Novel Approach of Reusing the Precious Ru in the Wastewater Derived from the Depolymerization of Lignite to Prepare Ru–AC Catalysts Doped with Nb₂O₅

Abstract

Hydrogenation reduction of ethyl levulinate (EL) into γ-valerolactone (GVL) conforms to the requirement of sustainable development of society. Generally, ruthenium-based catalysts are considered excellent catalysts in hydrogenation reactions. However, most of the Ru-based catalysts were commonly constructed with expensive high-purity Ru-containing compounds, which leads to the high cost of the catalysts. In this work, a novel route of using the ruthenium-containing waste solution generated from the depolymerization of lignite as ruthenium source to construct a Ru/activated carbon catalyst doped with niobium oxide (Ru/Nb-AC) was established. The results showed that nearly entire ruthenium in the waste solution (>99%) was transferred into the catalyst, indicating that the process could utilize ruthenium in the waste solution efficiently. Compared with the catalyst constructed with a high-purity ruthenium-containing compound (RuCl 3 ), the catalyst prepared using the Ru-containing waste solution showed similar activity in the hydrogenation of ethyl levulinate (EL) into γ-valerolactone (GVL) under identical reaction conditions. The catalyst could be used repeatedly five times without an obvious decrease in performance. Finally, the possible reaction mechanism for the transformation route of EL to GVL over the Ru/Nb-AC catalyst was proposed. This study provides a novel route for the construction of Ru-based catalysts in the biomass catalytic transformation process and also gives an efficient way of recycling and reusing Ru-containing waste solution after ruthenium ioncatalyzed oxidation (RICO) process of lignite.

Recent Progress in Turning Waste into Catalysts for Green Syntheses

“…Yao et al developed a novel method for fabricating Ru-based catalysts using Rurich waste from lignite depolymerization processes [42]. The recycled catalyst showed comparable efficiencies to conventional Ru catalysts in the hydrogenation of ethyl levulinate to γ-valerolactone, maintaining its activity across multiple cycles.…”