Temperature Programmed Oxidation Analysis

 

This topic provides an example of performing a TPO on WO3. Because TPR is often used as the preparation for TPO, the TPR process was included in this example.

Temperature Programmed Oxidation (TPO) examines the extent to which a catalyst can be re-oxidized. Generally, TPO analyses are used to measure the degree of reduction of certain oxides.

Usually the sample is pretreated and the metal oxides are reduced to the base metal. Then the reactant gas is applied to the sample in pulses or (alternatively) as a steady stream. The analyzer measures the uptake of the reactant gas.

TPO is often performed after TPR is performed. When the TPR experiment concludes, the sample is returned to room temperature. Then, the analysis gas is changed to 2-5% O2 + He. This gas mixture is flowed after the sample is at ambient temperature, then the temperature is ramped up to the same maximum temperature used for the preceding TPR analysis. The portion of the sample that had been reduced is re-oxidized, and the degree of reduction can be calculated.

If the TPR and TPO results are different, there are several possible causes: the sample material sintered such that only a surface oxide (and not a bulk oxide) is formed, or part of the sample was re-oxidized at room temperature while the TCD baseline was stabilizing.

 

When using any mixture of gases for TPR or TPO analyses, make sure the thermal conductivities of the two gases in the mixture are quite different for maximum sensitivity, SeeGas Charts .

Preparation

Pretreatment

TPR

Analysis

2 to 5% oxygen/helium is flowed through the sample while temperature is ramped, beginning at ambient temperature.

Cold Trap

None needed.

  Before performing an analysis, ensure the sample and analyzer are adequately prepared using the instructions in Prepare for Analysis.

Procedure

  1. Obtain the sample weight, then install the loaded sample tube and thermocouple on the analyzer. Close the furnace around the sample tube.
  2. Create a sample file for this analysis.
  1. Go to File > New Sample. Enter a file name or accept the default. Click OK, then click Yes to confirm.
  2. Complete the Sample file as needed.
  3. Select the Analysis Conditions tab and insert the experiment steps in the following table:
Insert Step Window Field Field Entry
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 (blend of 10% 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
Temperature Ramp Temperature Ramp Ramp Type Return to ambient
Change Gas Flows Gas flows Prep Gas None
Carrier Gas Hydrogen-Argon (blend of 10% hydrogen in argon)
Loop Gas None
Cold trap valve Bypass
Analysis valve Analyze
Loop valve Fill
Back pressure Prepare
Wait Wait Wait for operator Position cold trap dewar and close furnace
Wait Wait Wait until baseline is stable Select this option
Start Recording Start Recording One measurement every 1.0 seconds
Temperature Ramp Temperature Ramp Ramp Type Sample ramp
End temperature 980
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.

Change Gas Flows Gas Flows Prep Gas Helium
Carrier Gas Helium
Loop Gas None
Cold trap valve Bypass
Analysis valve Prepare
Loop valve Fill
Back pressure Prepare
Temperature Ramp Temperature Ramp Ramp Type Return to ambient
Experiment New Experiment Experiment Description Enter a description of the experiment
Type of analysis Temperature Programmed
Oxidation
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 Helium
Loop Gas None
Rate 50 cm3/min
Cold trap valve Bypass
Analysis valve Prepare
Loop valve Fill
Back pressure Prepare
Outputs Outputs Use default values
Peaks Peaks Use default values
Wait Wait Wait until baseline is stable Select this option
Start Recording Start Recording One measurement every

1.0 seconds

Temperature Ramp Temperature Ramp Ramp Type Sample ramp
End temperature 980
Ramp rate 20.0
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.

Change Gas Flows Gas Flows Prep Gas Helium
Carrier Gas Helium
Loop Gas None
Cold trap valve Bypass
Analysis valve Prepare
Loop valve Fill
Back pressure Prepare
Temperature Ramp Temperature Ramp Ramp Type Return to ambient
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 set the values.
  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.
  3. Read the cautionary window and make any necessary changes.
  4. Click Start to start the analysis.
 

When the analysis ends, the furnace begins to lower the sample to room temperature. To speed cooling of the sample, use the optional CryoCooler or KwikCool. Remove the sample tube when the analysis is complete.

  1. As the temperature increases, the sample is oxidized, and the application calculates the volume of oxygen taken up.
  1. Allow the TCD signal to return to the initial baseline after the peak has been displayed
 

Use the cotton gloves provided in the accessory kit to remove the sample tube before it has cooled. Rubber gloves may be used to handle the sample tube when it has cooled.

  1. When the displayed sample temperature reaches the ambient temperature, open the furnace. Using gloves, remove the sample tube.
 
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