Pulse Chemisorption Analysis Tutorial

A Pulse chemisorption analysis determines active surface area, percent metal dispersion, and active particle size by applying measured pulses of reactant gas to the sample, depending upon what technique is used. Pulse chemisorption is performed in the same manner as TPD, except that the sample is dosed with the analysis gas using the injection loop until each active site has reacted. After the active sites have completely reacted, the discretely injected gas volumes emerge unchanged. If TPD is performed after Pulse chemisorption, additional information about the distribution of active sites and the strength of active sites is collected.

The amount chemisorbed is the difference between the total amount of reactant gas injected and the amount that did not react with the active sites of the sample. The size of each pulse is determined by the loop, which is located on an electrically operated valve.

Procedure

  In the following example, Pulse chemisorption is performed on a sample of Pt/Al2O3 with CO. Alter the analysis conditions to accommodate a different analysis.
  Before performing an analysis, ensure the sample and analyzer are adequately prepared. See Prepare for Analysis.
  1. Obtain the sample mass, 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 Pulse
  • Insert > Instrument Settings
Gas Flow
Carrier/Reference Gas Loop, Injection, or Blend Gas Preparation Gas
None None Helium
  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
   
  Disable temperature control
— Disable vapor heating
 
 
Detector
  Block temperature 100 °C
  Enable detector    
 
Filament temperature
245 °C
  • Insert > Wait

Wait 5 minutes.
  • Insert > Instrument Settings
Gas Flow
Carrier/Reference Gas Loop, Injection, or Blend Gas Preparation Gas
None None Hydrogen
  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
   
  Disable temperature control
— Disable vapor heating
 
 
Detector
  Block temperature 100 °C
  Enable detector    
 
Filament temperature
245 °C
  • Insert > Temperature Ramp
Sample ramp
  • End temperature: 400 °C
  • Ramp rate: 10.0 °C/min
  • Hold time: 30 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 vapor heating
 
  Disable temperature control
Detector
  Block temperature 100 °C
  Enable detector    
 
Filament temperature
245 °C
  • Insert > Wait

Wait 30 minutes.
  • Insert > Temperature Ramp
Sample ramp
  • End temperature: 35 °C
  • Ramp rate: 10 °C/min
  • Hold time: 10 min
  • Insert > Instrument Settings
Gas Flow
Carrier/Reference Gas Loop, Injection, or Blend Gas Preparation Gas
Helium CO/He None
50 cm3 STP/min
25 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
  35 °C
5 °C/min
Flask: 20 °C
   
  Return to ambient temperature
— Disable vapor heating
 
  Disable temperature control
Detector
  Block temperature 100 °C
— Enable detector    
 
Filament temperature
245 °C

  • Insert > Wait

Wait 5 minutes.

  • Insert > Wait

Wait until baseline and temperature are stable.

  • Insert > Wait

Wait 5 minutes.

  • Insert > Start Recording

One measurement every 0.1 s
  • Insert > Start Repeat

Repeat until peaks are equal or 20 times.
  • Insert > Dose

Wait for 2 minutes.

 
  • The application automatically inserts a Stop Repeat step when a Start Repeat step is inserted. Ensure that a Dose step is inserted within the Start/Stop Repeat loop.
  • The application automatically inserts a Stop Recording step when a Start Recording step is inserted. Ensure that the Dose 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 vapor heating
 
  Disable temperature control
Detector
  Block temperature 100 °C
  Enable detector    
 
Filament temperature
245 °C

 

  1. Select the Report Options tab and modify 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 Calibration button in the Peak Editor.
  1. Read the cautionary window and make any necessary changes.
  2. 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.

 

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.

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