Studies Of Transition And Noble Metal Catalysts On The Heterogeneous Selective Hydrogenation Reactions

Aromatics as the important chemical raw materials have been widely appliedinto the petrochemical and chemical industries. Benzene, toluene and xylenes (BTX)are three kinds of petrochemical products which have been extensively used. TheBTX has not met the demand for chemical market when BTX was produced only bypyrolysis gasoline and coal carbonization with exhaustion of unreproducibleresoures. A great amount of byproduct of the C9+heavy aromatics had not obtainedenough development and utilization. The green catalytic hydrogenation technologyprovides an important method for transforming heavy aromatics into the basicpetroleum chemical industry product BTX, so as to improve the utilization of heavyaromatics.α，β-Unsaturated aldehydes are the important chemical raw materials andintermediates and the selective hydrogenation product, cinnamyl alcohol, is regardedas the important fine chemical intermediate, which have been widely used inperfume, medicine and cosmetics etc. Due to the hydrogenation of C=C is morefavorable than C=O on the thermodynamics and kinetics, the design and preparationof highly selective catalyst is the key of realizing the hydrogenation of C=O intoindustrialization. Cinnamaldehyde is the typical α，β-unsaturated aldehydes. Hence,the heterogeneous selective hydrogenation of the cinnamaldehyde (as the substrates)to produce cinnamyl alcohol is one kind of model reaction.In this work, we mainly studied the hydrodealkylation of1,2,4-TMB andselective hydrogenation of cinnamaldehyde to prepare BTX and cinnamyl alcoholrespecitively. Different types of catalysts were prepared and characterized.Combined the catalytic and characterization results, the structure, surface texture and catalytic properties of the catalysts were studied and discussed. The main researchcontents and results are as follows:1. The studies of hydrodealkylation of1,2,4-TMB on Ni-Mg-Al catalystsA series of Ni-Mg-Al catalysts were made through co-precipitation method, andtheir catalytic properties were investigated in the hydrodealkylation reaction of1,2,4-TMB. The effects of Mg content and the calcination temperature on catalyticperformance were mainly inspected. The experiment result prove that, the Ni-Mg-Alcatalysts with15wt%Mg content after calcination at773K exhibited the best1,2,4-TMB conversion and BTX selectivity at723K，3.0MPa reaction conditions.From the product distribution, it mainly occurred the hydrodealkylation reaction andno byproducts from disproportionation and isomerization reactions were detected.The results demonstrated that the appropriate amount of Mg species significantlyaffected the structural properties and made the Ni nanoparticles highly dispersed,which make the interaction stronger between Mg active species and the supports andincreased the redox ability of Ni when proper amount of Mg species appeared. Thesynergetic effects among between Lewis acid and Ni0, NiAl2O4and MgAl2O4may bethe key factor for obtaining high selectivity of BTX.2. Preparation of Sn-modified Ru/H-CMK-3catalysts and the exploration of itscatalysis of cinnamaldehyde hydrogenationThe carbon materials CMK-3with ordered mesoporous structure weresynthesized using SBA-15as hard template. Tin-modified Ru/H-CMK-3wasprepared by a novel reductant impregnation method using it as the support. Thehydrogenation of cinnamaldehyde was used as the probe reaction. The effect ofpreparation of catalysts and reaction conditions on the properties of the selectivehydrogenation of cinnamaldehyde was detailed studied in detail. The catalysts werecharacterized using XRD，BET，XPS and TEM. The results showed that themesoporous CMK-3carbon materials could better disperse the active species. Theintroduction of appropriate amount of Sn (Ⅳ) made the Ru electron-enriched. Themain active species of the catalysts is Ru nanoparticles. The interaction between Ru and Sn is more conducive to the activation of C=O. Meanwhile, the change of theconditions such as temperature and reaction pressure had great effect on the selectivehydrogenation of cinnamaldehyde.3. Selective hydrogenation of cinnamaldehyde to cinnamyl alcohol on Ru-basedcatalystsA series of Ru-based catalysts were prepared by impregnation method and theircatalytic propeties were tested in the hydrogenation of cinnamaldehyde. In this work,the bimetallic Ru-based catalysts and the different support of materials mainlyaffected the catalytic performances of the catalysts. Combining the characterizationand and the catalytic results, the Sn (Ⅳ) species with Ru were more conducive tohydrogenation of cinnamaldehyde of the C=O through the screening of the secondcomponent. The nanoparticle of Ru-Sn/TiO2catalysts showed the maximumselectivity of cinnamyl alcohol. The characterization proved that there were twovalence states for tin species, metal state and ion state. The existence of electrontransfer between them made the Ru electron-rich, leading to not only inhibition ofthe C=C hydrogenation but also activation of C=O. At the same time, the high stateof Sn species could also be used as the Lewis acid sites and increased thepolarization of C=O bond, making hydrogenation of C=O easier. In the duplicatereactions, active species was almost detected establishing that the process was a trulyheterogeneous reaction. Recycling experiments without obvious decrease ofconversation and selectivity indicates that catalysts have relatively high stability andrecyclability.