A (5:1 by motes) CO2 (or Ar)-C3H8 mixture was passed, 30 mL/min, through a microreactor (holding 1.5 g quartz glass) over 0.5 g of (i) CrOx/SiO2-A (333) or (ii) CrOx/SiO2-I (267 m(2)/g) at 873 K. Catalysts (i) were prepared by equilibrium adsorption from aq. 14 (or 180) mM Cr(NO3)(3) at pH 1-5 (or 5), shaked 10 h with SiO2, kept 7 days, filtered, washed, dried, and calcined 3 h/650degreesC in air. To prepare (ii), SiO2 was impregnated with aq. Cr(NO3)(3) to yield 5% Cr2O3/SiO2 (to be calcined like (i)). With (i), the higher pH resulted in 35% more Cr2O3 deposited. The final Cr(III) wt. contents were A/I = 1:5, yet A was more active, perhaps on account of higher Cr dispersion. CO2 rendered both A and I more active.