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Вплив складу оксидних систем на основі Mg(ІІ), Al(ІІІ), Zr(IV) на їх каталітичні властивості в процесах газофазного перетворення етанолу та 1-бутанолу з подвоєнням вуглецевого ланцюга / Effect of the composition of Mg(II), Al(III), Zr(IV) oxide systems on their catalytic properties in the processes of gas-phase conversion of ethanol and 1-butanol with doubling of the carbon chain (in Ukrainian)

Abstract

Development of catalytic processes for the production of industrially important substances using renewable raw materials is one of the promising areas of research in organic synthesis. Ethanol obtained from the non-food renewable raw materials can be used for the production of various valuable compounds such as 1-butanol and 2-ethyl-1-hexanol. In particular, it can be done via Guerbet condensation of alcohols, which consists in the elongation of the carbon chain and involves the dehydrogenation, aldol-crotonic condensation and reduction steps. 1-Butanol is widely used as a solvent, extractant, raw material for the production of esters, enamels and varnishes, and also as an additive to gasoline. 2-Ethyl-1-hexanol is used in the production of plasticizers, environmentally friendly detergents, solvents, adhesives, additives to diesel fuel. The process of 1-butanol and 2-ethyl-1-hexanol obtaining can be held in a flow system over solid-phase catalysts via stepwise conversion: ethanol → 1-butanol → 2-ethyl-1-hexanol, which may be an alternative to industrial method based on petroleum raw materials. The key condition is the presence of highly productive, selective and stable catalysts that will provide a high yield of the target products. The processes of conversion of ethanol to 1-butanol and 1-butanol to 2-ethyl-1-hexanol are multistage and need catalysts with active sites of different nature. Therefore, catalytic systems must contain on the surface strong basic sites and medium acid sites to accelerate the key steps of the process (dehydrogenation and aldol condensation) and suppress side reactions (dehydration of the initial alcohol). Promising systems for the development of effective catalysts for 1-butanol and 2-ethyl-1-hexanol are systems based on MgO-Al2O3 and ZrO2 with a possibility of regulation of structural-dimensional and acid-base characteristics during the synthesis by changing the ratio of active components in catalysts, by changing conditions of their preparation, and the introduction of modifying additives. Thus, it is possible to achieve the optimal ratio of surface acid and base sites, which in turn will increase the yield of the target products of the Guerbet condensation. Therefore, the development of effective magnesia, alumina and zirconia based catalysts for the processes of gas-phase conversion of ethanol and 1-butanol with doubling of the carbon chain is an important scientific and practical issue. The purpose of the work is to elucidate the influence of the composition of MgO-Al2O3(CeOx) and ZrO2-MxOy (M = Ce, Y) catalytic systems on the acid-base properties of their surface and to determine the ways of regulation of these properties to achieve high activity and selectivity in the conversion of ethanol to 1-butanol and 1-butanol to 2-ethyl-1-hexanol. To achieve this goal, the following tasks were solved: 1. Elucidation of the influence of the Mg/Al ratio in MgO-Al2O3 systems on the concentration and strength of surface acid and base sites and catalytic properties in the processes of ethanol to 1-butanol and 1-butanol to 2-ethyl-1-hexanol conversion. 2. Establishment of the effect of the modifying additive CeOx on the acid-base surface characteristics and catalytic properties (activity and selectivity) of MgO-Al2O3 systems in the process of ethanol to 1-butanol conversion. 3. Determination of the optimal composition of the MgO-Al2O3(CeOx) system to increase the performance of the target process. 4. Elucidation of the effect of modifying additives CeO2, Y2O3 on the physicochemical properties of ZrO2 based catalysts. 5. Determination of catalytic properties of ZrO2 based systems doped with CeO2, Y2O3 in the process of ethanol to 1-butanol conversion. Objects of the study: the processes of ethanol → 1-butanol → 2-ethyl-1-hexanol conversion over MgO-Al2O3(CeOx) and ZrO2-MxOy (M = Ce, Y) catalytic systems. Subject of the study: the influence of the composition of MgO-Al2O3(CeOx) and ZrO2-MxOy (M = Ce, Y) systems on their catalytic properties in the processes of ethanol → 1-butanol → 2-ethyl-1-hexanol conversion. Research methods: X-ray diffraction analysis; low-temperature ad(de)sorption of nitrogen; scanning electron microscopy; energy dispersion X-ray spectroscopy; nuclear magnetic resonance; electron spectroscopy of diffuse reflectance in the ultraviolet and visible region; X-ray photoelectron spectroscopy; infrared spectroscopy with the probe molecules; quasi-equilibrium thermodesorption of ammonia and carbon dioxide; thermoprogrammed desorption of ammonia and carbon dioxide with mass spectrometric control; kinetic method with chromatographic control of the reagents and resulting products. Scientific approaches to development of catalysts for multistage processes of gas-phase ethanol and 1-butanol conversion with doubling of a carbon chain are developed in the thesis. Based on elucidation of the influence of components of MgO-Al2O3(CeOx) and ZrO2-MxOy (M = Ce, Y) catalytic systems on their acid-base surface characteristics and determination of methods of their varying, the ways to achieve the high activity and selectivity of catalysts in gas-phase ethanol → 1-butanol and 1-butanol → 2-ethyl-1-hexanol conversion are proposed. The process of gas-phase condensation of 1-butanol to 2-ethyl-1-hexanol in the flow reactor over Mg-Al-oxide catalytic systems was realized for the first time. The possibility of sequential ethanol → 1-butanol → 2-ethyl-1-hexanol conversion at atmospheric pressure in the flow mode was confirmed. It will allow to obtain 2-ethyl-1-hexanol directly from ethanol. It is shown that for the efficient conversion of initial alcohols into target products (1-butanol and 2-ethyl-1-hexanol) the binary oxide catalyst MgO-Al2O3 should include Lewis acid-base pairs (Mg-O-Al) formed under the conditions of calcination of hydrotalcites. The highest yield of 1-butanol (18%) is achieved over the catalyst with a ratio of Mg/Al = 2, and the highest yield of 2-ethyl-1-hexanol (11%) is achieved over catalyst with a ratio of Mg/Al = 1. It is found that modification of Mg-Al oxide systems by Се3+ cations during the hydrotalcite synthesis leads to an increase in the concentration of acid and base sites on the catalyst surface, which provides an increase in the specific rate of 1-butanol formation comparing to unmodified catalyst. The highest yield of 1-butanol (14%) is achieved over the catalyst with a ratio of Mg/Al/Ce = 2:0.9:0.1. It is established that the CeO2, Y2O3 additives affect the phase composition of ZrO2, which determines the acid-base properties of its surface. As a result of stabilization of the tetragonal phase of ZrO2 by the addition of CeO2 and Y2O3 there is an increase in the basicity of the catalysts which leads to an increase in the selectivity of 1-butanol formation from ethanol in their presence. It is found that the sample with a 10 wt.% of CeO2 is characterized by the highest concentration of base sites on the surface among the studied ZrO2-CeO2 systems, which provides a twofold increase in the selectivity and productivity of the catalyst for 1-butanol formation comparing with unmodified ZrO2. It is shown that the introduction of a modifying additive Y2O3 and calcination of the Zr-Y-oxide system at 500 °C leads to an increase in the concentration of the base sites on the surface of the catalysts together with a decrease in the concentration of acid sites. Over the ZrO2-Y2O3 catalyst the high values of selectivity (up to 70%) and yield of 1-butanol (17%) are achieved. MgO-Al2O3 catalytic systems with the ratio of Mg/Al = 1 and 2 are suggested for ethanol → 1-butanol and 1-butanol → 2-ethyl-1-hexanol conversion processes, which provide productivity of 1-butanol formation 87 gBuOH/(kgcat·h) and 2-ethyl-1-hexanol 40 g2-EH/(kgcat·h). The priority of development is protected by the Patent of Ukraine for Utility Model. It is found that the usage of ZrO2-Y2O3 catalytic system (3.4 wt.% Y2O3, calcination temperature 500 °C) in the ethanol → 1-butanol conversion, provides selectivity for 1-butanol up to 70%, with the productivity of 27 gBuOH/(kgcat·h). The priority of development is protected by the Patent of Ukraine for Utility Model. These systems are promising for the creation of high-performance catalysts for the synthesis of 1-butanol and 2-ethyl-1-hexanol from ethanol.
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