Vinyl acetate is an important organic chemical raw material, mainly used in the production of polyvinyl alcohol resin, synthetic fibers, adhesives and water-soluble coatings, and other chemical products. China's energy landscape is dominated by coal, which could provide ample acetylene raw materials for the synthesis of vinyl acetate with a significant advantage. The acetylene method for producing vinyl acetate is an important process in coal chemical industry. Currently, the activated carbon supported zinc acetate was used as the mainstream industrial catalyst. However, the application of Zn(OAc)₂/AC industrial catalyst has been limited due to the low conversion rate of CH₃COOH conversion was only 25%-40% and short catalytic stability.
To overcome the above industrial bottleneck problem, researchers from Shihezi University developed phosphorus-doped activated carbon-supported zinc catalysts. Phosphoric acid was used as the acidity regulator, not only exhibited abundant Brönsted and Lewis acid sites as well as phosphorus-oxygen groups.
Characterization results revealed that P-doping significantly altered the catalyst properties. FTIR spectra showed a new C-O-P bond vibration peak at 1078 cm⁻¹ in P-doped samples. Raman spectroscopy indicated that appropriately P-doped AC had a higher ID/IG ratio, suggesting more defect sites closely related to catalytic activity. XPS analysis showed that compared to Zn/AC, the binding energies of Zn 2p1/2 and Zn 2p3/2 in Zn/0.01PAC shift positively from 1045.7 and 1022.6 eV to 1046.1 and 1023.0 eV, respectively. The increase of binding energy indicated that the decrease of the electron cloud density around the Zn atoms, which is beneficial for enhancing the adsorption capacity of the Zn sites for acetic acid.
NH₃-TPD and pyridine-FTIR analyses demonstrated that P-doping markedly enhanced weak acid sites and Lewis acid sites on the catalyst surface. Due to the electronegativity of P (2.19) is lower than that of C (2.55), the P atoms in the C-P bonds exhibited a positive charge density, while the C atoms displayed a negative charge density. This electron rearrangement resulted in a significant increase in Lewis acid sites on the carbon framework.
The optimized Zn/0.01PAC catalyst achieved approximately 80% conversion of acetic acid, dramatically higher than the 25%-40% of conventional catalysts. Kinetic analysis revealed that the apparent activation energy for Zn/0.01PAC catalyst was 7.09 kJ·mol⁻¹, which is markedly lower than the 31.38 kJ·mol⁻¹ observed for the Zn/AC catalyst.
Long-term stability tests showed P-doping enhanced resistance to carbon deposits, with carbon deposition of only 0.95% for Zn/0.01PAC compared to 1.28% for Zn/AC. ICP-OES analysis revealed zinc loss rate of 8.56% for Zn/0.01PAC versus 12.17% for Zn/AC. TEM images confirmed that the introduction of P species could enhance the dispersion but also inhibit agglomeration of Zn species during the reaction.
This advancement underscores the critical role of Lewis acid sites in augmenting catalytic activity. The findings of this research not only provide an efficient solid acid catalyst for the acetoxylation of acetylene but also establish a universal strategy for the precise modulation of AC surface acidity thereby laying a significant foundation for the industrial application of this reaction and future investigations.
DOI
10.1007/s11705-026-2634-x