Pulse thermal analysis (PulseTA^®) is based on the injection of a specific amount of gaseous or liquid reactants into a carrier gas stream while monitoring changes in mass, enthalpy and gas composition resulting from the incremental reaction extent [1, 2]. In contrast to conventional thermal analysis (TA) and all its modifications, the course of the reaction is controlled not only by temperature but also by transient change in the composition of the reactive atmosphere. 
PulseTA^® offers three principle opportunities of thermoanalytical studies, depending on the kind of injected gas:

I. Injection of an gas not reacting with the sample or decomposition products 
The opportunity of injecting a known amount of any gas into the carrier gas stream provides a quantitative calibration by relating the spectrometric (MS) or Fourier transform infrared spectroscopic (FTIR) signals to the injected quality of probe gas. The high sensitivity of the spectroscopic methods enables the determination and quantification of evolved species even when their concentration does not exceed 0.01 wt%. Determination of such small quantities is rather impossible using standard TA techniques.

II. Injection of a gas which reacts with the solid sample 
PulseTA^® allows dosing the reacting gas in small quantities facilitating the study of gas-solid reactions in differential mode. The most distinct feature of PulseTA^® is the fact that changes of the gaseous atmosphere during experiments occur in a limited, short period of time after each injected pulse of the gas. PulseTA^® allows monitoring gas-solid processes corresponding to a specific extent of reaction with desired temperature ramp (iso- or non-isothermally). The reaction can be stopped at any point between pulses, enabling elucidation of the relationship between the composition of the solid and the reaction progress. Depending on the temperature and pulse volume, any required reaction progress can be reached.
The conventional TA methods generally do not allow investigating processes in differential steps of reaction extent. The transient character of the pulse technique offers interesting opportunities which are important when studying in-situ gas-solid reactions and catalytic processes in transient mode.

III. Injection of a gas which adsorbs on the solid
Due to simultaneous monitoring of changes of mass and thermal effects PulseTA^® can be applied for investigating adsorption phenomena under atmospheric pressure. It allows investigating both, reversible (physisorption) and irreversible (chemisorption) processes. The observed exothermal effects in the DTA curve, in conjunction with the mass gain resulting from chemisorption, allow the determination of the heat of adsorption per mole of adsorbed gas. The quantification of the spectroscopic signals resulting from the desorption of chemisorbed species provides the useful information on concentration and strength of active sites. 
The application of PulseTA^® will be illustrated by results obtained by means of combined TA-MS system. A variety of different gas-solid interactions will be addressed such as decomposition of simple and complex inorganic salts, oxidation and reduction (by hydrogen, methane, carbon monoxide) of solids, adsorption and desorption phenomena, and catalytic heterogeneous reactions. The studies clearly demonstrate that the pulse technique offers new interesting opportunities for investigating the course and mechanism of gas-solid processes.

References

1. M. Maciejewski, C.A. Müller, R. Tschan, W.-D. Emmerich and A. Baiker,
   Thermochim. Acta, 295 (1997) 167.
2. M. Maciejewski, W.D. Emmerich and A. Baiker, Proc. 25-th North American 
   Thermal Society Conference, McLean, Virginia, USA, 1997, Ed. R.J. Morgan, p. 508.

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