A highly stable Ru/LaCO3OH catalyst consisting of support-coated Ru nanoparticles in aqueous-phase hydrogenolysis reactions

Abstract

Hydrothermal reduction under aqueous conditions is widely used to convert biomass into more valuable products. However, the harsh conditions inherent in the process can irreversibly alter the intrinsic structure of the support, as well as dissolve the metal ions into the aqueous solution. In this work, for the first time we have synthesized a new highly hydrothermally stable Ru/LaCO₃OH catalyst mostly consisting of Ru nanoparticles partially encapsulated by the LaCO₃OH support with a strong metal–support interaction (SMSI), which confers high stability and activity to the catalyst under hydrothermal reduction conditions in the hydrogenolysis of the biomass model molecules guaiacol and glycerol. During impregnation, the RuCl₃·3H₂O precursor initially reacts with LaCO₃OH to form a LaRu(CO₃)₂Cl₂ complex and LaOCl. XPS demonstrated that Ru was present in the oxidized state, TEM and XRD showed the absence of Ru⁰, and the XRD pattern showed the presence of the characteristic lattice fringe of LaOCl. While the LaRu(CO₃)₂Cl₂ complex was resistant to H₂ reduction at 350 °C, the complex underwent facile reduction to Ru⁰ under hydrothermal conditions at 240 °C. In the subsequent process, LaRu(CO₃)₂Cl₂ and LaOCl underwent hydrolysis, forming crystalline LaCO₃OH (confirmed by Ag⁺ titration and XRD patterns), Ru(OH)₃, and HCl. The Ru(OH)₃ was reduced in situ to Ru⁰ nanoparticles, as revealed by XPS and TEM analysis. The simultaneous hydrothermal reduction of Ruⁿ⁺ species and the formation of crystalline LaCO₃OH result in the formation of Ru nanoparticles encapsulated by a protective LaCO₃OH layer, as evidenced by HRTEM and DRIFTS CO adsorption measurements. The preparation of catalysts with this unique structure comprising metal nanoparticles protected by the support itself, which confers additional stability, is a novel strategy to prepare hydrothermally stable catalysts.