Studies On The Amorphous Ru-base Catalysts And Their Applications In The Hydrogenation Of Ethyl Lactate

As one of important chemicals, 1,2-propanediol (1,2-PDO) has been widely applied in pharmaceutical and chemical industries. It can be used as a monomer for polyester resins, as a defrozen and deicing fluid, as a solvent in food and pharmaceutical industries. It can also be used as a substitute for ethylene glycol in some occasions. The demand for 1,2-PDO has been increasing steadily in recent years.1,2-PDO is commercially produced by the hydration of propylene oxide that produced via the oxidation of propylene. This process involves either hydroperoxidation chemistry or the antiquated chlorhydrin process. Development of the alternative green processes for the synthesis of 1,2-PDO has attracted great attentions. It is reported that 1,2-PDO can be synthesized via direct hydrogenation of lactic acid using Ru/C and CU/SiO₂ catalysts, and lactic acid can be produced through the fermentation of a number of renewable resources such as carbohydrates derived from agricultural crops and biomass streams. This process provides a clean and economic approach to the production of 1,2-PDO from renewable carbohydrate feedstock instead of from non-renewable petroleum. Hydrogenation of ethyl lactate to 1,2-PDO is a challenging subject. Because hydrogenations of carboxylic acids and esters to the corresponding alcohols are often carried out under vigorous reaction conditions due to weak polarisability and intrinsic steric hindrance of the C=O bond of esters. However, for lactates or lactic acid that contain a reactive hydroxyl group, high reaction temperature is undesirable because it would lead to side reactions and consequently to a decrease in selectivity to 1,2-PDO. Therefore, development of active catalysts for the hydrogenation of esters to the corresponding alcohols under mild conditions is of great importance. The previous research of our group showed that amorphous alloy displayed better catalytic properties due to its structural specialties in some hydrogenation reactions than that of crystal counterpart.In this dissertation, the Ru that showed good intrinsic hydrogenation activity for carbonyl compounds was chosen as active species. Ru-based amorphous catalysts prepared by chemical reduction with KBH4 have been investigated systematically for the hydrogenation of ethyl lactate. The effect of preparation method, promoteraddition, support type and treatment and reaction conditions on the composition, surface structure, electronic properties of the catalyst and on its catalytic performance in hydrogenation of ethyl lactate were studied in detail by BET, in situ XRD, TEM, XPS, H2-TPD and FT-IR. By correlation of the reaction results with the kinetic study, the possible reaction mechanism was proposed and discussed. Moreover, a preliminary investigation on catalytic hydrogenation of methyl 3-hydroxy propionate that has the similar molecular structure was conducted and compared with that of ethyl lactate hydrogenation.1. Studies on the amorphous RuB catalysts prepared by chemical reduction method for the hydrogenation of ethyl lactate.It was found that compared with Pt, Co and Cu based catalysts prepared by chemical reduction, the Ru-based catalyst showed better catalytic performance. The impregnation sequence of reductant KBH4 and metal salt dramatically influenced the physicochemical properties of the RuB catalysts. A catalyst prepared by reductant impregnation had much higher activity than that prepared by initial impregnation of metal salt. The Ru particle size and thermal stability of the RuB/y-AbCb catalysts prepared by the reductant impregnation-chemical reduction method were dependent upon Ru loadings. In terms of the 1,2-PDO yield, the suitable Ru loading should be around 10 wt.%.The investigations of the effect of promoters (Co, Fe, Sn, Zn) on compositions, structures and properties of RUB/Y-AI2O3 showed that addition of tin or iron to the RuB catalysts led to an improvement of RuB dispersion and thermal stability of the amorphous structure. The electron density of Ru, the strength and capacity of hydrogen adsorption on RuB were also enhanced by the addition of tin or iron. On the other hand, addition of zinc or cobalt had little improvement in thermal stability of the RuB but led to a decrease in hydrogen adsorption capacity. The XPS demonstrated that tin, iron and zinc were mainly present in the oxidized states in the catalyst while nearly 50% of cobalt was present in elemental state. The catalytic evaluation revealed that the addition of the tin or iron resulted in an increase in both ethyl lactate conversion and selectivity to 1,2-PDO while the addition of cobalt or zinc led to a significant decrease in ethyl lactate conversion along with the increase in selectivity to 1,2-PDO. Correlation of the reaction results with the characterizations showed that the promotion of Sn and Fe might be arisen from its Lewis acidity acting as theadsorption sites for the oxygen atom of the carbonyl of ethyl lactate. Thus the oxidation state of the promoter is very important for the selectivity to 1,2-PDO. The further investigation showed that optimal content of Sn and Fe was ca 7 mol.% and 19 mol.%, respectively. Selectivity to 1,2-PDO of 91.5% at ethyl lactate conversion of 90.7% is obtained at Sn/Ru atomic ratio of 7% under mild reaction conditions (150°C, 5.5 MPa).The effect of supports on the catalytic properties has been studied. The surface acidity of the supports exhibited great influence on the composition and properties of the RuB catalyst. The RuB catalyst prepared using ZrC>2, TiC>2 or Y-AI2O3 as support showed better thermal stability and catalytic performance relative to that prepared using SiO2 or MgO as support. The influence of the support on properties and catalytic performance was explained in terms of the different surface functional groups and acidity of the support which may cause different type and extent of interactions of the support with Ru particles and of support with promoters, leading to the different Ru loading and dispersion, reduction degree of promoter. Under the same reaction conditions, the higher selectivity to 1,2-PDO of 98.1%, 93.5% at the conversion 81.4%, 85.6% was obtained over ZrC>2 and TiO2 supported RuSnB catalyst, respectively.The kinetic study for the hydrogenation of ethyl lactate over RuSnB/y-AbOa catalyst showed that the reaction is first order with respect to ethyl lactate and first order with respect to hydrogen at H2 pressure between 3.0 to 4.0 MPa, fraction order to hydrogen at H2 pressure between 4.0 to 5.0 MPa, and zero order to hydrogen at H2 pressure between 5.0 to 6.0 MPa. The activation energy for this reaction calculated is 82.64 kJ-mol"1.2. Preparation, characterization of novel carbon materials supported RuSnB catalysts and their catalytic properties for the hydrogenation of ethyl lactateThree carbon materials active carbon (AC), active carbon fiber (ACF) and carbon nano-fiber (CNF) were used as support for RuSnB catalyst. The effect of the type of carbon-based support on the RuSnB catalyst was studied. The activity test revealed that all three carbon materials supported RuSnB catalysts showed the higher selectivity to 1,2-PDO around 95%. CNF supported catalyst exhibited higher ethyl lactate conversion than that of the two others. The different activity of catalysts wasascribed to the different pore structure of the support, which may cause different degree of diffusivity of the reactant and products within the pores. Furthermore, the different activity as well as related to the different surface properties of the support, which may lead to the different interaction between Ru particles and supports. For CNF supported catalyst, the stronger interaction leading to the higher Ru loading, more homogeneous dispersion, and the formation of Ru crystal with exposal of some preferential planes.3. Preparation, characterization of mesoporous silica-supported RuSnB catalysts and their catalytic properties for the hydrogenation of ethyl lactate.Mesoporous silica MCM-48, HMS, MCM-41and SBA-15 were prepared and used as supports for the RuSnB catalyst, as a comparison conventional S1O2 supported catalyst was also prepared. It was found that the texture and porosity of the support had a significant influence on the chemical composition and dispersion of RuSnB particles, and hence on thermal stability and reaction performance of the catalyst. The catalysts supported by S1O2 and SBA-15 showed higher dispersion of active species, which led to higher conversion. Meanwhile, compared to that over other silica supported catalysts, the SBA-15 supported RuSnB catalyst also exhibited higher selectivity to 1,2-PDO, which related to the more uniform of active species. However, the active species on MCM-48 and HMS was heterogeneous which led to poor reaction behavior in ethyl lactate hydrogenation.Sn-containing SBA-15 was synthesized by using in-situ co-synthesis method with SnCl4-5H2O as Sn precursor. The location and state of tin species in the SBA-15 were studied by XRD, XPS, FT-IR, TEM and UV-Vis and was compared with the sample using impregnation to incorporate tin. It was found that for the co-synthesized Sn-SBA-15 a part of Sn was incorporated into the framework of silica, in which tin exist in four-fold coordinated and six-fold coordinated species. The new chemical bond Sn-O-Si was observed. Compared with the sample prepared by impregnation, the dispersion of Sn in the co-synthesized sample was more uniform and aggregation of SnOx was inhibited.RuB/Sn-SBA-15 catalysts were prepared by using Sn-containing SBA-15 support synthesized either by in-situ co-synthesis or by impregnation method. It was found that the way of tin introduction had remarkable influence on the dispersion of Ru, the...