Study on different synthesis methods of molybdenum-based oxide and sulfide catalyst and its performance in syngas to ethanol

Ethanol is a significant chemical feedstock, which can be employed not only as a raw material for chemicals and polymers, but also as an additive to petrol. It is typically produced in industry through either fermentation or ethylene hydration. In light of the growing demand for ethanol, it is imperative to investigate the potential of multi-channel production of ethanol. One-step ethanol production from syngas represents a significant method of ethanol production from non-fossil oil energy sources, and it is also an important means of clean utilization of coal. The cost of direct ethanol production from syngas is relatively low, but the distribution of alcohols with different carbon numbers in the alcohol product is wide, which makes subsequent separation difficult and restricts its large-scale development. Consequently, in the research of direct ethanol production from syngas, the key points to improve the process economics and promote the development of this technology are to improve the selectivity of ethanol and develop the efficient catalysts. Mo-based catalysts can be employed for low-hydrogen syngas. At the same time, it is challenging to deposit carbon, exhibits robust resistance to sulfur poisoning, and demonstrates excellent stability, which also extends the reaction cycle. However, the methanol content of the alcohol product is relatively high. Although the use of Fischer-Tropsch element modification can significantly reduce the methanol selectivity, it will inevitably lead to the problem of broadening the distribution of alcohols. In recent years, there has been a growing attention in the preparation of catalysts using non-thermal plasma technology. Non-thermal plasma comprises not only electrons, ions, molecules and free radicals, but also photons and excited substances. Previous studies have demonstrated that the non-thermal plasma method can induce alterations in the nucleation of the active phase and the crystal growth mode in the preparation of catalysts. Concurrently, for thermodynamically unfavorable reactions, the utilization of non-thermal plasma technology can disrupt the thermodynamic equilibrium limit, thereby facilitating the reaction. In this study, Mo-based oxide and sulfide composite catalysts were prepared from the precursor of molybdenum sulfide by two distinct methods: the conventional thermal method and the RF non-thermal plasma method. The catalytic performance of Mo-based oxide and sulfide composite catalysts for the synthesis of ethanol from syngas was then investigated. A range of analytical techniques were employed to investigate the physical and chemical properties of the molybdenum-based oxygen-sulfur complex catalysts synthesized by different preparation methods. These included XRD, UV-visible, HR-TEM, SEM, HAADF-STEM, XPS, CO-TPD, H₂-TPD, CO₂-TPD and In-situ DRIFTS. Moreover, the objective was also to ascertain the impact of the physical and chemical properties on the catalytic performance of the different catalysts. Among them, the MOS-P catalyst exhibited the best catalytic performance. Under the reaction conditions of 6 MPa, 320 ℃, and a space velocity of 4500 h⁻¹, the CO conversion reached 22.5%. The selectivity of total alcohols was 71.4%, with ethanol accounting for 29.1% of the total alcohols. This research will provide theoretical guidance for the directional conversion of syngas and serves as a reference for the design and preparation of new molybdenum-based materials.