Study On The Catalyst Design And Reaction Mechanism For The Production Of Propionic Acid From Bio-Lactic Acid

In recent years,the growing problems of environmental pollution,energy crisis and resource shortage have forced us to develop more environmentally friendly and clean production processes to fully and effectively utilize renewable resources.Lactic acid,a biomass derivative that can be converted into a variety of chemicals,has attracted a lot of attention due to its highly functional properties.Propionic acid is a common chemical widely used as a preservative in food,cereals and animal feed,an intermediate in chemical synthesis and a solvent.The production route of propionic acid prepared by hydrodeoxygenation of lactic acid not only provides a new direction for the utilization of renewable resources,but also differentiates from the traditional petroleum-based production route and provides a new idea for the green production of propionic acid.However,the catalyst activity,selectivity and stability in this process route still face serious challenges,therefore,an in-depth conformational relationship study is the key to breakthrough the catalytic lactic acid hydrodeoxygenation reaction for propionic acid production process.In this paper,we focus on the chemical reaction process of lactic acid hydrodeoxygenation to prepare propionic acid,and analyze the catalyst design,construction,characterization and theoretical calculations to reveal the structure-effect relationship and provide a scientific basis for the development of high-performance catalysts in the stage of"carbon peak"and"carbon neutral".In order to provide a scientific basis for the development of high-performance catalysts,the paper aims to reveal the structure-effect relationship and analyze the reaction mechanism from the design,construction,characterization and theoretical calculation.To this end,the main research of this paper is as follows.（1）Molybdenum-based catalysts with different morphologies,defects and configurations were prepared by solvent heat and combined with hydrogen annealing,and their structures were characterized and analyzed by XRD.The catalytic performance of the catalytic materials in the hydrodeoxygenation reaction of lactic acid was tested at 215°C,an initial pressure of H₂ of 3 MPa,a reaction time of 12 h,a catalyst mass of 0.5 g,and 20 g of 10 wt%lactic acid.The results showed that the best activity of the molybdenum-based catalyst containing defects was prepared by choosing N,N-dimethylformamide as the solvent,adding 2.5%activated carbon carrier,and annealing the H₂（5%）-Ar mixture at 400°C for 30 min.The reasonable construction of defects can effectively enhance the adsorption activation of lactic acid molecules on the surface of molybdenum-based catalysts,thus enhancing the reaction activity.（2）MoS₂/MoO₃ composite semiconductor structural materials were prepared by air-roasted oxidative desulfurization and applied to the reaction of lactic acid hydrodeoxygenation for the preparation of propionic acid.The structure and surface properties of the catalysts were characterized by SEM,TEM,XRD,XRF,XPS and EPR,and the photoelectric properties of the catalytic materials were characterized by electrochemical methods.Based on the analysis of the characterization results,it can be seen that MoS₂ and MoO₃ are intercalated and arranged,and both sulfur vacancies and oxygen vacancies exist.According to the theoretical calculation,the sulfur vacancy adsorbsα-C-OH of lactic acid with an adsorption energy of-0.84 e V,and the oxygen vacancy adsorbs hydrogen with an adsorption energy of-0.12 e V.The adsorption energy analysis reveals that the sulfur vacancy adsorbs activated lactic acid,while the oxygen vacancy adsorbs activated hydrogen.It was observed experimentally that there was a significant hot electron flow in the MoS₂/MoO₃ composite semiconductor,and electrons were transferred from MoO₃ to MoS₂.the transferred electrons were captured by the surface sulfur vacancies,which contributed to the C-OH bond breakage and enhanced the ability to reduce lactic acid;meanwhile,the ability of oxygen vacancies to dissociate hydrogen was enhanced due to the electron transfer.The experiments showed that the reaction process of lactic acid hydrodeoxygenation for the preparation of propionic acid was easily realized under the catalytic effect of MoS₂/MoO₃composite semiconductor materials,while a small amount of side reactions occurred,and the side products mainly included acetaldehyde,n-propanol and acrylic acid.At the reaction temperature of 215°C,the conversion of lactic acid could reach 90.4%and the selectivity of propionic acid could reach 88.4%.5 cycles of stability experiments were performed on the catalyst,and no significant decrease in activity was found.（3）MoS₂ catalysts with ultra-thin layers and abundant defects were obtained by lithium-ion intercalation treatment and applied to the reaction of lactic acid hydrodeoxygenation for the preparation of propionic acid.The structural and surface properties of the materials were characterized by TEM,AFM,XPS,XRD,and EPR,and the relevant optoelectronic properties of the catalytic materials were characterized by electrochemical methods.Based on the analysis of the characterization results,it is clear that the percentage of monolayer MoS₂ increases and the number of sulfur vacancies on the surface increases with the increase of the number of butyllithium treatments,while MoS₂ undergoes a transition from 2H phase to 1T phase.The catalytic effect of ^SSMoS₂ obtained by secondary butyllithium intercalation treatment was shown to achieve 96.8%lactic acid conversion and 93.3%propionic acid selectivity at a reaction temperature of 215°C,an initial pressure of 3 MPa H₂ and 12 h reaction time.By comparing the activity of other catalysts in the same series,it was determined that the active center of this catalytic material is a sulfur vacancy,which can activate both lactic acid molecules and hydrogen molecules,and has the characteristics of multiple energy.The catalyst was subjected to 8 cycles of stability experiments,and no significant decrease in activity was found,indicating that the catalyst is stable and has good application prospects.