Different Metal Support Interactions over NiK/Mixed Oxide Catalysts and Their Effects on Catalytic Routes in Steam Catalytic Cracking of Vacuum Residue

Abstract

NiK/ceria-zirconia (CZ) and NiK/ceria-zirconia-alumina (CZ-A) catalysts were investigated in order to further understand the roles of mixed-oxide supports in the steam catalytic cracking of vacuum residue (VR). Compared to thermal cracking, higher conversions and liquid yields were achieved over the catalysts. Steam decomposition occurring over the CZ and ZrO2 phases provided an alternative hydrogen and oxygen sources for hydrogenation and oxidative cracking, respectively. The introduction of Ni into the CZ support induced the formation of Ce-x(Zr-Ni)(1-x)O2-delta solid solution and the isolation of the ZrO2 phase via a strong metal support interaction, resulting in greater oxygen vacancy in the bulk structure. In contrast, the strong interaction of CZ and Ni phases with Al2O3 induced higher dispersions of CZ and Ni phases in the NiK/CZ-A catalyst, which resulted in a greater density of oxygen vacancies on the surface and higher CeO2 reducibility. As a result, the quality of the liquid products and naphtha yields were significantly improved by hydrogenation over the nickel metallic sites and oxidative cracking through the metal support interaction.