Ruthenium-based MOF catalysts for methanation of CO2 derivatives

Mitigating climate change is one of the biggest challenges of today's society. The most direct way to achieve this goal is to capture and use CO 2 as a source of energy and chemicals. This work, inspired by previous publications focused on homogeneous catalysis, proposes the transformation of the easy-to-prepare CO 2 derivatives dialkylureas into C1 chemicals using Ru-MOFs as heterogeneous catalysts. This choice is due to (i) the well-known ability of Ru to catalyze hydrogenation reactions and (ii) that Ru-complexes were the pioneer homogenous catalyst in converting CO 2 into an added-value C1 chemical, methanol. Apart from the already reported MOF Ru-HKUST-1, we have prepared a new Ru-MOF material, denoted Ru-BTC, analogous to the semiamorphous Fe-BTC. It has been found by XAS that Ru-BTC and Ru-HKUST-1 have different metal environment and oxidation states: only 3+ in Ru-BTC, a 50:50 mixture of 2+ and 3+ in Ru-HKUST-1. Both Ru-MOFs catalyzed the hydrogenation of N,N’-dimethylurea under relatively mild conditions, giving methane as the main product. Ru-BTC was particularly efficient: 67 % conversion and 96 % selectivity to CH 4 at 150 ºC and 30 bars of H 2 using a Ru/dimethylurea weight ratio of 1 %. Ru-MOFs were also able to transform CO 2 into CH 4 , again being Ru-BTC the most effective catalyst, but giving much poorer selectivity to CH 4 . Ru-MOFs, particularly Ru-BTC, were damaged under reaction conditions, but no significant Ru leaching was observed. • A new Ru-based MOF is described, which is analogous to the semiamorphous Fe-BTC. • It has the same linker as Ru-HKUST-1 but different metal environment/oxidation state. • Ru-BTC and, to a lesser extent, Ru-HKUST-1 catalyze the dialkylureas hydrogenation. • The reaction is under mild conditions and the main product is CH 4 . • Ru-MOFs can also catalyze the direct conversion of CO 2 to CH 4 but less efficiently.