Synthesis Of Nano-sized Au And Ag Catalysts And Their Study In The Selective Hydrogenation Of Crotonaldehyde To Crotyl Alcohol In Liquid Phase

?,?-unsaturated alcohols are important intermediates in the production of perfumes, pharmaceuticals and organic synthesis reaction. Presently, the unsaturated alcohols are commercially achieved by using NaBH4 or AlLiH4 as reductant, but this process involves a lot of pollutants. Heterogeneous catalysis via direct hydrogenation of?,?-unsaturated aldehydes are able to reduce the conjugated C=O double bond in the presence of molecular H2. This process provides a clean and economic approach to the production of?,?-unsaturated alcohols. However, the manipulation of the selectivity in the hydrogenation of?,?-unsaturated aldehydes is of considerable challenge, as it is thermodynamically more favored to produce saturated aldehyde or saturated alcohol than the unsaturated alcohol on metals. Therefore, development of the alternative green processes for the synthesis of?,?-unsaturated alcohols has an important academic value and economic benefit.It have been documented that lots of metal-based catalyst is prone to hydrogenate C=C bond instead of C=O. In recent years, gold and silver have attracted growing interest in catalyst research since they have shown greater activity in liquid hydrogenation reactions than traditional hydrogenation catalysts. In this dissertation, the gold and silver were chosen as active species. The Au and Ag catalysts have been investigated systematically for the hydrogenation of crotonaldehyde. The influence of surface structure, electronic properties and the interaction between metal and support of the catalyst were studied in detail by various analytical and spectroscopic techniques. In addition, by correlation of the hydrogenation reaction results with above results, the active sites were discussed.1. Studies on the Aminosilane-Functionalized SBA-15 for chemoselective hydrogenation of crotonaldehydeSBA-15 was functionalized by three kinds of aminosilane (ATPS: 3-aminopropyltrimethoxysilane, TPED: N-[3-(trimethoxysilyl)-propylethylene] diamine, TPDT:trimethoxysilyl propyl diethylenetriamine). The highly dispersed gold nanoparticles in mesoporous silicas were applied into chemoselective hydrogenation of crotonaldehyde to crotyl alcohol, and the effect of the gold size and the interaction between metal and support were investigated. According to the catalytic results, we found the Au/amine-SBA-15 catalysts exhibit surprisingly high reaction activity and selectivity to crotyl alcohol compared with the Au/SBA-15. The excellent catalytic performance is mainly attributed to the strong interaction between gold nanoparticles and support. The role of interaction made the gold nanoparticles highly dispersed into the channel of SBA-15. On the other hand, it modified the surface charge of gold nanoparticles, which is favorable for the polarization of the C=O bond and enhances the hydrogenation of this functional group. Their different selectivity behaviors were tentatively interpreted on the basis of XPS measurements. The degree of binding energy shift was:Au/APTS-SBA-15> Au/TPED-SBA-15> Au/TPDT-SBA-15, suggesting that there were more electron on the surface of Au/APTS-SBA-15 catalyst. The increased electron density on metallic gold not only alter the interaction of the active sites with the functional group and facilitate a partial transfer to the?c=O* orbital of the unsaturated bond, but also weaken the binding of the C=C group on the active sites. In addition, the gold loading and APTS content on the catalytic have been studied, it was found that the optimum yield of crotoyl alcohol was obtained on Au/APTS-SBA-15 with 10 wt% and there is no influence on interaction between active sites and supports.2. Preparation, characterization of Au/MWCNTs catalysts and their catalytic properties for the hydrogenation of crotonaldehydeThe Au/MWCNTs catalysts prepared by impregnation method have been investigated systematically for the hydrogenation of crotonaldehyde. And the effects of treatment condition and reduction method on catalytic performance in hydrogenation of crotonaldehyde were studied. The results showed that Au/MWCNTs catalysts exhibited strong hydrogenation of C=C bonds into butanal. The particle size of Au nanoparticles and electronic characterization were investigated systematically for hydrogenation crotonaldehyde. It was found that the original rate of hydrogenation of C=C decreased with the outer diameter of MWCNTs, however, the original rate over hydrogenation of C=O increased with the outer diameter of MWCNTs. Based on the TEM (transmission electron microscopy) characterization, we found the good relationships between the particle size of Au and the selectivity of butanal, that is, the biggher the particle size the lower the selectivity of C=C hydrogenation product. It was suggesting that the size effect is major factor influencing the products distribution.Besides above-mentioned method, the Au/APTS-MWCNTs catalysts were prepared by post-grafting method. The Au particle size was obviously smaller than the prepared by impregnation method with TEM (transmission electron microscopy) characterization. And the size of Au nanoparticles was became large increasing with the outer diameter of MWCNTs. The binding energy of gold catalysts was below 84.0 eV, manifesting that the rich-electron on the surface of gold nanoparticles. At the same time, N 1s binding energy of support showed that the electron on the surface of gold surface was supplied by amino of support. The effect of electron-rich metallic Au can account for the increased reactivity of the C=O group relative to the C=O group. Subsequently, the reaction conditions were optimized and displayed that zero-order for crotonaldehyde, one-order for hydrogen and 60 kJ mol-1 for the apparent energy of activation.3. Preparation, characterization of Au/AlOx and Au/CeAlOx catalysts and their catalytic properties for the hydrogenation of crotonaldehydeThe AlOx was prepared by sol-gel process associated with nonionic block copolymer as templates in ethanol solvent. Then, the Au/Alox and Au/y-Al2O3 were prepared by deposition precipitation method and applied into the hydrogenation of crotonaldehyde. It was found that Au/AlOx exhibited excellent performance on the hydrogenation of crotyl alcohol. Combined with kinds of characterizations, we found that the morphology of supports, structure and crystal structure played important role in the surface electron-structure of Au nanoparticles. Based on the XPS characterization, the gold has two species, one is metallic Au0, the other is oxidized Au?+. And there is synergy effect. At the same time, the calcination temperature has been investigated for the hydrogenation of crotonaldehyde. It was found that the size of Au naoparticles became large when the calcined temperature was raised. On the Au/A1Ox-N-773 catalyst with the 3.1 nm diameter of gold particles, the yield of crotyl alcohol reached 77%, and the selectivity of crotyl alcohol amounted to 78%. Finally, the Au/AlOx-N-773 catalyst has a good stability after five successive runs comparing Au/y-Al2O3 catalyst, confirming that the nature of the catalyst did not change during the reaction. Besides, the rare-earth element Ce was added during the preparation. It was found that the addition of Ce was favorable for improving the selectivity of crotyl alcohol, therefore, the yield of crotyl was 81% and the selectivity was up to 83%. There are two reasons:on one hand, the Ce ion were help for the much more Au?+ ion, on the other hand, Ce ion and Au?+ could be the Lewis acid site. Furthermore, the Lewis acid site can active C=O group and promote the produce the crotyl alcohol.4. Studies on the Ag and AgIn/SBA-15 catalysts for the chemoselective hydrogenation of crotonaldehydeSilver is widely used as an active component in oxidation reactions, surprizingly, it can also be used as a catalyst for reduction reactions, for instance, selective hydrogenation of unsaturated aldehydes such as acrolein and crotonaldehyde. Herein, we prepared and characterized the SBA-15-supported Ag and In-promoted Ag catalysts by modified "two solvents" strategy for crotonaldehyde hydrogenation to crotyl alcohol. On the optimum Ag9.0In3.0/SBA-15 catalyst, the initial selectivity amounts to 88%, and the maximum yield reaches 86%, which is one of the best results reported in the open literatures dealing with the?,?-unsaturated aldehydes hydrogenation to?,?-unsaturated alcohol. The investigations of the effect In on structures and properties of Ag catalyst showed that the addition of indium to Ag catalyst led to improvement the diepersion of Ag nanoparticles. Since the smaller Ag nanoparticles are favorable for dissociative adsorption of H2. The existing of indium greatly suppressed the hydrogenation of the C=C bond, and enhanced the hydrogenation of the C=C bond. On the other hand, the modified In3+ions function as Lewis acid sites, the crotonaldehyde molecule being adsorbed via the donation of a lone electron pair from the oxygen of the carbonyl group. Besides all, the hydrogenation of intermediate products was studied over Ag/SBA-15 and AgIn/SBA-15 catalysts. It was demonstrated that the monometallic Ag catalyst is prone to take place further hydrogenation comparing with bimetallic catalyst. Therefore, the addition of indium is contributory to high selectivity to crotyl alcohol.