Temperature Programmed Desorption
Temperature programmed desorption (TPD) measures the rate at which adsorbates leave a surface as it is heated at a controlled rate, usually repeated over a range of initial coverages. Analyzing the resulting spectra (by Redhead, leading edge, or complete analysis, or by fitting simulated spectra) yields desorption orders, pre-exponential factors and desorption barriers, which are often reported as adsorption energies when adsorption is non-activated.
DFT-derived coverage-dependent barriers for O2 TPD on Pt(111) (2014)
O2 TPD spectra from Pt(111) measured at 2 K/s were fit by integrating a second-order desorption rate equation in which the desorption barrier’s coverage dependence came from DFT and a cluster expansion, scaled by a Brønsted-Evans-Polanyi relation with only two fitted constants (Miller et al. 2013). A single such function reproduced all spectra (SSE 6.17 x 10-6), whereas linear barriers fit to individual spectra gave a spread of inconsistent results, and the same two constants predicted low-coverage desorption barriers on Ag, Pd, Rh and Ir within the uncertainty of literature TPD estimates. Summary: miller2014.
TPD quantification of isopropanol pathways on Fe/Mo2N and Pt/Mo2N (2024)
TPD of isopropanol on Mo2N films with Fe and Pt overlayers at several coverages was quantified per surface site by referencing peak areas to an H2 desorption peak of known carbon coverage, with mass spectrometer sensitivity factors applied to CO, propylene and acetone. The resulting activities (for example 0.016 ML total on Mo2N versus 0.088 ML on 2.1 ML Pt/Mo2N) and the 146 K downshift of the acetone peak on Pt/Mo2N tracked the conversion and selectivity trends of the corresponding powder catalysts in a flow reactor, showing how UHV TPD can guide supported catalyst design (Porter et al. 2024). Summary: porter2024.