Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!rutgers!aramis.rutgers.edu!athos.rutgers.edu!nanotech From: rjenkins@oracle.com (Robert Jenkins) Newsgroups: sci.nanotech Subject: One-Way Catalysts Message-ID: Date: 17 Jul 90 02:15:41 GMT Sender: nanotech@athos.rutgers.edu Organization: Oracle Corp., Belmont CA Lines: 78 Approved: nanotech@aramis.rutgers.edu One-way catalysts are (would be) a lazy form of Maxwell's Demon. They could trap energy from random thermal vibrations and store it in chemical bonds, which could later be burned or used to do useful work. It may be possible to produce them with today's technology, although designing them is tricky. If A <=> B is a chemical reaction where, at equilibrium, there is 1 part A to 100 B (1A:100B), then the reaction A => B occurs 100 times as often as B => A. B => A still occurs, just not that often. Often the dominant reaction releases heat. The dominant reaction is always said to increase entropy. Catalysts are not supposed to change the equilibria of reactions. If 1A:100B is the equilibrium without a catalyst, then 1A:100B is the equilibrium with a catalyst. The catalyst may speed up A=>B and B=>A one millionfold, but it will speed them up proportionately. (Note: could someone confirm this with actual measurements for reactions with equilibria between 1:1 and 1:100? I suspect that even known catalysts change equilibria, probably turning 1:2 into 1:5, or the like.) A one-way catalyst is a catalyst that *does* change the equilibria of the reactions it encourages. If 1A:100B is an equilibria, a one-way catalyst which encourages A=>B (but not B=>A) may not be too useful, but one that encourages B=>A (but not A=>B) would be useful, especially if B=>A absorbs heat. (If you could do CO2+2H2O => CH4+2O2, you could cool the fridge and air conditioner without supplying energy, and you could use the CH4 to run the stove. That reaction may be too extreme to run at a useful rate at room temperature, though.) There are lots of possible designs for one-way catalysts. One is to have an active site which only exists (or is only enabled) when it is filled with reactants. That would imply the product of the reaction can't bump into the active site (because it is only active when it is already clogged with reactants), so the catalyst can't encourage the reverse of the reaction. A C-shaped catalyst could have an active site which is formed when the tips touch. The molecule naturally rests with the tips separated. When reactants bind to the tips, though, that would have to alter the catalyst enough for its new natural shape to have the tips touching. Once the tips are touching (they are already clogged with reactants), you wait until random thermal agitation provides enough energy to run the catalyzed reaction. The reaction may immediately reverse itself (more than likely), in which case you gained and lost nothing. Or the reaction could only form the product (1 in 100 chance, using A and B), in which case the energy required to form the new bonds was drawn from heat. The catalyst would no longer be bound to the reactants (it might be bound to the product), so the catalyst's tips will separate again, removing the active site. (As I said, tricky to design.) Another approach is to have a { shaped molecule, reactants bind to the outside causing it to change to }. Another approach is to have electric potentials shift around and determine when the active site is enabled or not. Another approach would be a system that winds up and fires, like striking a match. It may even be useful to use energy to reconfigure the catalyst, providing that more energy is trapped by converting the reactants to a product. There are lots of approaches; there are probably better ones I haven't even imagined. - Bob Jenkins RJENKINS@oracle.oracle.com PS. I am not a chemist; please discuss and criticize my ideas, but not my presentation of them. PS. The second law of thermodynamics is not axiomatic; it is derived from other laws of physics and chemistry. One of those laws is that nothing can change the equilibria of reactions. So don't resort to entropy; argue with charge, momentum, and the other axioms of physics, from which the concept of entropy can be derived. Disclaimer -- These thoughts and opinions are entirely my own. [I'm not a chemist either, but I don't see why a catalyst shouldn't be one-way. A simple static shape could have binding sites for two reagents which formed a product which didn't fit the sites. This would involve an expression of energy in the reaction, however, and furthermore adding or removing either the reagents or products from solution with the catalyst would also affect the entropy, so I see no reason for this to affect the second law. I believe the second law is essentially statistical, and is a fairly direct mathematical consequence of the definitions of the various quantities and the time-reversible nature of the underlying physics. --JoSH]