Partial Hydrogenation of Waste Cooking Oil Biodiesel Catalyzed by Iron Oxide/Nickel Nanoparticles Supported on Steel Slags

Biodiesel, produced mainly through transesterification of vegetable oils or animal fats, is a promising alternative to fossil fuels due to its biodegradability and reduced environmental impact. Biodiesel synthesized from waste cooking oil (WCO) is even more appealing from an environmental sustainability point of view. However, the crude WCO biodiesel is not immediately suitable as a fuel due to inherent limitations such as poor oxidative stability and suboptimal cold flow properties. To overcome these issues, an upgrading reaction must be carried out, which consists of a partial hydrogenation of the polyunsaturated chains of FAMEs aiming at converting polyunsaturated compounds to monounsaturated ones while avoiding fully saturated products. This study introduces a strategic modification of waste steel slag (SS) to obtain a new catalyst effective in the WCO biodiesel upgrading step. A bimetallic Fe–Ni system onto SS was synthesized aiming at combining the stability and basic properties of the support with the high catalytic activity of the metals. Two methods for partial hydrogenation were employed: the conventional partial hydrogenation method with molecular hydrogen and the catalytic transfer hydrogenation using NaBH4. Both methods utilized heterogeneous nickel–iron oxide-based catalysts supported onto SS leading to a WCO biodiesel mixture rich in C18:1 chains.