A factory smokestack releases carbon dioxide into the air, and nearby stands a unit that captures this gas and, under sunlight, assembles ethylene molecules from it — the feedstock for plastic bags and pipes. Materials scientists have brought this scenario closer by modifying a crystal of the semimetal PdSn4 with a small amount of platinum.
In the original crystal, electrons move at the speed of a good runner—25,000 square centimeters per volt per second. This means charges lose almost no energy along the way. But for a chemical reaction, you need not only fast movement but also the right arrangement of electrons on atoms. The platinum additive redistributed charges among palladium, tin, and platinum atoms, creating sites on the surface where two carbon atoms from carbon dioxide readily bond with each other.
This result is not just a laboratory curiosity. Ethylene is one of the most sought-after products in the chemical industry; it is used to make polyethylene, antifreeze, and many other materials. If we can learn to produce it from carbon dioxide with high precision, then smokestack emissions become a feedstock rather than waste. And for that, we don't need to burn oil, just sunlight and a properly tuned crystal.
Ethylene is a plant hormone. Bananas release it as they ripen, and if you place an unripe fruit nearby, it will ripen faster. Now this same gas has been made from carbon dioxide on a platinum-containing crystal.
In Kim Stanley Robinson's novel 'The Ministry for the Future,' carbon dioxide from the atmosphere is turned into useful things to save the climate — similar to this technology, except there, entire factories work instead of crystals.