“…3. In the spectrum, the HZSM-5 has only one absorption band at about 300 nm, with the increasing of the Ni content, the absorption band becomes wide and shifts to about 320 nm, which has been ascribed to the band gap absorption in NiO [21]. Besides, two bands at 750 and 425 nm belonging to Ni 2+ in octahedral or distorted octahedral coordination are observed for the 2.21, 3.58 and 5.05 wt.% Ni/HZSM-5 samples.…”