Study On Catalytically Active Absorber In Solar CO₂Reforming Of Methane

Solar CO₂reforming of methane has attracted a great attention because thisreaction can realize energy storage of high-temperature heat from concentrated solarradiation and optimal utilization of resources of natural gas. Catalytically activeabsorber has a key role on absorption of solar energy and reforming of methane andbecomes focus of solar reforming of methane research.In the present work, a series of catalytically active absorber,Ru/Al₂O₃/AISI316,Ni/Al₂O₃（MgO）/AISI316,and La₂NiO₄（LaNiO₃）/Al₂O₃/AISI316were firstly fabricated by using AISI316metal foam as the matrix. The crystalstructures, surface properties of the resulting catalytically active absorber werecharacterized by means of XRD, H₂-TPR and CO₂-TPD techniques. Their activities ofthe metal foam based catalytically active absorber were tested in a continuous flowfixed-bed reaction system with a quartz tube reactor.The effects of the coating, catalyst-bed temperature, space velocity and feed ratioon the reactivity behavior of Ru/Al₂O₃/AISI316were systematic investigated. Theresults showed that CH₄conversion and H₂/CO ratio over Ru/Al₂O₃/AISI316foamincreased with a raise of the set temperature. At space velocities in the range of3×104-1.5×105mL/（gcat·h）, the methane reforming of CO₂of Ru/Al₂O₃/AISI316foamat900℃was more than90%, and relatively stable. The H₂/CO ratio decreased withthe increase of the space velocity then tended to stability. The conversion of CH₄increased with the raise of the CO₂/CH₄molar ratio, With the CO₂/CH₄feedratio（molar ratio=2）, the CH₄conversion was close to about100%at800℃. Theconversion of CH₄can be maintained at about75%for an extended period of100h at800℃. From the catalytic activities of AISI316, Ru/AISI316and Ru/Al₂O₃/AISI316,it can be induced that the Al₂O₃coating played a key role on the reactivity of theresulting samples. Compared to Ru/Al₂O₃，the better activity of Ru/Al₂O₃/AISI316depends on the high dispersion of active catalytic component. There were somechanges of components in AISI316foam matrix due to the hightemperature（600-1000℃） and the reactant atmospheres, but the long-term stability ofRu/Al₂O₃/AISI316foam was unaffected.In case of Ni/Al₂O₃（MgO）/AISI316, the activity for methane reforming of CO₂can be improved, particularly above700℃, by adding the promoter MgO into theAl₂O₃coating. By comparing Ni/Al₂O₃, Ni/Al₂O₃/AISI316had more high dispersionof active species NiO due to the introduction of AISI316metal foam to the support..From the peak area of adsorption and desorption behavior, the absorption ability of CO₂on Ni/Al₂O₃/AISI316was lower than that of Ru/Al₂O₃/AISI316When the perovskite-type compound oxides La₂NiO4and LaNiO₃were used asthe active catalytic component, La₂NiO₄/Al₂O₃/AISI316exhibited the higher activitythan LaNiO₃/Al₂O₃/AISI316. Compared to LaNiO₃，La₂NiO₄had the better catalyticactivity because Ni ion in La₂NiO₄can be reduced to smaller Ni0and highly dispersedon the formed La₂O₃Solar chemical reaction thermodynamics was analyzed. The optimum reactiontemperature of the solar high-temperature chemical reaction of the reactor wasobtained. The chemical storage efficiency of CO₂reforming of methane wascalculated using the experimentally measured concentrations of the reaction products.The effects of the solar energy density, catalyst-bed temperature, space velocity andfeed ratio on chemical storage efficiency of AISI316based catalytically activeabsorber were analyzed and summarized.