Temperature Programmed Reduction Analysis tutorial

 

 This topic provides an example of how to perform a TPR analysis of copper oxide. Copper Oxide Reference Material can be ordered from Micromeritics . Parts and accessories are located on the Micromeritics web page.

 

 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.
Trap A sorption or 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. See Prepare for Analysis.

Procedure

Peak Editor

Sample Files

  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. Ensure that the zeolite adsorbent has been regularly activated and that it is at room temperature.
  3. If using the optional cold trap instead of the soprtion trap, install it 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 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
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. Insert text: Add sample and setup trap.
  • 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
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 > Start Recording
One measurement every 1.0 s
  • Insert > Temperature Ramp
Sample ramp
  • End temperature: 400 °C
  • Ramp rate: 10 °C/min
  • Hold time: 30 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.
  • 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 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.
  1. 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 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.