摘要: A highly efficient cerium-modified Cu/hexagonal mesoporous silica (xCe-Cu/HMS) catalyst for the vapor-phase hydrogenation of dimethyl oxalate (DMO) into ethylene glycol (EG) was prepared using an ammonia evaporation method. The Ce promoter can significantly improve the performance of the catalyst, and the best catalytic performance was obtained after the introduction of 1.2% Ce promoter on Cu/HMS. The DMO conversion and EG selectivity got to 99.6% and 96.3%, respectively, under moderate conditions (200 °C, 2.0 MPa, H2/DMO = 100 and LHSVDMO = 1.2 h−1). Characterization results revealed that Ce modification can enhance the interaction between Cu and the support, improve the dispersion of Cu on HMS, and maintain the appropriate ratio of Cu+/(Cu++Cu0). In this study, a simple and low-cost method was used to synthesize Ce-modified Cu-HMS catalysts, which showed excellent catalytic performance in conversion of DMO to EG under moderate conditions.
摘要: Hydrogen production from electrolyzed water driven by sustainable energy is an effective way to achieve the hydrogen economy with zero carbon emission. Alkaline electrocatalytic hydrogen evolution reaction (HER) is one of the main energy transforming processes in the field of electrolytic water technology. The development of active and cost-effective nonprecious catalytic electrodes is of great importance to alkaline hydrogen evolution reaction. Amorphous nanosized nickel-boron alloy particles (NiB-COS) have been obtained by using chitosan oligosaccharides (COS) as a stabilizer via chemical reduction method. The as-prepared electrocatalysts have been used for the hydrogen evolution reaction (HER). The electrocatalysts have been characterized by using X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma analysis (ICP) and X-ray photoelectron spectroscopy (XPS). NiB-COS displays a significant increase in hydrogen evolution reaction properties in alkaline media, affording low overpotentials of 49.4 mV at 10 mA/cm2 and 15.1 mV onset overpotential for the hydrogen evolution reaction. Tafel slope of NiB-COS is 86.1 mV/dec. Remarkably, the formation of a nickel-boron alloyed phase and the decrease of particle size are helpful to improve HER activity of NiB-COS. The experimental data indicated that the NiB-COS showed excellent long-term stability as a very active electrocatalyst.
摘要: In this work we report the feasible modification of graphitic carbon nitride (g-C3N4) polymer through a post-functionalization progress. The resultant photocatalyst exhibits boron doping and mesoporous structure with a high surface area of 125 m2/g, leading in an increased surface activity for photocatalytic water splitting reaction. X-ray diffraction, X-ray photoelectron spectroscopy, PL emission spectra and UV-Vis spectra were used to detect the properties of as-prepared samples. Based on X-ray photoelectron spectroscopy analysis, boron is proposed to dope in the g-C3N4 lattice. Optical studies indicated that boron doped g-C3N4 exhibits enhanced and extended light absorbance in the visible-light region and a much lower intensity of PL emission spectra compared to pure g-C3N4. As a result, boron doped g-C3N4 shows activity of 10.2 times higher than the pristine g-C3N4 for photocatalytic hydrogen evolution. This work may provide a way to design efficient and mesoporous photocatalysts through post modification.
摘要: The structure-sensitive of Cu catalyst for furfural hydrogenation to furfuryl alcohol was explored by employing Cu(111) and Cu(211) model systems. Herein, the adsorption behavior of reactants and intermediates, and the possible reaction mechanism of furfuryl alcohol formation were investigated. For furfuryl alcohol formation, the preferred pathway is F-CHO + 2H→F-CH2O + H→F-CH2OH, in which the second H addition is the rate-determining step. Meanwhile, Cu(211) surface exhibits higher activity to furfuryl alcohol formation than that on Cu(111) surface. According to our analysis, the undercoordinated sites on the Cu(211) surface could facilitate H2 dissociation and stabilize the adsorbed furfural, thereby promoting the furfural hydrogenation and the furfuryl alcohol formation. This work provides a feasible approach for regulating the catalytic activity and selectivity in furfural conversion.