Location and chemical speciation of Cu in ZSM-5 during the water-gas shift reaction

Dimitriy Vovchok, James Tata, Ivan Orozco, Feng Zhang, Robert M. Palomino, Wenqian Xu, Leah Harper, Sheima J. Khatib, José A. Rodriguez, Sanjaya D. Senanayake

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

Cu/ZSM-5 catalysts were found to exhibit activity for the water-gas shift (WGS) reaction at temperatures over 300 °C. Nominal Cu loadings of 1, 5, and 10% on ZSM-5 were synthesized using the wetness impregnation technique and evaluated for WGS activity; with a clear trend favoring increased Cu loading (10% > 5% > 1%). X-ray diffraction (XRD) confirmed high dispersion of small Cu at low loadings while CuO crystallized at higher loadings. In-situ XRD showed an evolving transformation of CuO → Cu metal, with the appearance of a metallic copper phase at the optimum reaction conditions, particularly at the highest copper loading. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed the ability of the surface to activate H 2 O and adsorb CO, by the presence of HO-Al/Si and transient CO-Cu + surface species in two distinct locations (5 membered rings (2157 cm −1 ) vs channel intersections (2138 cm −1 ) within the ZSM-5 framework, that likely formed during the CuO → Cu transition. The lowest loaded Cu-ZSM-5 (1%) showed only the 5 membered ring occupied Cu + while the higher loadings showed both, with comparable temperature dependent behavior for the channel intersection Cu + . The amounts of Cu + species in each location were observed to be dependent on temperature while the 5-membered ring showed better thermal stability. In-situ ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) was used to further confirm the gradual changes to the chemical state of copper (CuO → Cu 2 O → Cu) under reaction conditions.

Original languageEnglish
Pages (from-to)216-224
Number of pages9
JournalCatalysis Today
Volume323
DOIs
StatePublished - Feb 15 2019

Keywords

  • AP-XPS
  • Copper
  • DRIFTS
  • Water-gas shift
  • XRD
  • Zeolite

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