Correlation of Electronic Structure with Catalytic Activity: H-2-D-2 Exchange across CuxPd1-x Composition Space


Gumuslu G. , Kondratyuk P., Boes J. R. , Morreale B., Miller J. B. , Kitchin J. R. , ...More

ACS CATALYSIS, vol.5, no.5, pp.3137-3147, 2015 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 5 Issue: 5
  • Publication Date: 2015
  • Doi Number: 10.1021/cs501586t
  • Title of Journal : ACS CATALYSIS
  • Page Numbers: pp.3137-3147

Abstract

The relationship between alloy catalyst activity and valence band electronic structure has been investigated experimentally across a broad, continuous span of CuxPd1-x composition space. CuxPd1-x composition spread alloy films (CSAFs) were used as catalyst libraries with a 100 channel microreactor to measure the H-2-D-2 exchange kinetics over a temperature range of 333-593 K at 100 discrete CuxPd1-x compositions spanning the range x = 0.30-0.97. The H-2-D-2 exchange activity exhibits a monotonic decrease over the composition range x = 0.30-0.97. A steady state, microkinetic model was used to estimate the energy barriers to dissociative H-2 adsorption, Delta E-ads(double dagger), and recombinative H-2 desorption, Delta E-des(double dagger), as functions of alloy composition, x. Their values fall in the ranges Delta E-ads(double dagger)(x) = 0.15 to 0.45 eV and Delta E-des(double dagger) (x) = 0.55-0.65 eV. Spatially resolved UV photoemission spectra were obtained from the CuxPd1-x CSAF and used to estimate the average energy of the filled states of the valence band as a function of alloy composition, epsilon(v)(x). The energy of the v-band center shifted monotonically from epsilon(v) = -3.3 to -3.9 eV across the composition range x = 0.30-0.97. This monotonic shift and its magnitude were corroborated by DFT calculations. The correlation of Delta E-ads(double dagger)(x) with epsilon(v)(x) across alloy composition space yields Delta E-ads(double dagger)(epsilon(v)) which decreases as the v-band energy shifts toward the Fermi level.