The present invention relates to a methane combustion catalyst including platinum and iridium supported on a tin oxide carrier for combusting methane in a combustion exhaust gas containing sulfur oxide. In the methane combustion catalyst, a ratio R.sub.TO of platinum oxides to metal platinum is 8.00 or more, wherein the ratio R.sub.TO is based on existence percentages of the metal platinum (Pt) and the platinum oxides (PtO and PtO.sub.2) obtained from a platinum 4f spectrum analyzed and measured by X-ray photoelectron spectroscopy (XPS) and calculated in accordance with the following expression. In the following expression, R.sub.Pt is an existence percentage of the metal platinum (Pt), R.sub.Pto is an existence percentage of PtO, and R.sub.Pto2 is an existence percentage of PtO.sub.2.
R.sub.TO=(R.sub.PtO+R.sub.PtO2)/R.sub.Pt[Expression 1]

Disclosed are a catalyst for synergistic removal of nitrogen oxides (NO.sub.x) and CO as well as a preparation method and use thereof. The preparation method comprises: performing vibratory ball milling, washing, drying and calcining on aluminum isopropoxide and/or titanium isopropoxide, chlorides of five or more different metal elements and P123 and/or polyethylene glycol (PEG), stirring the obtained high-entropy oxide inner core and a gel of H.sub.3PO.sub.4 and Ce(NO.sub.3).sub.3, and then performing vibratory ball milling, washing, drying and calcining to obtain an high-entropy oxide loaded with CePO.sub.4 seeds; and preparing, by using ammonia water, a clear solution containing pyrophosphate and Ce(NO.sub.3).sub.3 in equal stoichiometric ratios, then adding the high-entropy oxide loaded with the CePO.sub.4 seeds and urea and/or tetrapropylammonium hydroxide (TPAH) to form a slurry, and, after hydrothermal reaction, washing, drying and calcining a solid to obtain the catalyst.