Study On The Preparation And Catalysis Of Layered Double Hydroxide Films

Layered double hydroxides (LDHs) or hydrotalcite like compounds (HTlcs) are a class of anionic lamellar functional materials, showing that especial physicochemical properties can be obtained by changing the nature of the metal cations, the molar ratios of M²⁺ /M³⁺ as well as the type of interlayer anions. LDHs have been widely used as high activity catalysis, adsorption, separation, biology and medicine materials. Recently structured catalyst has received considerable attention because the catalyst is easy to separate and recycle. Up to date however, the exploitation of LDH films as catalysts remains a challenge. Therefore, the objective of the present work is to prepare LDH film on an anodic aluminum oxide/aluminum (AAO/Al) substrate. In addition, the structure, surface morphology and preparation mechanism of the resulting films were investigated by powder X-ray difrractometer, fourier transform infrared spectrometer (FT-IR), scanning electron microscopy (SEM), and energy dispersive X-ray spectrometer (EDS) attached to the SEM. The main results are as follows:1. MAI LDH films (M= Ni, Co and Cu) and MCuAl LDH films (M= Ni, Co) were prepared on the AAO/Al substrates by using in-situ process, in which ammonia is used as precipitating agent and AAO/Al as sole source of aluminum, and the pH are adjusted by NH₃H₂O-NH-4NO₃ buffer solution. The formation of highly porous and continuous LDH films is dominated by ionization equilibrium of ammonia and coordination equilibrium of M²⁺ and NH₃.2. The catalytic performances of activated NiAl and Ni/Cu-Al LDH films with different Ni /Cu molar ratios of 4:1, 3:2, 2:3, 1:4 were investigated by using the oxidation reaction of 4-nitrobenzyl alcohol. The results show that high porous Ni/Cu-Al LDH film with Ni/Cu ratio of 2:3 displays higher catalytic activity than those of NiAl LDH film and NiAl LDH powders reported.