Ni, Co & Cu substituted CeO2: A catalyst that improves H2/CO ratio in the dry reforming of methane

Abstract

This study focusses on developing a efficient heterogenous catalyst using a comparative approach of substituted and supported metal oxides. In this article two types of catalysts were prepared (I)Tri metal supported catalysts (NiCoCu/CeO2) and (II)-Trimetal substituted catalysts (Ce0.85Ni0.05Co0.05Cu0.05O2). The combination of transition-metal as Trimetal substituted catalyst is unique and novel and has not been explored earlier. The aim is to choose the right material which qualifies to be a potential DRM catalyst. The idea of comparing supported and substituted catalysts is to prove that substitution is indeed beneficial even though the surface may not have very high metal concentration. So, where the activity comes from? The activity comes from the activated oxygen which is generated on the surface as a result of the substitution. This activated oxygen is missing in the supported catalyst. In substitutional catalyst, the metals are substituted in the bulk while in the supported system the metals are confined to the surface. Both supported and substituted catalysts exhibit distinct differences in the dry reforming of methane (DRM) reaction. The NiCoCu substituted CeO2 exhibited high stability and activity under DRM reaction. Thermal gravimetric analysis (TGA) and transmission electron microscopy (TEM) explained that low amount of amorphous and graphitic carbon was deposited during the reaction in the substituted catalyst which is also removable easily. In comparison NiCoCu supported CeO2 catalyst is less reactive and less stable because carbon removal propensity is not good on the surface. Further investigation using the transient studies confirms the stability of the substituted catalyst is due to the ease of the reactions; C + OL → CO and CO2 + C → 2CO. The prevalence of methane decomposition step and the reactivity of the surface lattice oxygen (OL) is an essential tool to dictates the H2/CO ratio and the catalytic stability. Novelty of this work is in elucidating the exact role of surface oxygen in imparting the activity and stability to the DRM catalyst. This work also elucidates process mechanism for DRM in NiCoCu substituted CeO2 based on the transient reactivity of the catalyst. Our findings have significant implications in rationalizing the approach for the development of more efficient and effective DRM catalysts based on the principle of lattice oxygen.