Near Ambient Pressure XPS Investigation of CO Oxidation Over Pd3Au(100)

Abstract

19The CO oxidation behavior under excess oxygen and near stoichiometric conditions over the surface 20 of Pd3Au(100) has been studied by combining near-ambient pressure X-ray photoelectron 21 spectroscopy and quadrupole mass spectrometry and compared to Pd(100). During heating and 22 cooling cycles, normal hysteresis in the CO2 production, i.e. with the light-off temperature being 23 higher than the extinction temperature, is observed for both surfaces. On both Pd3Au(100) and 24Pd(100) the (√5x√5)R27° surface oxide structure is present during CO2 production under excess 25 oxygen conditions (O2:CO = 10:1), while at near stoichiometric conditions (O2:CO = 1:1) the surfaces 26 are covered with atomic oxygen. Au as alloying element hence induces only minor differences in the 27 observed hysteresis and the active phase compared to pure Pd. Alloying with Au thus yields a 28 different behavior compared to Ag, where reversed hysteresis is observed for CO2 production over 29 Pd75Ag25(100) at similar conditions [Fernandes et al., ACS Catal. (2016)

In situformation of the active sites in Pd–Au bimetallic nanocatalysts for CO oxidation: NAP (near ambient pressure) XPS and MS study

“…Deconvolution of the original spectra was based on literature data where different Pd species were identied under different conditions. 1,7,25,[30][31][32][33][34][35][36] Fig . 4 Au 4f spectra (left) and variation of Au 4f 7/2 binding energy and Au/C atomic ratio (right) with temperature taken for PdAu low sample under the reaction mixture (spectra were measured at 300 eV kinetic energy).…”

“…This journal is © The For example, the Pd 3d 5/2 peaks at binding energies (BE) of $335.0 eV and $335.6 eV were attributed to Pd in AuPd alloy 1,7,25,30 and metallic Pd, 1,30-32 , respectively. There are also some papers [34][35][36] where the Pd 3d 5/2 species with BE of about 336 eV was attributed to the CO-induced components of palladium due to adsorption of CO on bridge or on-top Pd sites. Moreover, Strømsheim et al 35 used a combination of NAP XPS and QMS for investigation of CO oxidation over Pd 3 Au(100) single crystal to show the presence of two different Pd states with similar Pd 3d 5/2 binding energy values (the difference was only 0.2 eV) corresponding to Pd-CO ads species and to oxidized Pd-O species.…”

“…There are also some papers [34][35][36] where the Pd 3d 5/2 species with BE of about 336 eV was attributed to the CO-induced components of palladium due to adsorption of CO on bridge or on-top Pd sites. Moreover, Strømsheim et al 35 used a combination of NAP XPS and QMS for investigation of CO oxidation over Pd 3 Au(100) single crystal to show the presence of two different Pd states with similar Pd 3d 5/2 binding energy values (the difference was only 0.2 eV) corresponding to Pd-CO ads species and to oxidized Pd-O species. Finally, our recent papers 25,37 identied the Pd 3d 5/2 peak at 337.2 eV as small Pd clusters attached to some defective sites on the HOPG surface.…”

“…It should also be noted that the intensity of the Pd 3d 5/2 signal at $336.0 eV revealed aer sample heating up to 200 C cannot be assigned to the Pd-CO state and most probably is due to oxidized Pd-O species. 35 Unfortunately, C 1s and O 1s spectra cannot be applied to prove this assignment due to overlapping of the C 1s signals from CO ads and HOPG, as well as O 1s signal from Pd-O with Pd 4d region. Furthermore, oxygen adsorbed on the HOPG surface will contribute to the total O 1s spectrum.…”

Near-Ambient Pressure XPS and MS Study of CO Oxidation over Model Pd-Au/HOPG Catalysts: The Effect of the Metal Ratio

“…The experimental spectra were analyzed based on reported deconvolution into individual components. The Pd encountered were assigned depending on the specific conditions of their occurrence [18,21,39,[41][42][43][44]. Thus, the Pd3d5/2 component at a BE of 335.5 eV corresponded to metallic palladium [18,21,41,42], while the one at 335.1 eV was attributed to Pd in the PdAu alloy [21,39,43,44].…”