Synthesis and Characterization of MgO-Doped / Acid Modified Metakaolin Supported Ni-Based Catalysts

Abstract

Catalytic steam reforming of bioethanol is an endothermic reaction for hydrogen production with high tendency of complete conversion at high temperature, but the catalyst is susceptible to deactivation due to the sintering of based metal and carbon deposition. MgO-doped/acid modified metakaolin supported nickel-based catalysts (with 5-25wt% nickel loading) were synthesized using wetness impregnation method and characterized. The physicochemical properties of the catalysts were examined using XRD, BET, SEM-EDX, XRF, FTIR and TG/DTA techniques. XRD patterns show the presence of nickel oxide, spinel MgAl2O4, NiAl2O4 in all the calcined catalyst samples, via characteristic peaks. Most of the crystallite sizes of the NiO particles in the synthesized catalysts were within 20.1-38nm, far less than the size effect threshold of 100nm, except CAT II, with crystallite size of 132.5nm, which could be attributed to the high tendency of NiO particles to agglomerate with MgO. Based on BET results, all the synthesized catalysts have pore diameter in the mesopore diameter range. SEM-EDX results show that there is nuclear interaction among MgO, NiO and Al2O3, as confirmed by XRD and XRF analyses. The FTIR analyses show that nickel phyllosilicate bond, Si-O-Al stretching vibration, OH stretching and metal-oxygen bond exist within the synthesized catalysts. The formation of MgAl2O4 and NiAl2O4 spinel phases is due to the interaction of active oxide components with acid modified metakaolin and MgO, which contributes to the catalyst thermal stability, as confirmed by TG/DTA analyses. These spinel structures would contribute to the catalysts’ activity and selectivity, as their structures could remain unchanged under severe reaction conditions. The mesoporous structure of the synthesized catalysts would aid the reactant gases to adsorb on its surface and easy diffusion through the catalyst’s channel after reaction. With better interaction among the support, promoter and based metal in the synthesized catalysts and available surface OH group, the formation and conversion of adsorbed formate intermediate during steam reforming reactions would be facilitated, and in turn reduce carbon deposition.