Systems and methods of reducing refinery carbon dioxide emissions by improving the overall synthesis gas yield in a fluid catalytic cracking unit having a reactor and a regenerator are discussed. In one example, a method comprises introducing spent catalyst and a feed gas comprising oxygen to the regenerator at gasification conditions. The method further comprises heating the spent catalyst to burn coke therefrom to produce a synthesis gas. The method further comprises combining the synthesis gas with a dry gas comprising hydrogen, creating the overall synthesis gas and thereby increasing the yield of the overall synthesis gas produced in the FCC unit.