Chemical looping can be used in a variety of forms to enable the separation of carbon dioxide emissions in a pure form suitable for sequestration or re-use, principally from combustion, reforming or the production of hydrogen. Chemical looping processes are generally second generation or novel technologies that are currently at lower levels of technological readiness than other options such as post combustion capture using amine solvents. A number are at the point where the next stage would be a demonstration plant. These processes use either a metal oxide or calcium carbonate as chemical intermediates since they are able to undergo reversible reactions with oxygen or carbon dioxide respectively. All chemical looping processes for carbon capture are high temperature processes, enabling them to be more energy efficient than low temperature processes such as amine scrubbing. With the exception of calcium looping for post-combustion capture, the capture of carbon dioxide emissions is also an inherent part of the process, rather than an additional step, downstream of the main process.