Reactivity of low-concentration Cu-doped modified Fe-based oxygen carrier in chemical looping: experiments and theoretical simulations

doi:10.11949/0438-1157.20200307

Abstract

Abstract:

Based on thermogravimetric experiment (TGA) and density functional theory (DFT) calculations, the reaction activity and microscopic molecular reaction mechanism of Cu low-concentration doped Fe₂O₃ oxygen carrier (Cu-Fe₂O₃) and H₂ in the process of chemical looping combustion were studied. TGA results showed that the low concentration of Cu-doped reduced the apparent activation energy of Fe₂O₃ reaction with H₂ (from 83.9 kJ/mol to 72.3 kJ/mol). And improved the conversion rate and lattice oxygen release rate of Fe₂O₃ oxygen carrier, which was attributed to the introduction of Cu element. From the atom/molecular level, DFT calculations verified that the low concentration of Cu-doped altered reaction pathway of Fe₂O₃ oxygen carrier reaction with H₂. The calculation results showed that the energy barrier of Fe₂O₃ oxygen carrier reaction with H₂ decreased from 2.30 eV to 1.81 eV (Fe atom top site) and 1.68 eV (Cu atom top site), respectively. The reaction preferentially occurred at the Cu atom site, followed at Fe atom site. Furthermore, the micro-structure characteristic change of Fe₂O₃oxygen carrier (Cu—O and Cu—Fe bonds introduced) is more favorable for the rapid lattice oxygen release in chemical looping process.

Key words: chemical looping, Cu-doped, Fe-based oxygen carrier, hydrogen, micro-structure, computational chemistry

摘要：

基于热重实验（TGA）和密度泛函理论（DFT）计算，对Cu低浓度掺杂Fe₂O₃载氧体（Cu-Fe₂O₃）与H₂在化学链燃烧过程中反应活性和微观分子反应机理进行研究。TGA结果显示，Cu低浓度掺杂降低Fe₂O₃载氧体与H₂反应表观活化能E_a （从83.9 kJ/mol降低至72.3 kJ/mol），因此，低浓度Cu掺杂由于原子尺度Cu掺杂缺陷的引入的确提高了Fe₂O₃载氧体转化率和晶格氧释放速率。DFT计算从分子水平证实Cu低浓度掺杂改变了Fe₂O₃载氧体与H₂反应路径，路径分析表明，Cu掺杂使Fe₂O₃载氧体与H₂反应能垒从2.30 eV分别降低至1.81 eV（Fe原子top位反应）和1.68 eV（Cu原子top位反应），Cu掺杂的Fe-基载氧体的氢还原反应优先发生在掺杂的Cu原子位，其次为Fe原子位。此外，计算结果表明，因Cu-O和Cu-Fe键的引入，低浓度Cu掺杂改变了Fe₂O₃载氧体微观结构，这对于载氧体的晶格氧快速释放是有利的。

关键词: 化学链, Cu掺杂, Fe-基载氧体, 氢, 微观结构, 计算化学

CLC Number:

TQ 530.11

Nini YUAN,Hongcun BAI,Mei AN,Xiude HU,Qingjie GUO. Reactivity of low-concentration Cu-doped modified Fe-based oxygen carrier in chemical looping: experiments and theoretical simulations[J]. CIESC Journal, 2020, 71(11): 5294-5302.

袁妮妮,白红存,安梅,胡修德,郭庆杰. 化学链过程中Cu低浓度掺杂改性Fe-基载氧体反应性能：实验与理论模拟[J]. 化工学报, 2020, 71(11): 5294-5302.

Figures/Tables 5

Fig.1 Primitive cell of α-Fe2O3(a)， α-Fe2O3(001) surface(b) and model of Cu-Fe2O3 oxygen carrier(c)

Fig.2 Characterization of oxygen carrier particles: XRD patterns of Fe2O3 and Cu-Fe2O3 oxygen carrier before and after the reaction(a); small range XRD pattern of fresh Fe2O3 and Cu-Fe2O3 oxygen carrier(b); SEM-EDX Mapping images of Cu-Fe2O3 oxygen carrier(c)

Fig.3 Conversion and Ea curves (inset) of oxygen carrier reaction with H2

Fig.4 Energy barrier diagram of oxygen carriers reaction with H2(band length unit:?)：reaction of Fe atom sites on Fe2O3 oxygen carrier(a); reaction of Fe atom sites on Cu-Fe2O3 oxygen carrier(b);reaction of Cu atom sites on Cu-Fe2O3 oxygen carrier(c)

Fig.5 Schematic diagram of Cu-Fe2O3 oxygen carrier reaction with H2

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