Influence Of Morphologic Properties Of Silica Supports On Pd/silicon Catalysts Synthesis For Cinnamaldehyde Hydrogenation

Mesoporous silicas have shown potential applications in catalytic reaction, adsorption, separation, biotechnology and pharmacy. The control of morphorlogies and structures of these matrrials mesoporous silicas makes them available for different molecular reactions when they are used as the support of noble metal catalysts. The functionality of the surface of these materials also significantly promotes their applications.Based on the previous study, the synthetic condition of mesoporous hollow sphere is further optimized in this dissertation. By supporting Pd(OAc)2 and H2PtCl6 on these silica materials to prepare the Pt or Pd supported catalysts, the influence of morphorlogy of the silica support on catalytic hydrogenation of alfa-beta unsturated aldehyde is investigated. The Pd supported catalysts have been prepared using three different silica materials with different morphology, including SBA-15 rod, SBA-15 hollow sphere (SBA-15HSP), MCM-41 solid sphere (MCM-41 SSP). TEM showed that Pd/SBA-15HSP is of rattle-type hollow structure which has a hollow shell with a solid Pd nanoparticle core and interstitial hollow space in between. For the liquid-phase adsorption of cinnamaldehyde, hollow spherical catalyst shows faster rate of approaching the equilibrium and exhibits higher amount of adsorption than the other supports. For the hydrogenation of cinnamaldehyde, Pd/SBA-15HSP shows much higher catalytic activity, giving a conversion of over 99%. The rattle type co-Pd/SBA-15HSP catalyst prepared by in situ method reached 99% conversion within 0.5 h in the catalytic hydrogenation of cinnamaldehyde. The confinement effect of hollow sphere for metal particles and the good adsorption property make the mesoporous hollow structure ideal for the preparation of nanocatalysts.The conclusions are drawn as the followings:1. When SBA-15HSP is synthesized in the acid condition, it is better to use HCl as the acid source than H2SO4 and HNO3. The mesoporous hollow so here with verticle channels can be obtained by less stirring time(1 h) and ageing at 80℃in moderate aggregation speed.2. The Pd nanoparticles encapsuled in the mesoporus hollow sphere shows higher catalytic activity than other non-capsuled catalysts in the hydrogenation of cinnamaldehyde. The co-Pd/SBA-15HSP catalyst reaches 99% conversion within 0.5 h.3. The Pd nanoparticles encapsuled in the mesoporus hollow sphere shows the highest catalytic activity in these silica supported Pd catalysts in the hydrogenation of isophorone. The co-Pd/SBA-15HSP catalyst reaches 60.3% conversion within 2 h. The sequence of catalytic activity of these catalysts is partly in consistent with the conclusions drown in the cinnamaldehyde hydrogenation part.It is a very important way to improve the catalytic performance by developing the support with appropriate structure and morphology.