Preparation Of Calcium-based Core-shell Structured Bifunctional Catalysts For Steam Methane Reforming And Sorbents For CO₂ Capture

Sorption-enhanced steam methane reforming(SESMR)is a promising technology for H2 production,which has advantages such as simplified process,improved thermal efficiency and increased CH4 conversion and H2 purity.This technology can be further enhanced at the particle scale by using core(sorbent)-shell(catalyst)structured bifunctional catalysts.In this work,three core-shell structured CaO-Ca9AL6O18@Ca5Al6O14/Ni bifunctional catalysts with varying CaO content and core/shell mass ratio were prepared by a two-step sol-gel method,and two others(Ni/CaO and CaO@Ca5Al6O14/Ni)served as references.The structural properties and catalytic performance of the catalysts were investigated.The results showed that all core-shell catalysts during cyclic SESMR operation had much better performance than Ni/CaO with regards to activity,stability and CaO utilization.The excellent performance of CaO-Ca9Al6O18@Ca5Al6O14/Ni was mainly due to the stabilization effect of Ca9Al6O18 and the support effect of Ca5Al6O14.The best catalyst was CaO-Ca9Al6O18@Ca5Al6O14/Ni with CaO content of 13 wt%and core/shell mass ratio of 0.2,showing high activity and stability over 60 SESMR cycles while maintaining nearly complete utilization of CaO.Then,the core-shell structured CaO-based sorbents were prepared,and the effects of preparation method,CaO content and operating conditions on the sorbent performance were studied.The results showed that the sorbents prepared by two-step sol-gel method had better performance than the sorbents by other methods.Among all the synthetic core-shell sorbents,the sorbent with a CaO content of 26.1 wt%had the best cyclic stability.Furthermore,although the capture capacity and stability of sorbent under severe regeneration condition were decreased,the stability of core-shell structured sorbents was still better than that of the homogeneous one during multiple sorption-regenation cycles.Finally,a preliminary study was conducted to evaluate the CO2 capture performance of another CaO-based sorbent containg CaO,Al2O3 and MgO,and the results demonstrated that the stability of this sorbent remains to be improved compared with that of sorbent only containg CaO and Al2O3.