Mechanism of N2O reduction by biomass gasification gas reburning
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摘要: 利用密度泛函理论和过渡态理论，在分子水平上研究了循环流化床锅炉再燃过程中生物质气CO对CaO催化N2O脱除的影响。构建了N2O分子在CaO（100）表面的吸附模型，同时对N2O分子在CaO（100）表面的分解及还原过程进行了探究。结果表明，N2O在CaO（100）表面的异相分解相比于N2O的均相分解所需的能垒更低，CaO的存在有利于N2O的分解；CaO（100）表面的O活性位点被N2O分解产生的原子O毒化，而再燃过程中生物质气CO促进了CaO（100）表面活性位点的再生，有利于CaO对N2O分解的催化作用。Abstract: A molecular modeling based on the density functional theory (DFT) and the transition state theory (TST) was performed to investigate the influence of biomass gas CO on the N2O decomposition catalyzed by CaO during reburning in the circulating fluidized bed boiler. The model for N2O adsorption onto the CaO(100) surfaces were constructed; and the processes of the N2O decomposition on the CaO(100) surface and the surface recovery of CaO(100) were investigated. The results illustrate that the energy barrier of N2O decomposition on the CaO(100) surface is much lower than that in homogeneous case, and CaO is therefore able to catalyze the N2O decomposition. The atomic O from N2O decomposition can poison the active sites O atom on the CaO(100) surface, while biomass gas CO can promote the regeneration of the active sites on the surface of CaO(100), which is beneficial for CaO to catalyze the N2O removal.
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Key words:
- biomass gas /
- reburning /
- CaO(100) /
- N2O /
- molecular simulation
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图 1 N2O的均相分解反应各驻点结构示意图
Figure 1 Structures of stagnation points of N2O homogeneous decomposition (Bond length: nm)
图 2 N2O的均相分解反应势能面
Figure 2 Reaction potential energy surface of N2O homogeneous decomposition
图 3 N2O分子在CaO(100)表面吸附的稳定构型
Figure 3 Stable adsorption structures of N2O on the CaO(100) surfaces (Bond length: nm; blue: N atom; red: O atom; green: Ca atom)
图 4 四种稳定构型在CaO（100）表面吸附后的局部态密度图
Figure 4 Partial densities of states of the four stable structures after adsorption on the CaO(100) surfaces (a) O-O, (b) O-Ca, (c) N-O, (d) N-Ca
图 5 N2O分子在CaO（100）表面吸附的最优构型
Figure 5 Optimal adsorption structure of N2O on the CaO(100) surface (Bond length: nm)
图 6 CaO（100）表面N2O的分解反应各驻点结构示意图
Figure 6 Structures of stagnation points of N2O decomposition on the CaO(100) surface (Bond length: nm)
图 7 CaO（100）表面N2O的分解反应势能面
Figure 7 Reaction potential energy surface of N2O decomposition on the CaO(100) surface
图 8 N2O参与的CaO（100）表面再生各驻点结构示意图
Figure 8 Structures of stagnation points of the recovery process on the CaO(100) surfaces with N2O (Bond length: nm)
图 9 N2O参与的CaO（100）表面再生反应势能面
Figure 9 Reaction potential energy surface of the recovery process on the CaO(100) surfaces with N2O
图 10 CO分子在CaO(100)表面吸附的稳定构型
Figure 10 Stable adsorption structures of CO on the CaO(100) surfaces (gray: C atom; red: O atom; green: Ca atom)
图 11 CO参与的CaO（100）表面再生各驻点结构示意图
Figure 11 Structures of stagnation points of the recovery process on the CaO(100) surface with CO (Bond length: nm)
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