Pyrolysis in nitrogen atmosphere is one choice if you have a tube furnace. You can do it at 400 to 500 oC under N2 gas atmosphere. Of course you have to prepare the sample prior to pyrolysis.
As described above you need to pyrolyse the sample in inert atmosphere to convert it into carbon. further the BET surace area can be increased via controlled oxidation (300-400°C or even lesser depending on material in air ).
you could also try to pyrolyse the material in contrrolled CO2 environment when in at temperature around 800°C would react with CO2 to for CO thus yielding more porous material with High BET surface.
If I converted the dry plant to carbon ander the 350-400C after that activated it by adding calcium chloride or zinc chloride and dry its in 250C ....what do u think is possible?