Acid-Assisted Hydrogenation of CO₂ to Methanol in a Homogeneous Catalytic Cascade System

Abstract

A catalytic cascade system for CO2 hydrogenation to MeOH under acidic conditions is described. The reaction uses three catalysts which promote stepwise formation and conversion of formic acid and formate ester intermediates. The activities and decomposition pathways of different catalyst candidates for each step were investigated. The combination Ru­(H)2[P­(CH2CH2PPh2)3]/Sc­(OTf)3/Ir­(tBuPCP)­(CO) was found to be the most active for CO2 hydrogenation to MeOH. An overall TON of 428 was achieved after 40 h at 155 °C in EtOH, resulting in a high concentration of MeOH (1.07 M). Catalyst speciation studies upon completion of the reaction indicated that the carbonyl complexes [Ru­[P­(CH3CH2PPh2)3]­(H)­(CO)]­(OTf), Ir­(tBuPCP)­(H)­(CO)­(OTf), and [Ir­(tBuPCP)­(H)­(CO)2]­(OTf) were formed as the major metal-containing species. Notably, [Ru­[P­(CH3CH2PPh2)3]­(H)­(CO)]­(OTf) was found to be inactive for CO2 hydrogenation, limiting the productivity of the reaction.

Reaction Network Analysis of the Ruthenium‐Catalyzed Reduction of Carbon Dioxide to Dimethoxymethane

“…Considering the significant differences of the experimental setups and the extrapolation of experimental parameters, this result is in good agreement with the reported experimental TON DMM,exp of 786 for the same temperature and the same applied pressures [9] . Increasing the temperature to 120 °C and H 2 pressure to 120 bar, the reaction is strongly shifted toward MeOH formation (Figure 3b), rationalizing previously reported results on MeOH optimization in other solvents [14,20,25] . At lower temperatures, all reaction rate constants are decreased, with the reduction of CO 2 to MF being least affected.…”

“…[9] Increasing the temperature to 120°C and H 2 pressure to 120 bar, the reaction is strongly shifted toward MeOH formation (Figure 3b), rationalizing previously reported results on MeOH optimization in other solvents. [14,20,25] At lower temperatures, all reaction rate constants are decreased, with the reduction of CO 2 to MF being least affected. In combination with lower H 2 pressures, the reaction can be tuned toward MF (Figure 3c) as has been shown in a previous screening of this catalytic system.…”

Inside‐and‐Out Semiconductor Engineering for CO2 Photoreduction: From Recent Advances to New Trends

“…Several advantages of homogeneous photocatalysts are depending on their atomically dispersed active sites, [ 428–430 ] tunable light absorption, [ 431–433 ] as well as high activity and selectivity. [ 434–439 ] Heterogeneous photocatalysts with relatively low cost are easy to synthesize and facile to be extracted and recycled for long‐term run. [ 440–442 ] Single‐site catalysts integrate the advantages from both homogeneous and heterogeneous catalysts, thus attracting great interests for photocatalytic CO 2 reactions.…”

Homogeneous (De)hydrogenative Catalysis for Circular Chemistry – Using Waste as a Resource

“…Although an overall transformation of CO 2 to methanol was successfully demonstrated, a low TON (up to 21) was observed. Recently, Goldberg has used the same approach and obtained a higher TON (428) using the catalytic combination of Ru(H) 2 [P(CH 2 CH 2 PPh 2 ) 3 ]/Sc(OTf) 3 /Ir‐(tBuPCP)(CO) [60] . After the seminal works of Milstein and Sanford, several examples have been reported where CO 2 is captured by a nucleophile such as amines and alcohols to form a species whose hydrogenation to methanol is more favorable compared to the direct hydrogenation of CO 2 to methanol.…”