Preparation And Catalytic Performance Of Confined Catalysts

The catalyst structure plays an important regulatory role in heterogeneous catalysis,and the interaction between the active site and the carrier has a direct effect on the reaction.In recent years,researchers have found that the confined structure can enhance the interaction between the catalytic active site and the carrier and improve the catalytic performance.In addition,the confined structure catalyst can fully exert the catalytic performance of the precious metal and improve the effective utilization of the precious metal.Hydrotalcite is a class of anionic layered clays whose core sheets have lattice confinement properties.At present,the use of hydrotalcite as a precursor material to prepare a confined structure catalyst has become a research hotspot.In this thesis,NiAlRu-LDH was used as the catalyst precursor.The double-confined structure RuNi metal nanocatalyst material,Ru/Ni/NiAlOx,was prepared by controlling the reduction temperature in a H2 atmosphere.Among them,the Ru nanoparticle are confined in the nickel shell and are simultaneously planted in the low-crystalline NiAlOx phase.In addition,another type of Ru-containing hydrotalcite(MgAlRu-LDH)was used as a precursor.the Ru nanoparticle catalyst material with confined structure was obtained through hydrogen reduction,Ru/MgAl-LDH,and Ru nanoparticles were limited in the layered structure of hydrotalcite.The structure,morphology,valence state and other properties of the two kinds of catalysts were lucubrated by various characterization methods.The formation mechanism of two kinds of Ru-based catalysts with confined structure is speculated.Finally,the two kinds of catalysts were applied to dimethyl terephthalate(DMT)selective hydrogenation reaction and carbon monoxide preferential oxidation(CO-PROX)reaction respectively.The catalytic performance and stability of the two kinds of catalysts with confined structure were investigated,and the influence of confined structure for catalytic activity was discussed.The research contents are as follows:(1)NiAlRu-LDH was used as a precursor,and hydrogen reduction is carried out at 350? to obtain a ruthenium-nickel metal nano-catalyst material with a double confinement structure,Ru/Ni/NiAlOx.The spherical aberration corrected STEM-HAADF and other characterization results show that ruthenium nanoparticles are confined to nickel shells and are simultaneously planted in the weakly crystalline NiAlOx crystal phase.Research on the reduction preparation process shows that Ru3+in the hydrotalcite laminate at about 100? is first reduced to monatomic Ru0.With the increase of temperature,Ru atoms gather to form Ru clusters.At about 200?,Ru clusters promote the reduction of its neighboring Ni2+through Spillover,forming RuNi bimetallic clusters.At about 300 ?,the hydrotalcite structure collapsed to form weakly crystallized NiAlOx,which gathered around the RuNi cluster.With the continuous reduction of Ni,the RuNi bimetallic cluster grew into RuNi bimetallic particles to obtain Ru/Ni/NiAlOx nanocatalyst material with double confinement structure.When the reduction temperature is further increased to 450?,the RuNi bimetallic particles form RuNi alloy particles,while NiAlOx forms Ni and AlOx,forming Ru/Ni/NiAlOx.(2)MgAlRu-LDH synthesized by double-drop method is used as precursor,heated to 200? in a H2 atmosphere to obtain a highly dispersed small particle size Ru-based catalyst confined between hydrotalcite layers,Ru/MgAl-LDH.Characterization methods by XRD,HRTEM and XPS show that the Ru atoms reduced at low temperature to form small particle size Ru nanoparticles and have good dispersion between the hydrotalcite laminates.The Ru/MgAl-LDH catalyst sample was applied to the CO-PROX reaction under the reaction conditions of normal pressure and GHSV of 9600 mL-h-1·g-1,it can maintain more than 90%of CO conversion in the temperature range of 140-180?.Moreover,the catalyst is less affected by space velocity and has long service life and good stability.The excellent catalytic performance is mainly due to the special confined structure.The confinement effect of the hydrotalcite laminate improves the dispersion of the Ru nanoparticles and avoids the aggregation of the metal Ru.