Copper Clusters Encapsulated in Carbonaceous Mesoporous Silica Nanospheres for the Valorization of Biomass-Derived Molecules

Abstract

Cu-based catalysts possess prominent properties in the selective hydrogenation of carbon-oxygen bonds but suffer from low stability due to high-temperature sintering. Dandelion-like nanosized mesoporous silica spheres (NMSSs) with short mesochannels can afford a nanoconfined space restraining the metal from aggregating. Herein, we report an air-assisted low-temperature carbonization of the surfactant template strategy for fabricating N-doped carbon-coated NMSSs (NC@NMSSs) encapsulated ultra-dispersed Cu cluster catalysts (Cu/NC@NMSSs). The as-obtained catalysts have demonstrated excellent performances in the hydrogenation of biomass-derived levulinic acid (LA) into γ-valerolactone (GVL), achieving a GVL yield as high as 96% and commendable stability in 100 h. The functional N species and CO groups on the NC coating layer play a critical role in stabilizing and dispersing Cu clusters. Theoretical calculations reveal that the pyrrolic and pyridinic N sites can enrich LA reactants. Accordingly, the apparent activation energy (E a) is reduced by half and the turnover frequency doubled compared to Cu/NMSS catalysts. Additionally, the catalysts displayed high hydrogenation activities for a variety of aldehydes, ketones, and nitroarenes. This work offers a convenient strategy for constructing promising Cu-based catalysts in upgrading biomass-derived compounds.

Efficient and Stable Cu‐Cu2O@NC Catalysts for Selective Catalytic Conversion of Glycerol to Lactic Acid

“…The peaks at around 952.2 eV and 932.3 eV for the Cu 2p spectra corresponding to Cu 2p 1/2 and Cu 2p 3/2 states are assigned to Cu 0 or Cu + . [30] There are no satellite peaks near the binding energy of 940 eV indicating the absence of Cu 2 + species on the surfaces of the Cu-Cu x O@NC catalysts. [27] The Cu 2p 3/2 peak of the Cu-Cu x O@NC-700 catalyst shifts to a higher energy position than those of Cu-Cu x O@NC-400 and Cu-Cu x O@NC-550 catalysts, which might be due to the electron transfer from Cu to N. Figure 3(c) shows the Cu LMM Auger spectra of Cu-Cu x O@NC catalysts.…”

Double-Confined Ultrafine Cobalt Clusters for Efficient Peroxide Activation

“…The CTAB@mSiO 2 displayed a weight loss of 28.7% at 150–500 °C, corresponding to the CTAB decomposition . As the temperature further increased, a slow decrease in weight (4.3%) at 500–650 °C derived from the decomposition of NC dots in mSiO 2 . As for the presynthesized Co/NC@mSiO 2 , about 4.8% of weight loss was observed from 100 to 200 °C with a DTG peak at 180 °C corresponding to the decomposition of Co­(NO 3 ) 2 ·6H 2 O .…”

“…25 As the temperature further increased, a slow decrease in weight (4.3%) at 500−650 °C derived from the decomposition of NC dots in mSiO 2 . 23 As for the presynthesized Co/NC@mSiO 2 , about 4.8% of weight loss was observed from 100 to 200 °C with a DTG peak at 180 °C corresponding to the decomposition of Co(NO 3 ) 2 •6H 2 O. 27 However, the mSiO 2 and presynthesized Co/mSiO 2 did not show any DTG peaks attributed to CTAB decomposition, illustrating that the CTAB micelles had been completely removed after calcination (Figure S3).…”

“…This could be ascribed to varying degrees of the reaction between Co clusters and mSiO 2 containing NC dots at the interface, giving rise to the formation of Co−N/Br or Co−O−Si bonds. Additionally, the high Co 2+ ratio of 73.6% (Tables S4 and S5) in Co/NC@ mSiO 2 proved that the SMSI effect between Co clusters and mSiO 2 containing NC dots optimized the electronic structures 23 and prevented the surface oxidation of Co clusters. The high-resolution C 1s spectrum of Co/NC@mSiO 2 exhibited three peaks assigned to C�C (284.4 eV), C−O− C (285.5 eV), and C�O (286.9 eV), 29 respectively (Figure 2i).…”

“…Nano-mesoporous silica spheres (mSiO 2 ) can well disperse the metal atoms mainly via physical confinement due to the abundant mesoporous channels, high specific surface area, and thermodynamic stability. , Nitrogen-containing surfactants such as cetyltrimethylammonium bromide (CTAB) are generally used as templates in the synthesis of mSiO 2 , which will generate numerous gas pollutants during their high-temperature removal. Recent studies found that CTAB can be used as promising precursors to prepare NC dots via the carbonization process. , The repulsive force between the metal particles is greater than the van der Waals force due to the increased CTAB molecules near the metal particles. In this case, the NPs would gradually change from agglomeration to monodispersion .…”