I have never tried it but i think 16Gb might not be supported. the supported CF size on 2811 series router is maximum 256 MB.
http://www.cisco.com/c/en/us/td/docs/routers/access/2800/hardware/installation/guide/hw/01_hw.html#wp1037629
Hope this helps.
Regards
Vinit
Thanks
--Vinit