Co-K-Mo/γ-Al_2O_3催化剂的合成低碳醇性能及其结构研究

Catalytic Properties for Mixed Alcohols Synthesis and Structure of Co-K-Mo/γ-Al_2O_3 Catalysts

氧化态K-K－MoO3／γ－Al2O3催化剂中添加Co（NO3）2后在空气中四个不同温度下焙烧再硫化，制得Co-KK－MoO3／γ－Al2O3催化剂，对其CO加氢合成低碳醇的催化反应性能进行了评价，运用XRD，LRS及EXAFS等手段对催化剂及其氧化态前躯体的结构进行了表征．活性测试结果表明加Co后于500－650℃焙烧制得的催化剂活性较高，且使C2＋醇比例增加．结构分析结果显示加Co后350℃焙烧时，Co主要以氧化物的形式覆盖在催化剂的表面，与钾钼物种作用较弱，硫化后Co以八面体配位的硫化物形式存在，焙烧温度升高后，Co组分与钾钼组分的作用增强，硫化后Co主要以四面体配位的硫化物形式存在；当焙烧温度达800℃时，生成了较多的难以被硫化还原的铝酸钴物种．催化剂的合成醇活性与Co的存在形式明显有关．

A series of oxidic Co-K-Mo/γ-Al2O3 catalyst samples, prepared by impregnating oxidic K-MoO3/γ-Al2O3 samples with aqueous solution of calculated Co (NO3)2 and then calcination in air at temperatures of 350 ℃, 500℃, 650℃ and 800℃, respectively, were sulfided and then investigated for the synthesis of mixed alcohols from CO hydrogenation at conditions of p=5.0MPa, T=350 ℃ and GHSV=4800h-1. The results demonstrate that the addition of cobalt promoter is favourable to from higher alcohols and the samples calcined at 500-650 ℃ after impregnating Co2+ possess superior propertiesfor the taed alcohols synthesis.The structures of Co and Mo species on the okidic and suffided samples were determined by XRD, LRS and EXAFS. For oxidic sample calcined at 350 ℃, cobalt exists as Co3O4 species and covers on the surface of K-Mo-O species, the structures of K-Mo-O species are same as that in K-MoO3/7-Al2O3 sample. After sulfidation, cobalt exists as sdede crystamtes with octahedral coordinated Co, and Mo as MoS2 crystallites. For oxidic samples calcined at 500-650℃, Co component interacts with the K-Mo-O species and destroys the long-range order of the K-Mo-O species gradually. After swhdation, Co tends to be ekisted as a sulfide with tetrahedral coordinated Co and Mo still as MoS2 crystallites. For oxidic sample calcined at 800℃, Co component exists mainly as Co(Al2O4) species, most of which can not be sulfied during sulfidation.