CeO_(2)-based catalysts are promising for use in various important chemical reactions involving CO_(2),such as the dry reforming of methane to produce synthesis gas and methanol.CeO_(2)has a superior ability to store ...CeO_(2)-based catalysts are promising for use in various important chemical reactions involving CO_(2),such as the dry reforming of methane to produce synthesis gas and methanol.CeO_(2)has a superior ability to store and release oxygen,which can improve the catalytic performance by suppressing the formation of coke.Although the adsorption and activation behavior of CO_(2)on the CeO_(2)surface has been extensively investigated in recent years,the intermediate species formed from CO_(2)on ceria has not been clearly identified.The reactivity of the ceria surface to CO_(2)has been reported to be tuned by introducing CaO,which increases the number of basic sites for the ceria-based catalysts.However,the mechanism by which Ca^2+ions affect CO_(2)decomposition is still debated.In this study,the morphologies and electronic properties of stoichiometric CeO_(2)(111),partially reduced CeO_(2)?x(111)(0<x<0.5),and calcium-doped ceria model catalysts,as well as their interactions with CO_(2),were investigated by scanning tunneling microscopy(STM),X-ray photoelectron spectroscopy,and synchrotron radiation photoemission spectroscopy.Stoichiometric CeO_(2)(111)and partially reduced CeO_(2)?x(111)films were epitaxially grown on a Cu(111)surface.STM images show that the stoichiometric CeO_(2)film exhibits large,flat terraces that completely cover the Cu(111)surface.The reduced CeO_(2)-x film also has a flat surface and an ordered structure,but dark spaces are observed on the film.Different Ca-doped ceria films were prepared by physical vapor deposition of metallic Ca on CeO_(2)(111)at room temperature and subsequent annealing to 600 or 800 K in ultrahigh vacuum.The different preparation procedures produce samples with various surface components,oxidation states,and structures.Our results indicate that the deposition of metallic Ca on CeO_(2)at room temperature leads to a partial reduction of Ce from the+4 to the+3 state,accompanied by the oxidation of Ca to Ca^2+.Large CaO nanofilms are observed on CeO_(2)upon annealing to 600 K.However,small CaO nanoislands appear near the step edges and more Ca2+ions migrate into the subsurface of CeO_(2)upon annealing to 800 K.In addition,different surface-adsorbed species are identified after CO_(2)adsorption on ceria(CeO_(2)and reduced CeO_(2)-x)and Ca-doped ceria films.CO_(2)adsorption on the stoichiometric CeO_(2)and partially reduced CeO_(2)?x surfaces leads to the formation of surface carboxylate.Moreover,the surface carboxylate species is more easily formed on reduced CeO_(2)-x with enhanced thermal stability than on stoichiometric CeO_(2).On Ca-doped ceria films,the presence of Ca^2+ions is observed to be beneficial for CO_(2)adsorption;further,the carbonate species is identified.展开更多
At the invitation of the International Initiatives of Change Association of Japan （IICAJ）, a 4-member delegation of the Chinese Association for International Understanding （CAFIU） visited Japan and was cordially r...At the invitation of the International Initiatives of Change Association of Japan （IICAJ）, a 4-member delegation of the Chinese Association for International Understanding （CAFIU） visited Japan and was cordially received.展开更多
The preparation of SmOx/Rh(100) and CO adsorption on this model surface have been investigated with Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption spect...The preparation of SmOx/Rh(100) and CO adsorption on this model surface have been investigated with Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption spectroscopy (TDS). The oxygen adsorption on the SmRh alloy surface leads to the aggregation of Sm on the surface. The thermal treatment of this oxidized surface induces the further agglomeration of SmOx on the Rh(100) surface. Compared with CO TDS on the clean Rh(100) surface, three additional CO desorption peaks can be observed at 176,331 and 600 K on the SmOx/Rh(100) surface. The CO desorption peak at 176 K may originate from CO adsorbed on SmOx islands, while the appearance of the CO adsorption peaks at 331 and 600 K, depending on the oxidation state of Sm, is attributed to CO species located at the interface of SmOx/Rh(100).展开更多
We report our investigation of the interaction of NO2 with the Au(997)vicinal surface by high-resolution photoelectron spectroscopy using synchrotron radiation as the excitation source.At 170 K,both core-level and val...We report our investigation of the interaction of NO2 with the Au(997)vicinal surface by high-resolution photoelectron spectroscopy using synchrotron radiation as the excitation source.At 170 K,both core-level and valence-band photoemission results illustrate the decomposition of NO2 on the Au(997)surface at low NO2 exposures,forming coadsorbed NO(a)and O(a)species.After annealing at 300 K,NO(a)desorbs from Au(997)whereas O(a)remains on the surface.Upon annealing at 750 K,we observe no signal for adsorbed oxygen on Au(997).These results clearly demonstrate that thermal decomposition of NO2 is an effective method to generate oxygen adatoms on Au(997)under ultrahigh-vacuum conditions.展开更多
文摘CeO_(2)-based catalysts are promising for use in various important chemical reactions involving CO_(2),such as the dry reforming of methane to produce synthesis gas and methanol.CeO_(2)has a superior ability to store and release oxygen,which can improve the catalytic performance by suppressing the formation of coke.Although the adsorption and activation behavior of CO_(2)on the CeO_(2)surface has been extensively investigated in recent years,the intermediate species formed from CO_(2)on ceria has not been clearly identified.The reactivity of the ceria surface to CO_(2)has been reported to be tuned by introducing CaO,which increases the number of basic sites for the ceria-based catalysts.However,the mechanism by which Ca^2+ions affect CO_(2)decomposition is still debated.In this study,the morphologies and electronic properties of stoichiometric CeO_(2)(111),partially reduced CeO_(2)?x(111)(0<x<0.5),and calcium-doped ceria model catalysts,as well as their interactions with CO_(2),were investigated by scanning tunneling microscopy(STM),X-ray photoelectron spectroscopy,and synchrotron radiation photoemission spectroscopy.Stoichiometric CeO_(2)(111)and partially reduced CeO_(2)?x(111)films were epitaxially grown on a Cu(111)surface.STM images show that the stoichiometric CeO_(2)film exhibits large,flat terraces that completely cover the Cu(111)surface.The reduced CeO_(2)-x film also has a flat surface and an ordered structure,but dark spaces are observed on the film.Different Ca-doped ceria films were prepared by physical vapor deposition of metallic Ca on CeO_(2)(111)at room temperature and subsequent annealing to 600 or 800 K in ultrahigh vacuum.The different preparation procedures produce samples with various surface components,oxidation states,and structures.Our results indicate that the deposition of metallic Ca on CeO_(2)at room temperature leads to a partial reduction of Ce from the+4 to the+3 state,accompanied by the oxidation of Ca to Ca^2+.Large CaO nanofilms are observed on CeO_(2)upon annealing to 600 K.However,small CaO nanoislands appear near the step edges and more Ca2+ions migrate into the subsurface of CeO_(2)upon annealing to 800 K.In addition,different surface-adsorbed species are identified after CO_(2)adsorption on ceria(CeO_(2)and reduced CeO_(2)-x)and Ca-doped ceria films.CO_(2)adsorption on the stoichiometric CeO_(2)and partially reduced CeO_(2)?x surfaces leads to the formation of surface carboxylate.Moreover,the surface carboxylate species is more easily formed on reduced CeO_(2)-x with enhanced thermal stability than on stoichiometric CeO_(2).On Ca-doped ceria films,the presence of Ca^2+ions is observed to be beneficial for CO_(2)adsorption;further,the carbonate species is identified.
文摘At the invitation of the International Initiatives of Change Association of Japan （IICAJ）, a 4-member delegation of the Chinese Association for International Understanding （CAFIU） visited Japan and was cordially received.
基金This work was supported by the National Natural Science Foundation of China (Grant No. 29873042)the State Key Laboratory of Catalysis+1 种基金 Dalian Institute of Chemical Physicsthe Chinese Academy of Sciences.
文摘The preparation of SmOx/Rh(100) and CO adsorption on this model surface have been investigated with Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption spectroscopy (TDS). The oxygen adsorption on the SmRh alloy surface leads to the aggregation of Sm on the surface. The thermal treatment of this oxidized surface induces the further agglomeration of SmOx on the Rh(100) surface. Compared with CO TDS on the clean Rh(100) surface, three additional CO desorption peaks can be observed at 176,331 and 600 K on the SmOx/Rh(100) surface. The CO desorption peak at 176 K may originate from CO adsorbed on SmOx islands, while the appearance of the CO adsorption peaks at 331 and 600 K, depending on the oxidation state of Sm, is attributed to CO species located at the interface of SmOx/Rh(100).
基金supported by the National Natural Science Foundation of China(20803072,20973161)National Basic Research Program of China(2010CB923302)the MPG-CAS partner group program
文摘We report our investigation of the interaction of NO2 with the Au(997)vicinal surface by high-resolution photoelectron spectroscopy using synchrotron radiation as the excitation source.At 170 K,both core-level and valence-band photoemission results illustrate the decomposition of NO2 on the Au(997)surface at low NO2 exposures,forming coadsorbed NO(a)and O(a)species.After annealing at 300 K,NO(a)desorbs from Au(997)whereas O(a)remains on the surface.Upon annealing at 750 K,we observe no signal for adsorbed oxygen on Au(997).These results clearly demonstrate that thermal decomposition of NO2 is an effective method to generate oxygen adatoms on Au(997)under ultrahigh-vacuum conditions.
