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Autothermal Reforming Of Methane With CO2 And O2 On Supported Nickel Catalysts In A Fluidized Bed Reactor (Oxidation Of Glycerol With Molecular Oxygen)

Posted on:2010-04-03Degree:DoctorType:Dissertation
Country:ChinaCandidate:J GaoFull Text:PDF
GTID:1101330332483146Subject:Physical chemistry
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Catalytic transformation of methane and carbon dioxide, the cheapest carbon-containing materials and the most problematic greenhouse gases, into more valuable compounds has attracted attentions of researchers. Combination of CO2 reforming and partial oxidation of methane, also called methane autothermal reforming [MATR] (Eq.(1)), has been substantial interest in recent years in alternative routes for the conversion of natural gas (methane) to syngas. This process has low-energy requirements due to the opposite contribution of the exothermic partial oxidation of methane (Eq. (2)) and the endothermic CO2 reforming on methane (Eq. (3)). By controlling the feed composition, H2/CO ratio in the product can be modified according to the need of the post processing. Oxygen in feed is helpful to avoid catalyst deactivation by carbon deposition.CH4+xCO2+(1-x)/2 O2→(1+x) CO+2H2,AH298=(285x-38)kJ/mol(016 nm) had no activities at higher space velocity (90,000 h-1) and deactivated rapidly at lowe space velocity (18,000 h-1). While small sized Ni (<9.5 nm) is more active and stable at space velocity (<54,000 h-1).Characterizations disclosed that methane decomposition rate decreases with the enlarging Ni particle size and the temperature of methane decomposition was lower on small sized Ni. CO2 can not dissociate on the Ni/SiO2. The results of pulse-MS illustrates that activity of CH4 decomposition was 9.8 s-1 on the 45.0 nm Ni catalyst, comparable with previously reported values. On the 4.5 nm Ni catalyst, the calculated activity of CH4 increased to 12.6 s-1. CO2 and O2 accelerated the conversion of methane, but the small particle Ni catalyst was more effective and stable. As the methane decomposition rate slows on larger Ni particles and at higher space velocity to ensure complete conversion of the oxygen, surface Ni will be gradually oxidized by remaining O2, leading to Ni deactivation:CH4+nNi→CHx-Nim+(4-x)H-Ni (x=0-3) (RDS) (4)C-Nim+(1/2)O2→CO+Nim (5)C-Nim+CO2→2CO+Nim (6)Ni+(1/2)O2→NiO (7)On the basis of above reaction mechanism, a series of different amount ZrO2-promoted SiO2 supported Ni catalysts prepared from [Ni(en)3]2+ were used for MATR to synthesis gas in a fluidized bed reactor in order to enhance the methane decomposition rate (RDS). It was found that Ni/5ZrO2-SiO2 with larger Ni-ZrO2 boundary exhibited the best activity and stability for MATR even at an extremely space velocity 90,000 h-1. Pulse-injected surface reactions and in situ XRD characterizations disclosed that CO2 dissociated exclusively at the boundary between Ni and ZrO2. The decomposition rate of CH4 was enhanced at the boundary between Ni and ZrO2.Catalytic oxidation of glycerol with molecular oxygen to glyceric acid was primarily studied in a base-free aqueous solution over Pt/MWNTs and Pt/AC catalysts at atmosphere. Pt/MWNTs was more active than Pt/AC for the easier accessibility of Pt on the external wall of MWNTs. Raman analysis confirmed the primary C-H was more active than the primary CO-H. It was found that the conversion of glycerol was effected strongly on the particle size of Pt on MWNTs. Smaller Pt particles are more active. On Pt/S-MWNTs(60-100) with 2.4 nm Pt particles, the conversion of glycerol and the yield of GLYA reached 84.0% and 58.0%, respectively.
Keywords/Search Tags:methane, MATR, Ni catalyst, synthesis gas, fluidized bed reactor, catalytic oxidation of glycerol, Pt/C, Pt/MWNTs
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