Despite the interest in niobia-based catalysts and the importance of biomass valorisation, studies on these catalysts typically utilize model substrates like simple sugars. In this study, a series of niobium oxide-based catalysts was prepared for the application in aqueous phase catalytic conversion of sugars extracted from sp microalga into value-added furans. The solid catalysts were firstly characterized by various techniques including X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Raman and X-ray photoelectron (XPS) spectroscopy as well as low-temperature N physisorption. Moreover, the acidity of the catalysts was assessed by using the temperature-programmed NH desorption (NH-TPD), by titration of water suspended catalyst with NaOH solution, and by P-bearing molecular probes loaded catalysts through P and H solid-state nuclear magnetic resonance (NMR) techniques. Herein, we focused on the catalytic transformation of sp. and glucose solution as model molecule into furans. The best NbO catalysts for valorizing sp. into furans exhibited a larger number of Brønsted acid sites, achieving conversion yields to 5-HMF and furfural of ca. 20–22 % with respect to the extracted sugars from algae. The results showed a discernible dependence of the conversion yields to 5-HMF and furfural on catalyst acidity, specific surface area, and the presence of the Brønsted acid sites. Conversely, when using the glucose solution as substrate is concerning, the highest yield to 5-HMF was reached by using a catalyst that showed also the presence of Lewis acid sites. A systematic investigation of the structure–activity relationships in niobium oxide application for aqueous phase dehydration using real biomass substrates to obtain furanic derivatives has not been documented thus far. Therefore, the current research is significant as it demonstrates the feasibility of transforming the carbohydrate content in microalgal biomass into furans by identifying the best catalyst to use.

中文翻译：

---

微藻小球藻的价值。在 Nb2O5 催化剂存在下转化为呋喃

尽管人们对铌基催化剂很感兴趣并且生物质增值很重要，但对这些催化剂的研究通常利用简单糖等模型底物。本研究制备了一系列氧化铌基催化剂，用于水相催化将从sp微藻中提取的糖转化为高附加值呋喃。首先通过X射线衍射分析（XRD）、扫描电子显微镜（SEM）、热重分析（TGA）、拉曼光谱和X射线光电子（XPS）光谱以及低温N物理吸附等技术对固体催化剂进行了表征。此外，通过使用程序升温NH脱附（NH-TPD）、用NaOH溶液滴定水悬浮催化剂以及通过P和H固态核负载催化剂的含P分子探针来评估催化剂的酸度。磁共振（NMR）技术。在此，我们重点关注sp的催化转化。和葡萄糖溶液作为模型分子转化为呋喃。用于稳定 sp 的最佳 NbO 催化剂。转化为呋喃时表现出大量的布朗斯台德酸位点，实现了约 5-HMF 和糠醛的转化产率。相对于从藻类中提取的糖而言，含量为 20-22%。结果表明，5-HMF 和糠醛的转化率明显依赖于催化剂酸度、比表面积和布朗斯台德酸位点的存在。相反，当使用葡萄糖溶液作为底物时，通过使用也显示路易斯酸位点存在的催化剂达到了 5-HMF 的最高产率。迄今为止，尚未有文献报道使用真正的生物质底物进行水相脱水以获得呋喃衍生物的氧化铌应用中的结构-活性关系。因此，当前的研究具有重要意义，因为它证明了通过确定最佳催化剂将微藻生物质中的碳水化合物含量转化为呋喃的可行性。