On The Understanding Of Designing Principles And Structure-activity Relationship Of Highly Efficient Nickel-based Catalysts For Ethanol Steam Reforming

Hydrogen energy has attracted extensive attention because of increasinglyshortage of energies nowadays. Hydrogen production from biomass-derivedcompounds is one of the most promising energy acquisition methods. Steamreforming of bio-ethanol for hydrogen production has become a research emphasis inenergy and catalysis fields since ethanol is renewable raw materials with highefficiency for hydrogen productivity. Nickel-based catalysts have been extensivelyapplied in steam reforming process due to its low price and strong ability of C-C bondrupture, exhibiting outstanding reactivity and hydrogen selectivity. However, one ofmajor problems of Ni-based catalysts is sintering of Ni particles and carbondeposition. This dissertation describes the designing principles and synthesis of aseries of highly active and stable Ni-based catalysts. We also studied the reactionpathway and kinetics of ethanol steam reforming on the catalysts. In addition, thisdissertation also discuss size effect of Ni-based catalysts for ethanol steam reformingfor H2production.This dissertation first discussed the preparation of four types of Ni-basedcatalysts with high activity and stability, which is listed as follows:(1) Skeletal Nicatalysts with high reactivity in low temperature steam reforming with a high H2yieldrate (~10mol/(molNi·min)) at350oC;(2) The specific role of Mg on Ni/MgO-CeO2catalysts for providing more oxygen vacancies and oxygen storage capacity comparedto bare CeO2with the best addition amount is7wt%(leading to95%H2selectivity at600oC);(3) Highly stable Ni-containing phyllosilicates nanotube catalysts (the bestcatalyst can survive100h stability test without structure destruction and can produce5.4molH2/molEtOHH2at600oC);(4) Core-shell like Ni-CeO2catalysts withnano-confinement effect by a conventional ball-milling method, which showedsuperior activity and stability in ethanol steam reforming.Structure-activity relationship of Ni-based catalysts has also been studied inethanol steam reforming using core-shell Ni@SiO2as a model catalyst. The resultsshowed that the amount of vacancy sites in Ni (211) face characterized by N2chemisorption increases with increasing Ni size, and the increasing trends decreasewhen Ni size is larger than30nm, which is same with TOF variation. Thus it can be concluded that the vacancy site is active site of ethanol steam reforming. Ni size alsoaffects stability, the stability becomes worse when Ni size increases due to anincreased carbon deposition rate.Additionally, this dissertation has put forward a reaction pathway of ethanolsteam reforming on a skeletal Ni catalyst with no support effect through temperatureprogrammed reaction spectroscopy. The results showed that the reaction pathwaymainly contains three surface reactions: ethanol decomposition, methane steamreforming, and water gas shift reaction. We also carried out kinetic study on skeletalNi catalyst based on the reaction pathway, and found that the activation energies forthe three reactions are187.7,138.5, and52.8kJ/mol, reapectively, thus ethanoldecomposition is the rate-determining step of ethanol steam reforming.