Novel solid-solution catalysts for the CVD synthesis of hollow graphene nanospheres: Enabling efficient hydrogenation catalysis

Abstract

The development of heterogeneous catalysts with high activity is highly desired for hydrogenation reactions, where the catalyst support plays a crucial role in enhancing the activity of hydrogenation catalysts. In this study, a novel hollow graphene nanosphere (HGS) with open pores was synthesized via chemical vapor deposition (CVD) using Mg_0.91Fe_0.09O and Mg_0.9Mn_0.1O solid-solution catalysts for the first time. The growth mechanism of HGS was elucidated through detailed characterization of the catalyst and HGS. It was found that the in situ formation of solid solutions during the CVD process is the key to HGS growth. The unique pore structures and high surface area of HGS made it an excellent catalyst support. A Ru/HGS catalyst was prepared via impregnation and evaluated for the hydrogenation of 1-methylindole (NMID). Ru/HGS exhibits superior catalytic performance (TOF = 75.6 min⁻¹), surpassing commercial Ru/Al₂O₃ (TOF = 41.8 min⁻¹). The activation energy for NMID hydrogenation using Ru/HGS was determined to be 41.7 kJ/mol, significantly lower than the 80.7 kJ/mol for Ru/Al₂O₃. The catalyst characterization analysis and DFT calculations reveal that Ru nanoparticles on HGS were smaller, better dispersed, and formed stronger interactions with the support, enhancing NMID adsorption and hydrogen activation, particularly on the Ru(101) surface, which explained the superior catalytic performance of Ru/HGS over Ru/Al₂O₃. Furthermore, the Ru/HGS catalyst demonstrated broad applicability and high efficiency in hydrogenating various N-heterocyclic compounds, including quinoline, pyridine, and indole derivatives. This study introduces a new strategy for designing advanced catalysts with enhanced efficiency for hydrogenation.