Synthesis and Acid Catalytic Activity of Al‐Doped Spiky‐Shaped Niobium Pentoxide

Niobium pentoxide (Nb 2 O 5 ) is a promising heterogeneous acid catalyst because of its water‐tolerant acidity. However, the reactivity of Nb 2 O 5 is limited to the surface of a bulk material; thus, its catalytic activity is generally lower than homogeneous catalysts. Nano‐sized Nb 2 O 5 shows superior activity but has low stability and recoverability. We develop spiky‐shaped Nb 2 O 5 composed of radially grown nanorods, which show high stability but low acidity. In this study, an Al‐doping method and the doping effect on the acidity and nanostructure of the spiky‐shaped Nb 2 O 5 are demonstrated. Al of 1–6 mol% is doped in Nb 2 O 5 while maintaining the spiky nanostructure using an Nb–Al composite oxalate as a precursor. Scanning transmission electron microscope analysis results show that the doped Al ions are homogeneously dispersed in the structure. Al doping increases the catalytic activity, where 4 mol% Al‐doped Nb 2 O 5 shows the highest production rate of 2‐phenyl‐2‐phenylaminoacetonitrile in a Strecker reaction. From the acid analysis and Raman spectroscopy, it can be concluded that the Al doping is effective in adjusting acidity and in enhancement of catalytic activity due to creation of NbO 4 and distorted NbO 6 . These are produced by defect formation and lattice distortion caused by differences in valence and ionic radius between Al and Nb.