Ru supported on acid-treated sepiolite (Ru/ASep) exhibits higher acidic sites with stronger Lewis acidity, facilitating the activation of N-FFA intermediate on the catalyst surface, contributing to the superior catalytic performance in reductive amination of furfural (FUR) to furfurylamine (FUA) compared to Ru supported on untreated sepiolite (Ru/Sep), affording an excellent yield.

Abstract

The catalytic reductive amination of bio-based carbonyls has emerged as a promising route for producing N-containing compounds, having a wide range of applications in pharmaceuticals and agrochemicals. In this work, Ru supported on acid-treated sepiolite (Ru/ASep) is designed for the reductive amination of furfural (FUR) to furfurylamine (FUA) using H₂ and NH₃ as reductant and nitrogen source, respectively. Ru/ASep exhibited two times higher catalytic activity compared to its counterpart, that is, Ru supported on parent sepiolite (Ru/Sep), yielding 98.4% FUA. The NH₃-temperature-programmed desorption (TPD) and NH₃-diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy studies show that Ru/ASep exhibited an increase in total acidic sites with relatively more Lewis acidic sites than Ru/Sep, contributing to C═N bond activation and leading to the formation of FUA in high yield. The CO₂-TPD results indicate that ASep possesses a large amount of basic sites, which contribute to a facile reduction of RuO_x to Ru⁰ in Ru/ASep, as confirmed by H₂-temperature programmed reduction (TPR) studies. H₂-TPD studies indicate a higher amount of H₂ activated over Ru/ASep, favoring the intermediate hydrogenation step to form FUA. Furthermore, the poisoning studies with KSCN indicated that Lewis acidic sites on the surface of Ru/ASep played a crucial role in the formation of FUA.