> There are things that will react with CO2 and form something that isn't combustible. Sure. There are plenty of such things. For example, elemental magnesium

> There are things that will react with CO2 and form something that isn't combustible. Sure. There are plenty of such things. For example, elemental magnesium will happily bind carbon dioxide into pretty inert magnesium carbonate. But to _get_ that elemental magnesium, you need to expend energy, because elemental magnesium can't be found in nature. There is only one realistic option: rock weathering. Silicate rocks can react with carbon dioxide to produce calcium carbonate and (eventually) silicon dioxide.