制备方法对钼基耐硫甲烷化催化剂性能的影响

Influence of preparation methods on Mo-based catalyst for sulfur-resistant methanation

合成气甲烷化是煤制天然气工艺的主要过程之一。与传统的镍基催化剂相比,钼基催化剂用于耐硫甲烷化可以省去精脱硫过程和水汽变换过程,具有一定的技术和成本优势。但是钼基催化剂活性相对较低,尤其是低温活性和高温稳定性有待提高。对比研究不同方法制备的MoO_3/ZrO_2催化剂在固定床反应器上的耐硫甲烷化性能,发现采用溶液燃烧法制备的催化剂在相同条件下具有较高的耐硫甲烷化活性,当空速为5000 h^(-1)、反应压力为3MPa、反应温度为300℃和400℃时其CO转化率可分别达到26%和79%。催化剂的N_2物理吸附、透射电镜、X射线衍射和Raman光谱等表征结果表明,溶液燃烧法制备的催化剂具有较小的ZrO_2晶粒尺寸和较大的比表面积,活性组分Mo物种在ZrO_2载体上的分散性更好。而采用共沉淀法和浸渍法制得的MoO_3/ZrO_2催化剂存在不同程度的Mo物种团聚现象,导致其耐硫甲烷化活性较低。

Methanation of syngas is one of the main processes of coal to synthetic natural gas. Compared with the traditional nickel based catalyst, molybdenum based sulfur-resistant catalyst for methanation has certain technical and cost advantages since it can avoid fine desulfurization process and water gas shift reaction. Unfortunately, the activity of molybdenum based catalyst is lower than Ni-based catalyst, especially the low temperature activity and high temperature stability. In this paper, the methanation performance of Mo-based catalyst prepared by different methods was investigated in a continuous-flow, fixed-bed reactor. The catalyst prepared by solution combustion with a gas hourly space velocity of 5000 h-1 and pressure of 3 MPa exhibited the highest activity with CO conversion of 26% and 79% at 300℃ and 400℃, respectively. The prepared catalysts were characterized by N2-physisorption, Transmission Electron Microscope（TEM）, X-ray diffraction（XRD） and Raman Spectroscopy（RS）. The catalyst prepared by solution combustion method showed a higher dispersion of Mo species on the surface of ZrO2 support, owing to its larger surface area and smaller ZrO2 particle size. In contrary, the large Mo species were formed on the catalysts prepared by co-precipitation and impregnation methods, which was considered as one of the factors resulting in their lower methanation activity.