The effects of the addition of colloidal silica (cSiO2) and solvents used in the catalyst preparation on the activity and stability of WO3-TiO2 catalysts are reported in this paper. The highly stable and selective WO3 supported cSiO2-TiO2 catalysts were prepared and tested in the vapor-phase glycerol oxy-dehydration. WO3-TiO2 catalysts with and without cSiO2 were characterized by XRD, SEM, NH3-TPD, infrared spectroscopy of pyridine (FTIR-Py), XPS, RAMAN, and N2 adsorption-desorption (BET). The highest medium strength acidity and optimum Brønsted to Lewis acid site ratio of WO3 catalysts were achieved upon the addition of colloidal silica (cSiO2) onto TiO2 support. The medium strength acidity of Brønsted acid sites was responsible for the improved acrolein selectivity and stability. The other major factors in glycerol conversion and acrolein selectivity were the glycerol content and liquid hourly space velocity. The yield to acrolein was up to 70% and kept almost constant in a 50 h continuous run at 300 °C. The gradual decrease in glycerol conversion was due to the build-up of oxygen-containing carbonaceous materials deposited on the catalyst surface.