H2S与CH4重整制氢Mo/Al2O3催化剂的稳定性研究

Stability research of Mo/Al2O3 catalysts during hydrogen sulfide reforming with methane for hydrogen production

关键词:  硫化氢  甲烷  重整制氢  簇状氧化铝  硫化钼  稳定性

Key words:  hydrogen sulfide  methane  hydrogen production by reforming  cluster Al₂O₃  MoS₂  stability

摘要:

目的 研究H₂S/CH₄重整制氢反应过程中,Mo/Al₂O₃催化剂在高CH₄含量下的稳定性问题。方法 分别采用簇状结构Al₂O₃(Cluster Al₂O₃)和商业Al₂O₃(Com Al₂O₃)为载体制备了Mo/Al₂O₃催化剂,考查在常压800 ℃、n(H₂S)∶n(CH₄)= 1∶5、体积空速20 000 h-1的反应条件下,H₂S和CH₄的反应 速率以及H₂生成速率随时间的变化；结合采用了SEM、XRD、HRTEM、BET、EA、TG、Raman以及NH₃-TPD、CO₂-TPD等多种表征分析手段与方法。结果 与Mo/Com Al₂O₃催化剂相比,Mo/Cluster Al₂O₃催化剂具有更好的催化活性和稳定性,其H₂的初始生成速率达8.4 mmol/(g·min),为前者的3.8倍,20 h后的下降幅度也显著小于前者；Cluster Al₂O₃载体虽然比表面积较小,但所负载的活性MoS₂颗粒分散性更好,且能保持高温稳定。结论 其原因可能与Cluster Al₂O₃表面拥有适宜的酸碱位强度及数量分布有关；同时,较小颗粒的MoS₂活性位更多,使得Mo/Cluster Al₂O₃催化剂在反应过程中表现更稳定,并能在一定程度上抑制CH₄裂解积炭。 

Abstract:

Objective It is to research the problem that Mo/Al₂O₃ catalyst is highly active for the reaction between H₂S and CH₄ to produce H₂, but couldn’t sustain a long term stability especially in a condition of high CH₄ content. Methods Two kinds of Mo/Al₂O₃ catalysts are compared in term of both H₂S and CH₄ reaction rates and H₂ generation rate varying with reaction time on stream under the conditions of 0.1 MPa, 800 ℃, n(H₂S)∶n(CH₄) = 1∶5, and gas hourly space velocity of 20 000 h-1; and the various characterization and analysis techniques and methods are also used with SEM, XRD, HRTEM, BET, EA, TG, Raman and NH₃-TPD/CO₂-TPD. Results The Mo/Cluster Al₂O₃ catalyst prepared with the cluster structure Al₂O₃ as the supporter has a better catalytic activity and stability than the Mo/Com Al₂O₃ catalyst obtained with the commercial Al₂O₃ supporter. The H₂ generation rate over the Mo/Cluster Al₂O₃ catalyst reached 8.4 mmol/(g·min) in the initial reaction stage, which was 3.8 times of the Mo/Com Al₂O₃ catalyst, and the decrease after 20 h is significantly less than the former; It is found that although the Cluster Al₂O₃ supporter possessed a lower specific surface area, the dispersion of active MoS₂ particles supported on Cluster Al₂O₃ is better and can make MoS₂ particles stabilized at high temperatures. Conclusion sThe reason could be assigned to the suitable acidic and alkaline strength and quantity distributions on the surface of Cluster Al₂O₃. Meanwhile, smaller-particle MoS₂ has more edge-exposed active sites, which make Mo/Cluster Al₂O₃ catalyst perform more stable during the H₂S/CH₄ reforming reaction,and also can inhibit carbon deposition caused by CH₄ cleavage to a certain extent.