A new kind of Ca-based regenerable CO2 absorbent, CaO/ Ca12Al14O33, was synthesized on the basis of the integration of CaO, as solid reactant, with a composite metal oxide Ca12Al14O33, as a binder, for applying it to repeated calcination/carbonation cycles. The carbonation reaction can be applied in many industrial processes, and it is important for practical calcination/carbonation processes to have absorbents with high performance. The cyclic carbonation reactivity of the new absorbent was investigated by TGA (thermogravimetric analysis). The effects of the ratio of active material to binder in the new absorbent, the mechanics for preparation, and the reaction process of the high-reactivity CaO/Ca12Al14O33 absorbent have been analyzed. The results obtained here indicate that the new absorbent, CaO/Ca12Al14O33, has a significantly improved CO2 absorption capacity and cyclic reaction stability compared with other Ca-based CO2 absorbents. These results suggest that this new absorbent is promising in the application of calcination/carbonation reactions.

The cyclic CO2 capture, transient phases change, and microstructure appearance of a new kind of Ca-based regenerable CO2 sorbent, CaO/Ca12Al14O33, obtained by the integration of CaO as solid reactant with a composite metal oxide of Ca12Al14O33 as a binder, were investigated by thermogravimetric analysis, XRD, and SEM at different preparation calcination temperatures. When the calcination temperature in the preparation stage is higher than 1000 °C, the cyclic CO2 capture of this new sorbent declines. The lowered CO2 capture may mainly be attributed to the formation of Ca3Al2O6, which decreases the ratio of CaO to binder in sorbent, and the severe sintering of sorbent occurs when calcined at such high temperatures in the preparation processes. These results suggest that the calcination temperature for this new sorbent should not be higher than 1000 °C in order to obtain its high reactivity. The performance of the new sorbent over 50 cycles was evaluated under mild and severe regeneration conditions, respectively. CaO/Ca12Al14O33 attained 41 wt % CO2 capture after 50 carbonation−calcination cycles under mild calcination conditions (850 °C, 100% N2), and the results obtained here indicate that the new sorbent, CaO/Ca12Al14O33, has significantly improved CO2 capture and cyclic reaction stability over multiple carbonation−calcination cycles compared with limestone and dolomite under mild calcination conditions. When more severe calcination conditions (980 °C, 100% CO2) were used, the capture of CaO/Ca12Al14O33 decreased from 52 wt % in the first cycle to about 22 wt % in the 56th cycle; however, the capture of CaO/Ca12Al14O33 sorbent over 56 cycles is still higher than that of dolomite and limestone under the same severe calcination conditions.

We find theoretically a new quantum state of matter-the valley-polarized quantum anomalous Hall state in silicene. In the presence of Rashba spin-orbit coupling and an exchange field, silicene hosts a quantum anomalous Hall state with Chern number C=2. We show that through tuning the Rashba spin-orbit coupling, a topological phase transition results in a valley-polarized quantum anomalous Hall state, i.e., a quantum state that exhibits the electronic properties of both the quantum valley Hall state (valley Chern number Cv=3) and quantum anomalous Hall state with C=-1. This finding provides a platform for designing dissipationless valleytronics in a more robust manner.

A new kind of ilmenite oxygen carrier was prepared by impregnating the raw ilmenite particles with K 2 CO 3 , Na 2 CO 3 , or Ca(NO 3 ) 2 . The cyclic reduction reactivity of the new oxygen carrier was investigated in a fluidized bed reactor. It has been found that the addition of foreign ions can significantly promote the reduction reactivity of ilmenite. The effect of foreign ions on enhancing the reduction reactivity of ilmenite is in the sequence of K + > Na + > Ca 2+ . The effect of the loading amount of K + on increasing the ilmenite reactivity is in the sequence of 15 wt % K + > 10 wt % K + > 5 wt % K + . The reduction reactivity of the ilmenite impregnated with 15 wt % K + can be improved ∼8 times faster than that of the activated raw ilmenite. This reactivity reaches up to the same level of the synthetic Ni-based carrier. The modified ilmenite obtains a porous structure caused by the migration of K or Na ions. One possible explanation for the reactivity enhancement of ilmenite with the addition of foreign ions, especially K + and Na + , is the migration of K + or Na + . Another explanation may be the active principle of the alkali-rich phase formed between the foreign ions and titanium iron oxides, that is, K 1.46 Ti 7.2 Fe 0.8 O 16 or Na 2 Fe 2 Ti 6 O 16 . This study proves that the reduction reactivity of the natural ilmenite can be promoted significantly by impregnating ilmenite with K + .

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