For the first time, researchers have demonstrated that carbon dioxide captured from the air can be directly converted into methanol (CH3OH) using a homogeneous catalyst. The benefits are two-fold: The process removes harmful CO2 from the atmosphere, and the methanol can be used as an alternative fuel to gasoline. http://phys.org/news/2016-01-carbon-dioxide-captured-air-methanol.html
A rather unsatisfactory article from PhysOrg - not for the first time. There is not one word about the thermodynamics of this process, which is fundamental to understanding what role, if any, it can play economically, nor anything about the stoichiometry of the reaction. I have found information about this 0n p.9 of this paper: http://infoscience.epfl.ch/record/32203/files/EPFL_TH1726.pdf The net reaction is CO2 + 3H2 -> CH3OH + H2O, and it is exothermic, the oxidation of the hydrogen providing the energy for the reduction of CO2, if you like. So, in contrast to some other CO2 conversion processes (synthetic photosynthesis, for example, which I think has recently been in the news), there is no need for an external energy input to drive the reaction. The Gibbs free energy at STP is slightly +ve (not surprising when you consider that 4 gas molecules are converted to only 2.), but this can be overcome by resorting to high pressure, to tilt the equilibrium in favour of fewer molecules. But the obvious issue, staring one in the face after reading the article, yet not commented on at all, is that the substance used to regenerate CO2 into fuel is hydrogen. Where would the hydrogen come from? We are back to the old issue about the hydrogen economy, viz. how the hydrogen is generated......which involves energy input.......from somewhere.............. At this point I am not at all clear what benefit this offers. I suppose a liquid fuel is easier to store and handle than high pressure hydrogen, but why would we go to the trouble of producing hydrogen (presumably from renewable or nuclear electricity), just to convert it to methanol, if we could run our transport on batteries etc instead? Perhaps someone more knowledgeable can comment on this.
I believe there is another recent thread on this topic and needless to say, the concept just isn't very compelling. It is at best an energy carrier, not a fuel, since CO2 is a waste product of combustion. It's like turning the ash in your fireplace back into wood and then burning it again. It will always take more -- a lot more - energy to unburn it than you get from burning it.
