## 4 Conclusions  
In summary, we have successfully synthesized the Nb/MCS catalysts by which MCS was prepared from the NR/HMS nanocomposite via carbonization, and Nb\({}_{2}\)O\({}_{5}\) was loaded onto MCS via incipient wetness impregnation, followed by calcination at 550 \({}^{\circ}\)C. The characterization results indicate that 10-Nb/MCS not only had good textural properties but also a high dispersion of Nb\({}_{2}\)O\({}_{5}\) crystallites on the MCS surface. By varying the Nb loading level, the molar ratio of Brensted/Lewis acid sites could be optimized. The 10-Nb/MCS catalyst showed a good performance in the conversion of glucose into HMF in a biphasic water-THF solvent, achieving the highest HMF yield of 57.9% at 93.2% glucose conversion, when the reaction was carried out using 0.018 g catalyst loading at 190 \({}^{\circ}\)C for 1 h. Furthermore, 10-Nb/MCS exhibited a high catalytic stability in the HMF synthesis from glucose in the biphasic solvent since it could be reused at least five times without a significant loss of activity. Its superior performance was ascribed to the suitable Brensted/Lewis acidity ratio (1.2), and the hydrophobic properties generated from the carbon moieties dispersed in the MCS nanocomposite. The overall results suggest a potential application of NR as a low-cost and sustainable carbon source in the preparation of high surface area and hydrophobic MCS support, and a practical use of 10-Nb/MCS in the acid-catalyzed conversion of glucose into HMF at a high concentration of glucose substrate.  
The following are available online at [[https://www.mdpi.com/article/10.3390/catal11080887/s1](https://www.mdpi.com/article/10.3390/catal11080887/s1)]([https://www.mdpi.com/article/10.3390/catal11080887/s1](https://www.mdpi.com/article/10.3390/catal11080887/s1)), Figure S1: Weight loss and DTA curves of pure silica HMS and MCS nanocomposite, Figure S2: C1s XPS spectrum of MCS nanocomposite, Figure S3: NH\({}_{3}\)-TPD profiles of HMS and MCS with different Nb loading amount.  
R.K.: Investigation, validation, and writing--original draft; S.Y.: Methodology, validation, writing--review and editing; C.N.: Conceptualization, funding acquisition, supervision, and writing--review and editing. All authors have read and agreed to the published version of the manuscript.  
This research was financially supported by the co-funding of Thailand Science Research and Innovation (TSRI) and Chulalongkorn University through Research Career Development Grant (Grant No. RSA6280046), and the Center of Excellence in Catalysis for Bioenergy and Renewable Chemicals (CBRC), Faculty of Science, Chulalongkorn University. The financial and technical supports from TSRI under the International Research Network: Functional Porous Materials for Catalysis and Adsorption (Grant No. IRN61W0003), and the Center of Excellence on Petrochemical and Materials Technology (PETROMAT), Chulalongkorn University.  
The data presented in this study are available in the article and the Supplementary Data.  
The authors are grateful to the analytical instrument service at Scientific and Technological Research Equipment Centre (STREC), Chulalongkorn University.  
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.