MCM‐41 Bound Ruthenium Complex as Heterogeneous Catalyst for Hydrogenation I: Effect of Support, Ligand and Solvent on the Catalyst Performance

Abstract

The functionalized MCM-41 mesoporous bound ruthenium complex was synthesized and characterized using elemental analysis, atomic absorption spectrophotometer, BET, XRD and FTIR. Hydrogenation of carbon dioxide to formic acid was investigated over these catalysts under supercritical CO 2 condition. The effect of reactant gas partial pressure, supports, solvents and ligands on the synthesis of formic acid was studied. These factors could influence the catalyst activity, stability and reuse performance greatly and no byproduct was detected. These promising catalysts also offered the industrial advantages such as easy separation.

Challenges in the Greener Production of Formates/Formic Acid, Methanol, and DME by Heterogeneously Catalyzed CO2Hydrogenation Processes

“…For example, over the first reaction cycle 8% of active metal leaching was indicated for the amine functionalized silica compared to the one functionalized with thiol (2.5% metal leaching) ascribed to the weaker complexation, but higher activity of the former. 79 Although in this case the Ru–H vibration was detected by FTIR, no characterization was reported for the spent catalyst. Rohr et al showed that multiple coordination using two bidentate ligands ( Figure 3 a) could greatly improve the stability of the catalyst by enhancing the binding strength to Ru compared to the cases where the active metal is weakly bound via a single coordination ( Figure 3 b).…”

“…For example, over the first reaction cycle 8% of active metal leaching was indicated for the amine functionalized silica compared to the one functionalized with thiol (2.5% metal leaching) ascribed to the weaker complexation, but higher activity of the former. 79 Although in this case the Ru−H vibration was detected by FTIR, no characterization was reported for the spent catalyst. Rohr et al…”

“…The group of Zheng evaluated the use of surface-grafted silica, including mesoporous MCM-41, containing various functional donor groups such as NR 2 , CN, and SH, to allow the coordination to Ru complexes (Figure b), and studied the roles of support and the donor ligand in CO 2 hydrogenation to formic acid and derivatives. ,− Comparing activities of the “precatalyst” structures (the active system is formed under reaction conditions) based on primary, secondary, and tertiary amine ligands, the secondary amine showed the highest TOF (1384 h –1 , Table , entry 2) in the presence of a base (NEt 3 ) . Secondary amines are generally known to be better electron donors, which could explain the increase in catalytic activity.…”

“…Immobilization strategies of molecular complexes on grafted solid support for CO 2 hydrogenation. These “precatalyst” structures are created based on (a) refs ( n = 1,3), ( n = 2), and ( n = 3); (b) refs − ; (c) ref ; (d) refs and ; and (e) refs , , and .…”

“…In general, leaching is observed when the active metal (Ru) was bound through a single coordination to a ligand grafted on support material via an alkyl chain, while the degree of metal leaching was dependent on the coordinating terminal group. For example, over the first reaction cycle 8% of active metal leaching was indicated for the amine functionalized silica compared to the one functionalized with thiol (2.5% metal leaching) ascribed to the weaker complexation, but higher activity of the former . Although in this case the Ru–H vibration was detected by FTIR, no characterization was reported for the spent catalyst.…”