N2O is a major by-product emitted during low-temperature selective catalytic reduction of NO with NH3(NH3-SCR), which causes a series of serious environmental problems. A full understanding of the N2O formation mechan...N2O is a major by-product emitted during low-temperature selective catalytic reduction of NO with NH3(NH3-SCR), which causes a series of serious environmental problems. A full understanding of the N2O formation mechanism is essential to suppress the N2O emission during the low-temperature NH3-SCR, and requires an intensive study of this heterogeneous catalysis process. In this study, we investigated the reaction between NH3 and NO over a Pd/CeO2 catalyst in the absence of O2, using X-ray photoelectron spectroscopy, NH3-temperature-programmed desorption, NO-temperature-programmed desorption, and in-situ Fourier-transform infrared spectroscopy. Our results indicate that the N2O formation mechanism is reaction-temperature-dependent. At temperatures below 250 ℃, the dissociation of HON, which is produced from the reaction between surface H· adatoms and adsorbed NO, is the key process for N2O formation. At temperatures above 250 ℃,the reaction between NO and surface N·, which is produced by NO dissociation, is the only route for N2O formation, and the dissociation of NO is the rate-determining step. Under optimal reaction conditions, a high performance with nearly 100% NO conversion and 100% N2 selectivity could be achieved. These results provide important information to clarify the mechanism of N2O formation and possible suppression of N2 O emission during low-temperature NH3-SCR.展开更多
Three Pd/CeO2 catalysts were,respectively,prepared by reduction-deposition and impregnation method(IMP)to investigate the effect of chemical state of Pd on CO oxidation.Two kinds of surface Pd species,namely PdO and P...Three Pd/CeO2 catalysts were,respectively,prepared by reduction-deposition and impregnation method(IMP)to investigate the effect of chemical state of Pd on CO oxidation.Two kinds of surface Pd species,namely PdO and Pdδ+(2<δ≤4)in PdxCe1-xO2,were identified in all Pd/CeO2 samples although their relative ratios in each sample were different.Surface PdxCe1-xO2 species were found to be very active for CO oxidation,and it could act as a channel by which active oxygen species can be transferred from CeO2 to Pd species for CO oxidation.Our results reveal that the preparation method can severely influence the chemical state of Pd which can further determine the activity for CO oxidation.展开更多
Composite supports CeO2-ZrO2-Al2O3（CZA） and CeO2-ZrO2-Al2O3-La2O3（CZALa） were prepared by co-precipitation method. Palladium catalysts were prepared by impregnation and their purification ability for CH4, CO and N...Composite supports CeO2-ZrO2-Al2O3（CZA） and CeO2-ZrO2-Al2O3-La2O3（CZALa） were prepared by co-precipitation method. Palladium catalysts were prepared by impregnation and their purification ability for CH4, CO and NOx in the mixture gas simulated the exhaust from natural gas vehicles （NGVs） operated under stoichiometric condition was investigated. The effect of La2O3 on the physicochemical properties of supports and catalysts was characterized by various techniques. The characterizations with X-ray diffraction （XRD） and Raman spectroscopy revealed that the doping of La2O3 restrained effectively the sintering of crystallite particles, maintained the crystallite particles in nanoscale and stabilized the crystal phase after calcination at 1000 ℃. The results of N2-adsorption, H2-temperatnre-programmed reduction （H2-TPR） and oxygen storage capacity （OSC） measurements indicated that La2O3 improved the textural properties, reducibility and OSC of composite supports. Activity testing results showed that the catalysts exhibit excellent activities for the simultaneous removal of methane, CO and NOx in the simulated exhaust gas. The catalysts supported on CZALa showed remarkable thermal stability and catalytic activity for the three pollutants, especially for NOx. The prepared palladium catalysts have high ability to remove NOx, CH4 and CO, and they can be used as excellent catalysts for the purification of exhaust from NGVs operated under stoichiometric condition. The catalysts reported in this work also have significant potential in industrial application because of their high performance and low cost.展开更多
The influence of sulfation on Pd/Ce0.75Zr0.25O2, Pd/Ce O2-Ti O2 and Pd/Ce O2 was investigated. Physical structure and chemical properties of different catalysts were characterized by N2 adsorption, X-ray diffraction（...The influence of sulfation on Pd/Ce0.75Zr0.25O2, Pd/Ce O2-Ti O2 and Pd/Ce O2 was investigated. Physical structure and chemical properties of different catalysts were characterized by N2 adsorption, X-ray diffraction（XRD）, CO chemisorption, X-ray photoelectron spectroscopy（XPS）, Fourier transform infrared spectroscopy（FT-IR） and X-ray fluorescence（XRF）. After 10 h SO2 sulfation, it was found that the decrement on CO oxidation catalytic activity was limited on Pd/Ce0.75Zr0.25O2 compared to Pd/Ce O2-Ti O2 and Pd/Ce O2. It demonstrated that Pd/Ce0.75Zr0.25O2 was more sulfur resistant compared to the other two catalysts. After sulfur exposure, catalyst texture was not much influenced as shown by N2 adsorption and XRD, and surface Pd atoms were poisoned indicated by CO chemisorption results. Pd/Ce0.75Zr0.25O2 and Pd/Ce O2-Ti O2 exhibited less sulfur accumulation compared to Pd/Ce O2 in the sulfation process. Furthermore, XPS results clarified that surface sulfur amount, especially surface sulfates amount on the sulfated catalysts was more crucial for the deactivation in sulfur containing environment.展开更多
Heterogenization of the homogeneous catalysis has been studied for almost 50 years.Single-atom catalysis has the advantages of both homo-and heterogeneous catalysis.It has been proposed,and subsequently experimentally...Heterogenization of the homogeneous catalysis has been studied for almost 50 years.Single-atom catalysis has the advantages of both homo-and heterogeneous catalysis.It has been proposed,and subsequently experimentally verified that single-atom catalysis is able to bridge homo-and heterogeneous catalysis,thus providing a new avenue to realize the heterogenization of homogeneous catalysis.Alkoxycarbonylation of aryl halides is an effective method for the direct synthesis of carboxylic acid derivatives,and is commonly catalyzed by Pd-based homogeneous complexes with N/P-containing ligands and organic/inorganic base.Herein,we firstly reported that Pd1/CeO2 single-atom catalyst showed good performance in the alkoxycarbonylation of aryl iodides reaction.Under base-free and ligand-free conditions,Pd1/CeO2 single-atom catalyst can transfer different aryl iodides to corresponding products.The catalyst can be easily recovered and reused four times without significant loss of reactivity.展开更多
基金support of the National Key Research and Development Program of China(2017YFB0310403)the National Natural Science Foundation of China(51872260,51390474,91645103)+2 种基金the Ministry of Science and Technology of China(2016YFE0105700)the Environmentally Sustainable Management of Medical Wastes in China(C/V/S/10/251)the Zhejiang Provincial Natural Science Foundation of China(Z4080070,LD19B030001)~~
文摘N2O is a major by-product emitted during low-temperature selective catalytic reduction of NO with NH3(NH3-SCR), which causes a series of serious environmental problems. A full understanding of the N2O formation mechanism is essential to suppress the N2O emission during the low-temperature NH3-SCR, and requires an intensive study of this heterogeneous catalysis process. In this study, we investigated the reaction between NH3 and NO over a Pd/CeO2 catalyst in the absence of O2, using X-ray photoelectron spectroscopy, NH3-temperature-programmed desorption, NO-temperature-programmed desorption, and in-situ Fourier-transform infrared spectroscopy. Our results indicate that the N2O formation mechanism is reaction-temperature-dependent. At temperatures below 250 ℃, the dissociation of HON, which is produced from the reaction between surface H· adatoms and adsorbed NO, is the key process for N2O formation. At temperatures above 250 ℃,the reaction between NO and surface N·, which is produced by NO dissociation, is the only route for N2O formation, and the dissociation of NO is the rate-determining step. Under optimal reaction conditions, a high performance with nearly 100% NO conversion and 100% N2 selectivity could be achieved. These results provide important information to clarify the mechanism of N2O formation and possible suppression of N2 O emission during low-temperature NH3-SCR.
基金financially supported by the National Key Research and Development Program of China(No.2016YFC0204300)the National Natural Science Foundation of China(Nos.21171055 and 21571061)。
文摘Three Pd/CeO2 catalysts were,respectively,prepared by reduction-deposition and impregnation method(IMP)to investigate the effect of chemical state of Pd on CO oxidation.Two kinds of surface Pd species,namely PdO and Pdδ+(2<δ≤4)in PdxCe1-xO2,were identified in all Pd/CeO2 samples although their relative ratios in each sample were different.Surface PdxCe1-xO2 species were found to be very active for CO oxidation,and it could act as a channel by which active oxygen species can be transferred from CeO2 to Pd species for CO oxidation.Our results reveal that the preparation method can severely influence the chemical state of Pd which can further determine the activity for CO oxidation.
基金supported by the National Natural Science Foundation of China (No. 20773090, 20803049)the National High Technology Researchand Development Program of China (863 Program, No. 2006AA06Z347)the Specialized Research Fund for the Doctoral Program of Higher Education(20070610026)
文摘Composite supports CeO2-ZrO2-Al2O3（CZA） and CeO2-ZrO2-Al2O3-La2O3（CZALa） were prepared by co-precipitation method. Palladium catalysts were prepared by impregnation and their purification ability for CH4, CO and NOx in the mixture gas simulated the exhaust from natural gas vehicles （NGVs） operated under stoichiometric condition was investigated. The effect of La2O3 on the physicochemical properties of supports and catalysts was characterized by various techniques. The characterizations with X-ray diffraction （XRD） and Raman spectroscopy revealed that the doping of La2O3 restrained effectively the sintering of crystallite particles, maintained the crystallite particles in nanoscale and stabilized the crystal phase after calcination at 1000 ℃. The results of N2-adsorption, H2-temperatnre-programmed reduction （H2-TPR） and oxygen storage capacity （OSC） measurements indicated that La2O3 improved the textural properties, reducibility and OSC of composite supports. Activity testing results showed that the catalysts exhibit excellent activities for the simultaneous removal of methane, CO and NOx in the simulated exhaust gas. The catalysts supported on CZALa showed remarkable thermal stability and catalytic activity for the three pollutants, especially for NOx. The prepared palladium catalysts have high ability to remove NOx, CH4 and CO, and they can be used as excellent catalysts for the purification of exhaust from NGVs operated under stoichiometric condition. The catalysts reported in this work also have significant potential in industrial application because of their high performance and low cost.
基金supported by the Introduction of Talent and Technology Cooperation Plan of Tianjin(14RCGFGX00849)
文摘The influence of sulfation on Pd/Ce0.75Zr0.25O2, Pd/Ce O2-Ti O2 and Pd/Ce O2 was investigated. Physical structure and chemical properties of different catalysts were characterized by N2 adsorption, X-ray diffraction（XRD）, CO chemisorption, X-ray photoelectron spectroscopy（XPS）, Fourier transform infrared spectroscopy（FT-IR） and X-ray fluorescence（XRF）. After 10 h SO2 sulfation, it was found that the decrement on CO oxidation catalytic activity was limited on Pd/Ce0.75Zr0.25O2 compared to Pd/Ce O2-Ti O2 and Pd/Ce O2. It demonstrated that Pd/Ce0.75Zr0.25O2 was more sulfur resistant compared to the other two catalysts. After sulfur exposure, catalyst texture was not much influenced as shown by N2 adsorption and XRD, and surface Pd atoms were poisoned indicated by CO chemisorption results. Pd/Ce0.75Zr0.25O2 and Pd/Ce O2-Ti O2 exhibited less sulfur accumulation compared to Pd/Ce O2 in the sulfation process. Furthermore, XPS results clarified that surface sulfur amount, especially surface sulfates amount on the sulfated catalysts was more crucial for the deactivation in sulfur containing environment.
基金financially supported by the National Natural Science Foundation of China (21776270)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB17020100)+3 种基金China Postdoctoral Science Foundation(2017M621170)DICP Outstanding Postdoctoral Foundation(2017YB02)Liaoning Revitalization Talents Programdedicated funds for methanol conversion from DICP
文摘Heterogenization of the homogeneous catalysis has been studied for almost 50 years.Single-atom catalysis has the advantages of both homo-and heterogeneous catalysis.It has been proposed,and subsequently experimentally verified that single-atom catalysis is able to bridge homo-and heterogeneous catalysis,thus providing a new avenue to realize the heterogenization of homogeneous catalysis.Alkoxycarbonylation of aryl halides is an effective method for the direct synthesis of carboxylic acid derivatives,and is commonly catalyzed by Pd-based homogeneous complexes with N/P-containing ligands and organic/inorganic base.Herein,we firstly reported that Pd1/CeO2 single-atom catalyst showed good performance in the alkoxycarbonylation of aryl iodides reaction.Under base-free and ligand-free conditions,Pd1/CeO2 single-atom catalyst can transfer different aryl iodides to corresponding products.The catalyst can be easily recovered and reused four times without significant loss of reactivity.
