Influence mechanism of trace K element on NOx adsorption of coal-based carbon materials at low temperature
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摘要: 本研究选取准东煤为碳材料前驱体,以水热耦合痕量K元素的方法对其进行活化。通过实验探究K质量浓度对碳吸附性能的影响,同时系统研究了材料的NOx低温吸附性能。实验结果表明,活化液中K2CO3质量浓度为0.0067 g/mL时,所制得的样品对NOx的吸附性能较好,其饱和NOx吸附时间为3200 s。通过低温N2物理吸附研究发现,该质量浓度下样品的孔结构发展较好,比表面积达到708.6 m2/g。此外,本研究通过XPS、SEM等手段对不同质量浓度K2CO3活化的碳基材料进行了物化表征,并对不同质量浓度K2CO3活化制备的样品进行了表面性质分析,通过FT-IR对样品表面的吸附过程进行研究,发现准东煤基碳材料优良的吸附性能与表面结构相关,研究中采用DFT手段对反应机理进行验证,结果表明,K可促进C−O键的形成,而活性C−O结构是促进NOx吸附的关键因素。通过该系列实验,本工作获得采用水热耦合痕量K元素制备准东煤基碳材料的最佳方法和最优工艺参数。Abstract: In this paper, Zhundong coal was used as the precursor of carbon material followed by activation by hydrothermal coupling with trace amount of K element. The influence of K concentration on the adsorption performance of as-prepared carbon material of NOx at low temperature was studied. The experimental results showed that when the concentration of K2CO3 in the activation solution was 0.0067 g/mL, the sample had good NOx adsorption performance, and the saturated NOx adsorption time was 3200 s. The pore structure of the sample developed well with the specific surface area of 708.6 m2/g. The samples were characterized by XPS, SEM and the adsorption process was studied by FT-IR. It was found that excellent adsorption properties of Zhundong coal derived carbon material were related with the surface structure. DFT method was employed to verify the reaction mechanism. The results showed that K could promote the formation of C–O bond which was the key factor for promoting the NOx adsorption. The best method and optimal process parameters for preparing Zhundong coal-based carbon materials by hydrothermal coupling with trace amount of K were obtained.
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Key words:
- trace K2CO3 /
- hydrothermal /
- carbon material /
- low temperature /
- adsorption /
- preparation
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图 3 碳材料吸附前后的XPS谱图
Figure 3 XPS spectra of activated carbon before and after adsorption
(a): O ls spectra of fresh AC-0.2; (b): C ls spectra of fresh AC-0.2; (c): O ls spectra of fresh AC-0.3; (d): C ls spectra of fresh AC-0.3; (e): O ls spectra of AC-0.2 after adsorption; (f): C ls spectra of AC-0.2 after adsorption; (g): O ls spectra of AC-0.3 after adsorption; (h): C ls spectra of AC-0.3 after adsorption
图 4 该组碳材料表面官能团含量
Figure 4 Surface functional group content of the activated carbons
(a): relative content of oxygen-containing functional groups on the surface of the carbon materials before adsorption; (b): relative content of oxygen functional groups on the surface of the carbon materials after adsorption; (c): relative content of carbon functional groups of the carbon materials before adsorption; (d): relative content of carbon functional groups of the carbon materials after adsorption
表 1 准东煤的工业分析
Table 1 Proximate analysis of Zhundong coal
Industrial analysis wad/% M A V FC 11.23 25.73 16.28 51.83 表 2 准东煤的元素分析
Table 2 Ultimate analysis of Zhundong coal
Elemental analysis wad/% C H O N S 66.36 4.57 15.91 0.55 0.86 表 3 碳酸钾质量浓度和配置
Table 3 Potassium carbonate concentration for preparation of the samples
Sample name ${ {\rm{K} }_2}{\rm{C} }{ {\rm{O} }_3}/({\rm{g} } \cdot {\rm{m} }{ {\rm{L} }^{ - 1} })$ Support 0.05K2CO3-AC 0.0017 5gASC 0.1 K2CO3-AC 0.0033 5gASC 0.2 K2CO3-AC 0.0067 5gASC 0.3 K2CO3-AC 0.01 5gASC 0.4 K2CO3-AC 0.013 5gASC 表 4 K2CO3系列碳材料的比表面积和孔径分布
Table 4 Specific surface area and pore size distribution of the as-prepared carbon materials
Sample A/(m2·g−1) v/(cm3·g−1) vmicro / vtotal vmeso / vtotal Size /nm total micro meso Raw coal 6.4 − 0.483 − − − − AC-0.05 492 0.2919 0.2314 0.1009 79.27% 34.57% 2.373 AC-0.1 632.5 0.3599 0.298 0.1291 82.80% 35.87% 2.276 AC-0.2 708.6 0.4208 0.3128 0.2139 74.33% 50.83% 2.375 AC-0.3 652.5 0.3776 0.1934 0.2848 51.22% 75.42% 2.315 AC-0.4 510.3 0.2917 0.2026 0.2026 69.45% 69.45% 2.286 表 5 K2CO3系列碳材料的NOx吸附量
Table 5 NOx adsorption capacity of K2CO3 series carbon materials
Sample Time/s wNOx /(mg·g−1) AC-0.05 2000 16.32 AC-0.1 2200 20.14 AC-0.2 3200 28.73 AC-0.3 3400 30.46 AC-0.4 2100 20.68 -
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