Boron modified Cu/Al2O3 catalysts for the selective reductive amination of levulinic acid to N‐substituted pyrrolidinones

Catalytic Conversion of Levulinic Acid to Pyrrolidone under Mild Conditions with Disordered Mesoporous Silica-Supported Pt Catalyst

Catalytic conversion of biomass-derived levulinic acid (LA) into high-valued 5-methylpyrrolidones has become an attractive case in studies of biomass utilization. Herein, we developed a disordered mesoporous Pt/MNS catalyst for this reductive amination process under room temperature and atmospheric pressure of hydrogen. The disordered mesoporous structures in support of Pt/MNS catalyst led the formation of highly dispersed Pt species via confinement effect, providing high specific area for enhancing the catalytic sites. With the synergistic effect between highly dispersed Pt species and mesoporous structures, 5-methylpyrrolidones were successfully synthesized from biomass-derived LA and primary amines with high selectivity. Mechanism studies indicated that introducing protonic acid would promote the reductive-amination process, and enamine intermediates could be detected during the in-situ DRIFT tests. Density functional theory (DFT) calculation confirmed that the hydrogenation of enamine intermediate was more accessible than that of imide intermediates, leading the excellent performance of the Pt/MNS catalyst. This work provided a green method to produce 5-methylpyrrolidone and revealed the impact of catalyst structural characteristics on the reaction process.

Reductive Amination of Levulinic Acid to Pyrrolidones: Key Step in Biomass Valorization towards Nitrogen-Containing Chemicals

Nowadays, the field of biomass conversion is gradually moving towards an encouraging stage. The preparation of nitrogen-containing chemicals using various biomass resources instead of fossil resources do not only reduce carbon emissions, but also diversify the products of biomass conversion, thus increasing the economic competitiveness of biomass refining systems. Levulinic acid (LA) can be used as a promising intermediate in biomass conversion for further synthesis of pyrrolidone via reductive amination. However, there are still many critical issues to be solved. Particularly, the specific effects of catalysts on the performance of LA reductive amination have not been sufficiently revealed, and the potential impacts of key conditional factors have not been clearly elucidated. In view of this, this review attempts to provide theoretical insights through an in-depth interpretation of the above key issues. The contribution of catalysts to the reductive amination of LA as well as the catalyst structural preferences for improving catalytic performance are discussed. In addition, the role of key conditional factors is discussed. The insights presented in this review will contribute to the design of catalyst nanostructures and the rational configuration of green reaction conditions, which may provide inspiration to facilitate the nitrogen-related transformation of more biomass platform molecules.

Conversion of Levulinic Acid and its Esters to 1,5-dimethyl-2-Pyrrolidone over a Nonnoble Metallic Ni@CeOx Catalyst

1,5-dimethyl-2-pyrrolidone (MNMP), as a highly efficient green solvent, can be obtained from biomass-derived levulinic acid and its esters with 100 % conversion and 96.8 % yield over a 10 % Ni@CeOx catalyst at 140 °C, 2 MPa H2 , 8 h, and with water as the solvent. Structure-property correlation investigations were performed with diverse characterization methods, including BET, XRD, XPS, TEM, HAADF-STEM, H2 -TPR, NH3 -TPD, CO2 -TPD and FT-IR, and the results revealed that the excellent catalytic performance of the 10 % Ni@CeOx catalyst was mainly resulted from the strong interaction between Ni and CeOx, which formed more catalytic active sites and contributed to higher reductive amination efficiency. Besides, the 10 % Ni@CeOx catalyst had a chemisorption effect on LA. This was also the key to the excellent catalytic activity of the 10 % Ni@CeOx catalyst. The 10 % Ni@CeOx catalyst exhibited great stability throughout 6 reaction runs and excellent catalytic efficiency in the kilogram scale preparation of MNMP. This work provides a low-cost, efficient, and environmentally friendly heterogeneous catalytic system for the production of MNMP.

Recent Advances in the Efficient Synthesis of Useful Amines from Biomass-Based Furan Compounds and Their Derivatives over Heterogeneous Catalysts

Bio-based furanic oxygenates represent a well-known class of lignocellulosic biomass-derived platform molecules. In the presence of H2 and different nitrogen sources, these versatile building blocks can be transformed into valuable amine compounds via reductive amination or hydrogen-borrowing amination mechanisms, yet they still face many challenges due to the co-existence of many side-reactions, such as direct hydrogenation, polymerization and cyclization. Hence, catalysts with specific structures and functions are required to achieve satisfactory yields of target amines. In recent years, heterogeneous catalytic synthesis of amines from bio-based furanic oxygenates has received extensive attention. In this review, we summarize and discuss the recent significant progress in the generation of useful amines from bio-based furanic oxygenates with H2 and different nitrogen sources over heterogeneous catalysts, according to various raw materials and reaction pathways. The key factors affecting catalytic performances, such as active metals, supports, promoters, reaction solvents and conditions, as well as the possible reaction routes and catalytic reaction mechanisms are studied and discussed in depth. Special attention is paid to the structure–activity relationship, which would be helpful for the development of more efficient and stable heterogeneous catalysts. Moreover, the future research direction and development trend of the efficient synthesis for bio-based amines are prospected.

Continuous synthesis of 2,2,6,6-tetramethyl-4-piperidinol over CuCrSr/Al2O3: effect of Sr promoter†

A continuous process was developed for catalytic hydrogenation of triacetoneamine (TAA) to 2,2,6,6-tetramethyl-4-piperidinol (TMP), both of which are indispensable raw materials of hindered amine light stabilizers. A series of promoter-modified CuCr/Al₂O₃ catalysts were prepared by co-precipitation method and evaluated by the above reaction. The effect of promoter on the catalytic performance was explored by characterization tools, in which, CuCrSr/Al₂O₃ exhibited excellent catalytic performance with nearly complete conversion of TAA and over 97% selectivity of TMP at 120 °C. The characterization results indicated that the doped Sr could decrease the size of Cu nanoparticles to provide more active sites, improve the ratio of Cu⁺/Cu⁰ to promote the adsorption of substrates, and reduce the surface acidity to depress side reactions, thus remarkably enhancing catalytic performance. This work provides a low-cost, reliable and efficient strategy for the continuous industrial production of TMP.

Sr-modified CuCr/Al₂O₃ catalysts effectively promote the continuous process of catalytic hydrogenation from TAA to TMP.

Levulinic Acid Is a Key Strategic Chemical from Biomass

Levulinic acid (LA) is one of the top twelve chemicals listed by the US Department of Energy that can be derived from biomass. It serves as a building block and platform chemical for producing a variety of chemicals, fuels and materials which are currently produced in fossil based refineries. LA is a key strategic chemical, as fuel grade chemicals and plastic substitutes can be produced by its catalytic conversion. LA derivatisation to various product streams, such as alkyl levulinates via esterification, γ-valerolactone via hydrogenation and N-substituted pyrrolidones via reductive amination and many other transformations of commercial utility are possible owing to the two oxygen functionalities, namely, carbonyl and carboxyl groups, present within the same substrate. Various biomass feedstock, such as agricultural wastes, marine macroalgae, and fresh water microalgae were successfully converted to LA in high yields. Finding a substitute to mineral acid catalysts for the conversion of biomass to LA is a challenge. The use of an ultrasound technique facilitated the production of promising nano-solid acid catalysts including Ga salt of molybophosphoric acid and Ga deposited mordenite zeolite, with optimum amounts of Lewis and Bronsted acidities needed for the conversion of glucose to LA in high yields, being 56 and 59.9 wt.% respectively. Microwave irradiation technology was successfully utilized for the accelerated production of LA (53 wt.%) from glucose in a short duration of 6 min, making use of the unique synergistic catalytic activity of ZnBr2 and HCl.