Comparative isotope-aided investigation of electrochemical promotion and metal–support interactions 1. 18O2 TPD of electropromoted Pt films deposited on YSZ and of dispersed Pt/YSZ catalysts

Comparative studies between classic and wireless electrochemical promotion of a Pt catalyst for ethylene oxidation

“…It appears that the backspillover of the promoting species onto the catalyst surface creates a double layer that changes the chemisorptive bond strength of the reactants on the catalyst, thereby modifying the catalytic reaction rate. This has been supported by the use of different analytical techniques, such as in situ TPD [7], work function measurements [8], and models exist to predict the behaviour of model systems [9][10][11].…”

Note on “The Electrochemical Promotion of Ethylene Oxidation at a Pt/YSZ Catalyst”

“…[2][3][4][5] This question has been addressed in great detail by numerous older [6][7][8] and more recent [9][10][11][12] papers, which were unfortunately not cited by the authors of ref. [1].…”

“…For example, Figure 1 from ref. [9] shows oxygen temperature-programmed desorption (TPD) spectra obtained from a Pt-catalyst electrode deposited on YSZ and using 18 O 2 for gaseous O 2 adsorption. One observes that the more weakly bonded state b 2 is populated primarily by 18 O oxygen atoms resulting from the adsorption of 18 O 2 from the gas phase while the more strongly bonded state b 3 , which desorbs at 100 K higher temperature, is occupied almost exclusively by 16 Oatoms resulting from the spillover of lattice 16 O from the YSZ support.…”

“…The authors criticized the currently accepted sacrificial promoter two-oxygen-species mechanism of electrochemical promotion [3][4][5] not for failing to explain their data, which is not at all the case as discussed Figure 1. Temperature-programmed desorption (TPD) spectrum of oxygen from an electrochemically promoted Pt/YSZ film, [9] after gaseous 18 O 2 adsorption at 275 8C at P18 O2 = 10 À6 mbar for 45 min (exposure 2 kL) followed by electrochemical 16 O 2À supply for 210 s with a constant current of + 15 mA after which the TPD run starts.[9] Also shown is the catalyst-potential, U WR , variation during the TPD run. Desorption was performed with a linear heating rate, b = 0.5 8C s À1 .…”

“…The existence of the two different states is also evident from the 16 O 18 O desorption peak, resulting from some isotopic scrambling in the catalyst surface, which takes place during the long timescale (~1400 s) of the experiment. [9] This time is much longer than the time (inverse of turnover frequency, TOF) associated with the catalytic process, which is electropromoted and is typically in the 0.1-10 s range. [3,10] Thus, this figure and many others [9,10] leave little room for any reasonable doubts about the validity of the sacrificial promoter, that is, a two-oxygen-species (or states) EPOC mechanism.…”