The oxidative coupling of methane over La203/CaO type-catalyst in a fixed-bed reactor is studied under a wide range of operating conditions （973〈T〈 1103 K, 55〈 Ptotal 〈220 kPa, and 3.7〈 mcat/VTp 〈50 kg.s/m^3）....The oxidative coupling of methane over La203/CaO type-catalyst in a fixed-bed reactor is studied under a wide range of operating conditions （973〈T〈 1103 K, 55〈 Ptotal 〈220 kPa, and 3.7〈 mcat/VTp 〈50 kg.s/m^3）. A ten-step kinetic model incorporating all main products was used to predict the behavior of the system. Methane conversions and C2 selectivities were calculated by varying methane to oxygen ratios in the feed under different operating conditions which were also compared with the rule of 100. The results show that deviation from this rule depends on the operating conditions. Within the range studied, an increase in pressure, temperature and contact time results in smaller deviation from the rule. This rule is best approximated when the catalyst operates near its optimal performance. For negative deviations, common to the most catalysts, it is found that the optimal performance should occur at methane conversion levels lower than 50%. A plot of selectivity versus conversion for high-yield reported performance data of a large variety of catalysts shows that data points concentrated roughly in 20%-50% methane conversion region, confirming the generality and prediction of modeling.展开更多
The catalytic performance of co mmonly used heteropolyacids （H3PW12O40, H4SiW12O40 and H3PMO12O40 synthesis of 4,4＇-methylenedianiline （4,4＇-MDA） from aniline and formaldehyde was evaluated and the result showed ...The catalytic performance of co mmonly used heteropolyacids （H3PW12O40, H4SiW12O40 and H3PMO12O40 synthesis of 4,4＇-methylenedianiline （4,4＇-MDA） from aniline and formaldehyde was evaluated and the result showed that H4SiW12O40 with moderate acid strength exhibited the best catalytic performance. Then HaSiW12O40@MIL-100（Fe） was prepared by encapsulating H4SiW12O40 within the pores of MIL-100（Fe） to facilitate its recovery and reuse. The prepared H4SiW12O40@MIL-100（Fe） was characterized by means of FT-IR, N2 adsorption-desorption, XRD, TG and then the catalytic performance was evaluated. The result showed that H4SiW12O40 was highly dispersed in the pores of MIL-100（Fe）, and both the Keggin structure of HaSiW12O40 and the crystal skeleton structure of MIL-100（Fe） could be effectively/preserved. Furthermore, H4SiW12O40@ MIL-100（Fe） showed excellent catalytic performance under the following reaction conditions： a molar ratio of aniline to formaldehyde = 5, a mass ratio of catalyst to formaldehyde = 1.2, a reaction temperature of 120 ℃ and a reaction time of 6 h. Under the above reaction conditions, the conversion of aniline was 41.1%, and the yield and selectivity of 4,4＇-MDA were 81,6% and 79.2%, respectively. Unfortunately, an appreciable loss in the catalytic activity of the recovered H4SiW12O40@MIL-100（Fe） was observed because of the blocking of the pores and the change of the acidity resulted from the adsorption of alkaline organics such as aniline and 4,4＇-MDA. The adsorbed alkaline organics could be cleaned up when the recovered catalyst was washed by methanol and DMF. Then the catalyst was effectively reused up to three cycles without much loss in its activity.展开更多
Ceria-based catalytic materials are known for their crystal-face-dependent catalytic properties.To obtain a molecular-level understanding of their surface chemistry,controlled synthesis of ceria with well-defined surf...Ceria-based catalytic materials are known for their crystal-face-dependent catalytic properties.To obtain a molecular-level understanding of their surface chemistry,controlled synthesis of ceria with well-defined surface structures is required.We have thus studied the growth of CeOx nanostructures(NSs)and thin films on Pt(111).The strong metal-oxide interaction has often been invoked to explain catalytic processes over the Pt/CeOx catalysts.However,the Pt-CeOx interaction has not been understood at the atomic level.We show here that the interfacial interaction between Pt and ceria could indeed affect the surface structures of ceria,which could subsequently determine their catalytic chemistry.While ceria on Pt(111)typically exposes the CeO2(111)surface,we found that the structures of ceria layers with a thickness of three layers or less are highly dynamic and dependent on the annealing temperatures,owing to the electronic interaction between Pt and CeOx.A two-step kinetically limited growth procedure was used to prepare the ceria film that fully covers the Pt(111)substrate.For a ceria film of^3–4 monolayer(ML)thickness on Pt(111),annealing in ultrahigh vacuum(UHV)at 1000 K results in a surface of CeO2(100),stabilized by a c-Ce2O3(100)buffer layer.Further oxidation at 900 K transforms the surface of the CeO2(100)thin film into a hexagonal CeO2(111)surface.展开更多
对不同催化剂(A和B)生产的PE 100管材专用料(牌号为TUB 121 N 3000,以下分别简称试样1和试样2)进行了结构分析和管材加工性能评价。结果表明,试样1的弯曲应力、相对分子质量及其分布、氧化诱导期小于试样2,但熔体强度大于试样2;两者管...对不同催化剂(A和B)生产的PE 100管材专用料(牌号为TUB 121 N 3000,以下分别简称试样1和试样2)进行了结构分析和管材加工性能评价。结果表明,试样1的弯曲应力、相对分子质量及其分布、氧化诱导期小于试样2,但熔体强度大于试样2;两者管材加工性能相当,静液压强度均能满足GB/T 15558.1—2003要求。展开更多
文摘The oxidative coupling of methane over La203/CaO type-catalyst in a fixed-bed reactor is studied under a wide range of operating conditions （973〈T〈 1103 K, 55〈 Ptotal 〈220 kPa, and 3.7〈 mcat/VTp 〈50 kg.s/m^3）. A ten-step kinetic model incorporating all main products was used to predict the behavior of the system. Methane conversions and C2 selectivities were calculated by varying methane to oxygen ratios in the feed under different operating conditions which were also compared with the rule of 100. The results show that deviation from this rule depends on the operating conditions. Within the range studied, an increase in pressure, temperature and contact time results in smaller deviation from the rule. This rule is best approximated when the catalyst operates near its optimal performance. For negative deviations, common to the most catalysts, it is found that the optimal performance should occur at methane conversion levels lower than 50%. A plot of selectivity versus conversion for high-yield reported performance data of a large variety of catalysts shows that data points concentrated roughly in 20%-50% methane conversion region, confirming the generality and prediction of modeling.
基金Supported by the National Natural Science Foundation of China(21236001,21476058,21506046)
文摘The catalytic performance of co mmonly used heteropolyacids （H3PW12O40, H4SiW12O40 and H3PMO12O40 synthesis of 4,4＇-methylenedianiline （4,4＇-MDA） from aniline and formaldehyde was evaluated and the result showed that H4SiW12O40 with moderate acid strength exhibited the best catalytic performance. Then HaSiW12O40@MIL-100（Fe） was prepared by encapsulating H4SiW12O40 within the pores of MIL-100（Fe） to facilitate its recovery and reuse. The prepared H4SiW12O40@MIL-100（Fe） was characterized by means of FT-IR, N2 adsorption-desorption, XRD, TG and then the catalytic performance was evaluated. The result showed that H4SiW12O40 was highly dispersed in the pores of MIL-100（Fe）, and both the Keggin structure of HaSiW12O40 and the crystal skeleton structure of MIL-100（Fe） could be effectively/preserved. Furthermore, H4SiW12O40@ MIL-100（Fe） showed excellent catalytic performance under the following reaction conditions： a molar ratio of aniline to formaldehyde = 5, a mass ratio of catalyst to formaldehyde = 1.2, a reaction temperature of 120 ℃ and a reaction time of 6 h. Under the above reaction conditions, the conversion of aniline was 41.1%, and the yield and selectivity of 4,4＇-MDA were 81,6% and 79.2%, respectively. Unfortunately, an appreciable loss in the catalytic activity of the recovered H4SiW12O40@MIL-100（Fe） was observed because of the blocking of the pores and the change of the acidity resulted from the adsorption of alkaline organics such as aniline and 4,4＇-MDA. The adsorbed alkaline organics could be cleaned up when the recovered catalyst was washed by methanol and DMF. Then the catalyst was effectively reused up to three cycles without much loss in its activity.
基金supported by the National Key R&D Program of China(2017YFB0602205,2016YFA0202803,2017YFA0303104)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB17020200)the National Natural Science Foundation of China(21473191,91545204)~~
文摘Ceria-based catalytic materials are known for their crystal-face-dependent catalytic properties.To obtain a molecular-level understanding of their surface chemistry,controlled synthesis of ceria with well-defined surface structures is required.We have thus studied the growth of CeOx nanostructures(NSs)and thin films on Pt(111).The strong metal-oxide interaction has often been invoked to explain catalytic processes over the Pt/CeOx catalysts.However,the Pt-CeOx interaction has not been understood at the atomic level.We show here that the interfacial interaction between Pt and ceria could indeed affect the surface structures of ceria,which could subsequently determine their catalytic chemistry.While ceria on Pt(111)typically exposes the CeO2(111)surface,we found that the structures of ceria layers with a thickness of three layers or less are highly dynamic and dependent on the annealing temperatures,owing to the electronic interaction between Pt and CeOx.A two-step kinetically limited growth procedure was used to prepare the ceria film that fully covers the Pt(111)substrate.For a ceria film of^3–4 monolayer(ML)thickness on Pt(111),annealing in ultrahigh vacuum(UHV)at 1000 K results in a surface of CeO2(100),stabilized by a c-Ce2O3(100)buffer layer.Further oxidation at 900 K transforms the surface of the CeO2(100)thin film into a hexagonal CeO2(111)surface.
