Temperature Programmed Desorption Analysis Tutorial

  This topic provides an example of how to perform a Temperature Programmed Desorption analysis using NH3 on calcium oxalate under helium with a 10 °C/min temperature ramp. Make the appropriate modifications for the material being analyzed.

Temperature Programmed Desorption (TPD) analyses determine the quantity, type, and strength of active sites available on the surface of a catalyst from measurement of the amount of gas desorbed at various temperatures.

After the sample has been outgassed, reduced, or otherwise prepared, a steady stream of analysis gas flows over the sample and reacts with the active sites. (Alternatively, Pulse chemisorption can be used to react with active sites.) Programmed desorption begins when the temperature is ramped linearly over time while a constant stream of inert carrier gas passes over the sample.

At a certain temperature, the heat will overcome the activation energy, breaking the bond between the adsorbate and adsorbent. The adsorbed species will then desorb. If different active metals are present, they usually will desorb the reacted species at different temperatures. The desorbed molecules enter the stream of inert carrier gas and are swept to the detector where the detector response is proportional to the gas concentrations. The quantity of desorbed species, combined with the stoichiometry factor, and the temperature at which pre-adsorbed species desorb, yield the quantity and strength of active sites, respectively.

If TPD is performed after coverage of the active sites by flow or pulse chemisorption, additional information about the distribution of active sites and the strength of active sites is collected.

Preparation

  Before performing an analysis, ensure the sample and analyzer are adequately prepared. See Prepare for Analysis.
Pretreatment Degas by flowing inert gas — such as helium, argon, or nitrogen — over the sample while ramping the temperature.
Analysis

Choose a gas mixture from the following table based on the needed results. Flow the gas over the sample, then ramp the temperature beginning at ambient.
Trap Not required
Needed Results Carrier Gas Analysis Gas
Active Metal Surface Area H2 Chemisorption argon hydrogen
Active Metal Surface Area CO Chemisorption helium (or
nitrogen)		 carbon monoxide
Acidity helium ammonia (15% maximum NH3, blended in helium)
  Before performing an analysis, ensure the sample and analyzer have been adequately prepared.

Procedure

These instructions analyze zeolite with ammonia (use 15% maximum NH3 blended in helium) at 3 to 20 ºC/min. Adjust the values in the example to accommodate the analysis you are performing.

  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 Other
  • Insert > Instrument Settings
Gas Flow
Carrier/Reference Gas Loop, Injection, or Blend Gas Preparation Gas
Helium 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 > Temperature Ramp
Sample ramp
  • End temperature: 350 °C
  • Ramp rate: 20 °C/min
  • Hold time: 10 min
  • Insert > Instrument Settings
Gas Flow
Carrier/Reference Gas Loop, Injection, or Blend Gas Preparation Gas
Helium 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
Helium None Ammonia
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 > Wait

Wait 60 minutes.
  • Insert > Instrument Settings
Gas Flow
Carrier/Reference Gas Loop, Injection, or Blend Gas Preparation Gas
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 30 minutes.
  • 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: 500 °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.
  • Insert > Temperature Ramp

Return to ambient.

  Create a new experiment and repeat the steps from the yellow highlighted step (shown previously) to here for each repetition..
  • 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. 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.
 

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.