助剂Co对硫化氢与甲烷重整制氢Mo/Al_(2)O_(3)催化剂稳定性的影响

Influence of Co Addition on the Stability of Mo/Al_(2)O_(3)Catalysts During Hydrogen Sulfide Reforming with Methane for Hydrogen Production

H_(2)S与CH_(2)重整制氢反应是一条新型的制氢技术路线,但目前用于该过程的高活性Mo/Al_(2)O_(3)催化剂存在着稳定性不佳的问题。以商业γ-Al_(2)O_(3)(Al_(2)O_(3))为载体,通过共浸渍方式在20%Mo/Al_(2)O_(3)催化剂中添加不同含量(质量分数为1%~20%)的Co助剂,在常压、反应温度为800℃、H_(2)S和CH_(2)体积比为1:5、体积空速为20000 h;的反应条件下,考察了H_(2)S和CH_(2)的反应速率及H_(2)生成速率随时间的变化。结果表明:Co的存在提高了CH_(2)的转化活性,且随Co添加量的增多CH_(2)反应速率持续提升,使得H_(2)生成速率相应提高,但同时也使催化剂上的积炭量增加,因此Co的添加未能有效减缓催化剂性能的衰退,另外,Co的存在也不利于H_(2)S转化。多种催化剂结构表征结果显示,CH_(2)裂解积炭反应的加快与Co_(3)Mo合金形成有关,其导致具有石墨烯层或纳米碳管结构的积炭大量生成。积炭覆盖MoS_(2)颗粒边缘活性位,以及活性颗粒自身的长大,是催化剂失活的主要原因。

The technology of H_(2)S reforming with CH_(2)for hydrogen production provides a new technical route to comprehensive utilization of both sour natural gases having high H_(2)S contents and the large amount of H_(2)S exhausted from refinery hydrodesulfurization plants.Mo/Al_(2)O_(3)catalyst is an active one for the reaction between H_(2)S and CH_(2)to produce H_(2),however,behaving a drawback of poor stability accompanying with itself.In order to modify the catalyst stability,in this paper,a series of Mo/Al_(2)O_(3)catalysts with different Co addition amount(mass fraction 1%-20%)were prepared using co-impregnation method and a commercialγ-Al_(2)O_(3)(denoted as Al_(2)O_(3))as the support.The catalytic performances of these catalysts were tested and compared in term of both H_(2)S and CH_(2)reaction rates and H_(2)generation rate varying with reaction time on stream under the conditions of 0.1 MPa,800℃,volume ratio of H_(2)S to CH_(2)1:5,and gas hourly space velocity of 20000 h;.The results showed that the addition of Co failed to effectively slow the performance decline of the 20%Mo/Al_(2)O_(3)catalyst and it could improve the CH_(2)conversion activity With the increase of Co amount,the CH_(2)reaction rate was improved,and the H_(2)generation rate was raised as a result of increased CH_(2)decomposition rate.Nevertheless,the presence of Co was not beneficial to H_(2)S conversion,and the carbon deposition amount on the catalyst also increased.The multiple characterization of catalyst structures and properties reveals that the acceleration of CH_(2)decomposition was associated with Co_(3)Mo alloy formation after Co adding to 20%Mo/Al_(2)O_(3)catalyst,leading to substantial carbon deposition with graphene layer or carbon nanotube structure.The cover of carbon deposition on the active edge sites of MoS_(2)particles and the growth of MoS_(2)particles at high reaction temperature are the main causes of catalyst deactivation.