Not Just Another Methanation Catalyst: Depleted Uranium Meets Nickel for a High-Performing Process Under Autothermal Regime

Abstract

Ni-based catalysts prepared through impregnation of depleted uranium oxides (DU) have successfully been employed as highly efficient, selective, and durable systems for CO2 hydrogenation to substituted natural gas (SNG; CH4) under an autothermal regime. The thermo-physical properties of DU and the unique electronic structure of f-block metal-oxides combined with a nickel active phase, generated an ideal catalytic assembly for turning waste energy back into useful energy for catalysis. In particular, Ni/UOx stood out for the capacity of DU matrix to control the extra heat (hot-spots) generated at its surface by the highly exothermic methanation process. At odds with the benchmark Ni/γ-Al2O3 catalyst, the double action played by DU as a “thermal mass” and “dopant” for the nickel active phase unveiled the unique performance of Ni/UOx composites as CO2 methanation catalysts. The ability of the weakly radioactive ceramic (UOx) to harvest waste heat for more useful purposes was demonstrated in practice within a rare example of a highly effective and long-term methanation operated under autothermal regime (i. e., without any external heating source). This finding is an unprecedented example that allows a real step-forward in the intensification of “low-temperature” methanation with an effective reduction of energy wastes. At the same time, the proposed catalytic technology can be regarded as an original approach to recycle and bring to a second life a less-severe nuclear by-product (DU), providing a valuable alternative to its more costly long-term storage or controlled disposal.