CO Adsorption on Clean and Oxidized Pd(111)

Abstract

The adsorption of CO on clean and oxidized Pd(111) surfaces has been investigated using a combination of high-resolution core level spectroscopy (HRCLS), reflection absorption infrared spectroscopy (RAIRS), and density functional theory (DFT) calculations. The HRCLS and RAIRS measurements reveal that CO adsorbs on Pd(111), Pd 5 O 4 and PdO(101) at 100 ± 10 K and that the CO coverage decreases with increasing oxidation state of Pd for the same CO exposures of 10 Langmuirs. Based on the DFT calculations, the CO layer on clean Pd(111) was found to include molecular adsorption in both hollow and bridge sites, whereas CO occupies a combination of bridge and atop sites on the Pd 5 O 4 and PdO(101) surfaces.

Kinetics of CO oxidation on palladium using microkinetics coupled with reaction route analysis

“…On the other hand, DFT model predictions (Zhang and Hu, 2001), propose a value of 1.6 eV (1 eV = 23.06 kcal/mol) for adsorption of CO on pre-adsorbed O on Pd (111). Similar energy predictions were also obtained from the DFT studies by Martin et al (2014) proposing a range of values from 1.82 eV-1.75 eV for CO adsorption on different adsorption sites on clean Pd (111).The equivalent range of chemisorption energy for CO adsorption has also been reported (Eichler, 2002;Zorn et al, 2011).This chemisorption energy of 34 kcal/mol is in good agreement with the ϭϱ experimental results (Engel and Ertl, 1979;Chou and Vannice, 1987a) and UHV studies (Szanyi et al, 1993;Stara and Matolin, 1994) on clean Pd (111). However, calorimetric studies (Conrad et al, 1974;Peter et al, 2013a) suggest coverage dependent activation energies for CO desorption on Pd (111). Conrad et al (1974) observed a constant value of CO desorption energy till coverage of 0.33 and then decreasing to 20 kcal/mol at higher coverages.…”

Effects of non-local exchange on core level shifts for gas-phase and adsorbed molecules

“…[35][36][37][38] Here, we present experimental and computational results for CO adsorption on PdO(101). We will show that inclusion of Fock exchange enhances the agreement between the calculated and measured CLS.…”

“…This CLS is clearly underestimated in PBE where it is calculated to be ∼1 eV. 35,44,45 Here, we investigate the influence of Fock exchange on the Pd 3d CLS between bulk palladium metal and bulk palladium oxide. As inclusion of both types of atoms in the same computational unit cell is advantageous to obtain accurate CLS, the calculations have been performed with a slab model consisting of commensurable Pd and PdO surfaces.…”

“…35,44 The experiments were performed on oxidized Pd nanoparticles, and oxidized Pd single crystal surfaces. In both cases, the difference between the 3d binding energy in the metal and the oxide was measured to be 1.6 eV.…”

Structure, chemisorption properties and electrocatalysis by Pd3Au overlayers on tungsten carbide – A DFT study

“…In fact, for Pd(111) we found the preference of fcc site with E ads (CO) amounting to À1.52 eV, in excellent agreement with the experimental data (À1.47 to À1.53 eV [49]). Also, the preference of highly coordinated sites on Pd(111) was observed experimentally [50,51]. Theoretical reports for CO adsorption energy fall in the range from about À1.1 to À1.9 eV [51].…”