Disclosed herein, without limitation, are activated carbon honeycomb catalyst beds and systems for removing mercury and other toxic metals from a process stream, i.e, from flue gas of a coal combustion system. The activated carbon honeycomb can for example remove greater than 90% mercury from flue gas with a simple design and without adding material to the flue gas. Also disclosed herein, and without limitation, are methods for manufacturing and using the disclosed honeycomb catalyst beds and systems.