inorganic chemistry - What type of chemical reaction is this?

So far we have learned about about single displacement, double displacement, gas evolving, neutralization, synthesis, disassociation, and combustion.

I was trying to solve the following chemical equation and I couldn't figure out under what category this reaction falls.

*Aqueous lithium hydroxide reacts with gaseous carbon dioxide to produce aqueous lithium hydrogen carbonate.

$$\ce{LiOH(aq) + CO2(g) -> LiHCO3(aq)}$$

If this is a synthesis, how can the base combine with $\ce{CO2}$?