碳纳米管促进Cu-基高效甲醇合成催化剂

Abstract

[中文文摘]用自行制备的碳纳米管 (CNTs)作为促进剂 ,研制出一类高效甲醇合成催化剂CuiZnjAlk OX wt%CNTs ,评价它们对CO/CO2 加氢成甲醇的催化活性 ,并与非CNTs促进的相应体系作对比研究 .实验发现 ,碳纳米管能显著地促进甲醇合成反应活性的提高 .在 493K ,5 .0MPa ,H2 /CO/CO2 /N2 =6 2 / 30 / 5 / 3(V/V) ,GHSV =80 0 0h-1的反应条件下 ,在Cu6Zn3 Al1 OX 12 .5wt%CNTs催化剂上 ,甲醇的时空产率达 10 6 4mgh-1(g catal) -1;产物中甲醇的选择性达 98%以上 ;而在相同的制备和反应条件下、在非促进相应催化剂Cu6Zn3 Al1 OX 上 ,甲醇的时空产率只达 72 9mgh-1(g catal) -1.H2 TPD观测揭示 ,常压下在CNTs材料、以及CNTs促进催化剂CuiZnjAlk OX wt%CNTs上 ,可以吸附存储着数量相当可观、在 42 3～ 5 73K温度范围处于可逆吸、脱附的吸附氢物种 .这一特性将有助于在甲醇合成反应条件下 ,营造较高氢稳态浓度的表面氛围 ,以有利于提高表面加氢反应的速率;与此同时,很可能由于加氢活性的提高,使得碳纳米管促进催化剂上甲醇合成 反应所需温度比非促进的相应体系下降15～25 K,这在相当大程度上将有利于提高CO 的平衡转化率和甲醇的平衡产 率. 本文结果表明,碳纳米管对H2 优异的吸附、活化及存储性能对于促进其所改进催化剂上甲醇合成反应活性的显著提高,起着关键作用.[英文文摘]With a kind of multi-walled carbon nanotubes (CNTs) synthesized catalytically in-house and the nitrates of the corresponding metallic components , highly active CNTs2promoted catalysts , CuiZnjAlk -OX-wt%CNTs,were prepared by co- precipitation method,and their catalytic performance for synthesis of methanol from H2/CO/CO2 was investigated and compared with the corresponding CNTs-free catalyst.It is experimentally found that incorporation of the CNTs into the CuiZnjAlk -OX can significantly advance the catalyst activity for methanol synthesis.Over a Cu6Zn3Al1-OX-12.5wt%CNTs catalyst and under reaction conditions of 493 K, 5.0 MPa, feed-gas H2/CO/CO2/N2=62/30/5/3(V/V),GHSV=8000h-1, conversion of CO reached 31%,with the corresponding methanol-STY at 1 064mg-CH3OHh -1(g-catal.)-1,which was about 1.46 times as high as that (729 mgh-1(g2catal.)-1)over the corresponding CNTs-free catalyst Cu6Zn3Al1 -OX.The H2-TPD measurement demonstrated that the CNTs material and prereduced CuiZnjAlk -OX-wt%CNTs system could reversibly adsorb and storage a considerable quantity of hydrogen under atmospheric pressure in temperature region from room temperature to ca.573 K. This peculiarity would be conducive to generating surface circumstances with higher stationarystate concentration of hydrogen-adspecies on the functioning catalyst,and in turn favourable to enhancement of speed of the surface hydrogenation reactions.Meanwhile , the operation temperature for methanol synthesis over the CNTs2promoted catalyst can be 1525 Klower than that over the corresponding CNTs-free catalyst,which would considerably contribute to an increase in equilibrium CO-conversion and CH3OH-yield.The results of the present work indicated that the carbon nanotubes could served as an excellent promoter,and that its peculiarity of adsorbing and storing H2 played an important role in promoting enhancement of reactivity of methanol synthesis over the CNTs-promoted CuiZnjAlk-OX catalysts.