Temperature Programmed Reduction Analysis

 

This topic provides an example of how to perform a TPR analysis of copper oxide. Copper Oxide Reference Material can be ordered from Micromeritics . Log in to your customer portal to access parts and accessories.

 

Some reactions begin at temperatures below ambient. In such cases, a dewar containing an appropriate coolant should be used instead of the furnace at the beginning of the experiment. For example, reduction of PtO should begin at approximately -50 °C, because the reaction begins at about -30 °C. Alternatively, the optional CryoCooler can be used.

Temperature Programmed Reduction (TPR) determines the number of reducible species present in the catalyst and reveals the temperature at which reduction occurs. An important aspect of TPR analyses is that the sample need not have special characteristics other than containing reducible metals.

The TPR analysis begins by flowing analysis gas (typically hydrogen in an inert carrier gas such as nitrogen or argon) over the sample, usually starting at ambient temperature. While the gas is flowing, the temperature of the sample is increased linearly with time and the consumption of hydrogen by adsorption/reaction is monitored. Changes in the concentration of the gas mixture are determined. This information yields the hydrogen uptake volume.

Preparation

Pretreatment Oxidize by flowing O2 over the sample.
Analysis Flow 5-10% hydrogen/argon while ramping the temperature. The analyzer records hydrogen consumption as a function of temperature. Nitrogen is sometimes used because it may be more economical than argon. Argon is recommended over nitrogen because the resultant peak(s) show no reaction between sample and gas.
Cold Trap A cold trap is required to remove traces of water formed as a product of the reduction.
  Before performing an analysis, ensure the sample and analyzer are adequately prepared using the instructions in Prepare for Analysis.

Procedure

  1. Obtain the sample mass then install the loaded sample tube on the analyzer. If the analysis begins below ambient, either place a dewar of coolant around the sample tube or close the furnace around the sample tube and install the CryoCooler. If the analysis begins at ambient, close the furnace around the sample tube.
  2. Install the cold trap (if using one), then place a dewar filled with coolant around the cold trap. Ensure that the dewar contains sufficient coolant to cover the cold trap loops.

A mixture of isopropyl alcohol (IPA) and liquid nitrogen (LN2) is the recommended coolant for this experiment. Place the isopropyl alcohol in a dewar and slowly pour LN2 into the dewar while stirring the mixture. Continue to add and stir the mixture until it becomes a slush. The mixture must be capable of achieving a temperature of about -90 ºC.

 

Extreme caution should be used when mixing the IPA/LN2. See Dewar Precautions.

  1. Create a sample file for this analysis.
  1. Go to File > New Sample.
  2. Complete the Sample Information window. Enter the correct weight and complete the optional fields.
  3. Select the Analysis Conditions tab and insert the experiment steps listed below:
Insert Step Window Field Field Entry or Selection
Experiment New Experiment Experiment description Enter a description of the experiment
Type of analysis Temperature Programmed Reduction
Zones TCD Detector

Block zone

100

Filament

175
Valve Zones

Cold trap

110

Analysis

110

Loop

110

Back pressure

110
Gas Flows Prep Gas Helium
Carrier Gas Hydrogen-Argon (10% blend of hydrogen in argon)
Loop Gas None
Rate 50 cm3/min
Cold trap valve Trap
Analysis valve Prepare
Loop valve Fill
Back pressure Prepare
Outputs Outputs Use default values
Peaks Peaks Use default values
Wait Wait Wait for operator Add sample and setup cold trap
Change Gas Flows Gas Flows Prep None
Carrier Hydrogen-Argon (10% blend of hydrogen in argon)
Loop None
Cold trap valve Trap
Analysis valve Analyze
Loop valve Fill
Back pressure Prepare
Wait Wait Wait until baseline is stable Select this option
Start Recording Start Recording One measurement every 1.0 seconds
Temperature Ramp Temperature Ramp Type Sample Ramp
End Temperature 400
Ramp Rate 10.0
Hold Time 0.00

The application automatically inserts a Stop Recording step when a Start Recording step is inserted. Ensure that the Temperature Ramp step is inserted within the Start/Stop Recording loop.

Termination Termination Return to ambient temperature Select this option
Leave detector enabled after analysis Option is not selected
Zones Not applicable
Gas Flows Not applicable
  1. Select the Report Options tab and modify the values as needed..
  2. Click Save, then click Close.
  1. Start the analysis.
  1. Go to Unit > Sample Analysis. From the Files list box, select the sample file created in the previous step. Edit the file as needed. Click Next.
  2. From the drop-down list, select the calibrations associated with each experiment in the sample file (if any). For this example, select None. Click Next.
  Calibration files can also be associated with a sample file after analysis using Set Calibration in the Peak Editor.
  1. Read the cautionary window and make any necessary changes.
  2. Click Start to start the analysis.


As the temperature increases, the copper oxide is reduced, the water produced by the reaction is collected in the cold trap (if used), and the amount of hydrogen consumed is detected and transmitted to the application. Use the Results view to display a chromatogram of the hydrogen consumed from the detector signal as a function of the ramping temperature.

A hydrogen consumption peak, which corresponds to the reduction capacity of copper oxide, is displayed. The maximum peak should occur at approximately 280 ºC. This temperature varies highly, depending on the CuO particle size. Larger particle size shifts the temperature upward to 330 °C or more. Under certain combinations of sample, hydrogen concentration, and flow rate, two peaks may appear due to the transition state of Cu2+ to Cu+ to Cu.

 
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