Preparation of NiAlZr-terephthalate LDHs with high Al and Zr content and their mixed oxides for cyclohexane dehydrogenation

Hydrotalcite-like materials were synthesized by pH-controlled precipitation method with Ni2+ and Al3+ cations and terephthalate as the compensation anion. Ni/Al ratios were 1.0 and 0.3, both high in aluminum content for what has been commonly reported in the literature for this type of materials. The incorporation of Zr(IV) in the structure of the materials was evaluated substituting Al(III) for Zr(IV), using Al/Zr ratios of 3.0 and 0.3. Characterization techniques, such as X-ray diffraction, thermogravimetric analysis, infrared spectroscopy and chemical analysis, demonstrated that NiAlZr-terephthalate hydrotalcite-like materials were obtained simultaneously with amorphous phases of ZrO2 and Al(OH)(3). The mixed oxides, produced by the calcination of the hydrotalcites, had interesting characteristics that could be useful for potential unsupported mesoporous nickel catalysts, with high surface areas, nanoparticles, variable reducibility temperature, thermal stability and different kinds of interaction of nickel with aluminum and zirconium, depending on the metal content. These NiAlZr oxides were evaluated as catalysts for cyclohexane dehydrogenation reaction after a reduction process. The resulting catalysts presented a high cyclohexane conversion and in some cases selectivity to benzene close to 90%, especially when zirconium was added and nanosized cristallites of NiO were formed.