Ni/MgO/Al2O3催化剂上以1-甲基萘为模型化合物高温焦炉煤气焦油的催化转化

采用共浸渍薄水铝石(AlOOH)方法制备了一系列Ni/MgO/Al₂O₃催化剂, 并采用N₂气吸附及Ｘ射线衍射等手段进行了表征. 选择1-甲基萘作为焦油模型化合物, 研究了该催化剂催化转化具有较低水蒸气/碳摩尔比(n_H2O/n_C) 的高温焦炉煤气(COG)中焦油催化反应性能. 考察了催化剂中MgO含量及反应条件等对催化剂性能的影响. 实验结果表明, 在775 ℃和n_H2O/n_C=0.7条件下, MgO改性的Ni/MgO/Al₂O₃催化剂对1-甲基萘催化转化为小分子气体反应具有较好的催化活性和稳定性; 热重分析表明, MgO的加入能显著提高催化剂的抗积炭能力. 在Ni/MgO/Al₂O₃催化剂上, 反应气中高浓度H₂S气体(0.25%, 体积分数)能够促进焦油催化转化为小分子气体, 这可能是由于H₂S在Ni表面的可逆吸附形成更适合于重整反应的活性位, 同时抑制了烷烃裂解吸附形成的碳在金属中的溶解、扩散并最终形成积炭过程.

Catalytic Conversion of 1-Methylnaphthalene as Tar Model Compound from Hot Coke Oven Gas over Ni/MgO/Al2O3 Catalysts

A series of Ni/MgO/Al₂O₃ catalysts were prepared by the method of co-impregnating boehmite(AlOOH) and characterized using N₂ adsorption and X-ray diffraction(XRD). 1-Methylnaphthalene was selected as a tar compound to investigate the performance of the Ni/MgO/Al₂O₃ catalysts for converting tar from hot coke oven gas(COG) with a low water to carbon molar ratio(n_H2O/n_C) into light fuel gases. The effects of MgO content and operating conditions were examined at 775 ℃ and n_H2O/n_C=0.7. The experimental results showed that the MgO modified Ni/MgO/Al₂O₃ catalysts possessed excellent catalytic activity and stability for the conversion of 1-methylnaphthalene to small gas molecules. TG analysis of the used catalysts showed that addition of MgO in the Ni/MgO/Al₂O₃ catalysts could significantly enhance resistance to carbon deposition. It was first found that the presence of higher concentration of H₂S(0.25%, volume fraction) could promote the conversion of tar to small gas molecules over the Ni/MgO/Al₂O₃ catalysts. This might be because the reversible adsorption of H₂S on the surface of metallic Ni led to the formation of ensemble of Ni sites more suitable for steam reforming and, meanwhile, inhibited dissolution and diffusion of carbon in metal Ni from dissociative adsorption of hydrocarbon, leading to the formation of coke disposition on the catalyst.