Efficient catalytic amination of diols to diamines over Cu/ZnO/γ-Al2O3

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.

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.

Differences in Deterioration Behaviors of Cu/ZnO/Al2O3 Catalysts with Different Cu Contents toward Hydrogenation of CO and CO2

The deterioration behaviors of Cu/ZnO/Al₂O₃ (CZA) catalysts upon different Cu contents were elucidated. The fresh and spent catalysts after being used in CO and CO₂ hydrogenation at 250 °C under atmospheric pressure were properly characterized using various techniques including X-ray powder diffraction, X-ray photoelectron spectroscopy, and temperature-programmed reduction for the changes of metal sites, while the textural and chemical properties and carbon deposition on spent CZA catalysts were analyzed by N₂ physisorption, energy-dispersive X-ray spectroscopy, and temperature-programmed oxidation. During the hydrogenation reaction for both CO and CO₂, the unstable Cu⁰ site on the spent CZA catalyst having a low Cu loading (sCZA-L) was oxidized to CuO and the aggregation of metal crystallite sites (Cu-ZnO and ZnO) was observed. Moreover, the amount of carbon deposition on sCZA-L (ca. >2%) is higher than the spent CZA catalyst having a high Cu loading (sCZA-H, ca. <0.5%). These phenomena led to a decrease in the surface area and the blockage of active sites. These findings can be determined on the catalytic deactivation and the obvious decrease in the catalytic activity of the CZA catalyst having a low Cu content (CZA-L, Cu:Zn = 0.8).

Cr and Co modified Cu/Al2O3 as efficient catalyst for continuous synthesis of bis(2-dimethylaminoethyl)ether

A series of transition metal doped Cu-based Al2O3 catalysts are prepared through coprecipitation-kneading method, and applied in the continuous synthesis of bis(2-dimethylaminoethyl)ether (BDMAEE) via amination of diethylene glycol (DEG) with...

Comparative study on the effect of different copper loading on catalytic behaviors and activity of Cu/ZnO/Al2O3 catalysts toward CO and CO2 hydrogenation

The ternary Cu/ZnO/Al₂O₃ (CZA) catalysts having different Cu loading were prepared by the co-precipitation method. Then, they were used in CO and CO₂ hydrogenation to produce methanol under atmospheric pressure at 250 °C. The high Cu loading CZA catalyst (CZA-H) resulted in the enhancement of structural features and textural properties (e.g., BET surface area and the crystallite size of copper species). Furthermore, the conversion of CO and CO₂ over CZA-H catalyst was apparently higher than that of the CZA-L (low Cu loading) catalyst. The major product of CO hydrogenation obtained from both catalysts was methanol, whereas in CO₂ hydrogenation, the main product was CO. Deactivation of catalysts was also crucial during CO and CO₂ hydrogenation. Therefore, the spent catalysts were determined to identify the nature of carbon formation. It revealed that amorphous and graphitic cokes were present. These cokes have different mechanisms in the elimination from the surface leading to influencing the deactivation process. The spent CZA-L was found to have higher carbon content, which was around 2.3% and 3.1% for CO and CO₂ hydrogenation, respectively. Besides the amorphous coke, the graphitic coke was also observed in CZA-L after time on stream for 5 h.