Reduction by Activated Carbon
The only case I know of where activated carbon causes reduction at room temperature would be filtration of ozone, $\ce{O3}$. Even fluorine will not oxidize plain carbon:

Carbon is stable in a fluorine atmosphere up to about $\pu{400 ^\circ C}$ .

Oh, well perhaps dioxygen difluoride, $\ce{FOOF}$, could also oxidize carbon (or could be reduced by carbon, should you prefer a passive voice). Read Derek Lowe's Things I Won’t Work With: Dioxygen Difluoride, if you'd care to test that. Please let me know so that I could arrange to  be elsewhere.