Spectro-thermal characterization of the nature of sulfate groups immobilized on tetragonal zirconium oxide: Consequences of doping the oxide with Al or Mg cations

•2 wt %-S/t-ZrO2 is resolved into low-temp species-I and high-temp species-II.•Species-II includes bridging (ZrO)2SO(OH) and/or multicentered (ZrO)3S = O sulfates.•Monolayer monomeric species-II is distinct by exposing Brønsted acidic sites.•Al-doping increases amount of sulfate species -II at the expense of species-I.•Mg-doping generates Mg-bound sulfate, which does not give rise to Brønsted acidity.