Rheological characteristics of nickel–alumina sol–gel catalyst

A sol–gel of nickel–alumina catalysts can be employed as a thin layer (< 100 μm) on the surface of plate reactors to reduce mass and heat transfer limitations compared with pellet catalysts. The knowledge of flow behavior of sol–gel systems is an important tool to characterize the sol–gel properties, stability, and applications. In this study, the steady rheological properties of the nickel-alumina sol–gel have been investigated as a function of nickel content (0–75 wt.%). Increasing the Ni content led to an increase in the apparent viscosity of sol–gel samples to reach the maximum at 30 wt.% Ni content, which in turn decreased upon further addition of Ni. The Herschel–Bulkley model fitted well the flow curves of sol–gel samples. Increasing the Ni content in the mixture led to behavior transition from Newtonian to shear thinning behavior. High content of Ni particles contributed to significant yield stress. Samples with nickel-free and low Ni content (5 wt.%) showed Newtonian behavior that passed into Bingham plastic at 10 wt.% and 15 wt.% Ni content. However, this in turn ran into shear thinning behavior with a yield stress at Ni content of ≥ 20 wt.%. On the other hand, adding Ni to the sample beyond 60 wt.% led to forming a weak gel. Shear thinning behavior accompanied with time independent behavior observed for nickel–alumina sol–gel are important properties for coating process.