Graphene sheets formed by the reaction of carbon monoxide (CO) with aluminum sulfide ($Al_2S_3$) at reaction temperatures ${leq}$ 800 $^{circ}$ were characterized by X-ray diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM). The graphene sheets, formed as CO was reduced to gaseous carbon by the reaction with $Al_2S_3$, in the temperature range 800 - 1100 $^{circ}C$, did not exhibit their characteristic XRD peaks because of the small number of graphene layers and/or low crystallinity of graphene sheets. Raman spectra of graphene sheets showed that the intensity ratio of the D band to the G band decreased and the 2D band was shifted to higher frequencies with increasing reaction temperature, indicating that the number of graphene layers increased with increasing reaction temperature.