Temperature-programmed reduction

The temperature -programmed reduction (TPR) is used to examine the thermal behavior of the reducibility or solids depending on the temperature. In general, hydrogen is used as reducing agent.

This method is used particularly in heterogeneous catalysis, for the characterization of catalysts.

Expiration

The solids or catalyst is first weighed in a sample vessel, which may be, for example, a simple U- pipe. This sample tube is placed in a furnace which is equipped with a temperature control. In addition, a thermocouple records the temperature in the heap of solids.

First, the sample vessel is charged with an inert gas ( nitrogen, argon ) flows in order to remove the air present. For pure inert gas stream by means of flow controllers hydrogen added ( for example, 10 percent by volume of hydrogen in nitrogen).

Now, the sample is heated in the oven defined. The heating rates are usually between 1 K / min and 20 K / min. The behind the sample vessel remaining hydrogen content is measured and recorded by suitable detectors ( thermal conductivity detector, mass spectrometer ). Hydrogen was consumed, a reduction process took place at the temperature just reached.

Results

Is presented the hydrogen consumption in the control as a function of temperature. From the resulting graph with possibly multiple peaks is information on the number of reduction processes can be derived. A carefully performed measurement also allows a quantitative determination of the hydrogen consumption and thus ( with knowledge of the weighed amount of substance ) to a determination of the degree of reduction.

Used for detecting the remaining hydrogen, a mass spectrometer, also the products of the reduction processes (water or organic products ) can be detected. This can bring further insights into the reduction mechanism itself.

Even though the measurement can not be quantified or the obtained peaks clearly the possible reduction processes can not be assigned, with the help of the TPR several samples compare with respect to their thermal behavior. This can be used in quality control.

Evaluation

It should be noted that the quality of the measurement results crucially on the parameters of heating rate β ( in K / min), amount of substance m ( in g), gas flow ( in mL / min) and hydrogen content in the reaction gas ( in vol - %) dependent.