Fully exposed Pd species on nanodiamond/graphene hybrid support for the efficient toluene hydrogenation reaction

Abstract

Liquid organic hydrogen carriers have emerged as promising hydrogen storage systems, offering notable advantages over conventional storage and utilization efficiency methods. However, designing a catalyst that operates at low temperatures and remains cost-effective poses a significant challenge. We successfully synthesized Pd species (single atoms, fully exposed clusters, and nanoparticles) on a nanodiamond/graphene (ND@G) hybrid support for toluene hydrogenation. The structure of as-developed Pd catalyst was investigated by HAADF-STEM, X-ray absorption fine structure, Raman, XRD, XPS, and other characterizations. Remarkably, the Pd_n/ND@G catalyst achieved a toluene conversion rate of 99.3% (100°C, 2.0 MPa H₂) without loss of catalytic ability after 5 runs, which exhibited excellent catalytic performance and stable activity. Furthermore, the Pd_n/ND@G catalyst exhibited an apparent activation energy as low as 62.36 ± 3.33 kJ mol⁻¹ and an initial turnover frequency of 33.1 h⁻¹ at 100°C. By adjusting the size and metal-dependent effects, we have achieved enhanced catalytic performance for toluene hydrogenation, thus paving the way for the design of efficient liquid organic hydrogen storage catalysts.