Um, nobody is talking about chemically converting the released carbon dioxide back into chemical compounds with stored chemical energy, like hydrocarbons and graphite. They’re talking about physically sequestering CO2, or binding the carbon into materials that aren’t combustible (like calcium carbonate).
Put another way: if I burned some hydrocarbons in a fireplace and put a balloon over the flue, I’d capture some carbon dioxide (and probably some water) in that balloon, and the carbon in that balloon would’ve cost me less energy to capture than was released in burning the hydrocarbons to begin with. So long as I could keep the balloon from leaking or deflating.