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Sulfur-resistant cobalt-molybdenum shift catalysts have been widely used in the fertilizer industry in recent years due to their good low-temperature activity, wide activity temperature range (160-500°C), strong sulfur resistance and toxicity resistance. At present, the potassium-containing cobalt-molybdenum shift catalyst using γ-Al2O3 as a carrier is mainly used in medium and low pressure (0.8~2.0MPa) shift systems. The process flow basically uses mid-stream low-shift technology, which means that the semi-water gas first reacts through a bed of Fe-based medium-temperature shift catalysts, and then the medium-shift gas is cooled by heat exchange and then enters a bed of low-temperature shift catalysts for reaction, reducing the CO content to the process requirements. At present, the sulfur-tolerant low-temperature shift catalysts developed in China are mainly Co-Mo-K/γ-Al2O3 catalysts. However, this type of catalyst suffers serious potassium loss in a water vapor atmosphere, has a short low-temperature activity duration, and is prone to reverse sulfurization when the operating temperature is higher than 320°C. In response to the above problems, the School of Chemistry and Chemical Engineering and Chemical Plant of Xiamen University introduced the third active component tungsten on the basis of preparing the traditional XH-2 catalyst (Co-Mo-K/γ-Al2O3), and developed a new product XH-3 catalyst (Co-Mo-WK/γ-Al2O3). The low-temperature activity of the XH-2 type catalyst is higher than that of the XH-3 type, while the high-temperature thermal stability of the XH-3 type is higher than that of the XH-2 type. The XH-2 and XH-3 type catalysts are combined in the same reactor, that is, the upper part of the XH-2 type filling furnace, and the middle and lower part of the XH-3 type catalyst filling furnace. This combined filling method (i.e., XH-2/3 type) can exert the catalytic characteristics of the two catalysts in different temperature zones and extend the service life of the catalyst. At present, the catalyst has been authorized for invention patent and passed the scientific and technological achievements appraisal. 1 Experimental part 1.1 Trial production of catalyst First, measure the potassium carbonate (K2CO3), cobalt nitrate, and ammonium molybdate E(NH4)6Mo7O14·4H2O] Or ammonium molybdate and ammonium metatungstate, stabilizer and deionized water are made into an active component loading liquid in a 1000L enamel reaction cylinder, then put the γ-Al2O3 (Shandong Aluminum Company) carrier into the loading liquid and soak it for 12 hours, and finally put the loaded carrier into hot air In a circulating drying oven (Changzhou Jinling Drying Equipment Co., Ltd.), the temperature was programmed to 135°C and dried for 12 hours to prepare XH-2 type Co-Mo-K/γ-Al2O3 catalyst and XH-3 type Co-Mo-WK/γ-Al2O3 catalyst. The comparative data of physical and chemical properties between XH-2 and XH-3 catalysts and similar domestic products (A) are shown in Table 1. http://www.nmtech.com.cn/jishuwang/upload1/070703857066203.jpg l.2 Catalytic performance evaluation The activity evaluation test of the original particle spherical catalyst was carried out in a 30mL pressurized activity evaluation system (0.80MPa). The gasification chamber and the reaction furnace are the same stainless steel tube of φ38mm×3mm×600mm. The upper part is the gasification section and the lower part is the reaction section. The water vapor required for the reaction is evaporated by pumping distilled water into the gasification chamber using a double plunger micro-metering pump, and the gasification temperature is controlled at 200°C. The components of the reaction raw gas are n(CO):n(H2):n(N2)=30:65:50. The catalyst is sulfurized with syngas containing CS2 volume fraction of 1% to 2% for 16 hours, and the maximum sulfurization temperature is 380°C. Catalyst activity was expressed as the conversion rate of CO. CO and Ne were analyzed using the TCD detector of the GD-102 gas chromatograph. The chromatographic column was 5A molecular sieve, column length was 2m, and N2 was used as the internal standard. 1.3 Industrial side line test The XH-2/3 catalyst was evaluated in the 60L conversion furnace of the second purification workshop of the Synthetic Ammonia Plant of Sanming Chemical Co., Ltd. The industrial side line device can be found in the literature. 1.4 Industrial application device In February 2006, the 12 tXH-2/3 combined catalyst was tried out for the first time in the fertilizer plant of Yanglv Chemical Co., Ltd., Zhangpu County, Fujian. The plant's synthetic ammonia production capacity is 60,000 t/a, and the conversion process adopts medium/medium/low/low processes (see Figure 1 for the process). The company uses the 12tXH-2/3 sulfur-tolerant shift catalyst produced by Xiamen University Chemical Plant on the upper two floors of the low-shift furnace of the 0.80MPa shift system. The catalyst filling method is shown in Figure 2. http://www.nmtech.com.cn/jishuwang/upload1/070703859035060.jpg 2 Results and Discussion Table 2 lists the comparative activity data of XH-2 and XH-3 catalysts and similar domestic industrial catalyst A at different temperatures and after being heat-resistant to 400°C. http://www.nmtech.com.cn/jishuwang/upload1/070703859418619.jpg Table 2 shows that at low temperatures (200, 250°C), the XH-2 catalyst shows higher activity, and at higher temperatures (300, 350, 400°C), the XH-3 catalyst shows higher activity ； After being heat-resistant to 400°C, the catalyst activity was XH-3 catalyst > XH-2 catalyst > Product A. It can be seen that the XH-2 catalyst has better low-temperature activity, and the XH-3 catalyst has better high-temperature activity and thermal stability. Molybdenum and tungsten belong to the VIB group. Due to the contraction effect of the lanthanide series, the properties of Mo and W elements are similar. The main oxidation numbers are both +5 and +6, the covalent radii are both 130, and the +6 valence ionic radii are both 62, but W The electronegativity (2.36) of W is larger than that of Mo (2.16), and the first ionization potential of W (770kJ/mol) is also larger than that of Mo (685kJ/mol), indicating that the metallicity of Mo is stronger than that of W. Due to the similar elemental properties of molybdenum and tungsten, the W/Mo atomic ratio is combined into a transformation catalyst with a ratio of 0.2 to 2.0. The activities of various combination catalysts are similar. Moreover, since W is more non-metallic than Mo, its high-temperature reduction sulfurization time is appropriately enhanced. According to literature reports, simple potassium-containing molybdenum-based shift catalysts are easily desulfurized above 320°C, while W-Mo-based shift catalysts have better activity at higher temperatures, which is closely related to the stronger non-metallic nature of W. In order to examine the stability, catalytic activity and compressive strength of the XH series catalyst under actual factory working conditions, a 60L side line test was conducted on the XH-2/3 catalyst at the synthetic ammonia plant of Fujian Sanming Chemical Co., Ltd. in September 2004. The side line test reactor is designed to simulate the reaction conditions of a section of the catalyst bed of the medium-variation reaction system. The factory conversion device adopts a medium to low conversion process, the system pressure is 1.8MPa, the semi-water gas flow rate is 46 000m3/h, the air velocity in one section is 2000h-1, the mass concentration of hydrogen sulfide at the inlet is 30~50mg/m3, and the CO volume fraction at the inlet of one section is 25%~27%. The results of the XH-2/3 catalyst industrial side line test are shown in Table 3 and Table 4 respectively. http://www.nmtech.com.cn/jishuwang/upload1/070703900281527.jpg It can be seen from Table 3 that the volume fraction of CO at the inlet of the side reactor furnace is 25% to 26%, the volume fraction of CO at the outlet is 4.8% to 5.1%, and the single-pass conversion rate of the XH-2 catalyst is 80%. ； As can be seen from Table 4, the volume fraction of CO at the inlet of the side reactor furnace is 25%, the volume fraction of CO at the outlet is 6.7% to 7.5%, and the single-pass change rate of the XH-3 catalyst is 70%. The space velocity of the side line furnace in the second test was 3 000 to 3 500 h-1, the reaction temperature range was 160 to 270°C, and the steam to gas volume ratio was 0.2 to 0.4. According to the design requirements of industrial conversion furnaces, the reaction temperature range is 200-250°C, the single-stage space velocity is 2500h-1, the steam-to-gas volume ratio is 0.3, and the CO single-stage conversion rate must reach 48%. This shows that the side line test results of the XH-2/3 catalyst meet the design requirements of industrial shift furnaces. After the lateral line test, the recovered sample particles were intact without damage or adhesion and agglomeration. The crushing strength was measured with a YPD-200 tablet hardness tester (Shanghai Huanghai Drug Testing Instrument Factory) ≥130N/cm, indicating that the catalyst does not pulverize in a long-term micro-water state and has high mechanical strength. The conversion process of Yanglu Fertilizer Plant in Zhangpu County was transferred to normal production on February 22, 2006. The mass concentration of hydrogen sulfide in semi-water gas was 30-50mg/m3, the pressure of the conversion system was about 0.75 MPa, and the system pressure difference after put into production was 0.03 MPa. The inlet temperature of the medium transformer is 310~320℃, and the inlet temperature of the low transformer is 200~230℃. The volume ratio of semi-water gas to gas in the intermediate conversion furnace is controlled to be 0.38 to 0.40. The operation data of catalyst replacement are shown in Table 5. It can be seen from Table 5 that the inlet temperature of the upper section of the low conversion furnace filled with the XH-2/3 catalyst of Xiamen University Chemical Plant is 200-210°C, the upper hot spot temperature is about 250°C, the bed reaction temperature rise is about 40°C, and the top and bottom temperatures of the lower layer are basically maintained at 250°C, that is, the load is light. The CO volume fraction of the medium variable gas is 4.5% to 5.4%, while the CO volume fraction of the low variable gas is 0.6% to 0.9%. The system production is stable and meets the process operation control indicators. http://www.nmtech.com.cn/jishuwang/upload1/070703901103968.jpg 3 Conclusion (1) XH-3 type sulfur-tolerant shift catalyst Co-Mo-KW/γ-Al2O3 introduces a third active component W on the basis of XH-2 type sulfur-tolerant shift catalyst Co-Mo-K/γ-Al2O3 to form a three-dimensional atomic family active component. The difference from traditional Co-Mo-K industrial catalysts is that this improves the heat resistance of the catalyst. (2) Scaled-up production and industrial side-line evaluation show that the low-temperature activity of the XH-2 shift catalyst is better than that of the XH-3 shift catalyst, while the heat resistance of the XH-3 shift catalyst is better than that of the XH-2 shift catalyst. (3) The 12t XH-2/3 combined catalyst was successfully tried in an ammonia synthesis plant, proving that the XH-2/3 catalyst can be used as a combined catalyst in the same shift furnace for medium and low pressure (0.8-2.0 MPa) shift systems.