NOVELTY - Spinel catalyst for hydrocarbon oxidation, comprises a catalytic group comprising LixMn2O4 spinels having a cubical Mn4O4 core, where 0 not less than x not less than 0.2.    USE - The spinel catalyst is useful for hydrocarbon oxidation; for oxidation of substituted furans to furan mono and di-carboxylic acids; for oxidation of alcohol; for purifying water of the organic hydrocarbons; for making hydrogen peroxide; for oxidation of ammonia to nitric acid; for partial deoxygenation of carbon dioxide; for reducing carbon dioxide to formic acid; for reducing carbon dioxide to methanol; and for forming ethene by oxidative coupling of methane (all claimed).    ADVANTAGE - Efficient water-oxidizing catalysts made from low-cost earth-abundant materials, particularly those used in connection with photoelectrochemicals (PECs) are provided. Transition metal oxides (TMOs) are provided exhibiting high activities, simpler synthetic routes, and compatibility with PEC device fabrication.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a method for oxidation of hydrocarbons involving contacting hydrocarbons and oxygen with the catalyst;    (2) a method for oxidation of substituted furans to furan mono and di-carboxylic acids involving contacting the furans and oxygen with the catalyst;    (3) a method for oxidation of alcohol involving contacting alcohol and oxygen with the catalyst;    (4) a method for purifying water of the organic hydrocarbons involving contacting oxygen and impure water containing hydrocarbon impurities with the catalyst;    (5) a photo-anode for the electrolysis of water comprising an electrode substrate; and a catalyst for the photoelectrolysis of water molecules, the catalyst includes a catalytic group comprising LixMn2O4 spinels having a cubical Mn4O4 core, where 0 not less than x not less than 0.2; and a conductive support substrate supporting catalytic groups and capable of incorporating water molecules, where at least some of the catalytic groups supported by the support substrate are able to catalytically interact with water molecules incorporated into the support substrate;    (6) a method for making hydrogen peroxide involving contacting molecular hydrogen and molecular oxygen produced from a photo-electrochemical cell with spinel catalyst of, where the photo-electrochemical cell comprises a chamber capable of containing an aqueous electrolyte; a cathode in contact with the aqueous electrolyte when the chamber contains aqueous electrolyte; and a photo-anode comprising an electrode substrate; and a catalyst for photo-electrolysis of water molecules, the catalyst comprising a catalytic group comprising LixMn2O4 spinels having a cubical M4O4 core, where 0 not less than x not less than 0.2; and a conductive support substrate supporting the catalytic groups and capable of incorporating water molecules; where at least some of the catalytic groups supported by the support substrate are able to catalytically interact with water incorporated into the support substrate; the photo-anode capable of being electrically connected to the anode in contact with aqueous electrolyte when the chamber contains the aqueous electrolyte;    (7) a method for oxidation of ammonia to nitric acid involving contacting molecular ammonia and oxygen with the spinel catalyst;    (8) a method for partial deoxygenation of carbon dioxide involving contacting molecular carbon dioxide with the spinel catalyst;    (9) a method for reducing carbon dioxide to formic acid involving contacting molecular carbon dioxide and water with the spinel catalyst;    (10) a method for reducing carbon dioxide to methanol involving contacting molecular carbon dioxide and water with the spinel catalyst;    (11) a method for forming ethene by oxidative coupling of methane, involving contacting methane and oxygen with the spinel catalyst; and    (12) a process for making a catalyst comprising LixMn2O4 having a cubical Mn4O4 core, where 0 not less than x not less than 0.2, involving providing an aqueous solution nanocrystalline lithium manganite (LiMn2O4); adding concentrated nitric acid (HNO3) drop wise to the aqueous solution of nanocrystalline LiMn2O4 until the pH of the solution is approximately 2 to form a precipitate; washing the precipitate with distilled water and centrifuging to remove the water one or more times until the removed water has a pH of approximately 7; and drying the washed precipitate overnight to obtain LixMn2O4 where 0 not less than x not less than 0.2.