陈玉民,董永恒,史承静,等. 非热等离子体强化Cu催化CO2加氢制甲醇机理探索[J]. 煤炭学报,2024,49(10):4276−4294. DOI: 10.13225/j.cnki.jccs.LC24.0407
引用本文: 陈玉民,董永恒,史承静,等. 非热等离子体强化Cu催化CO2加氢制甲醇机理探索[J]. 煤炭学报,2024,49(10):4276−4294. DOI: 10.13225/j.cnki.jccs.LC24.0407
CHEN Yumin,DONG Yongheng,SHI Chengjing,et al. Mechanistic exploration of non-thermal plasma-enhanced Cu-catalyzed CO2 hydrogenation to methanol[J]. Journal of China Coal Society,2024,49(10):4276−4294. DOI: 10.13225/j.cnki.jccs.LC24.0407
Citation: CHEN Yumin,DONG Yongheng,SHI Chengjing,et al. Mechanistic exploration of non-thermal plasma-enhanced Cu-catalyzed CO2 hydrogenation to methanol[J]. Journal of China Coal Society,2024,49(10):4276−4294. DOI: 10.13225/j.cnki.jccs.LC24.0407

非热等离子体强化Cu催化CO2加氢制甲醇机理探索

Mechanistic exploration of non-thermal plasma-enhanced Cu-catalyzed CO2 hydrogenation to methanol

  • 摘要: CO2耦合绿氢制甲醇可同时实现CO2规模转化利用和绿氢储存,甲醇可作为绿色低碳燃料或工业平台产品大规模应用,对推动碳捕集、利用与封存(CCUS)技术进一步发展具有重要意义。非热等离子体(NTP)能在温和条件下活化CO2进行加氢反应,耦合催化剂后可实现甲醇等特定产物定向调控,但其反应机理亟待明确。基于此,结合介质阻挡放电(DBD)实验与连续脉冲等离子体反应动力学模拟,对NTP强化Cu/γ-Al2O3催化CO2加氢制甲醇反应机理和过程耦合规律进行研究。实验证明,NTP与10% Cu/γ-Al2O3耦合可在80 ℃、0.1 MPa下实现18.74% CO2转化率和36.28% CH3OH选择性。放电参数在线监测和原位发射光谱(OES)测量结果表明,耦合Cu/γ-Al2O3后局部放电增强,使得平均电子能量和密度增加促进CO、H生成并参与表面反应而消耗,导致光谱强度减弱。进一步由敏感性和ROP分析发现,NTP中H、CO等活性物质通过CO2(S)+H→COOH(S)、CO+H(S)→HCO(S)、CO(S)+H→HCO(S)、CH3O(S)+H→CH3OH(S)等E-R反应替代对应高能垒L-H反应促进甲醇高效生成。分析反应路径得出,甲酸盐(HCOO*)路径是Cu/γ-Al2O3表面甲醇生成主要路径,其中反应CH3O(S)+H(S)→CH3OH(S)+Cu(S)是最大限速步,RWGS+CO氢化路径中通过CO2(S)→COOH(S)→CO(S)路线生成CO(S)并快速脱附为降低CH3OH选择性重要因素。不确定性分析表明,虽然提高CO2吸附速率可有效提高其转化率,但当H(S)不足时反而会增加CO选择性,最优CO2和H2吸附速率比为γ(H2)/γ(CO2)=7~8;提高CO(S)吸附稳定性并增强H2电子碰撞解离以促进H生成,可提高CO(S)→HCO(S)、CH3O(S)→CH3OH(S)等速率,协同实现27.4%、51%的CO2转化率和CH3OH选择性。

     

    Abstract: Combining CO2 and green hydrogen to produce methanol can simultaneously realize CO2 conversion and green hydrogen storage. Methanol can be used as a green low-carbon fuel or industrial platform product for large-scale application, which is of great significance to promote the further development of Carbon Capture, Utilization and Storage (CCUS) technology. Non-thermal plasma (NTP) can activate CO2 under mild conditions for hydrogenation reaction and obtain specific products such as methanol by combining with catalysts to tailor the reaction routes, but the underlying reaction mechanism is still unclear. Based on this, the reaction mechanism and process coupling laws of the NTP-enhanced CO2 hydrogenation with assistance of Cu/γ-Al2O3 for methanol production were investigated by combining hydrogenation experiments in a dielectric barrier discharge (DBD) reactor with continuously-pulsed discharge plasma simulations. The experiments investigation showed that 18.74% CO2 conversion and 36.28% CH3OH selectivity could be achieved by combining NTP and 10% Cu/γ-Al2O3 at 80 ℃ and 0.1 MPa. The on-line discharge parameters monitoring and in-situ emission spectroscopy (OES) showed that the localized discharge was enhanced by Cu/γ-Al2O3, which increased the average electron energy and density, thus promote the CO and H generation and their surface consumption reaction, resulting in the weakening of spectral intensity. Furthermore, the sensitivity and ROP analyses indicated that the active substances such as H and CO in NTP promoted methanol generation efficiently by alternating the corresponding L-H routes, which usually had higher energy barriers, via E-R reactions such as CO2(S)+H→COOH(S), CO+H(S)→HCO(S), CO(S)+H→HCO(S), and CH3O(S)+H→CH3OH(S). The reaction pathways analysis revealed that the formate (HCOO*) pathway was the main pathway for methanol generation on the Cu/γ-Al2O3 surface, where the reaction CH3O(S)+H(S)→CH3OH(S)+Cu(S) was the rate-limiting step. The generation of CO(S) via the CO2(S)→COOH(S)→CO(S) in the RWGS+CO hydrogenation pathway and its rapid desorption played a vital role in reducing CH3OH selectivity. Uncertainty analysis demonstrated that although increasing the CO2 adsorption rate could effectively improve its conversion, but would not increase CO selectivity when H(S) was insufficient. The optimal CO2 and H2 adsorption rate ratio was predicated to be γ(H2)/γ(CO2)=7~8. Improving CO(S) adsorption stability and enhancing H2 electron collisional dissociation to promote H generation could promote reactions of CO(S)→HCO(S) and CH3O(S)→CH3OH(S), thus facilitated a CO2 conversion of 27.4% and CH3OH selectivity of 51% synergistically.

     

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