| Chemical process intensification in modern is a novel sustainable development process technique which can reduce equipment size, increase efficiency, reduce energy consumption and environment impact. As a new technique in chemical process intensification, monolithic catalysts have obvious advantages, such as low pressure drop over the catalyst bed, favorable heat and mass transfer properties, and uniform profiles of concentration and temperature in comparison with the conventional fixed-bed catalytic reactors. Therefore, monolithic catalysts have been extensively applied to the control of emissions. However, the applications of monolithic catalysts in petroleum and chemical industry are being explored. In this study, we try to directly couple highly endothermic and exothermic reactions using the monolithic catalysts. In monolithic catalytic reactors, the endothermic reaction and the exothermic reaction simultaneously occur in both side of the wall of the monolithic catalytic reactor, and the heat needed for the endothermic reaction comes directly from the exothermic reaction, which highly miniaturizes reactor and significantly increases heat efficiency. According to the idea mentioned above, catalytic combustion of methane was used as an exothermic reaction system to couple with methane reforming with CO2, as an endothermic reaction system. A series of metallic monolith catalysts applied to both the two reaction systems were firstly prepared, respectively. The activities and stabilities of the catalysts were evaluated, and the intrinsic properties of the catalysts were characterized by XRD, SEM, TEM, N2adsorption-desorption, TPR and XPS. Secondly, a novel metallic monolith catalytic reactor for directly coupling of methane catalytic combustion and methane reforming with CO2was devised and its operation performance was experimentally studied. The main research contents and results are listed as follows:The preparation technology of Al2O3/FeCrAl composite support was investigated. The results showed that heat treatment conditions of FeCrAl foil considerably influenced the coating of washcoat layers. The formation of AI2O3layers on the surface of FeCrAl foil after heat treatment could improve the combination ability between washcoat layers and FeCrAl foil. The optimal heat treatment conditions were:calcination at900℃for25h or calcination at950℃for15-25h. The content of HNO3added influenced significantly the performance of the boehmite primer sol, A12O3slurry, SBA-15slurry and active component slurry, and an optimal content of HNO3could increase their dispersion and stability. In an optimal preparation condition, the weight loss of the washcoat layers was less than3wt.%.A series of metallic monolith catalysts applied to methane catalytic combustion in different operation temperature ranges were prepared which the active component included Pd, perovskite-type oxides and solid solutions. The results showed that in Pd-based catalysts the dispersion and resistance to sintering of Pd increased due to the incorporation of Pd into the channels of SBA-15, and Pd could remain oxide form during the reaction owing to high oxygen storage capacity provided by Ce1-xZrxO2solid solutions as auxiliary, which markedly improved the stability of the catalysts. In LaFe1-xMgxO3/Al2O3/FeCrAl monolithic catalysts, the Fe component played an important role in the catalytic activity. The activity and the stability of the catalysts could increase when LaFeO3was doped with Mg. The main reason is that the interaction between Fe and Mg could enhance the activity and stability after the partial substitution of Fe with Mg oxide. In Ce1-xCuxO2-x/Al2O3/FeCrAl and Ce1-xLaxO2-x/2/Al2O3/FeCrAl catalysts, there was synergistic effect between Ce and Cu or La leading to higher activity. Furthermore, synergistic effect was different with various atomic ratio of Ce to Cu or La. The results of TPR measurement showed that the interaction between active components and washcoat layers and FeCrAl foil also influence the performance of the metallic monolithic catalysts prepared.The urea-combustion method was applied to the preparation of a series of AAl112O,9(A=La, Sr, Ba, Ca, Ce), AMAl11O19(A=La, Sr; M=Cu, Mn, Fe, Ni, Mg) hexaaluminates which were high temperature catalytic combustion catalysts. The preparation and the relationship between structure and performance of hexaaluminates were studied. The results showed that the preparation time could be shorted to about40-60min, and the operation temperature was not less than400℃, which significantly decreased the operation temperature and preparation time.For endothermic reactions, a series of Ni-based monolithic catalysts were prepared. The activities and stabilities of catalysts increased by using SBA-15as support which had high specific surface areas and well-ordered mesopore structure. The30%Ni/SBA-15/Al2O3/FeCrAl catalyst had the best activity, and its CH4conversion and CO2conversion were about98%which was close to the equilibrium conversion. The20%Ni/SBA-15/Al2O3/FeCrAl catalyst exhibited excellent stability at850℃which the activity kept almost unchanged during the1300h stability test. The studies on deactivation behavior showed that carbon deposition was main reason for the deactivation of the Ni-based catalysts.Finally, a metallic monolith catalytic reactor for directly coupling of methane catalytic combustion and methane reforming with CO2was devised and developed. The direct coupling performance of the two reactions in this reactor was experimentally studied. The results showed that the heat needed for methane reforming with CO2reactions came directly from that produced by methane catalytic combustion reaction, and the direct coupling of highly endothermic and exothermic reactions was successfully demonstrated. Under an optimal condition, the conversion of methane in reforming reactions with CO2was about90%, and the heat efficiency was about82%when methane catalytic combustion reaction directly provided heat for methane reforming with CO2reactions. |
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