A method for preparation of a single-atom cobalt-based catalyst, which comprises the steps of: a) thermally treating silica as a support at a temperature ranging from 600 to 870°C to induce shrinkage of the support, and simultaneously to remove its surface hydroxyl groups, followed by subjecting the shrunken support to a high-temperature aqueous treatment to afford a pretreated silica having hydroxyl groups selectively activated thereon; b) preparing an aqueous dispersion of the pretreated silica; c) preparing a pH-adjusted aqueous dispersion of the pretreated silica by adding a base to the aqueous dispersion of the pretreated silica to adjust the pH of the dispersion to at least 10; d) separately, preparing a pH-adjusted cobalt precursor aqueous solution by preparing an aqueous solution of a cobalt precursor having an oxidation number of 3+ and adding a base to the aqueous solution; e) combining the pH-adjusted aqueous dispersion of the pretreated silica with the pH-adjusted aqueous solution of the cobalt precursor to afford an aqueous dispersion in which at least a part of the cobalt ions having an oxidation number of 3+ is adsorbed onto the surface of the pretreated silica; f) removing cobalt ions which remain not adsorbed onto the pretreated silica; and g) thermally treating the cobalt ion-adsorbed silica obtained in step f); wherein the cobalt having an oxidation number of 2+ exists in an isolated form of single-atom on the pretreated silica while being tetrahedrally coordinated at the trihydroxyl groups present on the surface of the pretreated silica, characterized in that the high-temperature aqueous treatment in step a) is conducted by the steps of: dispersing the thermally treated silica in an aqueous medium to give a thermally treated silica-aqueous dispersion; and boiling the thermally treated silica-aqueous dispersion at 70 to 150 °C. a) thermally treating silica as a support at a temperature ranging from 600 to 870°C to induce shrinkage of the support, and simultaneously to remove its surface hydroxyl groups, followed by subjecting the shrunken support to a high-temperature aqueous treatment to afford a pretreated silica having hydroxyl groups selectively activated thereon; b) preparing an aqueous dispersion of the pretreated silica; c) preparing a pH-adjusted aqueous dispersion of the pretreated silica by adding a base to the aqueous dispersion of the pretreated silica to adjust the pH of the dispersion to at least 10; d) separately, preparing a pH-adjusted cobalt precursor aqueous solution by preparing an aqueous solution of a cobalt precursor having an oxidation number of 3+ and adding a base to the aqueous solution; e) combining the pH-adjusted aqueous dispersion of the pretreated silica with the pH-adjusted aqueous solution of the cobalt precursor to afford an aqueous dispersion in which at least a part of the cobalt ions having an oxidation number of 3+ is adsorbed onto the surface of the pretreated silica; f) removing cobalt ions which remain not adsorbed onto the pretreated silica; and g) thermally treating the cobalt ion-adsorbed silica obtained in step f); wherein the cobalt having an oxidation number of 2+ exists in an isolated form of single-atom on the pretreated silica while being tetrahedrally coordinated at the trihydroxyl groups present on the surface of the pretreated silica, characterized in that the high-temperature aqueous treatment in step a) is conducted by the steps of: dispersing the thermally treated silica in an aqueous medium to give a thermally treated silica-aqueous dispersion; and boiling the thermally treated silica-aqueous dispersion at 70 to 150 °C. dispersing the thermally treated silica in an aqueous medium to give a thermally treated silica-aqueous dispersion; and boiling the thermally treated silica-aqueous dispersion at 70 to 150 °C.