Synthesis of highly effective stabilized-CaO sorbents via a sacrificial N-doped carbon nanosheet template

Calcium looping, a promising high-temperature CO2 capture technique, offers a midterm economic solution to mitigate anthropogenic CO2 emissions. The main challenge for calcium looping is the synthesis of highly efficient CaO-based sorbents that can be used over many reaction cycles. Here, a sacrificial N-doped carbon nanosheet template was developed which produces MgO-stabilized, CaO sorbents with fast adsorption rates, high capacities and remarkable long term performance over many cycles. The characterization results show that such a template was formed through in situ pyrolysis of an organic acid and nitrates in a simple heating process under nitrogen. The presence of a carbonaceous template prevented crystallite growth, featured highly macroporous nanosheet (~60 nm thick) morphologies, ensured homogeneously mixing of Ca and Mg, which is essential to attain minimal diffusion limitations, mitigated sintering, and produced structural stabilization. Thus, 10 mol% MgO acting as an inert stabilizer was sufficient to achieve a CO2 uptake of 0.65 g/g (corresponding to a capacity retention of 89.9%) after 10 cycles in realistic conditions, as confirmed by TGA analyses. This N-doped carbon template can be applied generally to form a wide range of porous and nanostructured stabilized-CaO sorbents with stable CO2 uptakes.