A series of binary In2O3/S (S = Al2O3, SiO2, and MgO) catalysts were fabricated by an incipient-wetness impregnation method, which were firstly applied in the ethylbenzene dehydrogenation under the presence of CO2 (EBDH-CO2). The synthesized catalysts were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption–desorption isotherm, temperature-programmed desorption of NH3 and CO2 (NH3/CO2-TPD), temperature-programmed reduction of H2 (H2-TPR), and X-ray photoelectron spectroscopy (XPS). It is found that the support can strongly impact on the crystalline phase, the dispersity, and the reduction properties of In2O3. The catalytic tests during the EBDH-CO2 show that as compared to In2O3/MgO and In2O3/SiO2 with the merely existence of bulk In2O3 particles, the In2O3/Al2O3 catalyst gives the highest catalytic activity and good stability, which can be principally ascribed to the synergistic effect of the bulk In2O3 and in situ metallic In formed by the reduction of the well-dispersed In2O3 on the Al2O3 surface. It therefore affirms that attaining an appropriate support to disperse the active phase In2O3 becomes the decisive factor to achieve both superior catalytic activity and satisfied selectivity towards styrene.