The conversion of glucose to 5-hydroxymethylfurfural (HMF) was studied in a biphasic system with niobia solid acid catalysts. We used carbon supported niobia since it shows improved hydrothermal stability. However, the carbon supported catalysts tend to be located in the organic phase due to their hydrophobic nature, while the reactant glucose is present in the aqueous phase. Therefore, we functionalized the carbon black support to increase the degree of hydrophilicity, allowing us to locate the catalyst either in the organic phase, in the aqueous phase or at the interface. The effect of the location of the niobia/carbon composites on the catalytic performance was investigated in the conversion of d-glucose to HMF in a biphasic system. It was found that the niobia catalyst located in the aqueous phase showed the highest d-glucose conversion (twofold greater than the others). We also compared the performance of catalysts obtained by deposition of niobia on functionalized carbon with a catalyst prepared by deposition precipitation-carbonization (DPC). The latter catalyst provides crystalline niobia particles while the other catalysts yield amorphous niobia. The crystalline niobia is more active for the acid catalyzed dehydration of isopropanol in the vapor phase. The DPC method provides a simple one pot synthesis to generate niobia particles embedded in a carbon support. .