Some common carbonless rocket fuels are hydrogen, hydrazine, and aluminum in solid rockets (boosters; ICBMs). That said, they usually have an even larger CO2 f

Some common carbonless rocket fuels are hydrogen, hydrazine, and aluminum in solid rockets (boosters; ICBMs). That said, they usually have an even larger CO2 footprint because processes used to make them take natural gas an an input, or use lots of electricity mostly coming from fossil fuels. The main reasons they're chosen are for their specific impulse (hydrogen) or long-term stability and readiness (solid fuel in ICBMs), rather than their CO2 emissions.