在不同焙烧温度和焙烧气氛下对共浸渍法制备的K_2MoO_4-NiO/SiO_2催化剂进行热处理,并采用X射线衍射、热重-差示扫描量热、氢气程序升温还原、拉曼光谱和电子白旋共振波谱等手段对催化剂进行了表征,同时考察了催化剂催化高硫化氧合成气一步法制甲硫醇的性能.结果表明,由于催化剂中所含柠檬酸氧化放热,空气中焙烧的催化剂发生严重烧结.随着焙烧温度的升高,八面体配位的Mo(O_h)逐渐向四面体配化的Mo(T_d)转变,导致催化剂的还原能力降低,配位不饱和Mo(CO吸附位)减少,因而CO转化率降低.甲硫醇的生成与Mo-S-K相密切相关,而MoS_2晶相表面主要生成烃类.与氮气中焙烧的催化剂相比,空气中焙烧的催化剂表面的MoS_2相较多,而Mo-S-K相较少,因此具有更高的烃类选择性和更低的甲硫醇选择性.
K_2MoO_4-NiO/SiO_2 catalyst samples prepared by the co-impregnation method were calcined at different temperatures and atmos-phere. X-ray diffraction, thermal gravimetric-differential scanning calorimetry, hydrogen temperature-programmed reduction, Raman spec-troscopy, and electron spin resonance techniques were used to characterize the catalyst samples. The catalytic performance of the catalyst for one-step synthesis of methanethiol from high H_2S-containing syngas was evaluated. The results showed that the catalyst calcined in air sin-tered seriously because of the heat release from citric acid oxidation. With the increase of calcination temperature, octahedral coordination Mo(O_h) gradually changed into tetrahedral coordination Mo(T_d), which made the reduction of Mo~(6+) more difficult, decreased the number of CO adsorption sites (coordinatively unsaturated sites) of Mo, and at last led to the decrease of CO conversion. Methanethiol synthesis was closely related to the Mo-S-K phase, and hydrocarbon synthesis was related to the MoS2 phase. Compared with the catalyst calcined in N_2, there were more MoS_2 phase and less Mo-S-K phase on the surface of the catalyst calcined in air, resulting in the higher selectivity for hy-drocarbon and lower selectivity for CH_3SH.
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