Toward maximizing the selectivity of diesel-like hydrocarbons from oleic acid hydrodeoxygenation using Ni/Co-Al2O3 embedded mesoporous silica nanocomposite catalysts: An experimental and DFT approach

Abstract

The development of an effective hydrodeoxygenation (HDO) catalyst is crucial for controlling product selectivity and catalyst stability. In this study, we synthesized monometallic (Ni and Co), as well as a bimetallic, NiCo embedded mesoporous composite catalysts using a simple one-step method involving meso-macroporous silica, boehmite, nickel acetate, and cobalt acetate. The synthesized range of catalysts (5, 10, 15 wt% Ni, 10 wt% Co, 10 wt% NiCo) were thoroughly characterized by various techniques. The characterization results showed that the present method leads to the growth of nano-catalyst on porous silica surface (M−Al2O3/SiO2, M = Ni, Co, NiCo). These composites exhibited strong metal-support interaction, improved surface and texture properties and significant amount of weak to medium acid sites. The M−Al2O3/SiO2 composite catalysts demonstrated improved catalytic performance in the HDO of oleic acid. At temperature of 375 °C, the conversion trend of catalysts followed the order; 10NiCo-Al2O3/SiO2 (89%) > 10Ni-Al2O3/SiO2 (87%) > 10Co-Al2O3/SiO2 (85%) > 10Ni/SiO2 (81%). Moreover, the yield of C15-C18 hydrocarbons was substantially enhanced at moderate temperature compared to unmodified silica support. Time-on-stream experiments further confirmed the relative stability of the composite catalysts over a period of 20 h. Furthermore, density functional theory (DFT) ab initio calculations were performed where the adsorption of oleic acid on icosahedral monometallic M13 (M = Co or Ni) and bimetallic Ni2Co2 nanocluster deposited on γ-Al2O3 (110) support was investigated. The adsorption strength for the most stable conformations followed the order: Ni13/amorphous SiO2 >Ni2Co2/Al2O3 >Co13/Al2O3 >Ni13/Al2O3. Bader charge transfer analysis indicated higher charge transfer at the interfaces of γ-Al2O3Al2O3(110) supported catalysts compared to Ni13/amorphous SiO2 surface.