CO2 is a key contributor to global warming and ocean acidification, and its recycling to valuable products by chemical conversion is an attractive research target. Thermodynamically, CO2 is the most stable molecular product of carbon combustion, and its valorization is energy demanding.1 Therefore, to activate CO2, a high energy-density carrying agent is required, in the form of photons, electrons, or chemical energy. H2 has a high gravimetric energy density, making it a suitable candidate for chemical conversion of CO2.2

The equilibrium conversion of CO2 and H2 decreases with increasing temperature, and the process should preferably be carried out below 300 C to avoid major recycling of unconverted reactants. At such moderate temperatures, Metal-Organic Framework (MOF) compounds are potential candidates as catalyst and/or catalyst support for CO2 hydrogenation reactions. Among possible reaction products, thermodynamics favor CH4 over higher alkanes, followed by alkenes, methanol and CO.

In this contribution, a series of Pt- and Pd-containing Zr-MOFs (UiO-66 and -67 based materials) were studied as CO2 hydrogenation catalysts.3-5 Emphasis was set on catalyst stability as well as the elucidation of catalyst active state by a combination of catalyst testing and characterization using XRD, N2 adsorption, FESEM, TEM, XAS, dissolution-NMR, CO chemisorption, IR spectroscopy and TGA. Catalyst activity and selectivity were altered by changing active metal and ligand composition.