Artículos SCI

Experimental results are reported on the (Ca-looping) multicyclic CO2 capture of CaO and nanosilica/CaO composites derived from Ca(OH)2 and nanosilica/Ca(OH)2 dry mixtures subjected in situ to linear and constant rate thermal analysis (CRTA) preheating programs in either air or air/CO2 atmospheres. By means of CRTA preheating the rates of the reactions taking place during pretreatment are kept at a constant and small value along the entire process. In agreement with a pore skeleton model, previously proposed in the literature for explaining the behavior of natural limestones thermally pretreated, our results suggest that air/CO2-CRTA pretreatment yields a thermally stable hard skeleton of poorly reactive CaO on which a soft skeleton of reactive CaO would be supported. The sorbent subjected to this preheating program exhibits a reactivation in the very first carbonation/calcination cycles, after which CaO conversion decays slowly with the cycle number. In contrast, linearly or air-CRTA preheated sorbents show a significant decrease of CaO conversion within the first cycles. In the latter case, CaO multicyclic conversion fits well to a model where it is assumed that the progressive reduction of surface area as the number of carbonation/calcination cycles is increased obeys to sintering of the preheated sorbent skeleton as it is subjected to repeated calcinations during cycling. In the former case, CaO conversion data conforms to the prediction by a model in which the loss of surface area is mainly due to sintering of a nascent CaO soft skeleton regenerated in the diffusive carbonation phase, which is enhanced by the air/CO2-CRTA pretreatment. As regards the effect of nanosilica, the results indicate that it slows down CaO sintering during pretreatment, which hinders the development of a stable CaO skeleton thus hampering reactivation and stabilization of conversion. On the other hand, as CaO sintering is also lessened during looping calcination, nanosilica is useful to increase the absolute values of CaO conversion.

Bi2WO6 and Bi2WO6–TiO2 (5% molar Ti) nano-heterostructures were synthesized by a hydrothermal method. The properties of the synthesized catalysts were characterized, having high photoactivity for Rhodamine B degradation under sun-like illumination, explained by a synergetic mechanism previously proposed through UV and visible induced processes, in which the photosensitization effect of Rhodamine B is considered. We now report that using Phenol, a molecule which does not lead the photosensitization process, the photoactivity decreased considerably, thus emphasizing how important is the model molecule selected as degradation substrate for evaluating the photoactivity. The photocatalytic properties of the synthesized catalysts have been evaluated by exposing a mixture of Rhodamine B and Phenol in water, to different illumination conditions. It can be confirmed that the photoinduced mechanism via the photosensitization of Rhodamine B is a key factor responsible for the increase on the photocatalytic activity showed by the Bi2WO6–TiO2 compound and that the degradation mechanism of Rhodamine B is not changed by the simultaneous presence of other transparent substrate as Phenol.