Localized Catalytic Active Centers Reconstructed In Functionalized Periodic Mesoporous Organosilica And Their Catalytic Performances

Study on synthesis of active center in support have been extensively investigated in recent years because of the catalysts fabricated using this method have high activity and selectivity, easy regenerated and reused etc. So far, the research of the preparation methods of catalysts and the optimization for reaction system were employed, with which great progress has been achieved in the synthesis active center on the carriers. However, such researches are conducted basically from the supports such as metallic oxide, activated carbon, SiO2 etc, and the surface and structure properties of these supports are difficult to control. Furthermore, the weak interaction between active site and the surface of supports is remained a major drawback to synthesis on steady active center in some supports. Therefore, how to design novel supports for stabilize active site becomes very important, which is also a prerequisite for resolve the application of supported catalysts in liquid system. Recently, a new class organic-inorganic hybrid material with bridging organic groups known as periodic mesoporous organosilica (PMOs) was developed. The bridging organic groups in the channel of PMOs can uniformly distribute on porous surface, which is conducive to fabrication of single catalytic active site. Furthermore, the bridging organic groups can be easily modified to endow the PMOs with different physical and chemical properties, which are very promising for the applications in the field of Heterogeneous catalysis. In this dissertation, a series of novel periodic mesoporous organosilica with organic functional moieties were synthesized. The main contents discussed were as follows:(1) Pt, Pd and Pt-Pd bi-metal nanoparticles (bi-MNPs) captured and stabilized by imine groups inside a periodic mesoporous organosilica of SB A-15 (PMO-SBA-15) and their catalytic performances in the hydrogenation of nitrobenzene were investigated. The PMO-SBA-15 was synthesized via a one-pot condensation process by hydrolysis of tetraethoxysilane (TEOS) in the presence of P123 involving the assembly of triethylenetetramine silsesquioxane organic precursor. Aqueous PtCl62- and Pd2+ ions were reduced by NaBH4 to form Pt and Pd nanopaprticles, which were captured in real-time by imine groups inside the channels of the PMO-SBA-15 possess mean size of ca.1.8,1.8 and 2.5 nm, respectively. The MNPs-PMO-SBA-15 was used as a catalyst for hydrogenation of nitrobenzene under 0.1 MPa H2 at 15-60℃. It was found that the bi-MNPs of Pt and Pd inside the PMO-SBA-15 were more active than the monometallic Pt or Pd nanoparticles.100% of nitrobenzene conversion and> 99% of selectivity to aniline were obtained over the Pt-Pd-PMO-SBA-15 catalyst. Furthermore, the Pt-Pd-PMO-SBA-15 catalyst could be conveniently recovered for reused without significant loss of catalytic activity and selectivity. On the other hand, The Pd-PMO-SBA-15 exhibited high catalytic activity in the selective oxidation of benzyl alcohol by hydrogen peroxide. The conversion ofbenzyl alcohol and the selectivity for benzaldehyde were as high as 97% and 100%, respectively, when the reaction was performed at 80℃for 4 h using hydrogen peroxide as the oxidant and water as the solvent.(2) H3PW12O40 (HPW) was supported on the ionic liquid (IL) containing amidocyanogen-modified mesoporous silicate matrix SBA-15 (NH2-IL-SBA-15) based on the electrostatic binding between Keggin structure of PW anion and amine (NH2-) provided mesoporous active catalyst PW-NH2-IL-SBA-15 with large surface areas. The novel PW-NH2-IL-SBA-15 was used as a heterogeneous catalyst in the environmentally friendly oxidation of benzyl alcohol with hydrogen peroxide under solvent-free conditions. The imidazolium IL moiety has resulted in the elevated catalytic performances and facile reuse of the catalyst. Under optimum conditions,92% of benzyl alcohol conversion and 91% of selectivity to benzaldehyde were obtained over the PW-NH2-IL-SBA-15 catalyst, which was higher than that over the PW-NH2-SBA-15 catalyst. Furthermore, the PW-NH2-IL-SBA-15 could be conveniently recovered for recycled use without significant loss of catalytic activity and selectivity.(3) The preparation of a novel periodic mesoporous organosilica of SBA-15 functionalized by ionic liquid to load phosphowolframic acid (PW) was used as a catalyst in the oxidation of benzyl alcohol. The mesoporous organosilica PMOs was synthesized via a one-pot condensation process involving the assembly of triethylenetetramine silsesquioxane organic precursor containing amine group and TEOS in the presence of P123. Phosphowolframic acid was stabilized by ionic liquid to obtain PW-IL-PMOs. The effects of the content of ionic liquid moieties and phosphowolframic acid loading in the catalyst of PW-IL-PMOs on the oxidation of benzyl alcohol were investigated. The PW-IL-PMOs exhibited high catalytic activity and reusability. Under optimum conditions, the conversion of benzyl alcohol and the selectivity for benzaldehyde were as high as 95% and 94%, respectively.