Differential Thermogravimetric Analyser coupled with Infrared Spectroscopy
(DTA / TGA-FTIR)
The DTA / TGA - FTIR setup can record the weight change of a sample as a function of temperature or time. Exothermic as well as endothermic processes can be identified. Evolved products are monitored by infrared spectroscopy (Figure 1). Reactants (i.e. oxygen, methane) can be added either continuously or as pulses.
The DTA / TGA-FTIR setup is used for in-situ catalyst studies. In a typical experiment, methane pulses (0.5 ml / pulse) are given over a pre-oxidised catalyst. The reaction products are analysed with the FTIR spectrometer. The result of a pulse experiment on a pre-oxidised ruthenium catalyst is shown in Figure 2. The oxidised ruthenium catalyst is reduced by methane (TG-curve: a weight loss is obseved). CO2 is exclusively produced in an exothermic reaction. With increasing level of reduction, CO2 formation decreases and CO is formed. After 8 pulses, a transition from exothermic to endothermic processes is observed. Interestingly, the formation CO2 is nearly zero and CO is the only product at this state of reduction.
Layout of the DTA / TGA-FTIR setup.
There are some more applications for DTA / TGA-FTIR experiments in heterogeneous catalysis: studies on the carbon formation on catalysts, temperature programmed reduction / oxidation studies (TPR / TPO) or continuous flow experiments which give information about the oxidation state of a working catalyst.
Results of a pulse TGA-FTIR experiment over a pre-oxidised ruthenium catalyst.