Current options for capturing carbon dioxide (CO2) emissions include storing CO2 deep in the earth or converting CO2 into carbonate, a rocky substance like the structure of ocean coral. Drawbacks of storage include fears about geological effects and mass escape of the gas. Conversion to carbonates remains inefficient.
Carbon Dioxide to FuelThose two options, chemically speaking, consist of leaving CO2 unconverted for storage or adding oxygen to produce carbonate. A trickier chemical pathway consists of removing oxygen from the carbon, adding hydrogen instead -- which produces methane (CH4). The methane can be used for fuel, creating a sustainable loop of fuel to CO2 to fuel.
You know there is no such thing as a perpetual motion machine, so you can imagine that the conversion to methane requires energy. A catalyst can reduce the energy requirements -- in this case copper is known to catalyze conversion of carbon dioxide to methane with relatively little energy input. This would already have been embraced as a great solution if it were not for one problem: the copper quickly forms an oxide coating, like the patina which turns red copper roofs a beautiful (and stable) silver-green color.
Gold Solves the Patina ProblemNow scientists at MIT report success creating a hybrid-copper-gold nanoparticle catalyst for converting CO2 to methane. The nanoparticle coating can be applied to the surface of electrodes. It leverages copper's excellent catalytic capacity while the gold prevents formation of oxide layers so the process can continue to operate at low energies.
To make the nanoparticles, researchers started with solutions of gold and copper nanoparticles (the red and green beakers at the back of the image above). Mixing these produces the red-brown solution at the front of the photo, from which the dark powder of hybrid gold-copper nanoparticles is extracted.
The team has proven the effectiveness of as little as one third gold in the mix for promoting the low energy reaction indicative of catalysis without film formation. Although gold is expensive, the electrode coatings can be used for long periods, contributing to a cost effective solution to the carbon dioxide greenhouse gas problem.