In order to better understand the mechanism of NO_(x)and N_(2)Oprecursors(NH_(3)and HCN)from aspartic acid(Asp)pyrolysis,decomposition reaction networks resulting in the generation of NH_(3)and HCN were investigated by employing density function theory methods.After several pathways were analyzed in detail,two series of pyrolytic reactions containing three possible pathways were proposed.All the reactants,transition states,intermediates and products were optimized,also the electronic properties on these crucial points were discussed,which shows that Cαacts as the most active site to initiate the pyrolysis reaction,where the direct Cα-Cβbond breakage,due to the atomic charge population of repulsion,led to one key route for the generation of HCN,and the transfer of Hαfrom Cαto Cβresulting in another key route for the generation of HCN,while the transfer of Hαfrom Cαto N atom of Asp resulting in the key route for the generation of HN3.Further,the kinetic analysis based on speed control method in each key reaction pathway was conducted to further compare the generation of HCN and NH_(3)under various temperatures.The above results are in accordance with the related experimental results.
Kang PengQin WuFu ZongqiangWang TipengJu LiweiTan Zhongfu
Fossil fuels are the main energy source to satisfy the worldwide energy demands.However,the energy demands are increasing and the supply of fossil fuels is decreasing,thus many countries are looking for other fuel sources.Differing from the traditional fuels,hydrogen is considered as one of the most promising energy sources due to its intrinsic features such as clean,efficient,safe and sustainable.Developing novel technologies for hydrogen production from renewable sources(such as biomass)becomes a core area for the investigation of hydrogen industry.Within this work,different pathways for hydrogen production including steam reforming,electrolysis,and biomass gasification have been systematically compared in terms of yield and cost.This comparison is unique since the systematic evaluation was conducted from many aspects for all the hydrogen production pathways,especially those by involving the biomass gasification that still lack of available literatures.The assessment methods involved energy analysis,exergy analysis and economic analysis.It was concluded that steam reforming remains the cheapest method of hydrogen production at 1.748$/kg,however,steam reforming is not an ideal process currently or for the future,gasification and electrolysis remains competitive with high yield but requires relatively high initial and annual expenditure.For biomass gasification,though its energy efficiency is lower than steam reforming,it has relatively higher mass yield,demonstrating the feasibility of this process for hydrogen production.Further for biomass gasification,the selection of correct feedstock is a key to maximize its yield,i.e.a yield of 82.47%is possible with corn stover fed gasification.
Kang PengGary MorrowZhang XiaoleiWang TipengTan ZhongfuJayant Agarwal
在化学链燃烧(CLC)过程中,载氧体表面的原子结构和电子特性决定了其化学反应活性.本文以Fe_2O_3为载氧体,探讨了其自然条件下主要裸露的高米勒数指表面(1-1 2)的结构性质,研究发现表面不同配位数的氧和铁原子(包括O2f、O3f、O4f、Fe4f和Fe5f)的键参数、电子态密度及电荷布居等存在明显差异.为探究这种差异对Fe_2O_3反应活性的影响,对比分析了CO在表面5种氧和铁原子位生成CO_2的吸附-反应机理.CO在表面低配位O原子O2f和O3f首先形成物理吸附,然后被晶格氧氧化生成CO_2,反应需要克服能垒分别为3.657 e V和3.401 e V;然而,CO在O4f位吸附时,首先克服1.864 e V能垒形成二齿形碳酸盐物种,之后克服1.097 e V的能垒形成CO_2.当CO在Fe4f和Fe5f位吸附时,CO与Fe原子成键,后经过活化与表面O原子成键,形成二齿形碳酸盐物种,能垒分别为0.416和0.219 e V,最终碳酸盐物种分别克服0.500和1.462e V的能垒生成CO_2.因此,可以推断表面高配位数的O4f、Fe4f和Fe5f原子,由于其较高的氧化态,在化学链燃烧过程中充当活性位的作用.本研究有助于了解铁基载氧体表面化学链燃烧反应的微观机理,并为载氧体表面结构性能调控制备提供理论借鉴.
Pretreatment mechanism ofβ-O-4 lignin(Lβ-O-4)during the phosphoric acid-acetone process involves a series of interactions between lignin and solvent molecule(H2O,CH3COCH3 and H3PO4)which lead to the adsorption,solubility and decomposition of lignin.Coniferyl alcohol guaiacyl glycerol(CAGG)with the predominant linkage(β-O-4 ether bond)was chosen as the modelβ-O-4 lignin(Lβ-O-4)for investigating the detailed pretreatment mechanism based on density functional theory calculations and molecular dynamic simulations.Interactions betweenβ-O-4 lignin and solvent molecules were firstly detected.Only physical interaction occurred betweenβ-O-4 lignin and the solvent molecule.The attractive van der Waals interaction favored CH3COCH3 molecules approaching to Lβ-O-4,showing a compatibility of Lβ-O-4 in CH3COCH3 solution.Furthermore,following the temperature effect on the dynamics processes,larger dynamics calculations and experiments were carried out to reveal the detailed dissolution and precipitation ofβ-O-4 lignin in various solutions.