Reversible Sulfidation of Pt_0.3Pd_0.7Nanoparticles Investigated by in Situ Time-Resolved XAS

Abstract

In the present study, in situ X-ray absorption spectroscopy (XAS) was used to monitor the structural evolution of isolated Pt 0.3 Pd 0.7 nanoparticles (NPs) subjected to different gaseous atmospheres. Time-resolved XAS measurements were performed at the Pt L 3 edge in the dispersive mode, during which X-ray absorption near edge spectra were sequentially collected. The NPs were initially activated under a reducing atmosphere at 300 °C (H 2 + He) and subsequently exposed to a sulfidation process at the same temperature (H 2 + He + H 2 S at 300 °C). Then, the sulfided NPs were thermally treated under a reducing atmosphere, and the reversibility of the sulfidation process was successfully accomplished, for the first time in these unsupported and well-characterized nanoscale systems. The atomic local order in the vicinity of the Pt atoms was investigated by extended X-ray absorption fine structure spectroscopy throughout all of these thermal treatments, monitoring the chemical stability of the metal−sulfur bonds and allowing kinetic modeling, from which the activation energies for the sulfidation process were estimated.

XDS: a flexible beamline for X-ray diffraction and spectroscopy at the Brazilian synchrotron

“…Novel experimental techniques at LNLS, e.g. X-ray total scattering, X-ray diffraction at high pressures, resonant/non-resonant X-ray emission spectroscopy with high energy resolution and XAS at high energies (above 18 keV) are becoming routine at XDS (Boita et al, 2014;Saleta et al, 2014;Saccone et al, 2015;Hunt et al, 2015).…”

Kinetics and Reversibility of Sulfur Reaction with Pt0.3Cu0.7 Nanoparticles

“…For these measurements, 31 mg of the Pt 0.3 Cu 0.7 nanoparticle powder and 30 mg of Boron Nitride (BN) were mixed and compacted to produce pellets with a diameter of 5 mm that were introduced into a specially designed reactor for DXAS experiments with control of temperature and gas flow. 8 Each sample was submitted to a sequence of activation, sulfidation, and reduction reactions under distinct gaseous environments. The Pt 0.3 Cu 0.7 NPs were monitored at different activation and sulfidation temperatures (250 °C, 300 °C, and 350 °C).…”

“…Once the sulfur-poisoned Pt 0.3 Pd 0.7 NPs (diameter 4.2 ± 0.8 nm) were thermally treated under a reducing atmosphere, the sulfidation process both on the surface and bulk was completely reversed. 8 Those investigations were achieved owing to X-ray absorption spectroscopy (XAS) characterization techniques, which enable in situ studies with temporal resolution and selective monitoring of the investigated element. 10 Multiple scattering effects in the XANES (X-ray absorption near edge spectroscopy) region provide details of the atomic arrangement around the absorber atom, and allow the identification of the chemical environment in its vicinity, for example, by energy displacements from the absorption edge.…”

Pd–M/C (M = Pd, Cu, Pt) Electrocatalysts for Oxygen Reduction Reaction in Alkaline Medium: Correlating the Electronic Structure with Activity

“…So, the partial substitution of Pd for Cu atoms, apart from reducing the cost of the catalysts, strongly influences their catalytic properties. In a series of papers, − we have investigated the reactivity of Pd–Pt NPs during sulfidation and reduction processes, elucidating the compositional and structural effects behind the resistance against sulfur poisoning of these materials in gas phase.…”