Steam Reforming And Syngas. Two-step Method With The Performance Of The Cerium-based Oxygen Carriers

Hydrogen energy is a unique renewable energy carrier, while synthesis gas is an important chemical raw material. Two-step steam reforming of methane (SRM) for hydrogen and synthesis gas production is a novel hydrogen production technology. Two-step SRM is consisted by methane reforming step and water splitting step, based on those two redox steps, synthesis gas and hydrogen can be respectively produced. This technology avoids the gas separation process because methane and steam are feed to the reactor, respectively. Also the reaction efficiency is higher. Therefore, Two-step SRM should be a promising prospect hydrogen production in further.A series of cerium based oxides oxygen carriers (CeO2,CeO2-WO3,CeO2-ZrO2,CeO2-Fe2O3 and CeO2-NiO) were prepared by co-precipitation method in this paper. It is found that CeO2,CeO2-ZrO2 and CeO2-Fe2O3 oxygen carriers are more suitable for methane reforming reaction for synthesis gas production. And then these three oxygen carriers were tested in cyclic Two-step SRM which has proved that Two-step SRM for the production of hydrogen and synthesis based on these three oxygen carriers is feasible. At last reaction involved in this process was discussed with the help of modern detecting technologies.In CH4-Temperature Programed Reduction test, CeO2,CeO2-ZrO2 solid solution and CeO2-Fe2O3 oxygen carriers show better performance for synthesis gas production step reaction, while CeO2-WO3 oxygen carrier is characterized with low reactivity worth, and CeO2-NiO solid solution oxygen carrier seems more suitable for catalytic cracking of methane. A CH4-Isothermal Reduction was employed to obtain more detailed data for synthesis gas by gas-solid reaction, CH4-Isothermal Reduction is investigated at 850℃.In order to control the reduction degree and avoid cracking of methane, reaction times of 6min,4min and 8min are found to be suitable for CeO2, CeO2-ZrO2 solid solution and CeO2-Fe2O3 oxygen carriers, respectively. In CH4-Isothermal Reduction reaction, reduction mechanisms for oxygen carriers can be explained as CeO2â†'CeO2-δ, Ce-ZrO2â†'Ce-ZrO2-δand Fe2O3â†'Fe3O4â†'FeOâ†'Fe. Synthesis gas with n(H2)/n(CO) close to theoretical value 2 can be obtained in CH4-Isothermal Reduction reaction. CeO2-ZrO2 solid solution and CeO2-Fe2O3 oxygen carriers exhibit a better oxygen release performance. CO uncontained H2 can be produced form the water splitting reaction between reduced CeO2, CeO2-ZrO2 solid solution and CeO2-Fe2O3 oxygen carriers and steam at 700℃. The H2 production period concentrates at the first 10 minutes, and almost completes at 20th minutes. H2 volume from reduced CeO2-ZrO2 solid solution and CeO2-Fe2O3 oxygen carriers are about twice of CeO2 one. In water splitting step, reduced CeO2 and CeO2-ZrO2 solid solution can be successfully recovered by the oxygen atom from H2O, whereas, Fe2O3 in CeO2-Fe2O3 oxygen carrier can not be completely regenerated.In order to test the cyclic redox capacities of those three oxygen carriers, cyclic Two-step SRM was performed. CeO2-ZrO2 solid solution and CeO2-Fe2O3 oxygen carrier can produce a higher quantity of synthesis and H2 than CeO2 one. CeO2-ZrO2 solid solution represents a excellent stability. With the increasing of redox cycle time, more CeFeO3 was detected in CeO2-Fe2O3 oxygen carrier sample, this phenomenon gives an in inspirer that CeFeO3 should be very stable in cyclic Two-step SRM.