Preparation And Reaction Mechanism Of Potassium-Supported Titanium-Aluminum-Based Carbonyl Sulfide Hydrolysis Catalyst In Blast Furnace Gas

With the continuous advancement of the in-depth treatment of flue gas in the iron and steel industry,the precise removal of sulfur-containing pollutants in blast furnace gas has gradually attracted attention in recent years.The elimination of carbonyl sulfide（COS）,the organic sulfur that accounts for the highest concentration of total sulfur in blast furnace gas,has become a top priority.As one of the COS treatment technologies,catalytic hydrolysis has the advantages of great efficiency,low reaction temperature and no side reactions,which has a broad application prospect in sulfur oxide removal from steel blast furnace gas.However,as the key link of this technology,COS hydrolysis catalysts still face the problems of poor low-temperature activity,low product selectivity and easy oxygen poisoning,which significantly hinder the application of this method.Therefore,this paper investigated the development of COS hydrolysis catalysts with excellent low-temperature activity,high product selectivity and strong resistance to oxygen poisoning.A series of conclusions were obtained as follows.Firstly,in this paper,TiO₂-Al₂O₃ composite carriers（Ti Al）were produced by doping titanium dioxide（TiO₂）with antioxidant properties based on high surface activity alumina（Al₂O₃）by single-phase precipitation,two-phase co-precipitation and mechanical mixing methods,respectively.And the ternary hydrolysis catalysts were obtained by loading alkali metals（Na,K）,transition metals（Fe,Co）and rare earth metals（Ce）using the impregnation method.The COS hydrolysis performance of the catalysts was evaluated using a fixed-bed reactor,and it was found that the Ti Al carrier prepared by the biphasic co-precipitation method had higher H₂S selectivity at low temperatures,which was nearly 10%higher than other methods.The loading of alkali metals could significantly enhance the low-temperature hydrolysis activity of Ti Al-based catalysts and broaden the reaction activity temperature interval.The K_0.2Ti_0.5Al catalyst had the best catalytic hydrolysis performance with COS removal rate up to 95%at 75°C,which was 40%higher than that of the Ti0.₅Al catalyst.Meanwhile,the COS conversion and H₂S selectivity reached almost 100%in the temperature interval from 75 to 150°C.Secondly,the microstructure and physicochemical properties of the catalysts were investigated based on various characterization tools such as N₂ adsorption-desorption test（BET）,X-ray diffraction（XRD）,field emission electron scanning electron microscopy（SEM）,CO₂ programmed temperature desorption（CO₂-TPD）and X-ray photoelectron spectroscopy（XPS）combined with in situ diffuse reflectance Fourier transform infrared spectroscopy（in situ DRIFTS）simulations.The structure-effect relationship between the macroscopic properties and the physicochemical properties of the catalysts was investigated deeply.The characterization results showed that the alkali metal loaded Ti Al-based catalysts had larger average pore size,more abundant surface basic sites,and lower concentration of surface adsorbed oxygen.More importantly,the adsorption activation ability of COS on the surface and the conversion to H₂S were greatly enhanced.The in-situ DRIFTS experiments confirmed that the loaded alkali metals could reduce the surface active site coverage induced by excess adsorbed H₂O,which contributed to the enhanced low-temperature hydrolysis activity.At the same time,the low-temperature hydrolysis reaction pathway was investigated.Thirdly,the long-term anti-oxidation performance of the selected potassium-loaded catalysts was investigated.Combining activity evaluation,pre-and post-poisoning catalysts characterizations（such as BET,XRD,XPS,CO2-TPD,TG）,and in situ DRIFTS simulation,the causes of catalyst poisoning deactivation and the anti-oxidation performance and mechanism of potassium-loaded catalyst were systematically analyzed.The results of activity evaluation showed that the K_0.2Ti_0.5Al catalyst could improve the anti-oxidation performance of the catalyst more effectively.Under the atmosphere of 0.5 vol.%O₂,the K_0.2Ti_0.5Al catalyst could maintain more than 90%removal rate for a long time,and the hydrolysis capacity gradually and steadily recovered to about 95%after cutting off O₂.In contrast,the Ti_0.5Al catalyst could only maintain a COS removal rate of about 90%for a short period of time,and then its hydrolytic activity gradually decreased below 80%.The combination of various characterization tools revealed that the deposited sulfate and active site sulfation were important causes of catalyst deactivation.In addition,the results of in situ DRIFTS simulation of the reaction showed that weakening the adsorption of O₂ on the catalyst surface and blocking the oxidation of intermediate transition species were the key reasons for the improvement of the antioxidant performance of the catalyst by K.Finally,theoretical computational studies at the molecular level were carried out using DFT theory.The parameters for structure optimization were screened,the carrier optimization models of TiO₂ and Al₂O₃ were constructed,and the adsorption simulations of COS and H₂O molecules on the catalyst surface were carried out.The adsorption energy calculation demonstrated that the introduction of K did enhance the adsorption ability of COS on the catalyst surface while weaken the adsorption of H₂O.The adsorption energy generated by COS on the surface was significantly higher than that generated by H₂O,indicating that the adsorption of COS on the catalyst surface was easier and facilitated the activation of COS at the active site,which was conducive to the low-temperature hydrolysis reaction.The calculated data and in situ DRIFTS results were verified against each other.The bonding between the atoms was determined from the density of partial states（PDOS）,and it was found that the C=S bonds were more prone to breakage than the C=O bonds.Both COS and H₂O molecules underwent orbital hybridization with the catalyst surface atoms,indicating that COS and H₂O were adsorbed on the catalyst surface in the form of strong chemisorption.