PNNL

Abstract

The ability to functionalize hydrocarbons with CO2 could create opportunities for high-volume CO2 utilization. Current methods to effect carbon–carbon bond-formation between hydrocarbons and CO2 require stoichiometric consumption of very resourceintensive reagents to overcome the low reactivity of these substrates1–7. Here, we report a two-step cycle that converts aromatic hydrocarbons, CO2, and alcohol into aromatic esters without consumption of stoichiometric reagents. Our strategy centers on the use of catalysts composed of an alkali carbonate (M2CO3, M+ = K+ or Cs+) dispersed over a mesoporous support. We show that nanoscale confinement disrupts the crystallinity of M2CO3 and engenders strong base reactivity at intermediate temperatures. The two steps of the semicontinuous cycle are: 1) CO32–-promoted C–H carboxylation, in which the hydrocarbon substrate is deprotonated by the supported M2CO3 and reacts with CO2 to form a supported carboxylate (RCO2M); and 2) methylation, in which RCO2M reacts with methanol and CO2 to form an isolable methyl ester with concomitant regeneration of M2CO3. Using M2CO3 supported on mesoporous TiO2 (M2CO3/TiO2), we show that the cycle can be iterated at least 10 times without any apparent loss in activity. Moreover, C–H carboxylation is readily achieved when M2CO3 is dispersed on other mesoporous materials (ZrO2, Al2O3, carbon), providing multiple avenues for catalyst improvement. Our results demonstrate a way to valorize CO2 using gas–solid reactions mediated by abundant materials.