碳纳米管促进的Co-Mo-K硫化物基催化剂用于合成气制低碳混合醇

 以自行制备的多壁碳纳米管(CNT)作为添加剂,制备共沉淀型CNT促进的Co-Mo-K硫化物基催化剂. 实验发现,与未添加CNT的催化剂相比,添加少量CNT可显著提高CO的加氢转化活性和生成低碳醇的选择性. 在5.0 MPa, 623 K, V(CO)∶V(H2)∶V(N2)=45∶45∶10, GHSV=3600 ml/(g·h)的反应条件下, Co1Mo1K0.3-10%CNT催化剂上CO的转化率达21.6%, 相应的总醇(C1～4醇)时空产率为241.5 mg/(g·h), 产物中C2+醇/C1醇=1.39 (C基选择性比). 添加少量CNT并不会导致Co1Mo1K0.3硫化物基催化剂上CO加氢反应表观活化能发生明显变化,但却导致工作态催化剂表面催化活性Mo物种(Mo4+)的摩尔百分率有所提高; 另一方面, CNT促进的催化剂对H2有更强的吸附活化能力,并能在相当大程度上抑制水煤气变换副反应的发生. 这些因素有利于提高催化剂的活性和选择性.

Co-Mo-K Sulfide-Based Catalyst Promoted by Multi-walled Carbon Nanotubes for Higher Alcohol Synthesis from Syngas

Using homemade multiwalled carbon nanotubes (CNT) as the promoter, sulfurized Co-Mo-K catalysts (denoted Co_iMo_jK_k-x%CNT) were prepared by the coprecipitation method. Their catalytic performance for the synthesis of higher alcohols from syngas was evaluated and compared with that of the CNT-free counterpart (Co_iMo_jK_k). Appropriate incorporation of a minor amount of CNT into Co_iMo_jK_k led to a significant increase in CO conversion and the selectivity for the higher alcohols. Under the reaction conditions of 5.0 MPa, 623 K, V(H₂):V(CO):V(N₂) = 60:30:10, and GHSV = 3600 ml/(g·h), the observed space-time-yield of total (C_1–4) alcohols reached 241.5 mg/(g·h) with 21.6% of CO conversion over the Co₁Mo₁K_0.3-10%CNT catalyst, which was 1.84 times that over the Co₁Mo₁K_0.3 catalyst. Ethanol became the dominant product of the CO hydrogenation under the conditions mentioned above. The water-gas-shift (WGS) side reaction was inhibited to a great extent over the CNT-promoted catalyst. The results of catalyst characterization indicated that the addition of a small amount of CNT into the Co₁Mo₁K_0.3 catalyst did not cause an obvious change in the apparent activation energy for the conversion of CO but led to an increase in the molar percentage of the catalytically active Mo species (Mo⁴⁺) in the total amount of Mo at the surface of the working catalyst. On the basis of the temperature-programmed desorption results, it could be inferred that under the conditions of the higher alcohol synthesis, there existed a considerably larger amount of reversibly adsorbed H species on the CNT-promoted catalyst, which would generate a surface microenvironment with high steady-state concentration of the adsorbed H species on the catalyst and thus increase the rate of a series of surface hydrogenation reactions. In addition, high steady-state concentration of adsorbed H species on the surface of the catalyst would effectively inhibit the WGS side reaction. These factors considerably contribute to the increase in the yield of the main product.