孔结构对低压合成气制甲醇选择性的影响

摘要

Cu/ZnO/Al2O3catalysts were prepared by a co-precipitation method using different binders under various pressures, and the micro-structure and catalytic performance of the prepared catalysts were studied by TEM and BET. The results show that the internal diffusion resistance increases with the increase of pelleting force, which causes the decrease of CO conversion and the increase of methanol selectivity. The reaction mechanism study and the comparison of the mean free path of CO and H2 under reaction condition show that the change of pore structure has different diffusion effects on each gas. Therefore, the reaction route was varied when the H2 concentration near active sites decreases, and the change of the reaction rate is also affected, which leads to the change of methanol selectivity. Experiments using binders with different molecular weights verified this mechanism.%采用共沉淀法在不同压片压力和黏结剂种类条件下制备 Cu/ZnO/Al2O3催化剂，通过TEM、BET 等表征手段考察了催化剂微结构以及催化特性的变化。研究表明，压片压力增大，内扩散阻力增大，导致CO转化率降低，而甲醇选择性增大。通过分析反应机理，比较反应条件下CO和H2分子运动平均自由程，得出孔结构变化对两种反应气体扩散影响不同。孔结构变化使孔道内活性中心表面H2相对浓度下降后，各反应路径受到的影响不同，反应速率下降的比例不同，从而导致反应的选择性改变。随后不同分子量黏结剂的实验验证了这一判断。