Their complex surface chemistry and high oxygen lattice mobilities place mixed metal oxides among the most important families of materials. Modulation of stoichiometry in mixed metal oxides has been shown as a very powerful tool to tune optical and catalytic properties. However, accessing different stoichiometries is not always synthetically possible.   Here we show that the thermal decomposition of the recently reported Metal Organic Framework MUV-101(Fe, Ti) results in the formation of carbon-supported titanomaghemite nanoparticles with an unprecedented Fe/Ti ratio close to 2, not achievable by soft-chemistry routes. The resulting titanomaghemite phase displays an outstanding catalytic activity for the production of CO from CO₂ via the reverse Water-Gas Shift (RWGS) reaction, with CO selectivity values of ca. 100 % and no signs of deactivation after several days on stream. Theoretical calculations suggest that the reaction proceeds through the formation of COOH* species, favoring in this way CO over other byproducts.