不同沉淀剂制备的铁基催化剂对浆态床F-T合成反应的催化性能

Catalytic Performance of Iron-Based Catalysts Prepared Using Different Precipitating Agents for Fischer-Tropsch Synthesis

以FeSO4·xH2 O为铁源,分别以Na2 CO3 和氨水为沉淀剂制备了目标组成相同的两种Fe Cu K SiO2 催化剂样品.采用原子发射光谱、低温N2 吸附、X射线衍射、X射线光电子能谱和M¨ossbauer谱等技术对催化剂进行了表征.在n(H2 ) /n(CO) =0 6 7,WHSV =2 0 0 0h-1,p =1 5MPa和θ=2 5 0℃的条件下,在带搅拌器的浆态床反应器中考察了催化剂对F T合成反应的活性、选择性和稳定性.结果表明,以氨水为沉淀剂的催化剂具有较大的比表面积,还原态催化剂体相中能产生较多的铁碳化物物种.在6 0 0h的运行实验中,两种催化剂样品均表现出良好的反应初活性,CO转化率超过80 % ,但氨水沉淀催化剂的稳定性明显高于Na2 CO3 沉淀催化剂,前者在6 5 0h内的失活速率仅为0 0 1% /h .两种催化剂样品均表现出较低的甲烷选择性和较高的重质烃选择性,在实验运行期间,CH4选择性均保持在3%左右,C5+ 的选择性则保持在84

The Fe-Cu-K-SiO2 catalysts were prepared using ammonia or sodium carbonate as the precipitating agent and FeSO4 center dot xH(2)O as the precursor. The catalysts were characterized by atomic emission spectroscopy, N-2 adsorption, X-ray diffraction, X-ray photoelectron spectroscopy and Mossbauer effect spectroscopy. The results showed that the ammonia-precipitated catalyst had higher surface area and larger pore volume than the catalyst prepared using sodium carbonate as the precipitant. The main phase of the catalyst was alpha-Fe2O3. Both Fe3O4 and iron carbides phases were formed after the catalyst was reduced in the syngas atmosphere, and more iron carbides were found in the reduced ammonia-precipitated catalyst. The catalytic performance for Fischer-Tropsch synthesis was evaluated in a stirred tank slurry reactor under the reaction conditions of n (H-2) /n (CO) = 0.67, WHSV = 2 000 h(-1), p = 1.5 MPa and 250 degrees C. The catalyst showed high initial activity, and the CO conversion was higher than 80%, but the catalyst prepared using ammonia as the precipitating agent was more active and stable during 600 h on stream, and its deactivation rate was very low (0.01%/h). Both catalysts exhibited low selectivity for light hydrocarbons with methane selectivity around 3.0%, and high selectivity for heavy hydrocarbons with C5+ selectivity around 84%. The selectivity for C(2)similar to C-4 olefins over the ammonia-precipitated catalyst was higher than that over the sodium carbonate-precipitated catalyst.