Coordinatively Unsaturated Aluminum Enables Methanol-Selective CO2 Hydrogenation With Zeolite-Supported Copper Catalysts.

We demonstrate the synthesis of Cu(AlOx)a(SiOy)b clusters under the confines of MER zeolite, which hydrogenate CO2 to methanol and dimethyl ether with 96% selectivity and a space time yield of 15.0 mmolC gCu -1 h-1 at 250 °C (4:1 H2:CO2 and 5 MPa). A crucial aspect of the synthesis involves MER zeolite calcination, leading to framework dealumination and loss of long-range order. These Cu(AlOx)a(SiOy)b clusters consist of a high density of coordinatively unsaturated aluminum sites, which are lacking in conventional copper catalysts with similar stoichiometry, and stabilize copper in a more oxidic form that is characterized by higher reduction temperatures. Other copper-containing zeolites consisting of stable frameworks that do not dealuminate upon calcination (Cu-Li-FAU and Cu-Li-RHO zeolites) exhibit 99% selectivity to CO under the same reaction conditions. When compared with these catalysts and an industrial CuZnAl catalyst, kinetic analysis shows the Cu(AlOx)a(SiOy)b clusters are more intrinsically selective for methanol over the reverse water gas shift reaction at low CO2 converions.