Tingting Yan,Lei Sun,Dongyang Xi,Dinghan Jin,Han Li,Linan Liu
SrNb 2 O 6 and SrNb 2 O 6 :Ho 3+ red phosphors were successfully synthesized by a novel molten salt method. Compared with the traditional synthesis method, the reaction rate is faster at lower temperature. Scanning Electron Microscopy showed the samples are rod-like crystals with an average size of 5 μm. Upon excitation at 638 nm, the samples exhibited red emission peaks in the range of 640–680 nm, which are attributed to the Ho 3+ 5 F 5 → 5 I 8 electronic transition. As the concentration of Ho 3+ increases, the luminescence intensity gradually rises, peaking at x = 0.03. To explore the stability of the crystal structure under pressure, we conduct high-pressure Raman scattering experiments on SrNb 2 O 6 . Significant changes in the Raman spectra indicate a reversible phase transition between 3.1 and 5.4 GPa. Geometric optimization based on density functional theory suggest that the phase transitions originate from increased coordination of Sr atoms.
Catalytic dehydration of fructose to 5-hydroxymethylfurfural (HMF) is a key reaction in biomass valorization and sustainable chemistry. The development of solid acid catalysts with high selectivity for HMF remains challenging due to the formation of undesired by-products, such as levulinic acid and formic acid in the reaction. In this study, SrNb2O6 catalysts with various morphologies were prepared by a facile one-step hydrothermal method, triggering synergetic catalysis for selective transformation of fructose to HMF. Among the Nb-based mixed oxides synthesized under varying conditions, including different pH environments and Nb concentrations, SrNb2O6 nanorods (denoted as SNO-NR, with pH = 13 and Sr/Nb ratio of 1:2) demonstrated the highest catalytic performance. Specifically, it achieved a 74.9% HMF yield and a selectivity of 78.5% in DMSO at 120°C for 1 hour. Comprehensive characterization analyses collectively indicated that an optimal acid capacity and a balanced Brønsted/Lewis acid ratio, which facilitate synergistic effects, are critical for achieving a highly selective conversion of fructose to HMF. Furthermore, it is also noteworthy that this SNO-NR catalyst was recyclable and stable for up to six runs with a minor reduction in its activity, confirming its remarkable robustness.
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