Diffuse temperature-programmed surface

Finally, although both temperature-programmed desorption and reaction are indispensable techniques in catalysis and surface chemistry, they do have limitations. First, TPD experiments are not performed at equilibrium, since the temperature increases constantly. Secondly, the kinetic parameters change during TPD, due to changes in both temperature and coverage. Thirdly, temperature-dependent surface processes such as diffusion or surface reconstruction may accompany desorption and exert an influence. Hence, the technique should be used judiciously and the derived kinetic data should be treated with care ... 

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. 

MoS2 is observed after sulfidation at temperatures above 300 °C. These results are easily reconciled with those from XPS and RBS described before, be it that the temperatures at which the changes occur are higher in the QEXAFS study, which is in fact expected for a temperature-programmed measurement. In addition, the QEXAFS were made on high-surface area catalysts, where diffusion limitations are likely, whereas the XPS studies concern planar, thin films, in which virtually all material is in contact with the gas phase. 

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... 

This section summarizes the chemistry of the SC isobutane regeneration process. To understand the nature of the hydrocarbons that remain adsorbed on the surface of the USY zeolite catalyst both before and after SC isobutane regeneration, a series of ex-situ temperature-programmed oxidation (TPO), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and ultraviolet-visible (UV-vis) analyses was performed on samples submitted to different TOS 10 under isobutane/butene reaction conditions. 

Generally speaking, the methods used to characterize carbonaceous material surfaces are referred to as wet and dry techniques. The former include potentiometric titrations and zeta potential or electrochemical methods the latter include temperature-programmed desorption (TPD) and spectroscopic methods such as x-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared spectroscopy (DRIFT). 

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