Effects of Alkali Element Doping and Synthesis Conditions on the Genesis of the Phase Composition of Alumina–Chromium Catalysts

Resumo

The influence of modifying additives and synthesis conditions on the genesis of the phase composition of alumina–chromium catalysts was studied by differential dissolution (DD) and X-ray diffraction (XRD) analysis. The salts of potassium (KNO₃) and lithium (LiCl) were added as additives. It was found that the individual nature of the additives affected the formation of phases. Although potassium and lithium cations occur in the same group of the periodic system, they differently react with a phase of γ-Al₂O₃ in the support: lithium forms a Li_xAl₁ solid solution with the crystallized finely dispersed γ-Al₂O₃ species, whereas potassium mainly remains on the surface of the finely dispersed Al₂O₃ species and partially forms potassium aluminate. The interaction of lithium cations with the active component Cr(VI) of the catalyst leads to the formation of lithium chromate analogously to the reaction of the potassium cation with \({\text{CrO}}_{4}^{{2 - }}.\) However, a portion of lithium cations is introduced into the structure of the substitution solid solution of Cr(III) in γ‑Al₂O₃ to form addition solid solutions (Al₁Cr_{x1– x2}Li_{y1 –y2}).