Chromia-forming alloys have good resistance to oxidizing agents such as O2, CO2, … It is accepted that the protection of these alloys is always due to the chromia layer formed at the surface of the alloys, which acts...Chromia-forming alloys have good resistance to oxidizing agents such as O2, CO2, … It is accepted that the protection of these alloys is always due to the chromia layer formed at the surface of the alloys, which acts as a barrier between the oxidizing gases and the alloy substrates, forming a diffusion zone that limits the overall reaction rate and leads to parabolic kinetics. But this was not verified in the study devoted to Inconel®625 the oxidation in CO2 that was followed by TGA, with characterizations by XRD, EDS and FIB microscopy. Contrary to what was expected and accepted in similar studies on other chromia-forming alloys, it was shown that the diffusion step that governs the overall reaction rate is not located inside the chromia layer but inside the alloy, precisely inside a zone just beneath the interface alloy/chromia, this zone being depleted in chromium. The chromia layer, therefore, plays no kinetic role and does not directly protect the underlying alloy. This result was demonstrated using a simple test that consisted in removing the chromia layer from the surface of samples partially oxidized and then to continue the thermal treatment: insofar as the kinetics continued without any change in rate, this proved that this surface layer of oxide did not protect the substrate. Based on previous work on many chromia-forming alloys, the possibility of a similar reaction mechanism is discussed. If the chromia layer is not the source of protection for a number of chromia-forming alloys, as is suspected, this might have major consequences in terms of industrial applications.展开更多
Various mesoporous chromia alumina catalysts were prepared by five different methods based on a metal-organic framework MIL-101 and their catalytic performances over isobutane dehydrogenation were investigated. The hi...Various mesoporous chromia alumina catalysts were prepared by five different methods based on a metal-organic framework MIL-101 and their catalytic performances over isobutane dehydrogenation were investigated. The highly dispersed chromium species were produced on catalyst KCrAI-I1 with largest specific surface area of 198 m2-g-1 prepared with aluminium isopropoxide (Al(i-OC3HT)3) by ultrasonic im- pregnation method. However, the catalyst KCrAI-I2 synthesized by stirring impregnation possessed crystalline a-Cr203 phase, which was poorly dispersed. Two types of Cr-rich and Al-rich CrzA12_zO3 solid solutions, designated as CrAI-I and CrAI-II phase, were formed over the catalysts KCrAI-I3 (prepared by Al(i-OC3HT)3 with nitric acid regulation), KCrA1-C4 (prepared by aluminium chloride hexahydrate) and KCrA1-N5 (prepared by aluminium nitrate nonahydrate). Catalytic evaluation results revealed that KCrAI-I1 exhibited the high isobutane con- version due to its highly dispersed chromium species. However, KCrAI-I3, KCrA1-C4 and KCrA1-N5 showed the higher isobutene selectivity (95.2%-96.4%) on account of the formation of chromia alumina solid solutions in the catalysts. Moreover, the solid solution over the chromia alumina catalysts could greatly suppress the coke formation.展开更多
The corrosion behavior of alumina-chromia refractory against two kinds of industrial slags (coal slag and iron smelting slag) at 1550℃ was investigated via thermodynamic simulations. In the proposed simulation mode...The corrosion behavior of alumina-chromia refractory against two kinds of industrial slags (coal slag and iron smelting slag) at 1550℃ was investigated via thermodynamic simulations. In the proposed simulation model, the initial slag first attacks the matrix and surface aggregates and subsequently attacks the inner aggregates. The simulation results indicate that the slag chemistry strongly affects the phase formation and corrosion behavior of the refractory brick. Greater amounts of alumina were dissolved and spinel solid phases formed when the brick interacted with iron smelting slag. These phenomena, as well as the calculated lower viscosity, may lead to much deeper penetration than that exhibited by coal slag and to more severe corrosion compared to that induced by coal slag. The thermodynamic calculations well match the experimental observations, demonstrating the efficiency of the proposed simulation model for evaluating the corrosion behavior of alumina-chromia refractory.展开更多
The slag composition corresponding to different coals varies significantly,which directly affects the operation of industrial entrained-flow gasifier and the service life of refractory bricks.In this study,the corrosi...The slag composition corresponding to different coals varies significantly,which directly affects the operation of industrial entrained-flow gasifier and the service life of refractory bricks.In this study,the corrosion resistance of several typical coal slags for gasification on high chromia refractory bricks was comparatively investigated by static laboratory crucible tests and thermodynamic simulations.The results demonstrated that the corrosion degree of high chromia refractory bricks by different coal slags was high-Ca/Na slag>high-Fe slag>high-Si/Al slag.The surface structure of the refractory was relatively flat after corrosion by high-Si/Al slag,and the primary corrosion reaction was the partial dissolution of the matrix by the slag.High-Fe slag was prone to the precipitation of iron phases as well as the formation of(Mg,Fe)(Al,Cr)_(2)O_(4)composite spinel layer at the slag/refractory interface.The high-Ca/Na slag was susceptible to react with the refractory to yield a low melting point phase,which led to the destruction of the matrix structure of the refractory and an isolated distribution of particles.In addition,the monoclinic ZrO_(2) in the refractory reacted with CaO in the slag to formed calcium zirconate,which loosened its phase toughening effect,was the primary factor that aggravated the refractory corrosion.展开更多
A series of SBA-15-supported chromia-ceria catalysts with 3% Cr and 1%--5% Ce (3Cr-Ce/SBA) were pre- pared using an incipient wetness impregnation method. The catalysts were characterized by XRD, N2 adsorption, SEM,...A series of SBA-15-supported chromia-ceria catalysts with 3% Cr and 1%--5% Ce (3Cr-Ce/SBA) were pre- pared using an incipient wetness impregnation method. The catalysts were characterized by XRD, N2 adsorption, SEM, TEM-EDX, Raman spectroscopy, UV-vis spectroscopy, XPS and H2-TPR, and their catalytic performance for isobutane dehydrogenation with CO2 was tested. The addition of ceria to SBA-15-supported chromia improves the dispersion of chromium species. 3Cr-Ce/SBA catalysts are more active than SBA-15-supported chromia (3Cr/SBA), which is due to a higher concentration of Cr^6+ species present on the former catalysts. The 3Cr-3Ce/SBA catalyst shows the highest activity, which gives 35.4% isobutane conversion and 89.6% isobutene selectivity at 570℃ after 10 min of the reaction.展开更多
SBA-15 and HMS supported chromia catalysts were prepared and characterized. Chromia is highly dispersed on the mesoporous supports when its loading is 7 wt%. The supported catalysts display high activity, selectivity ...SBA-15 and HMS supported chromia catalysts were prepared and characterized. Chromia is highly dispersed on the mesoporous supports when its loading is 7 wt%. The supported catalysts display high activity, selectivity and stability for dehydrogenation of ethylbenzene and propane. ESR measurement of the catalysts before and after reaction shows that the active species for dehydrogenation reaction might be Cr3+ species on the catalyst surface, and the activity of the catalyst is probably correlated with the dispersion of Cr3+ species.展开更多
The first chromia-pillared layered tetratitanate was prepared by the reaction of layered tetramethylammonium tetratitanate with chromium (III) acetate [Cr(OAc)3] aqueous solution and subsequent calcination of the resu...The first chromia-pillared layered tetratitanate was prepared by the reaction of layered tetramethylammonium tetratitanate with chromium (III) acetate [Cr(OAc)3] aqueous solution and subsequent calcination of the resultant solid product in air at 400°C. The obtained chromia-pillared layered tetratitanate has an interlayer distance of 1.06 nm and a high thermal stability up to 600°C. It was also found that calcination in N2 led to the chromia-pillared layered tetratitanate with relatively higher Brunauer-Emmett-Teller (BET) specific surface area (93.9 m2·g?1) and smaller average pore diameter (4.44 nm) than that in air (82.0 m2·g?1, 7.61 nm). Both Br?nsted and Lewis acid sites (mainly Lewis type) are present on the chromia-Pillared layered tetratitanate (500°C, N2, 8 h) and strong enough to still remain a small proportion of pyridine upon outgassing at 250°C. Moreover, ammonia temperature-programmed desorption (NH3-TPD) result showed that there were three NH3 desorption peaks at 160, 200 and 315°C, respectively. The corresponding acid amount is 41.3, 73.9 and 290.7 μmol·g?1. The total acid amount is 405.9 μmol·g?1.展开更多
The Cr2O3-SiO ? catalyst was prepared by a sol-gel method. It displays two times higher catalytic activity for the dehydrogenation of ethylbenzene in the presence of CO2 than the regular SiO2-supported chromia catalys...The Cr2O3-SiO ? catalyst was prepared by a sol-gel method. It displays two times higher catalytic activity for the dehydrogenation of ethylbenzene in the presence of CO2 than the regular SiO2-supported chromia catalyst.The higher amount of Cr 6+ present in the former catalyst accounts for its superior catalytic performance in the dehydrogenation reaction.展开更多
文摘Chromia-forming alloys have good resistance to oxidizing agents such as O2, CO2, … It is accepted that the protection of these alloys is always due to the chromia layer formed at the surface of the alloys, which acts as a barrier between the oxidizing gases and the alloy substrates, forming a diffusion zone that limits the overall reaction rate and leads to parabolic kinetics. But this was not verified in the study devoted to Inconel®625 the oxidation in CO2 that was followed by TGA, with characterizations by XRD, EDS and FIB microscopy. Contrary to what was expected and accepted in similar studies on other chromia-forming alloys, it was shown that the diffusion step that governs the overall reaction rate is not located inside the chromia layer but inside the alloy, precisely inside a zone just beneath the interface alloy/chromia, this zone being depleted in chromium. The chromia layer, therefore, plays no kinetic role and does not directly protect the underlying alloy. This result was demonstrated using a simple test that consisted in removing the chromia layer from the surface of samples partially oxidized and then to continue the thermal treatment: insofar as the kinetics continued without any change in rate, this proved that this surface layer of oxide did not protect the substrate. Based on previous work on many chromia-forming alloys, the possibility of a similar reaction mechanism is discussed. If the chromia layer is not the source of protection for a number of chromia-forming alloys, as is suspected, this might have major consequences in terms of industrial applications.
基金supported by the National Basic Research Program of China(No.2011CB201404)the National Natural Science Foundation of China(No.21133011)Suzhou Science and Technology Bureau of Applied Foundation Research Project(SYG201219)
文摘Various mesoporous chromia alumina catalysts were prepared by five different methods based on a metal-organic framework MIL-101 and their catalytic performances over isobutane dehydrogenation were investigated. The highly dispersed chromium species were produced on catalyst KCrAI-I1 with largest specific surface area of 198 m2-g-1 prepared with aluminium isopropoxide (Al(i-OC3HT)3) by ultrasonic im- pregnation method. However, the catalyst KCrAI-I2 synthesized by stirring impregnation possessed crystalline a-Cr203 phase, which was poorly dispersed. Two types of Cr-rich and Al-rich CrzA12_zO3 solid solutions, designated as CrAI-I and CrAI-II phase, were formed over the catalysts KCrAI-I3 (prepared by Al(i-OC3HT)3 with nitric acid regulation), KCrA1-C4 (prepared by aluminium chloride hexahydrate) and KCrA1-N5 (prepared by aluminium nitrate nonahydrate). Catalytic evaluation results revealed that KCrAI-I1 exhibited the high isobutane con- version due to its highly dispersed chromium species. However, KCrAI-I3, KCrA1-C4 and KCrA1-N5 showed the higher isobutene selectivity (95.2%-96.4%) on account of the formation of chromia alumina solid solutions in the catalysts. Moreover, the solid solution over the chromia alumina catalysts could greatly suppress the coke formation.
基金financially supported by the Preliminary Research Project for National Basic Research Program of China (No. 2012CB724607)the Research Planning Project of Basic and Advanced Technology of Henan Province, China (No.162300410043)
文摘The corrosion behavior of alumina-chromia refractory against two kinds of industrial slags (coal slag and iron smelting slag) at 1550℃ was investigated via thermodynamic simulations. In the proposed simulation model, the initial slag first attacks the matrix and surface aggregates and subsequently attacks the inner aggregates. The simulation results indicate that the slag chemistry strongly affects the phase formation and corrosion behavior of the refractory brick. Greater amounts of alumina were dissolved and spinel solid phases formed when the brick interacted with iron smelting slag. These phenomena, as well as the calculated lower viscosity, may lead to much deeper penetration than that exhibited by coal slag and to more severe corrosion compared to that induced by coal slag. The thermodynamic calculations well match the experimental observations, demonstrating the efficiency of the proposed simulation model for evaluating the corrosion behavior of alumina-chromia refractory.
基金financial support from the Joint Funds of the National Natural Science Foundation of China(U21A20318).
文摘The slag composition corresponding to different coals varies significantly,which directly affects the operation of industrial entrained-flow gasifier and the service life of refractory bricks.In this study,the corrosion resistance of several typical coal slags for gasification on high chromia refractory bricks was comparatively investigated by static laboratory crucible tests and thermodynamic simulations.The results demonstrated that the corrosion degree of high chromia refractory bricks by different coal slags was high-Ca/Na slag>high-Fe slag>high-Si/Al slag.The surface structure of the refractory was relatively flat after corrosion by high-Si/Al slag,and the primary corrosion reaction was the partial dissolution of the matrix by the slag.High-Fe slag was prone to the precipitation of iron phases as well as the formation of(Mg,Fe)(Al,Cr)_(2)O_(4)composite spinel layer at the slag/refractory interface.The high-Ca/Na slag was susceptible to react with the refractory to yield a low melting point phase,which led to the destruction of the matrix structure of the refractory and an isolated distribution of particles.In addition,the monoclinic ZrO_(2) in the refractory reacted with CaO in the slag to formed calcium zirconate,which loosened its phase toughening effect,was the primary factor that aggravated the refractory corrosion.
文摘A series of SBA-15-supported chromia-ceria catalysts with 3% Cr and 1%--5% Ce (3Cr-Ce/SBA) were pre- pared using an incipient wetness impregnation method. The catalysts were characterized by XRD, N2 adsorption, SEM, TEM-EDX, Raman spectroscopy, UV-vis spectroscopy, XPS and H2-TPR, and their catalytic performance for isobutane dehydrogenation with CO2 was tested. The addition of ceria to SBA-15-supported chromia improves the dispersion of chromium species. 3Cr-Ce/SBA catalysts are more active than SBA-15-supported chromia (3Cr/SBA), which is due to a higher concentration of Cr^6+ species present on the former catalysts. The 3Cr-3Ce/SBA catalyst shows the highest activity, which gives 35.4% isobutane conversion and 89.6% isobutene selectivity at 570℃ after 10 min of the reaction.
文摘SBA-15 and HMS supported chromia catalysts were prepared and characterized. Chromia is highly dispersed on the mesoporous supports when its loading is 7 wt%. The supported catalysts display high activity, selectivity and stability for dehydrogenation of ethylbenzene and propane. ESR measurement of the catalysts before and after reaction shows that the active species for dehydrogenation reaction might be Cr3+ species on the catalyst surface, and the activity of the catalyst is probably correlated with the dispersion of Cr3+ species.
基金Project (No. 29573108) supported by the National Natural Science Foundation of China
文摘The first chromia-pillared layered tetratitanate was prepared by the reaction of layered tetramethylammonium tetratitanate with chromium (III) acetate [Cr(OAc)3] aqueous solution and subsequent calcination of the resultant solid product in air at 400°C. The obtained chromia-pillared layered tetratitanate has an interlayer distance of 1.06 nm and a high thermal stability up to 600°C. It was also found that calcination in N2 led to the chromia-pillared layered tetratitanate with relatively higher Brunauer-Emmett-Teller (BET) specific surface area (93.9 m2·g?1) and smaller average pore diameter (4.44 nm) than that in air (82.0 m2·g?1, 7.61 nm). Both Br?nsted and Lewis acid sites (mainly Lewis type) are present on the chromia-Pillared layered tetratitanate (500°C, N2, 8 h) and strong enough to still remain a small proportion of pyridine upon outgassing at 250°C. Moreover, ammonia temperature-programmed desorption (NH3-TPD) result showed that there were three NH3 desorption peaks at 160, 200 and 315°C, respectively. The corresponding acid amount is 41.3, 73.9 and 290.7 μmol·g?1. The total acid amount is 405.9 μmol·g?1.
文摘The Cr2O3-SiO ? catalyst was prepared by a sol-gel method. It displays two times higher catalytic activity for the dehydrogenation of ethylbenzene in the presence of CO2 than the regular SiO2-supported chromia catalyst.The higher amount of Cr 6+ present in the former catalyst accounts for its superior catalytic performance in the dehydrogenation reaction.