Role of Alcohols(EtOH,MeOH) in nitro reduction used for Metal(Sn,Fe)
LHM...Look at this mechanism that I posted as an answer to an earlier SE Chem question/answer relating to the reduction of nitrobenzene by metals.  



In most reactions that occur on metal surfaces, many of the mechanistic details are not fully understood (see @Martin's comments in the earlier post).  Nonetheless, this mechanistic scheme shows several steps where a proton ($\ce{H+}$) is required.  These proton transfers are necessary to complete the reduction process.  This is why these reactions are typically run in solvents, like ethanol, that have available protons that can be donated in order to complete the reaction...ron