X-ray diffraction and magnetochemical investigation of Ni-Al₂O₃ catalysts for the simultaneous hydrogenation and dealkylation of cresols

Conclusions

• 1. A characterization was given of the changes in the phase composition of the hydroxides of nickel and aluminum, coprecipitated with NH₄OH, the mixed oxides obtained from them by calcining at 350 and 900°, and Ni-Al₂O₃ catalysts of the hydrogenation and dealkylation of cresols, obtained from the mixed oxides calcined at 350° by reduction at 350°, as a function of the nickel content.

• 2. The coprecipitated hydroxides contain only one crystalline phase, and when Al(OH)₃ is amorphous (up to 8% Al₂O₃), then the oxides are obtained with the texture of NiO, while when Ni(OH)₂ is amorphous, the oxides are obtained with the texture of Al₂O₃. The reduced catalysts containβ-Ni with linear crystal dimensions of 60–100 A and NiO, while the crystalline γ-Al₂O₃ or NiAl₂O₄ is absent. Precipitation of the hydroxides with KOH gives a two-phase system-crystalline Al(OH)₃ and Ni(OH)₂.

• 3. The reduced mixed catalysts give ferromagnetic resonance (FR) spectra varying little as a function of the composition, degree, and conditions (continuous-flow system, static conditions, 350 and 450°, duration) of the reduction and thermal processing under vacuum at 950°, apparently on account of the high thermal stability of the catalysts and the insufficiently great differences in the dispersion of the nickel. The FR spectra of nickel in the mixed catalysts differ greatly from the FR spectra of nickel from NiO, probably on account of an increase in the spin-electron relaxation time in the presence of Al₂O₃.

• 4. Proportionality was noted between the intensity of the FR line and the value of the saturation magnetization, i.e., it was shown that the FR line is due to all the metallic nickel contained in the catalysts.