Preparation And Properties Of Noble Metal Nanocatalysts Supported By Resorcinol-formaldehyde Resin

Metal nanoparticles(NPs) of various sizes have many areas of application, including chemical sensing biolabelling photonics two- and three-dimensional superlattices and catalysis. Their preparation often involves colloidal sols with a well-defined particle size distribution, in which the NPs are stabilized in solution by the adhesion of specific surfactants or ligand molecules, which ensure that the NPs cannot coalesce. However, metal colloidal NPs with smaller size(below 10 nm) show poorer stability, although it has been verified to usually exhibit better catalytic activity. Based on this fact, loading metal NPs onto solid supports such as aluminum oxide, titania, silica etc. is considered to be helpful to improve the performance and stability of the metal NPs and facilitate the separation of catalysts. The stabilized NPs are then typically deposited onto a solid surface to enable them to have utility in a chosen application. The deposition of pre-formed NPs onto supports is highly advantageous, as precise control of the particle size and structure of the pre-formed NPs can be achieved. Moreover, the particle size of NPs synthesized by the colloidal method is less affected by the surface chemistry and morphology of the support than is the case when other methods are used. Nevertheless, when metal NPs were directly loaded onto the surface of the supports, the supported metal NPs also have poor stability. It has been verified that metal NPs embedded inside the porous supports showed improved stability compared to these located at the surface of the nonporous supports. However, it is difficult to insert the NPs into the pore of the support by directly mixing NPs and supports. the size of Au NPs and thus their activity and stability since size of the resulting Au NPs is usually dependent on the pore size of the supports. Therefore, It is important to directly prepare an appropriate support with loading Au NPs with controllable sizes.Resorcinol-formaldehyde resin(RF) is a widely used polymer in industry. Formation of monodispersed RF sphere particles, having excellent chemical stability, porous structure and possess abundant hydroxyl groups, has been verified to be feasible by the extended St?ber method. This spherical particles have porous in structure, whcih has been considered to be one of candidates as both the support material and the reducing agent to directly prepare metal NPs. In this thesis, we studied in detail preparation and properties of supported noble metal nanocatalysts supported by resorcinol-formaldehyde resin as following:First part of this thesis, we systematically investigated the kinetic process on preparation of RF NPs in St?ber system. In this reaction system, ammonium hydroxide was used asthe catalytic to controlling the formation of RF particles in presence of resorcinol and formaldehyde in a mixed solvent including water and ethanol. Experimental indicated that RF particles could be well obtained by controlling the p H of reaction solution by adding ammonium hydroxide. This is attribute to separating the process of nucleation and growth by change dosage and ratio of water and ethanol. As a result, RF particles is well controlled in a wide range form 195 to 1400 nm, and have extremely narrow size distribution after give a optimal experimental conditions.In second part, Au NPs were directly synthesized by directly immersing the 200 nm sized RF particles into the solution of tetrachloroauric acid(HAu Cl4) without reduce agent. Here, the RF is served as both the support and reductant. One one hand, the size of as prepared Au NPs is dependent on the p H of reaction solution. On the other hand. when p H of reaction system was set at IP(2.3), the size of the Au NPs loaded into the RF particles was also tunable in the range of 3.7-14.0 nm by changing the concentration of HAu Cl4. At an extent work on catalysis in presence of Dispersed Distribution Type(DDT), it has been proved that the as prepared Au NP with various sizes show excellent catalytic activity and stability, even if after five cycle experiments on degradation DDT.In third part, based on the result reported in second part, Au Ag alloyed NPs were prepared by using RF particle as template. Likewise, the loaded Au Ag alloy NPs is abstained by controlling the p H of reaction solution in presence of gold and silver precursor. Experimental indicate that the size of alloyed particles is well controlled. Normally, the particles have a average diameter of 4.0 nm as confirmed by TEM measurement. It has been found that reaction temperature is also a crucial on controlling the size of particles. To check the catalytic activity of alloyed particle, the experimental were carried out by oxidation of OPD to evaluate their properties. Experimental showed that alloy particles show high catalytic activity, especially for the RF-Au Ag3(sizes of bimetal particles 4.0 nm) particles with the ratio of 3:1( the atomic ratio of Au;Agin one particles is1:3), conversion reached 100 % and TOF 0.926 s-1and stability. Importantly,,the catalytic activity show almost unchanged after five times recycles, indicating high stability on this alloyed particle.In forth part, based on the discussed above, Pd was introduce into this reaction system. On one hand, we prepared three kind of particles including RF-NH2 Pd Au, RF-NH2Au@Pd and RF-NH2Pd@Au NPs by using the RF template. Overall, the size of these particle have a average size of 3.0 to 4.0 nm, which has been confirmed by TEM images. The structure of these particles were well characterized by XRD measurement, which further confirmed the core/shell structure. On the other hand, catalytic experiment in presence of benzyl alcohol was carried out for three kinds of particles. Experimental results indicated these particle showed excellent catalytic properties when of benzyl alcohol is used to qualify the catalytic activity. TOF of the RFNH2 Pd Au2(the ratio of Pd:Au in one particles is1:2) and RF-NH2 Pd Au3(Pd Au2 and Pd Au3(the ratio of Pd:Au in one particles is1:3) were 985 and 852 h-1, respectively. Selectivity of them was 97.2 % and 98.1% respectively(conversion reached 100 %). Importantly, these particle still show high catalytic activity, even after several recycles, indicating that these loaded catalysts have excellent stability. The synthesis and characterization on preparation of RF particles loaded metal catalysts would open a new rout for further application in some field.