As petroleum-related products dominate
the global fuel market,
acid gas resistant materials are in demand. ZnO is one of the widely
used materials as SO2 sorbent and catalyst/catalyst support.
To understand the surface structure sensitivity in interaction with
SO2, morphology controlled ZnO wire and plate with nonpolar/polar
facets have been investigated as model materials in this work. Morphology
and crystal structure of nano- to micro-sized ZnO wire and plate were
confirmed by SEM, XRD, and Raman characterizations. SO2 interactions with the ZnO plate (dominated by polar facet {0001})
and ZnO wire (dominated by nonpolar facet {101̅0}) were investigated
by in situ IR coupled with temperature-programmed
desorption (TPD) as well as XPS. SO2 interaction with ZnO
resulted in more sulfate species on the wire than on the plate while
some sulfates and sulfites still remained on both surfaces after heating
to 350 °C. TPD showed higher SO2 desorption capacity
on the ZnO plate surface at a lower temperature than on the nonpolar
wire surface, indicating a stronger interaction between SO2 and the nonpolar surface of ZnO. Acid–base properties probed
by adsorption microcalorimetry and reducibility of ZnO probed by H2-TPR were analyzed to understand the difference in SO2 behavior on different ZnO surfaces. The similar reducibilities
of the two ZnO surfaces from H2-TPR indicate that the SO2–ZnO interaction is more related to the surface structure
and acid–base property of ZnO, supported by the higher density
of both acid and base sites probed by NH3 and CO2 on the ZnO wire than on the plate. The results from this work suggest
that polar surface of ZnO can be the preferred facet when engineering
ZnO-based materials with enhanced SO2-resistance.