Experimental methods in chemical engineering: Temperature‐programmed desorption— TPD

Temperature‐programmed desorption (TPD) characterizes the surface active sites of functional materials, such as adsorbents (metal hydrides, porous carbons, zeolites, metal–organic frameworks, for example) and catalysts. Solids surfaces are pre‐treated to remove moisture, contaminants, and previously adsorbed species, then a probe molecule (, , , ) saturates the surface. After an inert purge, a furnace ramps the temperature and a mass‐spectrometer (MS) or thermal conductivity detector (TCD) monitors the effluent. We deduce the binding energy of the probe molecule, the surface strength, and kinetic mechanism based on the shape and position of the concentration peaks generated by the MS or TCD. The Redhead equation estimates desorption energies for systems with simple kinetics, negligible re‐adsorption, and coverage‐independent activation energy. The Polanyi–Wigner equation is more robust and relates the desorption rate to surface coverage, desorption barrier, desorption order, and temperature. Among the 50 of the 250 scientific disciplines in Web of Science Core Collection physical chemists apply the technique most followed by chemical engineers. The five themes of research are centred on: (1) zeolites, hydrogenation, and methanol; (2) oxidation, nanoparticles, and reduction; (3) adsorption, decomposition, and kinetics; (4) , , and Ni; and (5) catalyst, biodiesel, and transesterification.