Temperature Programmed Desorption Technique

Despite the fact that TPD is widely used because of its simplicity the main drawbacks of this technique have to be pointed out. 

From MS results the nature of acid sites can be determined. Upon heating in vacuum two stages of weight loss and two stages of product evolution can be observed. The molecules associated with low-temperature desorption can probably be assigned to a number of different types of species, including molecules associated with Lewis 

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Application of a Temperature-Programmed Desorption Technique to Catalyst Studies... 

Finally, new methods of analysis have recently been developed that may allow characterization of single atoms on surfaces such as atomic force microscopy.9 In certain cases, in situ experiments can be done such as the study of electrodes, enzymes, minerals and biomolecules. It has even been shown that one atom from a tip can be selectively placed on a desired surface.10 Such processes may one day be used to prepare catalysts that may enhance selectivity. Other methods that show promise as regards detection of surface catalytic intermediates are temperature programmed desorption techniques.11 Selective poisoning of some surface intermediates with monitoring via temperature programming methods may also allow the preparation of more selective catalysts. 

Stoeckli, F., Moreno-Castilla, C., Carrasco-Marin, F., and L6pez-Ram6n, M.V. (2001). Distribution of surface oxygen complexes on activated carbons from immersion calorimetry, titration and temperature-programmed desorption techniques. Carbon, 39(14), 2235-7. 

The temperature-programmed desorption technique consists of the following steps (1) catalyst pretreatment, (2) preadsorption of the adsorbate, (3) evacuation after preadsorption to remove the physically adsorbed gas, (4) programmed desorption of the residual chemisorbed gas into the stream of a carrier gas, (5) detection of the desorbed gas in the carrier, (6) trapping and analysis of the desorbed gas to establish its identity. In the following, some extensions of the theoretical treatment and several examples of the applications will be given and it is hoped to show that the method is capable of providing useful information. 

Alumina catalysts studied by the temperature-programmed desorption technique were prepared mainly by precipitating with ammonia aluminum hydroxide gel from an aluminum nitrate solution (2). The gel thus prepared was dried at 110° overnight and stored. Before use the catalyst was treated with air for 2 hours at 600° and evacuated in the reactor at the same temperature for more than 60 hours, until no more water condensed in the trap T (Fig. 1) during the evacuation. An alumina catalyst was also prepared by the hydrolysis of purified aluminum isopropoxide dissolved in isopropyl alcohol. This catalyst was dried and activated in the same manner as described above. In the... 

In some cases the temperature-programmed desorption technique can be also used to study the catalytic reactions which occur on the active sites. When it is possible to select a temperature at which the catalyst... 

Chevrot et al. [164] presented a new experimental technique to study low temperature constant rate thermodesorption of different adsorbates. In the cited paper they analyze water thermodesorption from mesoporous silica MCM-41 and the results are compared with data obtained with adsorption gravimetry. According to the authors this technique has better sensitivity and resolution than the traditional temperature programmed desorption technique. Other advantages of this technique are that a small quantity of sample is needed, solids with lower smface area can be studied, and the lower temperature at which the equipment can operate (163 K). 

Cvetanovic, R. J. and Amenomiya, Y. (1967) Application of a Temperature-Programmed Desorption Technique to Catalyst Studies. In Advances in Catalysis Eley, D. D., Pines, H. and Weisz, P. B. Eds. Academic Press New York, Vol. 17, p. 103. 

R. Cvetanovic and Y. Amenomiya, Application of a temperature-programmed desorption technique to catalyst studies. Advances in Catalysis, vol. 17, pp. 103-149, 1967. 

Temperature-programmed desorption techniques are also successfully used to estimate pore sizes of adsorbents consisting of amorphous materials or arrays of... 

Causton P, McEnaney B. Determination of active surface area of coal chars using a temperature-programmed desorption technique. Fuel 1985 64(l 1) 1447-1452. 

Temperature-programmed desorption technique offers very useful and important methodology which can be applied for the characterization of materials used as catalysts. There are two main fields of applications ... 

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