A series of nonprecious metal nanoparticles (NPs) supported by metal-organic framework MIL-101 were synthesized using four methods and their catalytic performance on hydrogen evolution from ammonia borane (NHBH) was studied. The results showed that the crystalline Co NPs with size of 4.5-8.5 and 14.5-24.5 nm had low activities featuring the total turnover frequency (TOF) values of 9.9 and 4.5 mol mol min, respectively. In contrast, the amorphous Co NPs with size of 1.6-2.6 and 13.5-24.5 nm exhibited high activities featuring the total TOF values of 51.4 and 22.3 mol mol min, respectively. The remarkably different activities could be ascribed to the different crystallinity and size of Co NPs in the catalysts. Moreover, the ultrasound-assisted in situ method was also successfully applied to bimetallic systems, and MIL-101-supported amorphous CuCo, FeCo and NiCo NPs had the catalytic activities with total TOF values of 51.7, 50.8, and 44.3 mol mol min, respectively, which were the highest in the values of the reported non-noble metal Co-based catalysts. The present approach, namely, using the synergistic effect of crystallinity and size of metal NPs, may offer a new prospect for high-performance and low-cost nanocatalysts.

Two N-doped carbon materials, N-doped Vulcan XC-72 carbon labelled as NXC and graphite carbon nitride labelled as C3N4, were selected as supports to prepare a series of bimetallic AuM (M = Co, Ni) nanoparticles (NPs) using three different reduction ways towards mixed metal ions AuCl4 − and M 2+ , and then the as-synthesized supported bimetallic AuM NPs were used as catalysts for hydrolytic dehydrogenation of ammonia borane (NH3BH3). All the catalysts exhibited high dispersion and small size of bimetallic NPs; however, they exhibited remarkably different catalytic activities featuring total turnover frequency (TOF) values from 6.4 to 42.1 molH2⋅molcat -1 ⋅min -1 . Among all the catalysts, the NXC-immobilized AuCo NPs through in situ synthesis using NaBH4 and NH3BH3 as reductants exhibited the highest activity with a total TOF value of 42.1 molH2⋅molcat -1 ⋅min -1 , which was among the highest values for Co-based catalysts ever reported for hydrolytic dehydrogenation of NH3BH3. This remarkably enhanced activity may be attributed to the synergistic effect of N-doped NXC support and AuCo NPs and the resulting highly efficient activation of N-B bond in NH3BH3. In addition, the AuCo catalysts showed good recyclability, demonstrating that they had high stability/durability.High-performance hydrogen generation from hydrolysis of ammonia borane has been achieved over porous nitrogen-doped carbon-immobilized bimetallic nanoparticles.

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