Aircraft tires are inflated with nitrogen for a couple reasons.
First, dry nitrogen gas is used instead of compressed air because compressed air could contain some moisture. At touchdown, the tires can generate enough heat to cause any moisture within the air volume to turn to steam, which would create excessive pressures in the tire.
Second, jet aircraft tires require very high inflation pressures. Much higher than commercial air compressors operate at. So cylinders of industrial dry nitrogen gas compressed to 1500psig or more are used to inflate the tires.