Co/HMS和Co/SiO_2催化剂的表征及在费-托合成反应中的催化性能

Characterization and Catalytic Performance of Co/HMS and Co/SiO_2 Catalysts for Fischer-Tropsch Synthesis

HMS介孔分子筛经水热处理得到无定形SiO2,分别以无定形SiO2和HMS为载体,用浸渍法制得了15%Co/SiO2和15%Co/HMS催化剂.研究表明:氧化态Co/SiO2和Co/HMS催化剂中的钴物种以Co3O4形式存在,且Co3O4晶粒粒径均较相应催化剂的孔径大,故有部分钴物种存在于催化剂外表面;氧化态Co/HMS催化剂中的钴物种堵塞孔道较为严重;Co/HMS催化剂中存在较强的金属载体相互作用,因此Co/HMS催化剂较Co/SiO2催化剂难还原;Co/HMS催化剂还原后具有较高的钴分散度,使其具有优异的费托合成反应性能.

The 15 % Co/HMS and 15 % Co/SIO2, catalysts were prepared by incipient wet impregnation and characterized by N-2 adsorption- desorption, XRD, XPS, TPR and TG. The amorphous SiO2 used was derived from HMS in boiling water for 12 h. The strong metal-support interaction for the Co/HMS catalyst was affirmed by TPR and XPS. The Co3O4 crystallite size of the oxidized Co/HMS catalyst was smaller than that of the oxidized Co/SiO2 catalyst. XRD results indicated the location of partial cobalt oxide crystallites on the external surface of the oxidized Co/HMS and Co/SiO2 catalysts. Mesoporous pores were blocked by cobalt oxide for the oxidized Co/HMS according to the N-2 adsorption -desorption. The Co/HMS catalyst presented higher F-T activity owing to the better cobalt dispersion and appropriate cobalt reduction. Under the conditions of V (H-2) / V (CO) = 2. 0, GHSV = 500 h (-1) and p = 2. 0 Pa, the CO conversion over Co/HMS was kept about 85 %, and the methane selectivity, of about 8. 0 % and C-5 ∼ C-18 hydrocarbon selectivity of 70 % were obtained as the reaction temperature increased from 473 to 493 K. Reduction for a long time ( 16 h) before reaction led to the sintering and agglomeration of cobalt crystallites in Co/SiO2, so that the F-T activity became lower. The CO conversion over Co/SiO2 gradually increased from 66 % to 98 % when the reaction temperature increased from 503 to 523 K, but the hydrocarbon distribution was not so good as that over Co/HMS.