Why is Area under Desorption Curve (TPD) the total particles desorbed?

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SUMMARY

The area under the Temperature Programmed Desorption (TPD) curve represents the total number of particles desorbed, as the desorption rate is plotted against temperature, which correlates with time. The integration of the curve, despite its units appearing as molecules/cm/sec/degC, reflects the variable desorption rate at each temperature, emphasizing that the time spent at each temperature step influences the total desorption. Understanding this relationship clarifies the integration results and the significance of the TPD graph.

PREREQUISITES
  • Temperature Programmed Desorption (TPD) fundamentals
  • Graph interpretation skills in scientific contexts
  • Basic calculus for understanding integration
  • Knowledge of desorption kinetics
NEXT STEPS
  • Research the mathematical principles of integration in physical chemistry
  • Explore advanced TPD techniques and their applications
  • Learn about the impact of adsorptive choice on desorption results
  • Investigate time-dependent desorption kinetics in various materials
USEFUL FOR

Chemists, materials scientists, and researchers involved in surface science and adsorption studies will benefit from this discussion, particularly those focused on interpreting TPD data and optimizing desorption experiments.

nyxynyx
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I'm currently reading about Temperature Programmed Desorption (TPD) and is wondering why in the graph of desorption rate (molecules/cm2/sec) against temperature (deg C), the area under the curve is the total number of particles desorbed? Isnt the units (molecules/cm/sec/degC) if u integrate the curve?
 
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I think you’ll find it’s because although it is plotted against temperature, the temperature is really a factor of time. The desorption rate isn’t constant at each temperature, and the curve is dependent on the time spent at each previous temperature step.

So if you think of the graph as desorption rate against time (s) instead, then it become clear why the integration result isn’t what you expect.

I hope that helps. Also, here is an article on choice of adsorptive which you may find interesting:
http://www.quantachrome.co.uk/en/Adsorptives_for_Physisorption_Experiments.asp
 

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