Effect of in situ N-doping on the microstructure, oxygen vacancies and CO2 capture performance of CaO-based sorbent

Abstract

In this paper, a novel N-doped CaO-based sorbent with porous chain-like characteristics and in situ activation of heteroatoms was developed based on natural limestone, which has proven effective in overcoming the major issue of rapid reactivity loss during calcium looping. Under a hydrothermal environment, N-containing calcium precursor was constructed through the electrostatic interaction between the dissociation product of hydrated lime and the polymerization product of urea, causing in situ introduction of nitrogen in CaO and the formation of chain-like structure. A continuously increasing CO₂ capture performance can be observed for the N-doped CaO-based sorbent and the highest CO₂ uptake capacity (0.723 g-CO₂/g-sorbent) was achieved after 4 cycles. After 15 cycles, the CO₂ uptake capacity can still be maintained at about 0.644 g-CO₂/g-sorbent. This excellent performance can be attributed to the formation of active doping region and the N-doping induced rich oxygen vacancies. In addition, the construction of porous chain-like structure was also prone to obtain a higher specific surface area and a further improvement in the CO₂ absorption efficiency. More importantly, the N element exposed on pore walls can effectively inhibit the fusion and agglomeration of the grains during circulation, thereby improving the cyclic durability of the sorbent. The proposed in-situ N-doped strategy can provide a novel inspiration for the modification of limestone-based CO₂ sorbent addressed for industrial applications.