Cu1–xCoxFe2O4 ferrospinels in alkylation: Structural changes upon reaction

A series of Cu1−xCoxFe2O4 (x = 0, 0.25, 0.5, 0.75, 1.0) ferrospinels has been studied in the gas phase alkylation of phenol. The reaction conditions were optimized to give a maximum yield of 2,6-xylenol over o-cresol. Fresh and spent catalysts were characterized by XRD, Mössbauer spectroscopy, TPR and TPD, TG and DTA methods. Various structural changes were observed due to exposure of the fresh catalysts to the reaction mixture. Namely, phase separation to CuO and magnetite in the x = 0 and 0.25 samples, various extents of reduction (changing monotonically with the copper content, and resulting in partial reduction and redistribution of iron in tetrahedral (A) and octahedral [B] sites) and extended formation of carbonaceous deposits are detected. In spite of these profound changes the catalytic activity is maintained with only a slight decrease during extended time-on stream (40 h).