RESUMEN
Accurately decoding the three-dimensional atomic structure of surface active sites is essential yet challenging for a rational catalyst design. Here, we used comprehensive techniques combining the pair distribution function and reverse Monte Carlo simulation to reveal the surficial distribution of Pd active sites and adjacent coordination environment in palladium-copper nanoalloys. After the fine-tuning of the atomic arrangement, excellent catalytic performance with 98% ethylene selectivity at complete acetylene conversion was obtained in the Pd34Cu66 nanocatalysts, outperforming most of the reported advanced catalysts. The quantitative deciphering shows a large number of active sites with a Pd-Pd coordination number of 3 distributed on the surface of Pd34Cu66 nanoalloys, which play a decisive role in highly efficient semihydrogenation. This finding not only opens the way for guiding the precise design of bimetal nanocatalysts from atomic-level insight but also provides a method to resolve the spatial structure of active sites.
RESUMEN
A carbon matrix-supported Ni catalyst with surface/subsurface S species is prepared using a sacrificial metal-organic framework synthesis strategy. The resulting highly dispersed Ni-S/C catalyst contains surface discontinuous and electron-deficient Niδ+ sites modified by p-block S elements. This catalyst proved to be extremely active and selective for alkyne hydrogenation. Specifically, high intrinsic activity (TOF = 0.0351 s-1) and superior selectivity (>90%) at complete conversion were achieved, whereas an analogous S-free sample prepared by the same synthetic route performed poorly. That is, the incorporation of S in Ni particles and the carbon matrix exerts a remarkable positive effect on catalytic behavior for alkyne hydrogenation, breaking the activity-selectivity trade-off. Through comprehensive experimental studies, enhanced performance of Ni-S/C was ascribed to the presence of discontinuous Ni ensembles, which promote desorption of weakly π-bonded ethylene and an optimized electronic structure modified via obvious p-d orbital hybridization.
RESUMEN
Multi-crystalline N-doped Cu/CuxO/C foam catalysts are successfully synthesized from N-coordinated HKUST-1/cellulose and applied in 4-nitrophenol (4-NP) reduction. Effects of N content and basicity on Cu morphology, crystal lattice and size, component dispersion and oxidation states in catalysts are systematically investigated. Moreover, transforming powder catalysts to foam morphology is proposed to further enhance catalytic performance and facilitate more feasible industrial applications. Results reveal that alkaline N-dopant simultaneously inhibits the growth of Cu crystals to only 3-5â¯nm and restrains Cu(II) reduction in HKUST-1 during calcination. This facilitates the formation of a special multi-crystalline Cu/Cu2O/CuO structure. Furthermore, Cu2O species on catalyst surface increase with increasing alkaline strength and N dopant content. Graphitic nano-structure catalyzed by Cu sites in HKUST-1 greatly enhances electron transfer in 4-NP reduction leading to 21 times faster kinetics and better recycle performance by melamine-doped Cu/CuxO/C foam catalyst than bare Cu/C catalyst directly from HKUST-1. Moreover, carbon foam derived from CMC can further amplify Cu dispersion and inhibit its agglomeration, thus promotes catalyst stability during cycling performance. Therefore, the proposed in-situ N doping and foam shaping strategy can efficiently enhance catalytic activity and reaction stability for 4-NP reduction, which can be envisaged of potential value for other similar industrial catalysis.
