You may wish to try Fe and NH4Cl in refluxing ethanol/water reaction system instead, this works best for me to reduce nitro groups and the workup is simple. Since you already have Fe (powder form works best), the rest of the reagents should be easily available.

Iron-Ammonium Chloride - A Convenient and Inexpensive Reductant

Krishnamurthy Ramadas & Natarajan Srinivasan

Synthetic communications 1992, 22, 3189

http://www.tandfonline.com/doi/abs/10.1080/00397919208021132?journalCode=lsyc20

For your question, I don't think it will be so easy to see the gas being released unless a substantial amount of formic acid/formate salt is being used, especially the H2 which is most likely going to be adsorped on the catalyst.

Dear Terence,

I have very awful experience with reduction of aromatic nitro groups.With a lot off published procedures I do not successfully reduce nitro group, prcedures give couple product, hard and complicated work up, dirtily reaction and another.... Now, I was used SnCl2, Fe/HCl, Fe/NH4Cl, Fe/HCOONH4, NiCl2/NaBH4 and with a lot off another I did not reduce nitro group.One advise, do not used this system for reduction nitro group.

I am reduce with Pd/H2 with 1 mol% od iodine.

Best,

Nenad

The Fe and NH4Cl in THF and water or as mentioned above Ethanol/water at reflux condition is the best way to reduce nitro group to Amine. Even i tried for the molecule which having two nitro group. Its very simplest way to reduce nitro to amine.

Terence Spencer Crofts

It appears that your catalyst, at least have low activity.

We have in several project needed to perform the Ar-NO2 --> Ar-NH2 transformation, and have experience that "old" Pd/C catalyst frequently was the origin to obstacle successful reduction/hydrogenation of Ar-NO2. In a recent project, we needed access to 2-NH2Ph-Ph, for which we decided to search for and develop an simple nitrogrup reduction protocol. For this purpose we established a protocol that used indium powder as the reduction agent. The method is fast and operates with a variety of substituents present in the substrate. Moreover, it is really simple to obtain a pretty clean crude, you only filter of the inorganic (In) residue.

You can read details in: Tetrahedron Letters 2016, 57, 1224–1226, but here follows the general procedure:

Procedure:

2-Nitrobiphenyl (1 mmol, 0.2 g) was dissolved in EtOH (4 mL) and transferred to a tube reactor. Then, a mixture of NH4Cl (2 mmol, 0.107 g) in H2O (1.2 mL) and indium powder (3 mmol, 0.344 g, 99.99% 100 mesh, use preferably a freshly opened bottle or stored under Ar) were added whereupon a magnetic stirrer bar was transferred to the tube. The tube was then sealed and the reaction mixture was stirred and heated at 120 oC for 3 h. The reaction mixture was cooled to room temperature and diluted with ethyl acetate (30 mL). The resulting mixture was filtered through a pad of celite to remove the catalyst. Another portion (20 mL) of ethyl acetate was used to wash through the filter pad. The resulting transparent organic phase was dried over Na2SO4, filtered and the solvent was removed under reduced pressure

using a rotary evaporator to obtain the target compound.