摘要
CH4与CO_2干重整反应对于环境保护和天然气资源的合理利用具有重要意义。SiO_2和Al_2O_3是适用于甲烷干重整反应的两种典型的催化剂载体。为了阐明这两种载体对催化剂性能的影响,本研究采用等体积浸渍法制备了Ni/Al_2O_3和Ni/SiO_2催化剂,并利用BET、TEM、H2-TPR、XRD、TG和Raman等技术对还原和反应后的催化剂进行了表征。结果表明,由于载体的性质不同,Ni基催化剂在甲烷干重整中的催化性能也不同。Ni/SiO_2催化剂的初始活性较高,但由于其金属-载体相互作用较弱,催化稳定性较差,在800℃下反应15 h其催化活性急剧下降;较弱的金属-载体相互作用使得Ni/SiO_2催化剂上的Ni颗粒较大,有利于积炭前驱物种的生成,导致催化剂快速失活。而对于Ni/Al_2O_3催化剂,金属-载体相互作用较强,Ni颗粒较小,但由于Ni与Al_2O_3生成了NiAlxOy物种,有效活性位减少,其催化活性相对较低,但催化稳定性较好,干重整反应进行50 h其活性保持稳定; Ni与Al_2O_3之间较强的相互作用有利于形成小且稳定的Ni粒子,能减少积炭,因而具有优异的催化稳定性。
Dry reforming of methane( DRM) with CO_2 is of great significance in the environmental protection and the utilization of natural gas. SiO_2 and Al_2 O_3 are two typical catalyst supports used in DRM. To elucidate the effect of these two supports on the catalytic performance,in this work,Ni/SiO_2 and Ni/Al_2 O_3 catalysts are prepared by the incipient wetness method and characterized by BET,TEM,H2-TPR,XRD,TG and Raman technologies. The results indicate that the performance of Ni-based catalyst is closely related to the properties of support and the Ni/SiO_2 and Ni/Al_2 O_3 catalysts are rather different in their DRM performance.Ni/SiO_2 catalyst exhibits higher initial activity but poor stability; its catalytic activity decreases rapidly in 15 h for DRM at 800 ℃.Because of the weak metal-support interaction,Ni species on the Ni/SiO_2 catalyst is present as large Ni particles,which may promote the formation of coke precursors,viz.,the multi-carbon Cn species,leading to the fast carbonaceous deposition and catalyst deactivation. In contrast,the Ni/Al_2 O_3 catalyst displays a lower activity but a much higher stability; its activity in DRM keeps stable in 50 h. Although Ni particles in the Ni/Al_2 O_3 catalyst is much smaller,the strong metal-support interaction promotes the formation of NiAlxOy species during the catalyst preparation process,which may lead to a decrease in the content of active Ni species and give the Ni/Al_2 O_3 catalyst a relatively low catalytic activity in DRM; however,the strong metal-support interaction between Ni and Al_2 O_3 is also of benefit to the formation and stabilization of small Ni particles,which can alleviate the carbanceous deposition and afford the Ni/Al_2 O_3 catalyst a better stability.
引文
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