posted on 2014-07-03, 00:00authored byHe Zhang, Junming Sun, Vanessa
L. Dagle, Barr Halevi, Abhaya K. Datye, Yong Wang
A series
of Pd/ZnO catalysts with different Pd loadings were prepared
using needlelike ZnO crystallites (ZnO-N) with predominant (10–10)
nonpolar facets exposed and commercial ZnO (ZnO-P) without any dominant
facets. The Pd/ZnO catalysts were characterized using complementary
techniques, such as nitrogen physisorption, X-ray diffraction (XRD),
high-resolution transmission electron microscopy (HRTEM), and Fourier
transform infrared spectroscopy analysis of adsorbed CO (CO-FTIR).
The effect of ZnO crystallite faceting on the activity and selectivity
of the Pd/ZnO catalysts was studied in methanol steam reforming (MSR).
It was found that the Pd-rich phases (PdxZny, x > y) are predominantly formed at low Pd loadings on both ZnO
supports
(ZnO-N and ZnO-P), resulting in high CO selectivity. As Pd loading
increases, the x/y ratio in the
PdxZny phases
decreases, leading to decreased CO selectivity. At similar Pd loadings,
Pd/ZnO-P catalysts are more selective in MSR than Pd/ZnO-N, which
is due to more facile formation of the stable PdZnβ phase on polar ZnO (0001) facets than on nonpolar ZnO (10–10)
facets. The current study provides insight into the structure–performance
relationships in Pd/ZnO catalysts for MSR, helping shed light on the
rational design of selective MSR catalysts to minimize CO formation.