| Reactive sorption enhanced reforming (ReSER) is a new technology for hydrogen production with energy saving and CO2emission reduction. And it is significant for the chemical industry, the refinery industry and future energy economy. So far, the activity of the sorption complex catalyst has reached a high level. However, the stability of the complex catalyst is much insufficient for industrial application. Therefore, how to improve the stability of complex catalyst is a needed problem to solve before its industrial application.In this paper, the La2O3-modified NiO-CaO/Al2O3complex catalyst was prepared by isometric impregnation with lanthanum nitrate, and the sorption complex catalyst used in the ReSER process was tested on the fixed-bed reactor. The reason why La2O3modification improved the stability of the catalyst was analyzed by the characteration of the changes of microstructure, morphology and reduction performance of complex catalyst after the addition of La2O3. Meanwhile the effect of high temperation oscillation loopings to the microscopic structure of the catalysts was studied.The microstructure, morphology and reducibility of the La2O3-modified sorption complex catalyst were characterized by means of BET, TEM, XRD and TPR. And the sorption capacity and sorption stability were measured by TGA. The result showed that the surface area of the catalyst became29.18m2/g after La2O3modification, comparing to the catalyst surface of33.37m2/g without La2O3modification. However, the pore size increased by15%after the modifaction. Moreover, after the La2O3modification, nickel grain size in the complex catalyst decreased from32.4nm into21nm.And the TGA results showed that both the sorption capacity and sorption capacity stability were enhanced.The activity and stability of the catalyst used in the ReSER process was evaluated on a laboratory-scale fixed-bed reactor. The surface area and the Ni grain size of the complex catalyst after reaction were also characteried, as well as the sorption capacity and its stability. Our results showed that modifying the sorption complex catalyst with La2O3improved the carbon space velocity from792h-1to1386h-1and its stability up to30cycles of the ReSER process for hydrogen production, while only seven cycles were obtained without La2O3modification. The characteration result showed the source of the stability improvement that the La2O3in the catalyst functioned to restrain the decrease of the supporter surface area and reduce the sintering of nano-CaCO3, which could limit the decay of the sorption capacity and stability of the catalyst, but also increased the interaction between nickel oxide and the supporter, which improved the stability of the catalyst by increasing the dispersion of nickel grains and inhibited the growth of nickel grain size.During the stability evaluation process, the complex catalysts experienced carbonation-calcination loopings in the high temperature condition. It was of great importance to study the effect of high temperation carbonation-calcination loopings to the microscopic structure of the catalyst and to the stability of the catalyst for hydrogen production.600-800℃and600-700℃high temperature carbonation-calcination loopings were conducted to study the influence to surface area、pore size and Ni grain size. It was found that during the600-700℃high temperature carbonation-calcination loopings, La2O3modification improved the stability of the surface area and the sorption capacity of the catalyst. Because of the La2O3modification, the structural stability of the catalyst enhanced during the600-800℃high temperature carbonation-calcination loopings. As the additon of La2O3promoted the production of calcium aluminate, which made the catalyst dense and stable.To sum up, the paper revealed that although the specific surface area of the fresh sorption complex catalyst after La2O3modification reduced, La2O3modification not only restrained the decrease of the supporter surface area and diminished the sintering caused by the contact of nano CaCO3which could increase the sorption capacity and stability of the complex catalyst during hydrogen production, but also inhibited the production of nickel spinel. And the most important was that it improved the interaction between nickel oxide and the supporter, which increased the dispersion of nickel grains and inhibited the growth of nickel grain size. So the stability of the sorption complex catalyst with La2O3modification improved greatly in ReSER hydrogen production. The result of the study had great significance to the industrial application of the sorption comples catalyst in the ReSER process. |
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