In addition to the structure in the dehydrated state, the structure of supported vanadia catalysts under redox reaction conditions is directly related to the catalytic performance. Vanadia catalysts are usually reduced to some extent during a redox reaction, and the reduced vanadia species have been proposed as the active sites [4, 19-24]. Therefore, information on the valence state and molecular structure of the reduced vanadia catalysts is of great interest. A number of techniques have been applied to investigate the reduction of supported vanadia catalysts, such as temperature programmed reduction (TPR) [25-27], X-ray photoelectron spectroscopy (XPS) [21], electron spin resonance (ESR) [22], UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) [18, 28-32], X-ray absorption fine structure spectroscopy (XAFS) [11] and Raman spectroscopy [5, 26, 33-41]. Most of these techniques give information only on the oxidation state of vanadium species. Although Raman spectroscopy is a powerful tool for characterization of the molecular structure of supported vanadia [4, 29, 42], it has been very difficult to detect reduced supported... 

S. and Jackson, S.D. (2005) On the structure of vanadium oxide supported on aluminas UV and visible Raman spectroscopy, UV-visible diffuse reflectance spectroscopy, and temperature-programmed reduction studies. Journal of Physical Chemistry, 109, 2793-800. 

A wide range of techniques has been used on both fresh and used catalysts to characterize the nature of the oxide surface, for example X-ray powder diffraction (XRD) [10-12], UV-Visible diffuse reflectance spectroscopy (UV-Vis DRS) [11, 12], Raman spectroscopy [10, 11, 14—17], X-ray photoelectron spectroscopy (XPS) [11, 12, 18], electron paramagnetic resonance (EPR) [12, 19], infrared spectroscopy [10, 20] and temperature programmed reduction (TPR) [16, 21]. Given the number of... 

The molybdenum dispersion also depends on the phosphorus content of the catalyst. Atanasova et al. (68, 87) reported that the dispersion of molybdenum and nickel, measured by X-ray photoelectron spectroscopy (XPS), shows a steep increase due to the presence of phosphorus at low loadings. The dispersion of molybdenum in NiMoP/Al catalysts increases further as a result of calcination, whereas that of nickel decreases. In contrast, Sajkowski et al. (83) reported, on the basis of an extended X-ray absorption fine structure (EXAFS) investigation, that phosphorus does not affect the size of the polymolybdate species, Mangnus et al. (31) inferred that the stacking of molybdates does not increase as a result of the addition of phosphorus since the height of a temperature-programmed reduction (TPR) peak at 400°C due to the reduction of deposited multilayered molybdenum oxo-species was found to be independent of the phosphorus content. However, Chadwick el al. (60) concluded from XPS measurements that the dispersion of molybdenum decreases upon addition of phosphorus. 

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