Abstract
N-doped metal materials with enhanced stability and abundant porosity have attracted tremendous attention in catalytic reactions. Herein, a simple solvothermal approach was demonstrated to significantly enlarge the pore dimension of conventional microporous zeolitic imidazolate framework (ZIF) incorporated with two kinds of central metals (Co, Zn), while maintaining the original ZIF crystal morphology. Upon further pyrolysis, the resulting mesoporous Co-Zn/N-C material could possess the highly dispersed metal particle on the N-doped carbon, with satisfactory pore volume and surface area. The partial vaporization of Zn and the stabilizing effect of N, illustrated by XRD, HRTEM, HAADF-STEM with mapping, SEM, Raman Spectrum, BET, and TGA, were able to remarkably increase the accessibility of substrate toward active sites and prevent the aggregation of metal particles, respectively. Under mild reaction conditions, the N-stabilized Co-Zn/N-C exhibited good activity and selectivity in transfer hydrogenation of various nitro compounds to corresponding amines, where a synergistic role among Co, Zn, and N was responsible for its superior performance to other tested catalysts. In addition, the N-doped non-noble metal/carbon heterogeneous catalyst was fairly stable and could be reused several times without obvious deactivation.
Highlights
With the progress of modern society, the increasing requirement of fine chemicals and other important materials such as dyes, pigments, food additives, pharmaceuticals, and herbicides have brought a series of problems, demanding prompt solution from scientists around the world (Li et al, 2018; Sudarsanam et al, 2019)
To more intuitively understand the catalyst morphology, SEM, TEM, and STEM-HAADF were utilized to characterize Co/N-C-800 and Co-Zn/N-C-800 (Figures 2a–f). Both materials have the tubular graphene structure and the metal particles are fully dispersed on the carbon carrier, which is consistent with a previous report
The metal nanocatalysts would be generated from the reduction of the metal ions/clusters with reducing gases (e.g., CO) in situ generated from the pyrolysis of organic species, and these metal nanocatalysts were capable of further catalyzing the organic units to form the graphene structures and N-doped carbon nanotubes (Chen et al, 2008; Xia et al, 2016; Gong et al, 2019)
Summary
With the progress of modern society, the increasing requirement of fine chemicals and other important materials such as dyes, pigments, food additives, pharmaceuticals, and herbicides have brought a series of problems, demanding prompt solution from scientists around the world (Li et al, 2018; Sudarsanam et al, 2019). A simple solvothermal method was utilized to prepare the Co-Zn-ZIF material, followed by high-temperature pyrolysis in N2 to get the mesoporous Co-Zn/N-C catalyst, which was proved to be highly efficient for hydrogenation of nitrobenzene to aniline using formic acid as a hydrogen donor.
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