Temperature Programmed Oxidation Analysis tutorial

 

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, See Gas Charts.

Preparation

Pretreatment

TPR

Analysis

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

Trap

Not required.
  Before performing an analysis, ensure the sample and analyzer are adequately prepared. See 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 containing the appropriate analysis conditions and report options.
  1. Go to File > New Sample.
  2. Complete the Sample Description window using appropriate values.
  3. Select the Analysis Conditions tab.
  4. Select AutoChem III  in the View conditions for drop-down box.
  5. Insert the following experiment steps. After each step, click OK to close each window to move to the next step.

Experiment Steps:

  • Insert > Experiment
Description Enter a description of the experiment
Type of Analysis Select Temperature Programmed
  • Insert > Instrument Settings
Gas Flow
Carrier/Reference Gas Loop, Injection, or Blend Gas Preparation Gas
Hydrogen-Argon None Helium
50 cm3 STP/min
  cm3 STP/min
50 cm3 STP/min
  Different reference rate
  cm3 STP/min
   
Flow Path
Vapor valve Blend valve Loop valve Analysis valve Trap valve
— Bypass
— Bypass
— Fill
— Prepare
  Bypass
  Vapor
  Blend
  Inject
  Analyze
— Trap
Temperature
Vapor Valves Sample port Sample Rate
Reflux: 20 °C
110 °C
60 °C
    °C
  °C/min
Flask: 20 °C
   
  Return to ambient temperature
— Disable temperature control
— Disable vapor heating
 
 
Detector
  Block temperature 100 °C
  Enable detector    
 
Filament temperature
245 °C
  • Insert > Temperature Ramp
Return to ambient.
  • Insert > Instrument Settings
Gas Flow
Carrier/Reference Gas Loop, Injection, or Blend Gas Preparation Gas
Hydrogen-Argon None None
50 cm3 STP/min
  cm3 STP/min
10 cm3 STP/min
  Different reference rate
  cm3 STP/min
   
Flow Path
Vapor valve Blend valve Loop valve Analysis valve Trap valve
— Bypass
— Bypass
— Fill
  Prepare
  Bypass
  Vapor
  Blend
  Inject
— Analyze
— Trap
Temperature
Vapor Valves Sample port Sample Rate
Reflux: 20 °C
110 °C
110 °C
    °C
  °C/min
Flask: 20 °C
   
— Return to ambient temperature
  Disable temperature control
— Disable vapor heating
 
 
Detector
  Block temperature 100 °C
— Enable detector    
 
Filament temperature
245 °C

  • Insert > Wait

Wait for operator. Add text: Setup trap and close furnace.

  • Insert > Wait

Wait until baseline and temperatures are stable.
  • Insert > Start Recording
One measurement every 1.0 s.
  • Insert > Temperature Ramp
Sample ramp
  • End temperature: 980 0 °C
  • Ramp rate: 10.0 °C/min
  • Hold time: 0.0 min
 

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 Record loop.

  • Insert > Instrument Settings

Gas Flow
Carrier/Reference Gas Loop, Injection, or Blend Gas Preparation Gas
Helium None Helium
10 cm3 STP/min
  cm3 STP/min
10 cm3 STP/min
  Different reference rate
  cm3 STP/min
   
Flow Path
Vapor valve Blend valve Loop valve Analysis valve Trap valve
— Bypass
— Bypass
— Fill
— Prepare
— Bypass
  Vapor
  Blend
  Inject
  Analyze
  Trap
Temperature
Vapor Valves Sample port Sample Rate
Reflux: 20 °C
110 °C
60 °C
    °C
  °C/min
Flask: 20 °C
   
— Return to ambient temperature
  Disable temperature control
— Disable vapor heating
 
 
Detector
  Block temperature 100 °C
Enable detector    
 
Filament temperature
245 °C

  • Insert > Experiment

Description Enter a description of the experiment
Type of Analysis Select Temperature Programmed Oxidation

  • Insert > Instrument Settings

Gas Flow
Carrier/Reference Gas Loop, Injection, or Blend Gas Preparation Gas
Oxygen-Helium None None
50 cm3 STP/min
  cm3 STP/min
  cm3 STP/min
  Different reference rate
  cm3 STP/min
   
Flow Path
Vapor valve Blend valve Loop valve Analysis valve Trap valve
— Bypass
— Bypass
— Fill
  Prepare
— Bypass
  Vapor
  Blend
  Inject
— Analyze
  Trap
Temperature
Vapor Valves Sample port Sample Rate
Reflux: 20 °C
110 °C
60 °C
    °C
  °C/min
Flask: 20 °C
   
— Return to ambient temperature
  Disable temperature control
— Disable vapor heating
 
 
Detector
  Block temperature 100 °C
— Enable detector    
 
Filament temperature
245 °C
  • Insert > Wait
Wait until baseline and temperatures are stable.
  • Insert > Sttart Recording
One measurement every 1.0 s
  • Insert > Temperature Ramp
Sample ramp
  • End temperature: 980 °C
  • Ramp rate: 20.0 °C/min
  • Hold time: 0.0 min
 

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 Record loop.
  • Insert > Instrument Settings
Gas Flow
Carrier/Reference Gas Loop, Injection, or Blend Gas Preparation Gas
Helium None Helium
10 cm3 STP/min
  cm3 STP/min
10 cm3 STP/min
  Different reference rate
  cm3 STP/min
   
Flow Path
Vapor valve Blend valve Loop valve Analysis valve Trap valve
— Bypass
— Bypass
— Fill
  Prepare
— Bypass
  Vapor
  Blend
  Inject
— Analyze
  Trap
Temperature
Vapor Valves Sample port Sample Rate
Reflux: 20 °C
110 °C
60 °C
    °C
  °C/min
Flask: 20 °C
   
— Return to ambient temperature
  Disable temperature control
— Disable vapor heating
 
 
Detector
  Block temperature 100 °C
  Enable detector    
 
Filament temperature
245 °C
  • Termination: Double click Termination step in the experiment list box (or click Termination, then click Edit).
Temperature
Vapor Valves Sample port Sample Rate
Reflux: 20 °C
110 °C
60 °C
    °C
  °C/min
Flask: 20 °C
   
— Return to ambient temperature
  Disable temperature control
— Disable vapor heating
 
 
Detector
  Block temperature 100 °C
  Enable detector    
 
Filament temperature
245 °C
  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 AutoCool. 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
  2. When the displayed sample temperature reaches the ambient temperature, open the furnace. Using gloves, remove the sample tube.
 

Use the cotton gloves provided in the accessory kit when handling heated surfaces. These cotton gloves are not intended to protect hands when heated surfaces are above 60 °C.