The aggregation of CuO particles on the 60%CuO/ZrO2 may
have lowered the surface CuO concentration below that in the
bulk. The 30%CuO/ZrO2-CP had a lower surface Cu concentration
than the 30%CuO/ZrO2, suggesting the relative enrichment of
ZrO2 at the surface of this catalyst during the coprecipitation process.