Dry and wet impregnation of metal precursors remain the most widely used method for synthesis of supported metal catalysts due to its simplicity and ease of synthesis in large scale. However, supported catalysts prepared by impregnation method suffer from non-uniform dispersion of the metal and relatively large metal particles due to agglomeration and sintering during drying and calcination steps. Here, we report a simple pyrolysis assisted impregnation method which can produce uniformly dispersed and smaller metal nanoparticles through the formation of a protective carbon over-layer on the metal particles. A carbon layer generated in the pyrolysis step forms a metal@carbon core-shell structure that protects the metal nanoparticles from agglomerating and sintering at high temperatures due to coalescence and Ostwald ripening. In a typical synthesis of Ni/SiO<sub>2</sub> (10 wt% loading) by impregnation method, supported Ni nanoparticles with a mean size of 25nm and wide size distribution (10-50 nm) was achieved, whereas by the pyrolysis assisted route, much smaller Ni nanoparticles (mean particle size ~5nm) were formed with higher uniformity (3-9 nm). The synthesis process is extremely facile and doesn’t involve use of surfactants or additional separation steps, as is common in colloidal metal nanoparticle synthesis, making it attractive for larger scale application. The synthesized catalysts were characterized by HRTEM, XRD, XPS, ICP-OES, TPR, EXAFS and chemisorption studies. The supported Ni catalyst synthesized by the pyrolysis assisted impregnation method showed better performance in high temperature catalytic reaction like CO methanation than its counterpart synthesized by traditional impregnation and calcination. Characterization of the spent catalyst shows that the catalyst displayed high sintering resistance and dispersion even after extended exposure to the high temperature reaction conditions.

Highly dispersed metal catalyst synthesized through a metal@carbon core-shell precursor through simple impregnation method

2019 Spring National Meeting

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