Impact of chemical and physical modification of zirconia on structure, surface state, and catalytic activity in oxidation of α-tetralol

Two series of ZrO2 samples—pure ZrO2 and ZrO2 doped by 3% of Y2O3—prepared at 400, 500, and 600 °C were studied. The samples were characterized by powder XRD, TEM, SANS, IR spectroscopy, and nitrogen adsorption at 77 K. Monoclinic ZrO2 was the dominating phase in the samples of pure zirconia, while Y-doped zirconia mainly consisted of tetragonal ZrO2. An increase in the calcination temperature led to the growth of the zirconia nanoparticle (NP) size and a decrease of the specific surface SBET. The size of Y-doped zirconia NPs (9–16 nm by XRD) was smaller compared to pure ZrO2 (12–19 nm), synthesized at the same temperatures. The content of the surface defects in the tetragonal Y-doped ZrO2 was estimated by analysis of IR spectra and other indicators and grew with the increase of the calcination temperature. The strength and content of the acidic surface sites were determined by potentiometric titration. The doping of ZrO2 by Y3+ led to the formation of the sites with lower pKa. The catalytic activity of ZrO2 and Y-doped ZrO2 in the reaction of α-tetralol oxidation by m-chloroperoxobenzoic acid was studied, and it was found that α-tetralone was the main product. The catalytic activity of the Y-doped zirconia samples in α-tetralol oxidation, expressed as conversion or turnover frequency (TOF) per 1 m2 or ZrO2, increased with the increase of the total concentration of the surface acidic centers. Graphical abstract