Characteristics and mechanism of chemical looping ammonia generation by chromium-doped aluminum-based N-carrier
Aluminum-based nitrogen carriers for chemical looping ammonia generation represent a novel technique with promising potential for the efficient production of ammonia and the clean utilization of carbon-based energy sources like coal.However,at the temperatures requisite for nitridation reactions,the aluminum-based nitrogen carriers inevitably transform into α-Al2O3,which possesses lower activity and adversely affects the efficiency of ammonia synthesis.To address this issue,a series of Cr-doped CA-x％(x=0,2.5,5.0,7.5,10.0)nitrogen carrier samples were prepared using the co-precipitation method for the study of their characteristics in chemical looping ammonia synthesis reactions.XRD and XPS analyses confirm that Cr atoms are uniformly doped into the Al2O3 lattice,enhancing its oxy-gen activity.When the five nitrogen carrier samples were tested in nitridation-ammoniation reactions,the CA-5％sample demonstrated superior ammonia synthesis performance,with an ammonia yield approximately 3 times higher than that of the undoped counterpart.The inclusion of Cr also facilitates both nitridation and ammoniation reactions.Utilizing Material Studio software to construct a model for the nit-ridation reaction of the nitrogen carrier,analysis of the computational results reveal that Cr doping significantly reduces the formation of CO during the nitridation process and the energy barrier for the dissociative adsorption of N2.After Cr incorporation,the stability of lattice oxy-gen in Al2O3 decreases,rendering oxygen atoms more prone to dissociate from the surface of the nitrogen carrier and to react with N2 to form aluminum nitride.Finally,repeated nitridation-ammoniation reaction experiments conducted with CA-5％nitrogen carrier affirm the cyclic stability of Cr-doped aluminum-based nitrogen carriers.
chemical looping ammonia generationnitrogen carrierchromium dopingoxygen activityDFT calculationcycle stability
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