沉淀方法对FeMnCu/ZnO合成低碳醇催化剂性能的影响

Effect of precipitation methods on FeMnCu/ZnO catalyst for synthesis of higher alcohols

以分步连续沉淀法和共沉淀法制备了一系列FeMnCu/ZnO复合氧化物合成低碳醇催化剂,对其CO加氢合成低碳混合醇的反应性能进行了考察,并用ICP、XRD、BET、H2-TPR对其结构进行了表征。结果表明,沉淀方法不同对催化剂的催化性能有较大的影响。在T=503K、P=8.0MPa,GHSV=8 000h-1,H2/CO=2(体积比)的条件下,分步沉淀法制备的FeMn-Cu/ZnO催化剂醇的收率和C2+OH的质量分数均高于共沉淀法制备的催化剂。其中“Fe atop Cu”催化剂醇的收率最高,达到0.26g/mLca.th,同时“Fe atop Cu”催化剂C2+OH的质量分数也最高,可达31.72%。XRD研究表明,分步沉淀法制备的催化剂促进了CuO和ZnO的分散,提高了催化剂的催化性能。BET测试结果表明,分步沉淀法有扩孔的作用,有利于长链醇的生成。TPR研究发现,共沉淀法制备的催化剂Cu物种较难还原,这是共沉淀催化剂合成醇性能较低的原因之一。

The FeMnCu/ZnO catalysts for higher alcohols synthesis were prepared by coprecipitation and sequential precipitation methods. The texture and structure properties of FeMnCu/ZnO catalysts were characterized by ICP, BET, XRD, and TPR. The catalytic activity for C1-5 alcohol synthesis was determined in a fixed bed flow reactor system. The results showed that the catalytic performance of the catalysts was influenced by the precipitation methods remarkably. The alcohol yield and alcohol selectivity of sequential precipitation catalysts were obviously higher than that prepared by coprecipitation method. The alcohol selectivity of 33.5% with C2^＋ alcohol selectivity of 31.72% was obtained over ＂Fe atop Cu＂ catalyst under the reaction condition of T = 503 K,p = 8.0 MPa, GHSV = 8 000 h^-1, H2/CO = 2 （volume ratio）. It was found that sequential precipitation exhibited larger pore size, which could be favorable for long chain molecules to diffusion. The catalysts prepared by sequential precipitation method showed better dispersion of CuO and ZnO. Therefore, the performance for higher alcohols synthesis over catalysts prepared by sequential precipitation can be promoted. The copper ions in sequential precipitation were found to be reducible as compared with coprecipitation catalyst due to their initial temperature of reduction. Combined with the performance of the CO hydrogenation, better performance for higher alcohols over catalysts prepared by sequential precipitation can be ascribed to a mount of reducible Cu species.