Clean and Sustainable Methodology

A Resonant Inelastic X-ray Scattering Study
of Pt-Fe Intermetallic Compound Nanoparticles: Effect of Stoichiometry on the
Valance Electronic Structure of Pt

Evan C. Wegener,
Brandon C. Bukowski, Zhenwei Wu, A. Jeremy Kropf, Guanghui Zhang, Jeffrey
Greeley, Jeffrey T. Miller

Alloying
is a synthetic tool commonly employed to tune the electronic structure of
transition-metal nanoparticles and improve their catalytic properties. To
directly measure the valance d-states responsible for the reactivity of these
metals, L-edge valance-to-core resonant inelastic X-ray scattering (RIXS) can
be used. In this work, RIXS measurements were performed on a series of
silica-supported Pt-Fe bimetallic catalysts (nominal Fe:Pt atomic ratios of 0.7, 2.9, and 4.4) to study
the effect of alloy composition on the 5d-states of Pt. From in situ synchrotron X-ray diffraction
and extended X-ray absorption fine structure analysis it was seen that Pt and
Fe formed ordered intermetallic compounds (IMC) and that the phase varied with catalyst
composition. As the Fe:Pt ratio increased first the
Pt₃Fe phase formed, then PtFe, and lastly
PtFe₃. The RIXS measurements on the IMC catalysts revealed that
compared to monometallic nanoparticles the average energies of the unfilled and
filled 5d-states of Pt were shifted higher and lower, respectively. As the
stoichiometry of the IMC phase became more Fe rich, the magnitude of the shifts
increased. Density functional theory (DFT) calculations reproduced the
directionality of the experimentally observed shifts and provided additional
insight via the projected Pt 5d density of states and calculated carbon
monoxide binding energies. The presented results demonstrate the utility of
RIXS in measuring changes to the valance electronic structure of metals, which
are relevant for catalysis, and the ability to connect experiments to
theoretical calculations.