The machine would be powered by electricity, otherwise what would be the point and the machine would essentially suck in all the greenhouse gasses there are and pump out safe gases into the atmosphere or into storage containers ready for practical use. Similar to how plant photosynthesis works.
As you can see from the diagram above, the bad gases mean the greenhouse gases (Methane, Carbon Dioxide, Carbon Monoxide) and other various harmful gases will go in here and then they will be converted and released into good gas like Oxygen. Although I am no scientist, I think it's a viable plan to slowly eradicate greenhouse gases from this planet.
Example:
If we want to cover carbon dioxide into oxygen, we can put some plants in the container itself and see them convert it to oxygen, of course we have to control the level of input, because we cannot put all the carbon dioxide in the container, we need to see how much the planets can handle. We will also need to understand the optimal conditions to put them, such as how much water or sunlight they should be receiving and in what conditions are we to place the plants.