I've been looking for the same thing, but instead of looking for other ways to cut the NOx fumes I tried looking for ways to make H2O2. I ended up finding some hypothetical means of dealing with nitric fumes. I don't really know if all these qualify as alternate methods, since they all kind of revolve around the H2O2 reaction, but there's some different end products and price points.
Disclaimer: I have no idea what the hell I'm doing. I haven't done any real chemistry since high school and now I've been reading about it for about a week. Do your own homework. All of this is hypothetical, I haven't tried any of it. Some of these reactions are akali base/acid neutralization reactions and are probably very exothermic so don't blow up.
Method 1: Hydrogen Peroxide
Let me say that I don't think you have to add the H2O2 to the reaction, although you can. If you use a retort or condensor and filter the NOx gasses through H2O2 it will convert it to fairly pure, renewed HNO3 dilluted by whatever water is in your H2O2 plus whatever water vapor is condensing off your reaction. 2 NO2 + H2O2 -> 2 HNO3. If you're boiling nitric off AR, or distilling nitric or making new nitric this is very handy as you can't chuck it in the reactor anyway. Also, by not applying heat to the H2O2 because it's not in the reactor, if you're using heated solution, it's probably more stable. (Downside, it won't turbocharge your solution.) I like this because besides supressing nasty NOx fumes, you get to recycle and reuse your nitric acid so I get to be incredibly cheap and stingy. The big downside is, H2O2 costs as much or even more than nitric does - and that's if you buy nitric, instead of making it for 1/5th of the price! Not seeming economical.
At any rate, I mention this because none of these, as I imagine then, are going to be 'in the reactor' methods but all solutions to filter the evaporated nitric or NOx through.
Method 2: Just plain water
4 NO2 + 2 H2O + O2 -> 4HNO3. (Alla Nurdrage's youtube vid on making nitric acid, method #1). No H2O2 but lots of H2O and some O's on the side, kinda like a 'poor man's hydro peroxide'. Filtering the gas through plain aerated water will reconvert some of the nox into fresh nitric, cuts down on the fumes, and it's cheap as you can get, basically free. Downside is, it's not very efficient. You probably won't get all the fumes out and some will still bubble through the water. And the resulting nitric acid will be very dillute. It will probably work a bit more efficiently if you oxygenate the water with a fishtank bubbler or something.
The 2 above are documented on youtube and on the forum. From here on out these are my own cockamamie newb ideas, so...
Method 3: Wash your NOx fumes with soap!
Sodium perborate (online price check yields a 55lb bag for $72.60 and a 6lb bucket for $12.30) dissolved in water. It's chemically very similar to Borax. It's considered a bleaching agent because it produces H2O2 in water (so it's still a H202 reaction), with the remaining boron stuff I would guess probably acting like a soapy sudsing agent.
NaBO3 + H2O = H2O2 + NaBO2
2NO2 + H2O2 -> 2 HNO3 (+NaBO2 swimming around)
The problem here is, now your left with more nitric, but what the heck do you do with very dillute soapy nitric? I have no idea what the heck that sodium metaborate is going to do in the nitric, if it will react to produce more NOx, or if it will screw up any other reactions with the nitric. Maybe you can process it out first before using it, but I don't know how at the moment. So this one is kind of half baked. I suspect there's some cool things you can do with cheap and abundant boric acids and boric soaps if you know more about that stuff but I don't.
The last 2 methods do not recycle more nitric, but are neutralization reactions that produce water and salt. But it seems like a convienent salt.
Method 4: sodium peroxide (online price check: holy crap, forget it. Also DHS will probably arrest you when you try to import it from China). It makes peroxide and lye in water and has the same products as method #5. But while researching it, I did learn you can heat sodium metabisulfite to make your own lye, but I've no idea if that's cost effective and it does produce dangerous sulfur dioxide fumes.
Method 5: miracle stain remover / soda ash
Sodium percarbonate (online price check: 100lbs for $62.96, 10lbs for $17.08; caution: one supplier wants $120.90 for a 50lb bag and tacks on a $35 hazmat shipping charge plus regular shipping). Stuff is marketed as a cleaning agent, a flake form of hydrogen peroxide.
2 (Na2CO3-1.5H2O2) (aq) → 2 Na2CO3 + 3 H2O2
2NO2 + H2O2 -> 2 HNO3
Na2CO3 + 2HNO3 -> 2NaNO3 + CO2 +H2O
The end products are water, carbon dioxide, and sodium nitrate!
NaNO3 + H2SO4 -> Na2SO4 + HNO3
Dehydrate it into a nice, pleasant, stable, solid, neutralized, non-fuming salt and stick it in a jar. Use it for whatever you use sodium nitrate for, including - if you want more nitric acid - adding it to sulfuric and distilling fresh concentrated nitric acid.
Using sodium nitrate to make nitric produces sodium sulfate - AKA Glauber's Miracle Salt - a 17th century laxative, and/or sodium bisulfate, both of which are fairly benign as well.
There are probably a zillion other ways you could process it with aqueous alkaline salts, but I'm really liking the sound of soda ash and I might want to try it, if I can deal with the heat it might produce (it is an acid/base reaction!) It seems like it nails 5 birds with 1 stone - it's cheap as all get out, it will process and eliminate NOx fumes, you can recycle your nitric acid, and you've got a better way to store it than bottling red fuming death in your freezer, and the salt byproducts all seem trashcan chuckable.
AND you've also got pounds of soda ash to neutralize stuff with, if you don't mind peroxide getting in. Multitpurposing means less chemicals to store and run out of and restock and worry about overall.
AND you can also store and use the stable percarbonate to make hydrogen peroxide for other uses, if you don't mind getting sodium carbonate in your peroxide. 7 birds... OK.. maybe not a great oxidizer anymore due to the basic soda ash but possibly wash your clothes with it or something. 6.5 birds. Miracle stain remover indeed.
