Effect Of The Interaction Between Metal And Support Of Ni/Al₂O₃ Catalysts On Carbon Deposition During Dry Reforming Of Methane

Dry reforming of methane（DRM）makes full use of two greenhouse gases,which provides a potential solution for the problem of greenhouse effect and global warming in the future.At the same time,the syngas produced by this reaction is the theoretical raw material of Fischer-Tropsch synthesis.There are also many side reactions in the reaction process,in which the decomposition of methane and the disproportionation of carbon monoxide are easy to lead to the carbon deposition of catalyst.The embedding of carbon species generated in the reaction process may cover the active component surface,leading to the deactivation of catalyst;while the carbon tubes may block the reactor.Therefore,the design of a catalyst with high activity and good stability at high temperature by studying the mechanism of carbon deposition and controlling the type of carbon deposition is the most important task in the industrialization of dry reforming of methane.In this work the problem of carbon deposition in the high temperature dry reforming of methane is mainly solved.Firstly,the Ni/Al₂O₃catalysts is pretreated by the way of the two-step calcining for many times aim to control the size of the active component Ni particles and the interaction between the metal and the support,so as to realize the regulation of carbon deposition types,and to achieve the high temperature stability.In this,Ni²⁺was introduced into the catalyst system by traditional impregnation method with MIL-53（Al）as the template.Two kinds of catalysts,Ni/NiAl₂O₄-I and Ni/NiAl₂O₄-II,were obtained by direct high-temperature calcination and low-temperature calcination in inert atmosphere followed by high-temperature calcination.It was found that the morphology of the catalyst observed by SEM was lamellar and massive.Through the analysis of temperature programmed reduction of hydrogen,it was found that the process of reduction-oxidation-reduction makes the freeα-Ni O with weak interaction between metal and support to transform into theβ-Ni O with relative strong interaction between them,which realizes the regulation of interaction between metal and support.The results of TEM show that the active component Ni is evenly dispersed on the support,and the particle size of Ni nanoparticles on the reduced Ni/NiAl₂O₄-II is smaller.The dry reforming performance of two catalysts was studied.The results showed that under the pressure of 0.1 MPa and air speed of 60000 m L·g^-1·h^-1,two kinds of catalysts could also keep good activity,where methane and carbon dioxide conversion of Ni/NiAl₂O₄-II reached 37%and 50%at 650℃,respectively.Stability experiments were conducted at 650℃for a long time of50 h at the same condition,the results showed Ni/NiAl₂O₄-I catalyst was good,but the reactant conversion of Ni/NiAl₂O₄-II was reduced at a slower speed.The study found that there are a lot of carbon in reactor pipeline for Ni/NiAl₂O₄-I catalyst.we found that the carbon existed in the form of nanotubes without the parcel by observing the SEM images.Therefore,the catalytic performance of catalysts is not changed.However,carbon nanotubes have not been observed in the SEM pictures of Ni/NiAl₂O₄-II,but the carbon deposition mainly existed in the form of the embedding carbon covering the active component,which hinders the contact of the reaction gas with the active component.Thus,the conversion rate of the reactions gradually decreases with time.Therefore,two different treatment methods had great influence on the type of carbon deposition of catalysts.