Ready, steady, copper! The efficient copper-catalyzed formation of amides, from benzylic alcohols and hydrochloride salts of primary- and secondary amines, uses cheap and readily available copper oxide, as well as tert-butylhydroperoxide (TBHP) as an oxidant.
Enzyme immobilization is an important strategy to enhance the stability and recoverability of enzymes and to facilitate the separation of enzymes from reaction products. However, enzyme purification followed by separate chemical steps to allow immobilization on a solid support reduces the efficiency and yield of the active enzyme. Here we describe polypeptide constructs that self-assemble spontaneously into nanofibrils with fused active enzyme subunits displayed on the amyloid fibril surface. We measured the steady-state kinetic parameters for the appended enzymes in?situ within fibrils and compare these with the identical protein constructs in solution. Finally, we demonstrated that the fibrils can be recycled and reused in functional assays both in conventional batch processes and in a continuous-flow microreactor.
Nitrogen-functionalized active carbon-supported ultrasmall Pd nanoparticles were conveniently prepared by using a postloading method. The Pd catalyst was highly active and selective for the hydrogenation of nitroarenes at room temperature under ambient pressure. Reducible groups such as ketone, carboxylic acid, and ester were not hydrogenated, and the corresponding anilines were obtained quantitatively. The Pd catalyst demonstrated high stability and could be reused 10 times without the loss of catalytic performance.
The selective hydrogenolysis of biomass-derived xylitol to ethylene glycol and propylene glycol was performed on Cu–SiO2 catalysts prepared by a precipitation–gel method with different Cu contents and pretreatment temperatures. As a result of the uniform distribution of Cu particles on these catalysts, their activities and combined selectivities to ethylene glycol, propylene glycol, and glycerol increased consistently with the increasing Cu particle size and reached maximum values at around 11 nm in the range of 4.0–38.0 nm. After the reaction conditions and catalyst pretreatment temperatures were optimized, a high combined yield to the target glycols of up to 70.4% was achieved on 90%Cu–SiO2 catalyst at ≈100% xylitol conversion. The 90%Cu–SiO2 catalyst can be recycled in successive runs without a significant loss of activity and selectivity by recalcination and reduction treatment after each run.
Coke-induced deactivation is one of the major challenges in the field of heterogeneous catalysis. Herein, the performance of the Pt/Al2O3 catalyst for the hydrogen-free dehydrogenation of cyclohexane was improved by doping with a small amount of Ca. The Ca-modified Pt/Al2O3 catalyst exhibited a cyclohexane conversion of 97.0?% and maintained a conversion above 75?% after 48 h, whilst the unmodified catalyst was deactivated from 87.0 to 2.7?% under the same conditions. Characterization techniques, including in situ DRIFT, XPS, thermal analysis, and temperature-programmed techniques, revealed that the presence of Ca effectively suppressed the deep dehydrogenation of H-rich carbonaceous components and promoted coke desorption by increasing the H/C ratio of H-deficient coke. This promotion effect of Ca was also associated with neutralizing the residual Cl ions and promoting immediate dehydrogenation.