[Apolo]

Hi to everybody

There are some classification or groups of "Reducing Agents"?
For example: Solids, metals, gas.

I understand perfectly his function, but exist a classification?

Actually i work with nanoparticles (by sol-gel) of Fe and the reducing agent is "Ethylene Glycol" but some people (chemistry students) say that a "gas" like Hydrogen can be used to reduce the nanoparticles.

please help me

[Hunter2]

There is no classification. Some substances can work as a reducer, some work as a oxidiser. both is combinde in redox reaction. Your friends are right, hydrogen is a good reducer, because it likes to go to water.
The  ethylenglycole is a week reducer it will be oxidised with some steps between to oxalatic acid or even to carbondioxide.