Synthesis, Characterization and Catalytic Evaluation of Cobalt and Niobium Oxide Solids Modified with Alkaline Earth Metals

ABSTRACT Cobalt and niobium oxide solids modified with alkaline earth metals (Mg, Ca, and Sr) were synthesized and characterized to compare the second element effect on the catalyst structural and chemical properties. The materials were prepared by co-precipitation of cobalt nitrate and niobium oxalate solutions using ammonium hydroxide as precipitating agent. The samples were characterized by XRD, SEM, Ra-man, BET, TPR, ammonia TPD and cyclohexane dehydrogenation reaction (CHD). Results showed that Mg, Ca or Sr addition changed cobalt niobate crystalline structure, leading to alkaline earth metal nio-bates with lower crystallinity. It was observed that Mg, Ca or Sr increased the solids acidity and changed cobalt niobate reduction behavior so that the lowest amount of metallic cobalt was obtained when Mg was incorporated. Modifiers also decreased cobalt niobate dehydrogenation activity. This effect was higher with Mg or Sr addition.

摘要：采用碱土金属（镁Mg、钙Ca、锶Sr）对氧化钴与氧化铌固体进行改性，合成并表征了一系列样品，以对比第二组分对催化剂结构与化学性质的影响。本研究以氢氧化铵为沉淀剂，通过共沉淀硝酸钴与草酸铌溶液的方式制备目标材料。采用X射线衍射（XRD）、扫描电子显微镜（SEM）、拉曼光谱（Raman）、BET比表面积分析法、程序升温还原（TPR）、氨气程序升温脱附（ammonia TPD）以及环己烷脱氢反应（CHD）对样品进行表征。结果表明，掺入镁、钙或锶会改变铌酸钴的晶体结构，生成结晶度更低的碱土金属铌酸盐。研究观察到，镁、钙或锶的引入可提升固体的酸度，并改变铌酸钴的还原行为；其中掺入镁时，体系中金属钴的含量最低。此外，改性剂还会降低铌酸钴的脱氢活性，且该抑制效果在添加镁或锶时更为显著。