The CoMo or NiMo in front of the H2 plant is a pretty normal hydrotreating catalyst, although usually in extrusions of a fairly large size. The bed needs incoming sulfur and hydrogen in order to function. It can deactivate over time with coke formation or loss of sulfiding.

As you know from the other beds you can get some activity from increasing temperature but it is limited. Also, in a lot of plant designs, its difficult to have much temperature control on this bed.

There is a very good reference book on Syngas plants you might find usefull. It is the "Catalyst Handbook" by Twigg. Its out of print but used copies can be found on the net.

Let's add that the catalyst isn't just Co/Mo or Ni/Mo but their sulphided forms.

Practise:
1- Increase the inlet temperature as long as temperature is less than 400°C, at outlet.
2- replace catalyst(if you cannot regenerate it).You need to have some minimum sulfur to keep the catalyst active for HDS, check with catalyst manufacturer for how much S is needed, usually 2 ppm or so...

By the way how will you chack organic chloride slippage at HDS reactor outlet? you would need special sampling system for it..
Don't you have ZnO beds downstream of HDS reactor?

The Reformer catalyst will get poisoned if Sulfur slips...

we have ZnO bed at the outlet of hydrogenator,in fact we have two Zinc adsorbers and the last one in the series acting as a guard vessel to facilitate the online Zinc oxide changeover.
we have closed sampling system fo taking the sample.what specific sampling are you talking about?
santosh