新型体相Ni-Mo-W型加氢催化剂的沉淀机理研究

采用共沉淀法制备Ni-Mo-W型体相催化剂前躯体,通过干燥、成型、焙烧制得Ni-Mo-W型体相催化剂,采用X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、扫描电镜(SEM)对催化剂进行表征,对硝酸镍溶液与钼酸铵、偏钨酸铵溶液共沉淀过程的机理进行了研究。结果表明,原料Ni(NO_3)_2·6H_2O,(NH_4)_(10)W_(12)O_(41)·xH_2O,(NH_4)_6Mo_7O·_4H_2O经沉淀剂氨水调节pH,在适当条件下完成沉淀过程,其沉淀物组成以(NH4)Ni_2Mo_2O_8(OH)·H_2O、Ni_4W_6O_(21)(OH)_2·4H_2O为主,经焙烧形成NiMoO_4、NiWO_4。溶液中的镍更容易与钨酸根离子结合,所以镍、钨会首先反应生成层状复合物的主体层板,钼酸根离子随后进入层中,与层板发生相互作用,最终生成体相Ni-Mo-W型催化剂前躯体。

STUDY ON COPRECIPITATION MECHANISM OF NEW Ni-Mo-W BULK HYDROGENATION CATALYSTS

The Ni-Mo-W catalyst precursors were prepared by co-precipitation method and then the Ni-Mo-W catalysts were finally obtained by drying, molding, and calcination. The synthesized catalysts were mainly investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XRS), scanning electron microscopy (SEM). The coprecipitation mechanism of nickel nitrate solution, ammonium molybdate, and ammonium tungstate solution was studied. The results show that after the pHs of material Ni(NO3)2?6H2O，(NH4)10W12O41?xH2O，(NH4)6Mo7O?4H2O was adjusted by ammonia water, coprecipitation under appropriate conditions was conducted. The composition of the precipitate is mainly composed of (NH4)Ni2Mo2O8(OH)?H2O and Ni4W6O21(OH)2?4H2O. NiWO4 and NiMoO4 were obtained after calcination of the precipitate. Ni-Mo-W compounds have layered structure. It is found that nickel ion first combines with tungsten acid radical ion, forming layered compound board, and then the molybdate come into the layer, resulting in Ni - Mo - W bulk catalyst precursor.