Two Pathways for Partial Methane Oxidation

There are many ingenious methods people have come up with to carry out partial methane oxidation. For the most part, these methods rely on one of two pathways.

Direct Synthesis:

The first of these is to find clever ways to carry out the exact difficult process I described previously: abstract a single hydrogen, and replace it with a single oxygen atom, then stop the reaction.

Many ingenious methods have been devised to make this process more selective and efficient. One popular route is to use single-atom catalytic sites that are only able to remove single hydrogen before they become saturated. Another is to use specially engineered frameworks (known as zeolites) to act as artificial enzymes. These routes show promise but have their own drawbacks, such as being very difficult to synthesize at scale.

Syngas Pathway:

The second pathway takes place in two steps. While it isn’t as efficient as the first pathway, it requires a lot less precision. First, the methane is oxidized under low-oxygen conditions. This removes all the hydrogen, but rather than resulting in water and carbon dioxide, it produces a mixture of hydrogen and carbon monoxide (or, depending on the specific conditions, a mixture of hydrogen and carbon dioxide). This mixture is commonly referred to as synthetic gas, or “syngas”, for short. In the next step, the two components of syngas are reacted together under different conditions to yield methanol.

While this second pathway is quite promising, it is made significantly more difficult by virtue of the two steps of the reaction occurring under totally different conditions. Whereas the first step only takes place at low pressure and low temperature, the second step takes place at high pressure and high temperature. This also presents an opportunity; because the first step is highly exothermic, and produces more gas than it starts with (the number of moles increases), it should theoretically be possible to use the energy released in the first step to power the second step. The question is how to make this work in practice.

The strategy we’re investigating right now is the construction of “nanoreactors”, tiny spheres of metal oxides filled with even smaller particles of metals known to catalyst different the steps of the syngas pathway. The hope is that by confining methane within these nano-reactors, it may be possible to maintain some of the heat and pressure created in the first reaction step to drive the second step.

There are many techniques we will need to develop to make these reactors, and it is unclear how strong an effect it will be possible to generate. However, even if this goal proves impractical, we also hope to use the controlled conditions of the nanoreactor to study the dynamics of the partial methane oxidation reaction and understand how to build more sinter resistant catalysts.

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