5 ms·

Because the inverse reaction is empirically known to be exothermic, I was initially perplexed at how this could even be possible, until I read some of the other

Because the inverse reaction is empirically known to be exothermic, I was initially perplexed at how this could even be possible, until I read some of the other articles about microdroplets. (I’m not sure I understand the paper’s proposed mechanism TBH as it seems to be claiming to be exothermic based on an unshared simulation run). It seems like a bunch of Stanford researchers in this lab are studying the whole hydrogen peroxide microdroplet thing, which is what makes this possible, because peroxide is a reactive specie that’ll make a lot of regularly endothermic reactions exothermic when used instead of water. But why do microdroplets produce peroxide when that is itself endothermic? I found a good explanation of this phenomenon (seems to be a hot topic in the Chemistry world in the past couple years) how it may actually be a reaction between ozone and water in https://pubs.rsc.org/en/content/articlelanding/2022/sc/d1sc06465g https://pubs.rsc.org/en/content/articlelanding/2022/sc/d1sc0... So my takeaway TLDR is, this may actually be a reaction between O3, N2, and H20. Or between H202 and N2. Ozone is not highly concentrated in air and is the limiting reagent (note that this experiment produced very little ammonia). So this seems unscaleable/impractical without producing large quantities of Ozone. I’m an academia-pessimist and it seems like while in the past year a decent amount of research has come out debunking this whole “spontaneous peroxide” thing (it’s still cool, but it’s not a silver bullet and it makes results like these less impactful knowing it’s actually ozone powering the whole thing) the original groups of spontaneous peroxide researchers are pumping out as much microdroplet research as possible before everybody accepts it’s dependent on ozone. The newer papers should at least propose this mechanism in the name of intellectual honesty.

pjc50 3y ago
> So my takeaway TLDR is, this may actually be a reaction between O3, N2, and H20 Could you quantify how that works to produce NH4? I'm having trouble guessing how that adds up without producing NOx instead.
- opportune 3y ago
  Due to some newly discovered and not-yet-explained property of microdroplets (like a very high surface area:mass ratio) they readily react with air to produce peroxide, H2O2. The theory I’m describing, based on experiments testing peroxide formation at varying ozone concentration, is that the water molecules are reacting with the small amounts of ozone commonly present in air. In chemistry, some molecular configurations are very stable and some are very unstable. Unstable things tend to react with other things in such a way that total stability increases; when it happens, energy is released (exothermic). Going from a stable configuration to an unstable one requires either a counterparty that was super unstable and became less so while reacting (still exothermic), or an input of energy (endothermic - basically never happens at equilibrium unless you’re directly applying high heat). However, just because a reaction is more stable at the end than the beginning doesn’t mean it will just occur, because in reality there are several stages the participants need to go through over an imperceptibly small time scale, some of which may actually require an input of energy to reach (activation energy). Ozone is highly unstable but in air at STP, unless it meets another ozone, none of the normal molecules in air will react with it because they’re all super stable already (even N2, idk if the reaction can technically be exothermic but it has super high activation energy if it does) or O2 which couldn’t help it get more stable. It seems like new research suggests ozone can react with water at STP to form peroxide (H202). Water is normally quite stable by itself, but H2O2 isn’t. I don’t think the proposed mechanism in the paper makes sense but my guess is that one catalyst is causing peroxide to decompose into H2 and O2 while releasing energy, as it is wont to do. Then we get the haber process H2+N2 reaction, which is technically exothermic but with very high activation energy. But fortunately the fresh H2 molecule has a lot of energy and the second catalyst helps reduce the requirements further. And 3H2 + N2 = 2NH3 which is ammonia.
- moremetadata 3y ago
  [dead]
duped 3y ago
> So this seems unscaleable/impractical without producing large quantities of Ozone I'm not a chemist but this piqued my interest: isn't it possible to produce large quantities of Ozone directly with electricity?
- opportune 3y ago
  Quick search says 1.2kg/kWh theoretical max: https://www.sciencedirect.com/science/article/abs/pii/S0042207X1830366X https://www.sciencedirect.com/science/article/abs/pii/S00422... Each ozone molecule at 48g/mol I think will map to 2/3 of an ammonia molecule at 17g/mol. So you’d get 0.23kg NH3/kWh. And I found a link saying the actual Haber Bosch energy usage requires 26GJ/ton which is 3.6kWh/kg or 0.27kg NH3/kWh: https://www.sciencedirect.com/topics/engineering/haber-bosch-process https://www.sciencedirect.com/topics/engineering/haber-bosch... Anybody feel free to check my math. Worth noting actual Ozone yields are supposedly much lower than theoretical maxes at around 12% efficiency (which may require cryo temps and pure oxygen under pressure) bringing yield down to 0.03kg NH3/kWh. Doesn’t seem to take lower electricity in practice considering this is only one energy requirement vs the haber Bosch process counting the full energy input, though maybe it’s less capital intensive. I guess Ozone is deceptively hard to make because the little ozone generators we use as disinfectants require very little actual ozone to do their job.
  - duped 3y ago
    The interesting part isn't whether it's more or less energy efficient to me but whether it can be done entirely with renewables.
    - tourmalinetaco 3y ago
      That could be a decent take if not for the fact that “green” energy is incredibly inefficient, and most of the world is anti-nuclear. At the end of the day its not even about how renewable or energy efficient something is, it’s about what’s cheap. And multibillion dollar companies will always go for what’s cheap, regardless of the environmental impact.

pjc50 3y ago

> So my takeaway TLDR is, this may actually be a reaction between O3, N2, and H20 Could you quantify how that works to produce NH4? I'm having trouble guessing how that adds up without producing NOx instead.

opportune 3y ago
Due to some newly discovered and not-yet-explained property of microdroplets (like a very high surface area:mass ratio) they readily react with air to produce peroxide, H2O2. The theory I’m describing, based on experiments testing peroxide formation at varying ozone concentration, is that the water molecules are reacting with the small amounts of ozone commonly present in air. In chemistry, some molecular configurations are very stable and some are very unstable. Unstable things tend to react with other things in such a way that total stability increases; when it happens, energy is released (exothermic). Going from a stable configuration to an unstable one requires either a counterparty that was super unstable and became less so while reacting (still exothermic), or an input of energy (endothermic - basically never happens at equilibrium unless you’re directly applying high heat). However, just because a reaction is more stable at the end than the beginning doesn’t mean it will just occur, because in reality there are several stages the participants need to go through over an imperceptibly small time scale, some of which may actually require an input of energy to reach (activation energy). Ozone is highly unstable but in air at STP, unless it meets another ozone, none of the normal molecules in air will react with it because they’re all super stable already (even N2, idk if the reaction can technically be exothermic but it has super high activation energy if it does) or O2 which couldn’t help it get more stable. It seems like new research suggests ozone can react with water at STP to form peroxide (H202). Water is normally quite stable by itself, but H2O2 isn’t. I don’t think the proposed mechanism in the paper makes sense but my guess is that one catalyst is causing peroxide to decompose into H2 and O2 while releasing energy, as it is wont to do. Then we get the haber process H2+N2 reaction, which is technically exothermic but with very high activation energy. But fortunately the fresh H2 molecule has a lot of energy and the second catalyst helps reduce the requirements further. And 3H2 + N2 = 2NH3 which is ammonia.
moremetadata 3y ago
[dead]

duped 3y ago

> So this seems unscaleable/impractical without producing large quantities of Ozone I'm not a chemist but this piqued my interest: isn't it possible to produce large quantities of Ozone directly with electricity?

opportune 3y ago
Quick search says 1.2kg/kWh theoretical max: https://www.sciencedirect.com/science/article/abs/pii/S0042207X1830366X https://www.sciencedirect.com/science/article/abs/pii/S00422... Each ozone molecule at 48g/mol I think will map to 2/3 of an ammonia molecule at 17g/mol. So you’d get 0.23kg NH3/kWh. And I found a link saying the actual Haber Bosch energy usage requires 26GJ/ton which is 3.6kWh/kg or 0.27kg NH3/kWh: https://www.sciencedirect.com/topics/engineering/haber-bosch-process https://www.sciencedirect.com/topics/engineering/haber-bosch... Anybody feel free to check my math. Worth noting actual Ozone yields are supposedly much lower than theoretical maxes at around 12% efficiency (which may require cryo temps and pure oxygen under pressure) bringing yield down to 0.03kg NH3/kWh. Doesn’t seem to take lower electricity in practice considering this is only one energy requirement vs the haber Bosch process counting the full energy input, though maybe it’s less capital intensive. I guess Ozone is deceptively hard to make because the little ozone generators we use as disinfectants require very little actual ozone to do their job.
- duped 3y ago
  The interesting part isn't whether it's more or less energy efficient to me but whether it can be done entirely with renewables.
  - tourmalinetaco 3y ago
    That could be a decent take if not for the fact that “green” energy is incredibly inefficient, and most of the world is anti-nuclear. At the end of the day its not even about how renewable or energy efficient something is, it’s about what’s cheap. And multibillion dollar companies will always go for what’s cheap, regardless of the environmental impact.