A method comprises receiving a carbon dioxide recycle stream having carbon dioxide and hydrocarbons. The carbon dioxide recycle stream is fed to a catalytic reactor. The hydrocarbons are converted to carbon dioxide in the catalytic reactor by a catalytic reaction without combustion to form a purified carbon dioxide recycle stream. Electrical energy is generated by using heat produced by the catalytic reactor in the conversion. Another method comprises receiving a recycle stream having carbon dioxide, C1-C2 hydrocarbons, and C3+ hydrocarbons. The C3+ hydrocarbons are separated from the carbon dioxide and the C1-C2 hydrocarbons. The carbon dioxide and the C1-C2 hydrocarbons are fed to a catalytic reactor at a pressure greater than about 300 pounds per square inch (psi), and the C1-C2 hydrocarbons are converted to carbon dioxide, water, and heat.