Unraveling the Impact of Niobia Promotion on Pt/Al2O3 for Enhanced Catalytic Performance in Benzyltoluene Reactions

Abstract

Liquid organic hydrogen carriers (LOHCs) are promising materials for hydrogen storage due to their convenient and stable physical properties. Recent studies have focused on benzyltoluene for its favorable properties; however, its low efficiency in hydrogenation and dehydrogenation processes limits its applicability. Therefore, an approach to overcoming this challenge through catalysis is necessary. In this study, Pt/Al2O3 catalysts promoted with Nb (Pt-Nb) exhibited enhanced activity and selectivity in both hydrogenation and dehydrogenation of benzyltoluene (optimal at 5 wt % Nb). The selective blocking of hyperactive undercoordinated Pt sites by niobium oxide played a crucial role in enhancing the selectivity and stability. Additionally, the electron-withdrawing effect and increased occurrence of hydrogen spillover resulting from its acidic properties could modify the interaction with the hydrogen. Notably, the introduction of the niobium promoter seems to create additional adsorption sites for hydrogen, thereby enhancing the efficiency of LOHC molecules to bind on the Pt surface. It was discovered that the terrace sites of Pt catalysts could act as gathering points for reverse-spillover hydrogen during LOHC reactions. Therefore, when promoted with Nb, the active Pt terrace sites become capable of efficiently adsorbing LOHC molecules while simultaneously serving as sites for reaction with returning hydrogen. In summary, the addition of the niobium promoter elevates the efficiency of the platinum terrace, which serves as the active site, while suppressing the adverse effects of undercoordinated Pt sites. However, the growth of NbO x with increasing Nb content blocks the active terrace Pt sites, underscoring the need for appropriate optimization processes.