Designed Synthesis And Catalytic Evaluation Of Alginate-derived Monolithic Nanosilver-containing Cataltyic Composites

Metal nano-catalyst inherits the advantages of nano-catalyst and stands out among others,has been successfully applied in the oxidation,hydrogenation,dehydrogenation and hydrocarbon isomerization reaction process.But now mostly metal nano catalyst for powder,restrictions on the size,the process inevitably will be done in the catalyst partial loss and cause difficult separation,and under the conditions of reaction system flow,this kind of catalyst can cause pollution in the product system,so the comprehensive cost and performance considerations,it is crucial to prepare metal nano-catalyst with recyclability and ability to cope with dynamic catalytic system which can really fit actual production needs.Aniline organic compounds as a kind of important chemical intermediates are widely used in the synthesis of chemical products.Applications load type nanometer metal catalysts in liquid phase catalytic hydrogenation reduction process,not only can improve the conversion rate of reaction,improve the production of aniline compounds,also can save the use of the precious metal,reduce the cost.This paper used liquid phase catalytic hydrogenation reduction method of nitrophenol preparation of aminophenol as an example.Two kinds of nano silver catalyst was prepared by sodium alginate,and material characterization,performance testing in detail,proved that the calcium alginate as carrier for preparation of nanometer silver catalyst can efficiently applied in the preparation of aminophenol,and especially showed good performance in dynamic catalytic experiments.For the first part of study,nanosilver/alginate composite beads,which can effectively apply to the degradation experiment of p-nitrophenol under batch and fix-bed conditions,have been fabricated successfully via a simple one-pot encapsulation method.Three-dimensional alginate hydrogels cross-linked with calcium ions were used as supporting matrix for “confinement” of nanosilver,leading to the formation of nanosilver/alginate composite beads without significant aggregation of active nanoparticles.The samples were characterized by X-ray diffraction,scanning electron microscopy,transmission electron microscopy and X-ray photoelectron spectroscopy.As-fabricated bead-like samples showed excellent catalytic efficiency at ambient temperature,material with 10% silver content costed 170 seconds to catalyze hydrogenation of highly toxic p-nitrophenol under batch condition;good stability was also demonstrated in the process of dynamic catalytic degradation,which showed continuous high conversion performance for 4-NP about 40 minutes at 298 K and redisual concentration can reach 33.5 ?g/L at flow rate of 1mL/min.Pseudo-first order kinetic model can well describe the relationship between concentration and time,the rate constant k is 0.0149 s-1.More favorably,the way to recycle the catalyst is very simple,namely filtration only is enough.In addition,the catalytic capability did not decline significantly after 10 recycles,average conversion content can still be 95%.On the basis of forepart,three-dimensional Ag/PEI/alginate hydrogel beads have been prepared successfully via a facile and simple one-pot assembly method,which can be used efficiently in catalytic hydrogenation reaction of p-nitrophenol under batch and fixed-bed experiment.PEI is used to reduce and limit the growth of nano-silver particle and alginate microsphere is used as the catalyst carrier,leading to form well silver nanoparticles dispersion.Several characterizations were applied to the materials,such as X-ray diffraction,scanning electron microscopy,transmission electron microscopy and X-ray photoelectron spectroscopy.As-prepared catalysts only spent 120 seconds finishing reaction at ambient temperature(20% silver load)and stable catalytic performance with high conversion percentage for 4-NP at 298 K under fixed-bed condition.The relationship between concentration and time was well depicted by Pseudo-first order kinetic model.The catalytic performance for recycled catalyst remained highly efficient,and the conversion efficiency of 96.4% can be maintained after 10 cycles.