Xiancheng Ma,Liqing Li,Shaobin Wang,Mingming Lu,Hailong Li,Weiwu Ma,Tim C. Keener
A porous carbon (ZC) was prepared at 900 °C using zeolitic imidazolate framework-8 (ZIF-8) as a solid template for CO 2 adsorption. The ZC was further treated by ammonia functionalization to improve CO 2 uptake. The textural and surface characteristics of ZC samples were determined by X-ray diffraction (XRD), N 2 adsorption, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). It was revealed that ammonia treatment at 600 °C considerably enhanced the specific surface area and N-content of ZC. However, the pyrrolic-N group was decreased, yet the pyridinic-N group was increased with an increased temperature. The pyrrolic-N significantly enhanced CO 2 adsorption. The ammonia treatment, on the one hand, increases the alkalinity of ZC sample and the base–acid interaction between N-containing functional groups with CO 2 . On the other hand, the ammonia treatment increased pyrrolic-N group (NH) into carbon surface facilitating the hydrogen-bonding interactions between proton of pyrrolic-N and CO 2 molecules.
Achieving an optimal acid-base synergy and uniform dispersion of active sites on catalyst surface is essential for high catalytic performance in the side chain alkylation of toluene with methanol (SATM). Herein, we report that ammonium (NH₃) treatment of Cu-modified NaX zeolite catalysts effectively modulates acid-base properties and enhances the dispersion of Cu active sites across the catalyst surface. A series of Cu-modified catalysts were prepared with and without NH₃ treatment and further modified with NaOH to evaluate their synergistic effects. Comprehensive characterization techniques, including Scanning Electron Microscopy (SEM), HAADF-STEM and EDS, Pyridine FTIR, Temperature-Programmed Desorption of NH₃ (TPD-NH₃), X-ray Photoelectron Spectroscopy (XPS O 1 s), and regression analysis, were used to correlate catalyst structure, and acid-base property and nature of acid sites with catalytic performance. Results reveal that NH₃ incorporation into the Cu-modified NaX framework significantly enhances catalytic efficiency by tuning acid-base properties and promoting a homogeneous distribution of Cu active sites. Notably, the 3Cu-4Na-N catalyst achieved a superior yield of ethylbenzene and styrene production, reaching 84.9 %, compared to 64.3 % for the 3Cu-4Na catalyst under identical conditions. Methanol conversion reached 97.7 %, with the catalyst demonstrating robust stability over 168 h of operation. Additionally, 3Cu-4Na-N catalyst exhibited the highest turnover frequency (TOF) reaching 27.3 h -1 , confirming its superior intrinsic activity. This study highlights the critical role of NH₃ in advancing Cu-NaX catalysts for SATM and provides a promising strategy for optimizing catalytic performance through controlled acid-base interactions and active site dispersion.
Lejun Chen,Yonggang Lei,Yue Yang,Jianying Huang,Weiying Zhang,Kim Hoong Ng,Yuekun Lai
Metal-doping is a common strategy for establishing active sites on photocatalyst, but appropriately exposing them for maximized atomic utilization remains a great challenge in photocatalytic research. Herein, we propose a metal organic framework (MOF)-assisted approach to synthesis copper-modified titania (Cu-TiO 2 /Cu) photocatalyst with homogenously distributed and highly accessible active sites in its matrix. Significantly, an MOF precursor, namely NH 2 -MIL-125, with co-chelation of titania (Ti) and copper (Cu) was subjected to mild calcination, subsequently results in Cu-modified TiO 2 with highly accessible channels to its inner surface. These channels provide not only a large reactive surface (>400 m 2 g -1 ); they also enable facile modifying route for the pre-deposited Cu in prior to photoreaction. Specifically, NH 3 treatment was applied to partially reduce deposited Cu ions (Cu + and Cu 2+ ) into Cu nanoparticles, where their interplays realize improved optical properties and charge separation during photoreactions. Furthermore, the NH 3 -induced Cu nanoparticles could also serve as the adsorptive site for H + , thereby enabling 5629 μmol h -1 g -1 H 2 generation over the optimum photocatalyst of Cu 20 /TiO 2 /Cu 500 . Such performance is associated to 35.44 and 1.71-fold improvements compared to pure TiO 2 (Cu 0 /TiO 2 ) and untreated Cu-ion modified TiO 2 (Cu 20 /TiO 2 ), respectively. This work offers a new synthetic strategy for obtaining photocatalyst with evenly distributed and highly accessible active sites, thus improving the commensurability of photocatalytic H 2 generation from the industrial perspective.
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