Peparation,Structure And Performance Of Highly Dispersed Supported Metal Catalysts For Hydrogen-water Isotopic Exchange

Tritiated water damages the human body and environment seriously,which brings safety problems.The treatment of tritiated water have become an unavoidable matter for nuclear power,nuclear fuel reprocessing as well as future fusion energy.Currently,hydrogen-water catalytic exchange is a kind of important hydrogen isotopic exchange technology,especially vapor phase catalytic exchange?VPCE?.It has been attracted attention due to its simple craft,non-corrosiveness,high separation factor as well as non-noble metal catalysts.In VPCE,preparing high-efficiency catalyst is a key for technique.What's more,its reaction mechanism needs still to further be studied.In addition,compared with Pt-based catalysts reported in Canada,non-noble metal Ni-based catalysts can bring higher catalytic activity by adjusting catalytic structure and also can decrease cost,which promotes industrial process in China.In this work,layered double hydroxides?LDH?with special layer structure and dispersive cation can improve dispersion of reactive metal?Ni?,which decreases Ni loading and promote catalytic reaction efficiency.LDH has already used as catalyst precursors,catalyst supports,adsorbents and ion exchangers in different research directions,e.g.,gas removing,selective hydrogenation,electro-catalysis oxidation due to their interlayer structure and exchangeability of interlayer ion.At the same time,a kind of relative material with LDH are synthesized by introducing active metal?Pt?Pd etc.?into the LDH structure.These advantages of LDH inspire us to fabricate an efficient VPCE catalyst from LDH and prompt us to study its mechanism in VPCE.The results are as follows:?1?NiAl-LDHs nanosheets are prepared by coprecipitation hydrothermal method and effects of synthetic conditions on form of LDH will be discussed by adjusting content,temperature and time.Experimental results show that hydrothermal temperature and time have an influence on the crystallinity and Crystallite size of LDH.With the hydrothermal temperature increased,crystallinity of LDH was increased and Crystallite size of LDH was increased from 7.8nm to 12.5nm.Additionally,hydrothermal time also can improve crystallinity of LDH and can increase Crystallite size obviously in hydrothermal time of 36h.?2?NiAl-LDO catalyst derived from NiAl-LDH precursor are prepared by high-temperature calcination.Analyses show that layered structure of NiAl-LDO is as similar as counterpart of NiAl-LDH precursor and elements were dispersed homogeneously.At the same time,specific surface area of NiAl-LDO is increased to 185.63m²/g.Compared with impregnated NiO/Al₂O₃ catalysts,catalytic activities are increased 5 to 20times under 400?in VPCE due to its homogeneous metal dispersion and morphology and is obvious under 200?.Experimental analyses show that both Ni⁰ and Ni²⁺are useful active sites in VPCE.A reaction mechanism of Ni based catalyst in VPCE is deducted in this section.?3?a series of NiAl-LDH precursors are prepared by adjusting Ni/Al ratios.These precursors are calcinated and reduced to acquire Ni_xAl-LDO-R catalysts with Ni metal size between 11nm and 18nm.With the Ni/Al ratio increased,metal-support interaction of Ni_xAl-LDO-R catalysts are changed.Experimental results show that Al lose an electron to obtain more hexahedron of Al³⁺and Ni²⁺get electron to form Ni⁰.In addition,the high catalytic activity observed when the Ni/Al ratio=2 benefits from balanced metal-support interaction and suitable Ni content.