Catalytic performance of CoAlZn and NiAlZn mixed oxides in hydrogen production by bio-ethanol partial oxidation

摘要

CoAlZn and NiAlZn mixed oxides were prepared by sol-gel method and tested in partial oxidation of bio-ethanol (POE). At lower temperatures, CoAlZn showed higher ethanol conversion and higher selectivity to H_2 and CO than NiAlZn. At higher temperatures, ethanol conversion on both catalysts reached 100%, while selectivity (S) to H_2 and CO became higher on NiAlZn. At 750 ℃, NiAlZn showed S(H_2) of 95%, S(CO) of 90%, while for CoAlZn these values were 90% and 83% respectively. Both catalysts were resistant to coking, but the amount of carbon deposits was still lower on NiAlZn. During 50 h on-stream, ethanol conversion and selectivity to H_2 and CO on NiAlZn remained unchanged demonstrating stable performance of the catalyst. The difference in catalytic behavior was ascribed to different reducibility and lattice oxygen mobility in the mixed oxides. TPR and DRIFT-monitored pyridine desorption tests revealed that in the respective materials, NiO particles were reduced easier than Co_3O_4 and NiAlZn had more mobile lattice oxygen with higher capacity to form vacancies than CoAlZn. Higher concentration of metallic Ni species coupled with more abundant mobile oxygen afforded correspondingly higher rates of C-H bond cleavage and carbon removal as CO on NiAlZn than on CoAlZn.