Design,Preparation And Performance Of The Paddle-type Structured Catalysts

The structured catalyst has the advantages of enhanced mass transfer,low pressure drops,and easy separation,and can independently optimize the reaction kinetics,convection transfer,and mass transfer,showing great application prospects in heterogeneous catalysis.Numerical simulation results show that many structured catalysts with special three-dimensional(3D)structures can greatly enhance the mass transfer,but it is difficult to process these complex structures with traditional extrusion preparation and it is hard to coat catalytically active species.Therefore,we combined digital manufacturing technologies,such as 3D printing and laser sintering,with the interface properties control to construct the paddle-type strctured catalysts with high catalytic activity,which possessed both stirring and catalysis functions.This paddletype structured catalyst had a secondary structure to support active species,which strengthened the mass transfer process and improved the catalytic efficiency of heterogeneous reactions.The main contents are as follows:(1)A paddle-type structured catalyst with a fractal structure was fabricated by 3D printing with photosensitive resin as substrate material.The Ag catalyst was grown on the impeller through surface swelling effect and electroless deposition to obtain the paddle-type structured catalyst(Ag-impeller).Numerical simulation analysis showed that,at 350 rpm,the mass transfer coefficient of the fractal stirrer was 0.5 m s-1 higher than that of the normal stirrer with the same blade surface area,and the specific volume power was 3.0 kW m-3 lower tha1 that of the normal stirrer with the same blade height.The experimental results showed that the Agimpeller exhibited high catalytic activity and cycling stability in the reduction of 4-nitrophenol.The catalytic performance of the Ag-impeller did not significantly decrease after 10 cycles,and the conversion rate of 4-nitrophenol still remained 100%.(2)A monolithic impeller was fabricated by 3D printing with iron-doped polylactic acid composite material.The amorphous FeOOH nanosheet was in situ formed from the exposed Fe particles after oxidation etching of H2O2 to construct the paddle-type structured catalyst.The nanosheet secondary structure was beneficial to expose more active sites and improve the catalytic activity.Besides,the paddle-type structured catalyst exhibited excellent cycling stability for the photo-Fenton reactions.The degradation rate of methylene blue(MB)only decreased by 0.9%after 10 cycles.Even if the impeller was scaled up 10 times,the 800 mL MB solution(100 ppm)could be degraded by 81.2%,which revealed the catalytic performance remained unchanged.(3)A paddle-type catalyst with a hierarchical structure was constructed by integrating the 3D-printed frame with the stainless-steel(SS)mesh loading catalysts.The hydrothermal synthesized Ni(OH)2 nanosheets on the SS mesh featured 3D open frameworks with tremendous sites for anchoring and tuning the electronic structure of the Pd nanoparticles(NPs).The X-ray absorption fine structure analysis demonstrated that Pd NPs had both Pd0 and Pd2+,which accelerated the Suzuki coupling reaction.So,the paddle-type structured catalyst showed high catalytic activity and cycling stability.By adjusting the solvent of the reaction system,the solubility difference between the reactants and the products was used to realize the separation of the products in the ethanol/water solvent.(4)Using laser-assisted processing,a thin layer of metal oxide with microstructure was prepared on the SS sheet,which improved the specific surface area of the substrate and served as a carrier to load Pd NPs.The paddle-type structured catalyst was further assembled with a 3D-printed frame,which effectively shortened the preparation period and exhibited universal applicability to various metals.The optimal microstructure with enhanced mass transfer can be obtained by changing the laser processing parameters to modulate the composition,morphology,and wettability of the oxide layer.Taking advantage of easy amplification of 3D printing and laser processing,the impeller can be easily scaled up.After amplification,the conversion rate of 240 mmol Br-Ar remained above 92%and the selectivity of biphenyl was 99.7%in a 1.2 L system of Suzuki coupling system.