I have not done such works, but I don't think the existence of amorphous activated carbon could affect the 2Theta positions in XRD patterns of Chromium metal or oxide. 

Impurities in activated carbons will only give additional peaks, generally very narrow compared to the pattern of carbon (see Fig. 4 of the attached paper as an example). So you can expect your broad 002 band at the same position as usual.

Many other papers about activated carbons on my RG profile. And more to come.

Alain

Dear Dr. Chang:

Typically, heavy metals does not compose a X-ray diffractogram of a kind of activated-carbon. However, depending on the raw material used in the carbon actived preparation several heavy metal can be present. In this sense, metal and oxide can be detected, again a dependence of raw-materials is stressed. It is possible by speculation to hypothesize the existence of a great number of carbon raw-materials that exhibt both heavy metal and oxides, as an example, the reprocessing of electrodes of some portable and dry-batteries. Recently, I have generate engineered carbon-metal and carbon-oxide material, with potential application at photocatalysis.  See, here, the carbon was produced from partial pyrolise of  a polyesther, here the first find can be noticed, new compounds C-metal are not formed, it seems that a great temperature and/or pressure are necessary, also further inert atmosphere.

The diffraction lines detected, its necessary to know the limit sensibility of the diffractometer, are one of proper compounds. In this sense, metallic Zn was synthesized in situ dispersed in the carbon, all diffraction lines of metallic zinc has been detected. Due difference of molecular weight, in a general way,  the heavy metal has a small number of diffraction lines compatible with its cubic/hexagonal/... symmetry. Thus, its necessary to consult (manual/software) a JCPDS card or equivalent data base. it is important to comment that a very small fraction of metal and/or oxide are possible, that turn the indexation difficult, or if some superimposition of lines occurs. In this case, small amount of interest material, the diffraction lines of minor intensity are absent depending on the detection limit of diffractometer, in fact submerged in the noise, the indexation of phase (metal/or oxide) should procede in a conventional way, that is to find the three most intense diffraction line of the interest compound at the carbon medium, at end the relative intensity being proportional to intensities described in the JCPDS card or equivalent, the presence of compound can be highligthed.