1Fully automatic chemical adsorption instrumentCore functions and experimental methods
The fully automatic chemical adsorption instrument achieves precise characterization of catalyst active sites through integrated technologies such as pulse chemical adsorption, temperature programmed desorption (TPD), temperature programmed reduction (TPR), and temperature programmed oxidation (TPO)
Pulse chemical adsorption
Principle: Inject adsorbent gas (such as H ₂ CO)， Calculate the number of active sites based on the amount of unadsorbed gas.
Application:
H ₂ pulse measurement of dispersion of metal active components (such as supported catalysts).
CO pulse distinguishes the valence state differences of transition metals (such as Ni ² ⁺ and Ni ⁰).
Operation points:
The stable pulse peak (no longer changing) is considered saturated adsorption.
The injection volume needs to be adjusted according to the specific surface area of the sample (e.g. BET 200 m ²/g sample volume is about 0.2 g).
Temperature programmed desorption (TPD)
Principle: After low-temperature adsorption, the adsorbate undergoes programmed temperature desorption, and the intensity distribution of active sites is analyzed through desorption peaks.
Application:
NH ∝ - TPD distinguishes the strength of acidic sites (strong acid, medium acid, weak acid).
CO ₂ - TPD analysis of the total alkali content and alkali strength distribution of alkaline molecular sieves.
Operation points:
Pre treatment: Blow at 400 ℃ for 1 hour with inert gas (such as Ar) at 30 mL/min.
Adsorption: Inject NH ∝/CO ₂ to saturation and purge with helium gas at 100 ℃ for 2 hours.
Desorption: Rise from 10 ℃/min to 600 ℃ (NH ∝ - TPD) or 900 ℃ (CO ₂ - TPD).
Temperature programmed reduction (TPR)
Principle: Reductive gases (such as H ₂) are heated to reduce metal oxides, and the interaction between the metal and the carrier is analyzed through the reduction peak.
Application:
Determine the influence of additives in multi metal catalysts on the metal support interaction.
Compare the reduction properties of fresh and regenerated catalysts and infer the reasons for deactivation.
Operation points:
Pre treatment: Blow at 400 ℃ for 1 hour under Ar atmosphere, cool to 100 ℃.
Reduction: 10% H ₂ - Ar mixture, raised to 800 ℃ at 10 ℃/min.
Programmed Temperature Oxidation (TPO)
Principle: Analyze the carbon type and quantity on the surface area of the catalyst through oxidation peak analysis.
Application:
Determine the amount, intensity, and regeneration process of carbon deposition.
Study the mechanism of carbon deposition and the pathways to resist carbon deposition.
Operation points:
Pre treatment: Raise the He atmosphere to 150 ℃ and blow for 0.5 hours, then lower it to 50 ℃.
Oxidation: 5% O ₂/He mixture, rising from 10 ℃/min to 900 ℃.
2、 Operation process and precautions
Power on and preparation
Gas path inspection: Ensure that the flow rate of the carrier gas (such as Ar, He) is stable and the connection is correct.
Software settings:
Unlock the main program (enter password such as demo or altamira).
Check that the gas at the port is consistent with the actual connection.
Pipeline leak detection:
Set Ar gas 25cc and pass the gas path through a U-shaped tube using a three-way valve and a six way valve.
Leak check at the top of the U-shaped tube and the fastening point of the thermocouple.
Sample installation
Weigh the sample:
The air traffic control quality record is m1, and after adding the sample, record m2. The sample size is 0.05-0.1g.
Install sample tube:
Install fixed jackets, card sleeves, and O-rings at both ends of the thickness.
Align the card slot vertically, tighten the card sleeve, and close the furnace door.
Experimental parameter settings
Temperature program:
Adsorption: Maintain a constant temperature of 60 ℃ for 2 hours.
Blowing: Maintain a constant temperature of 100 ℃ for 1 hour.
Desorption/Reduction: 100 ℃ to 700 ℃ (10 ℃/min).
Gas flow rate:
Carrier gas: 30 mL/min (such as Ar).
Reaction gas: 10% H ₂ - Ar mixture, 30 mL/min.
Experimental execution and monitoring
Automatic operation:
Select the testing method and set the data save path.
Enter the sample quality and click Immediate Start.
Real time monitoring:
Observe whether the desorption peak or reduction peak meets expectations.
If any abnormalities occur (such as pressure fluctuations), immediately stop the machine for inspection.
Experiment completion and cleaning
Shutdown steps:
After the peak plot is completed and the baseline is stable, turn off TCD.
Turn off the host power, operating software, and gas.
Sample tube cleaning:
Remove the U-shaped tube and rinse it clean with purified water or ethanol.
Data saving:
Export data as. tp (dedicated data file) or. txt (text format).
3、 Data Analysis and Interpretation
TPD/TPO data analysis
Analysis of desorption peak:
Peak temperature: characterizes the strength of acid/base centers (the higher the temperature, the greater the strength).
Peak area: represents the number of acid/base sites (the larger the area, the more there are).
Example:
In NH ∝ - TPD, two desorption peaks represent two types of acidic centers.
In TPO, different temperature peaks represent the types of carbon deposits (such as hard carbon and soft carbon).
TPR data analysis
Restoration peak analysis:
Number of peaks: the number of reduction centers (such as double peaks representing two oxidation states of metals).
Curve area: Hydrogen consumption (reflecting the difficulty of metal oxide reduction).
Example:
In supported catalysts, the addition of additives causes a shift in the reduction peak temperature, indicating an enhanced interaction.
Pulse adsorption data analysis
Dispersion calculation:
Calculate the exposure ratio of metal active components based on the H ₂ pulse adsorption capacity.
Example:
The dispersion of Ni based catalyst was determined by H ₂ pulse measurement, and the results were consistent with TEM characterization.
4、 Common Problems and Solutions
Baseline instability
Reason: Fluctuations in carrier gas flow rate and TCD contamination.
Solution: Check the sealing of the air circuit, clean or replace the TCD.
Abnormal desorption peak
Reason: Incomplete sample pretreatment and insufficient injection of adsorbate.
Solution: Extend the preprocessing time and increase the number of pulses.
Poor data repeatability
Reason: Uneven sample size and low temperature control accuracy.
Solution: Ensure that the sample is crushed to below 200 mesh and calibrate the temperature sensor.