Preparation And Catalytic Hydrogenation Of Confined Structure Hexahedral Ni-based Catalyst

Metal nanoparticles (NPs) have received considerable interest due to their excellent performance in a variety of reactions in industrial processes. It is well known that the shape of NPs plays a significant role in enhancing the activity and selectivity of a structure-sensitive reaction, by controlling not only the exposed crystal facets but also the proportions of surface atoms at corners,edges, and planes. While, in recent years, has found confinement in microenvironment strongly impacts the structure of active sites of catalyst metal with the surrounding structure of the interaction and catalytic performance. Nowadays, there are more attention to the preparation and catalytic properties of the confined structure NPs of some precious metals(such as Pt, Pd, Rh, etc.). For the non-noble metal NPs, the research of the synthesis, the growth process and the catalytic performance of the non-noble metal NPs are rare.In this thesis, NiAl-LDH-TA hydrotalcites were used as precursors, and Ni-based nanocrystals with hexahedral morphology confined in Ni(Al)Ox-C were obtained under N2 atmosphere. The crystal composition, surface valence,morphology were characterized by XRD, insitu FT-IR, Raman, XPS, TG-DTA,TPR, HRTEM and spherical astrometry STEM-BF and STEM-EDXS mapping. The mechanism of the formation of Ni NPs and their confined structure is discussed. Finally, Ni/Ni(Al)Ox-C catalyst with confinement hexahedral morphology was applied to PNP and semi-hydrogenation of phenylethylene. The activity and selectivity of the catalytic reaction were analyzed. Then the mechanism of its catalytic process was explored to obtain the structure-activity relationship between catalyst structure and reaction performance. The research details as follows:(1) Confined Ni nanoparticles catalyst Ni/Ni(Al)Ox-C was fabricated by NiAl-LDH-TA precursors obtained by ion exchange under N2 atmosphere treatment 400 ? . Meanwhile it was confirmed that it was Ni(Al)Ox as the base and the Ni metal confined in the range by HRTEM and spherical aberration correction electron microscope. The interlayer C was subjected to explosive reduction from the Ni(Al)Ox edge and Ni-nanoparticles confined in the Ni(Al)Ox-C substrate with an average particle size of about 4-5 nm.(2) Based on the analysis of the structural properties of the catalyst samples at different reduction temperatures, the mechanism of the Ni-NPs and the reduction mechanism of the hexagonal structure is deduced. We deduce the mechanism of the reduction process: 1. the collapse of the preparation phase:from room temperature to 300 ? stage, this stage is the gradual loss of water,interlayer ions and gradually decomposed to form a uniform Ni(Al)Ox and active reduced carbon species. 2. A rapid nucleation stage of about 300 °C: the rapid reduction of lead in the initial stage of the formation of rich nickel core.3. Ni nuclear growth stage: the hexagonal Ni metal particles with a diameter range of about 4-5 nm in Ni(Al)Ox are further assembled with small particles.4. The metal Ni particles grow up the process, Ni particles can no longer maintain its hexahedral structure into a spherical shape.(3) Ni/Ni(Al)Ox-C catalyst with confinement hexahedral morphology was applied to PNP hydrogenation reduce. The rate constants of the first order reaction of this kinetics were calculated by the analysis of UV-vis. It was applied to the catalytic hydrogenation of PNP, quickly completed in 60 s and the rate constant reached 6.7 ×10-2 s-1. This is related to the hexahedral morphology of the catalyst and the larger specific surface area, exposing more active sites and the contact between the metal and the oxide carrier has a strong adsorption effect on the reactants, which lead to a large catalytic activity.(4) Ni/Ni(Al)Ox-C catalyst with confinement hexahedral morphology was applied to semi-hydrogenation of phenylethylene. It was found that the hexahedral morphology had little effect on the selective hydrogenation activity of phenylacetylene, and the conversion rate reached 95% after 240 min, which may be related to the degree of reduction. While, its catalytic hydrogenation to styrene selectivity is relatively well, 240 min can still maintain 85%, which should be related to its Ni(Al)Ox-C defined structure, which can quickly desorb the styrene, To prevent further over-hydrogenation. As a whole, the selective hydrogenation of phenacetylene, which was maintaining a certain catalytic activity, meanwhile maintaining a high selectivity...