> An uncoated catalyst works just fine, he said, but only produces methane<p>Given that Putin's about to turn off natural gas to Europe, there's no need to go all the way to gasoline. Being able to produce methane from CO2 would be a pretty useful technology all by itself.<p>Suppose you mix up a batch of catalyst, porosify it somehow, and put it into a vessel ready to accept input CO2 to turn into methane. What do you send into the input? Lab grade 99.97% pure CO2? Smokestack output from some industrial factory? Plain old air pulled straight from the ambient atmosphere?<p>What kind of temperature and pressure does it need to be? You get energy by burning methane to produce CO2, doesn't that mean thermodynamically you have to supply equal energy to reverse the process? Is that energy supplied in the form of heat and pressure, or does it come from somewhere else?<p>Where does the hydrogen come from and where does the oxygen go? Does it need water or steam input too?<p>If we assume input energy is the dominant cost of the system, can we put some economic numbers to it? How much methane per second would be produced by a 1 kW solar panel? How many years of methane production does it take for the methane output to repay the cost of the solar panel?<p>Can we figure out if the catalyst cost is small enough to be negligible? How much catalyst do you need to support a 1 kW solar panel? How much does that much ruthenium cost at current prices? How long would it take methane output to pay for the cost of panel + catalyst?<p>Are the methane and oxygen outputs come out mixed together, or do they form separate streams? If they're mixed together, how do you separate them? How do you make the system safe, considering the potential explosiveness of the mixture of methane and oxygen before they're separated?