Thermoprogrammed desorption

The nature (Bronsted or Lewis centers), the number, and the strength of the acidic sites of the Pd/Al203 and Pd/Zr02 solids have been checked using infixed spectroscopy of adsorbed pyridine and thermoprogrammed desorption of ammonia. 

This work is devoted to the synthesis of Zr02 by various methods, the synthesis of zirconium-containing pentasils and Zr02 - -zeolite based binary carriers. These materials were used as carriers of transition metal oxides (chromium, cobalt) and their catalytic properties were characterized in the selective reduction of NO by methane and propane-butane mixture, the acidic properties of the samples were investigated by thermoprogrammed desorption and IR-spectroscopy methods. 

In order to elucidate the reasons for the dependence of the catalytic properties of these samples on their preparation method, we studied the acid surface properties of cobalt- and chromium-modified Zr02 catalysts by ammonia thermoprogrammed desorption and IR-spectroscopy. Our results again indicated that the activity of these catalysts in the SCR of NOx by hydrocarbons is a function both of the surface acidity and content of the active metal. The acid site concentration of the starting Zr02 samples prepared by various methods is significant (0.13 and 0.23 mmol/g) but these samples are inactive, while 10% CriOilZtOi prepared by the sol-gel method displays considerable activity in the reaction studied with lower surface acidity. The acid site concentration of the sample with the same composition prepared by the precipitation method is reduced by a factor of 2.5 and, thus, this catalyst has much lower activity in the selective catalytic reduction. 

Fig. 35 shows two thermoprogrammed desorption (TPD) curves obtained with the AC material galvanostatically charged with difRa nt loads in 6 mol L KOH at-500 mA g [127], In one experiment, the charging time is limited to 15 minutes for only charging the... 

The surface area of the catalysts was measured by conventional BET methods (nitrogen physisorption at -196°C using a Quanta Chrome-NOVA 1000 instrument). The actual metal loading was measured by inductively-coupled plasma / optical emission spectroscopy (ICP/OES). The acidity and basicity of the synthesized catalysts were measured by NHj and COj thermoprogrammed desorption, respectively, using an AMI-100 (Zeton-Altamira, Pittsburgh, PA) characterization system. The catalyst samples were reduced in 10% H /Ar at 450°C for 8 hours, followed by treatment in 10% NH,/He or 10% COj/He at 35°C and then by desorption up to 400°C with a heating rate of 10°C/min. 

Another interesting comparison of various thermal analysis techniques, namely adsorption microcalorimetry, thermoprogrammed desorption, and thermoprogrammed reaction using constant rate thermal analysis (CRTA), has been performed by Fesenko et al. in order to study the reactivity of zeolites in terms of the adsorption or desorption of base probe molecules [24]. As an example, CRTA was applied to the desorption of isopropylamine from Na-Y zeolite and its acidic form HY. 

Novel complex hydrides (LiBH4/LiNH2/MgH2) are also under study and the addition of various nanosized additives as nickel, cobalt, iron, copper, manganese was followed by thermoprogrammed desorption technique (TPD) [24]. 

The size and morphology are characteristic parameters of metal particles. It is possible to determine them by various techniques transmission electron microscopy (TEM) [105-107], X-ray photoelectron spectroscopy (XPS) [108], X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAES) [109, 110], thermoprogrammed oxidation, reduction or desorption (TPO, TPR or TPO) and chemisorption of probe molecules (H2, O2, CO, NO) are currently used. It is therefore possible to know the particles (i) size (by TEM) [105-107], extended X-ray absorption fine structure (EXAES) [109, 110]), (ii) structure (by XRD, TEM), (iii) chemical composition (by TEM-EDAX, elemental analysis), (iv) chemical state (surface and bulk metal atoms by XPS [108], TPD, TPR, TPO) and... 

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