| It was focus that the reforming reaction between methane and carbon dioxide in the modern chemical research, Beacause the achievement of reforming could not only resolve the energy lack crisis,but also could contain the speed of green house effect,so it was prositive meaning to sustainable development for human.The research of methane’s reforming with carbon dioxide primary through the chemical experiments, and it were certain that metal Ni,Pt,Rh and Ru not only have finer activity to reforming reaction,but also the mechanism were almost consistency by each metal.The process of CH4/CO2reforming reaction have not achieve industrialization because the great amount carbon were accemulated to make catalyst to lose activity. Supercritical carbon dioxide have special characteristic to contain the carbon deposition of catalyst,but the theory research about it has not existed at home and on abroad.In order to explore many mechanism about CH4/CO2reforming reaction,we have maken the great amount theory research through B3LYP,MP2and HF methods in coordinate with Lanl2dz>6-31G(d) and6-31G(2d,p) in the quantum chemistry.We also have explanned and analysised the matter relationship about every react mechanism by chemical thermodynamics and react kinetics,and also explore the gas adsorption behavior on the surface of catalyst through MS software.In the absence of the catalyst,the freeradical reforming mechanism could been divided to many calculate modules:the dehydrogenation of CHx, the activiation and reaction of carbon dioxide,the decomposition of carboxyl or the compound included carboxyl,the participation and action about hydroxide radical,the decomposition of CHxO,the other reactions.The gained results have indicated that the main dehydrogenation of CHx were lost hydroxide atom step by step,and the progress of lost many hydroxide atoms at the same time were impossible at low temperature,and all dehydrogenation process of CHx were endothermic; the activiation and reaction of carbon dioxide parmary indicated that reaction between activiatal carbon dioxide and H-,CH3·,CH2·,CH-.The research results have indicated that the form process of carboxyl was very easy, and the form channel were various;the decomposition of the carboxyl or the compound included carboxyl were easy at low temperature,the major react were direct decomposition into carbon monoxide, the intermediate as-COOH and CH3COO were also easy to take place the decomposited into carbon monoxide or CH3O;the hydroxide radical also could combine CH3·,CH2·,CH·into sterols,but it was difficult to produced water by caquire one hydrogen atom;the decomposition of CH3O and·CH2OH were more complicate,but the decomposition of other CHxO were very easy and through direct dehydrogenation;the decomposition of methanol were three channels,and both methanols combin into ether were easy take place at low temperature;the other reactions as2H·â†'H2,2CH·â†'C2H6and2·OHâ†'H2O+·O·were possible been taken place.The originate reaction of freeradical reforming mechanism needed high temperature above3430.13K,but it were more difficult to attain in the chemical experiment.For this reason,the reforming reaction between methane and carbon dioxide should been depended on the catalyst behavior,the gained results were as follows:(1) As metal Ni,Pt,Rh,Ru play the role of catalyst,the dehydrogen reforming reaction of methane were indicated that methane have took off hydrogen atom step by step through combine with catalyst metal, the intermediner which had beencomplete dehydrogenation finally took place reforming with carbon dioxide,all react process were endothermic,the second step were the rate-determing reaction,and the activation energy was287.1781kJ·mol-1, sum of enthalpy energy all steps was242.7819kJ-mol-1,that is similarly close to the true data by chemical experiments.(2) The primary idea of oxide reforming mechanism were carbon dioxide could be combined with metal generate oxide,which could be to play the most significant role in reforming reaction.That were two react channels in the oxide reforming mechanism,the third step were the rate-determing reaction in the first channel, and the activation energy was177.5526kJ-mol"1, but the first step were the rate-determing reaction in the second channel,and the activation energy was305.2310kJ·mol-1.therefore,the first channel was more easier.Under the supercritical carbon dioxide condition,the reaction was more easier,the activity of metal were:Ni>Pt>Rh>Ru,and the reaction over metal Ru were most difficulty.(3) The primary idea of surface oxygen reforming mechanism were the surface oxygen could be to play the most significant role in reforming reaction.The research had indicated that surface surface oxygen had high selective activity to CH2=Ni and C—Ni, the reaction which the surface oxygen were participated to were exothermic,the others almost were endothermic,the second step was the rate-determing reaction and the activation energy was430.9377kJ·mol-1.. Under the supercritical carbon dioxide condition,the reaction was more easier.The reaction mechanism and the rate-determing reaction were same by four metals,which were the react process between surface oxygen and CH2R.The reaction over metal Rh were most difficulty, and the activity of metals were:Ni>>Pt>Ru>Rh.(4) The primary idea of hydroxide radical reforming mechanism were the hydroxide radical could be to play the most significant role in reforming reaction.It were found that hydroxide radical have distinct selective activity to CH3Ni and CHNi,which was different from oxide or surface oxygen. About the hydroxide radical reforming mechanism,almost all of steps were endothermic except for the reaction both the adsorption of hydrogen and the process of CHNi with hydroxide radical were exothermic.The second step was the rate-determing reaction,and the the activation energy was360.6608kJ·mol-1. Under the supercritical carbon dioxide condition,the reaction was more easier. The reforming reaction between methane and carbon dioxide over Pt,Rh,Ru were more similarly with Ni,and the rate-determing step were same about the produce process of hydroxide. The reaction over metal Rh or Ru were more difficulty, and the activity of metals were:Ni>Pt>>Rh>Ru.(5) We had done some theory calculation about the gas adsorb behavior over catalyst surface through MS software. At first,we had success construct the various surface over metal Ni, Pt, Rh, Ru.secondly,we had accomplished the geometry structure and energy optimization about some small material such as CH3OH and·CH2OH.At Last,we had tried to calculated small material’s behavior over different metal catalysts about different adsorp position.The results about gas adsorb behavior was line with the experiment results.To sum up the above argument,the reforming reaction between methane and carbon dioxide could be achieved over four metal support.Although the different mechanism had distinct different characteristic,but all of them could explain the concrete process about the reforming reaction,and the results were in line with the experimental results and all of this have more theory significance. |
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