Re-based catalysts are capable for the hydrogenation of C=O bond and can be potentially applied in catalytic hydrogenation. Prof. Liang Changhai and his group have made a series of new advances in the design, preparation and catalytic performance of efficient Re catalysts over the past decades.
Recently, researchers in AM&CE for the first time studied the catalytic mechanism of Co-Re interaction induced by catalyst structure in the hydrogenation of unsaturated aldehydes. A series of Co-Re bimetallic catalysts (Isolated structure, Janus-Type structure and Core (Co)-Shell (Re) structure) with different contact interface structures were prepared. With the increase of the contact degree between active metals, the interaction is enhanced and the reduction of Re precursors is effectively promoted. DOS calculation results confirmed that the low-valent Re component is more conducive to the adsorption of hydrogenation intermediates. In addition, low-valence active metal phase also enhanced the hydrogen activation ability of the active site and further improved the catalytic performance of citral hydrogenation. At the same time, the interaction between metals promoted the shift of electrons from Re to Co, which was beneficial to the adsorption of electron-rich aldehyde functional groups on the surface of Re component in citral. Based on the different mechanisms mentioned above, the catalysts with Janus-Type structure and Core-Shell structure have higher reactivity than those with single metal and isolated structure. However, the formation of Co-Re interaction led to excessive contact between metals and inhibited the hydrogenation of citral to a certain extent, which were further confirmed by kinetic analysis fitting results.
The research work is collaborated with Prof. Gwendoline Lafaye of Poitier University in France. Relevant results were published in ChemSusChem (2019, 12, 807-823) and selected as the front cover. ChemSusChem is one of the most authoritative and influential academic journals in the international chemistry field, with an impact factor of 7.411 in 2018.
In recent years, the advanced materials and catalytic engineering team has developed microwave-assisted pyrolysis for the preparation of single metal Re/C catalysts. This method can shorten the preparation period of catalyst remarkably without introducing any solvent. The catalyst exhibits excellent catalytic activity and stability in the hydrogenation of succinic acid in aqueous phase. It can selectively convert succinic acid to tetrahydrofuran and butyrolactone (Catal. Sci. Technol., 2015, 5, 2441-2448).
Based on this work, Re-M (M = Ru, Pt, Rh) bimetallic catalysts were prepared efficiently by the same method. The mechanism of synergistic effect between metals on the catalytic conversion of succinic acid was studied from the point of view of kinetics. Results show that the Ru component in Re-Ru/C catalyst is beneficial to the hydrogenolysis of succinic acid, while the Re component can effectively promote the hydrogenation of succinic acid. On the other hand, the key factors affecting the selectivity of succinic acid hydrogenation products depend on the activation and hydrogenation of butyrolactone, the intermediate product. The synergistic effect between Re-M changes the activation state of the intermediate product and hydrogen to promote the ring opening selectivity of butyrolactone to 1,4-butanediol. However, when Re-M components forme intermetallic interactions, the synergistic effects of different types/strengths on the selectivity of butanediol are very limited. Strong interaction is more conducive to inhibit the hydrogenation effect of catalysts, limiting the further cracking of reaction products and avoiding the accumulation of by-products. (Catal. Sci. Technol., 2017, 7, 5212-5223; Ind. Eng. Chem. Res., 2017, 56, 4672-4683).
At the same time, further breakthroughs has been made, in collaboration with Prof. John R. Monnier and prof. John R. Regalbuto of the University of South Carolina, in the preparation of Re-Ir/C catalysts and the hydrogenation of succinic acid in aqueous phase (ACS Catal., 2018, 8, 6486-6494). Highly dispersed Re-Ir/C catalysts were prepared by strong electrostatic adsorption and used in the hydrogenation of succinic acid. It was found that the formation of the interaction between Re and Ir could significantly improve the catalytic activity of succinic acid hydrogenation reaction and produce butyrolactone with high selectivity. Bimetallic nano-alloy catalysts exhibit more excellent catalytic activity and stability than traditional metal catalysts due to their suitable electronic, geometric, spatial and ordered structure properties in aqueous acid hydrogenation.
