【Frontiers in HaiChuan Technology】Dalian Institute of Chemical Physics achieves ethylene production via acetylene hydrogenation at room temperature and pressure
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Dalian Institute of Chemical Physics achieves ethylene production from acetylene hydrogenation at room temperature and pressure. Publication date: 2024-11-08. Recently, a team led by researchers Deng Dehui and Yu Liang from the Energy and Environmental Small Molecule Catalysis Research Center (Group 509) of our Institute’s Key Laboratory of Catalytic Fundamentals, in collaboration with researcher Huang Rui from the School of Chemistry at Dalian University of Technology, made new progress in the research on converting acetylene (C2H2) into ethylene through hydrogenation. By using a Pd/WS2 catalyst with palladium atoms confined within tungsten sulfide, the team achieved high activity and stability in the hydrogenation process at room temperature and pressure, providing a new method for ethylene production under mild conditions. Ethylene (C2H4) is an important basic raw material in the chemical industry. It is currently produced primarily through the high-temperature cracking of naphtha, a process that is complex and requires high energy consumption. Due to the excessive consumption of oil resources and China’s high dependence on crude oil imports, it is important to develop diversified production routes for ethylene. Given China’s resource profile of abundant coal and limited oil, producing ethylene through coal-to-acetylene conversion followed by acetylene hydrogenation represents a promising alternative to the traditional petroleum-based route for ethylene production. However, acetylene hydrogenation to produce ethylene is currently commonly used for the removal of trace amounts of acetylene from ethylene. The high reaction temperatures (>100°C) make it difficult to control selectivity, and it has drawbacks such as high energy consumption, tendency to form carbon deposits, and poor stability. Therefore, it is of great significance to develop new approaches for the hydrogenation of acetylene to ethylene that are low-temperature, highly active, and highly stable. The Dundee team has long been dedicated to research on the catalytic conversion of small molecules related to energy and the environment. Earlier on, it made a series of advances in new catalytic reactions and processes for the hydrogenation of small molecules to produce high-value chemicals (Nat. Catal., 2023 ； Nat. Commun., 2023 ； Nat. Catal., 2021 ； Nat. Commun., 2021). On this basis, the team developed a WS2-confined Pd atom catalyst that enabled the direct hydrogenation of acetylene to ethylene under normal temperature and pressure, with a C2H2 conversion rate of >99%, a C2H4 selectivity of >70%, and a C2H4 production rate of 1123 mol C2H4 per mol Pd per hour – four times higher than that of typical PdAg/Al2O3 and commercial Lindlar catalysts. It exhibited almost no degradation after 500 hours of stable operation. Through ball-aberration electron microscopy, in-situ spectroscopy, and theoretical calculations, the team confirmed that under the coordination of sulfur atoms in WS2, Pd atoms with missing electrons possess high H2 dissociation ability, acetylene hydrogenation ability, and ethylene desorption ability, thereby achieving high acetylene conversion activity and ethylene selectivity. This work provides scientific and technical support for the low-temperature, low-carbon emission production of ethylene from coal-based acetylene. The relevant research findings were published in Nature Communications under the title “Ambient-condition acetylene hydrogenation to ethylene over WS2-confined atomic Pd sites”. The above work was funded by projects such as the **Key Research and Development Program** and the National Natural Science Foundation.
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Cu nanoparticles (MPs) were prepared via solvothermal synthesis in ethylene glycol (EG) using CuSO4·5H2O as a precursor. The morphology of the Cu catalyst was characterized using SEM and HAADF-STEM. As shown in Figure 2a, the results indicate that the Cu MPs are uniformly distributed with a diameter of approximately 1 μm. Cu MPs were loaded onto carbon paper coated with a microporous gas diffusion layer, designated as Cu/GDL-CP, and their E-HAE properties were measured. First, the author determined the E-HAE activity of the catalyst using LSV, as shown in Figure 2b. In the Ar-saturated solution, at -0.3 V, the current density of the sample remained close to zero, indicating poor HER activity. In a C2H2-saturated solution, the current density increases significantly due to the electrocatalytic hydrogenation of acetylene, and the onset potential rises to -0.24 V. Furthermore, by comparing the current density for ethylene production at different potentials between the Cu/GDL-CP and Cu/CP electrodes, as shown in Figure 2c, the geometric current density of ethylene generation (jC2H4) on Cu/GDL-CP was consistently higher than that on Cu/CP. The results showed that the gas diffusion layer (GDL) can effectively promote the E-HAE process while suppressing HER. The distribution of E-HAE products depends largely on the electrode potential. As shown in Figure 2d, at -0.3 V, the main products are ethylene and 1,3-butadiene, with FEs of approximately 53% and 47%, respectively. As the potential decreased, the FE for ethylene gradually increased, reaching a maximum of 83.2% at -0.6 V, whereas the FE for 1,3-butadiene decreased significantly to
The electronic and geometric structure of the Cu catalyst was investigated using in-situ X-ray absorption fine structure (XAFS) experiments. The testing device is shown in Figure 3a. According to Figure 3b, the K-edge XANES spectra of Cu under different conditions all resemble those of Cu foil, with the white line shifted slightly toward higher energy, indicating slight oxidation of the Cu catalyst, which may be related to the catalyst being exposed to air. In a saturated Ar electrolyte at -0.6 V, the white line shifts to lower energy levels compared to the open-circuit potential (OCP), indicating electroreduction occurring on the catalyst surface. Compared to the electrolyte saturated with Ar, in the electrolyte saturated with C2H2, the white line shifts again toward higher energy values at both -0.6 V and OCP. This indicates that C2H2 adsorbs on the catalyst surface, and the increase in the catalyst’s oxidation state is caused by the transfer of electrons from Cu to the antibonding π orbitals of C2H2 (*C2H2). In-situ Raman spectroscopy characterization in the OCP state also confirmed this result. As shown in Figure 3c, in the saturated C2H2 electrolyte, the absorption peak at 1690 cm-1 corresponds to the C≡C of *C2H2 adsorbed on the Cu surface, which is significantly shifted relative to that of gaseous C2H2. Therefore, since the electrons transferred from Cu fill the antibonding orbitals, the C≡C bond of *C2H2 may be weakened and activated. To study the reaction intermediates of E-HAE, the authors performed in-situ attenuated total reflection- Fourier transform infrared (ATR-FTIR) spectroscopy, which is highly sensitive to surface species. The in-situ ATR-FTIR spectra at different potentials are shown in Figure 3d. At -0.1 V, there is a positive peak at 1630 cm-1, which can be attributed to the desorption of H2O from the catalyst surface ； There are two negative peaks at 1594 and 1670 cm-1; the one at 1594 cm-1 can be attributed to the formation of *CH=CH2 (*C2H3), which is an intermediate in the reduction of C2H2, while the one at 1670 cm-1 can be attributed to *C2H2 adsorbed on the Cu surface. As the electrode potential becomes more negative, the peak at 1594 cm−1 for (*C2H3) increases significantly, indicating that the hydrogenation of *C2H2 to *C2H3 is closely related to the electrode potential; in other words, *C2H3 is a key intermediate in the formation of C2H4. Based on these results, the authors proposed a possible reaction pathway for E-HAE on Cu catalysts; as shown in Figure 3e, C2H2 is first hydrogenated to form the *C2H3 intermediate, and then further hydrogenated to yield ethylene, or undergoes coupled hydrogenation to produce 1,3-butadiene as a byproduct.