Solids and solutions of sodium phosphates with various chain lengths have been studied by using the techniques of diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and attenuated total reflection-Fou...Solids and solutions of sodium phosphates with various chain lengths have been studied by using the techniques of diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and attenuated total reflection-Fourier transform infrared (ATR-ETIR) spectroscopy, respectively. A systematic study of the infrared spectra of the solid sodium phosphates has been conducted on the basis of the information available it? the literatures to establish the assignments of the infrared vibrations of the different groups in the phosphate molecules. The infrared spectra of the solutions of sodium phosphates have been analyzed according to the infrared study on the relevant solids, in conjunction with the study of the phosphate species distribution in solution on the basis of the acid-base reaction equilibria. The results obtained have revealed the correlations between the infrared absorption spectra and the structure of the different P-O groups in different kinds of phosphates and are useful in the analysis of phosphate solids and solutions widely used in the various operations of mineral processing.展开更多
为了研究纳米γFe2O3催化剂选择性催化还原法（SCR）脱硝反应机理,采用微分反应器测量了纳米γFe2O3催化剂上SCR反应的动力学参数,并构建了SCR反应动力学模型.实验数据分析结果表明,NH3,NO和O2的反应级数分别为0,0.78~0.93和0.09~0.11,...为了研究纳米γFe2O3催化剂选择性催化还原法（SCR）脱硝反应机理,采用微分反应器测量了纳米γFe2O3催化剂上SCR反应的动力学参数,并构建了SCR反应动力学模型.实验数据分析结果表明,NH3,NO和O2的反应级数分别为0,0.78~0.93和0.09~0.11,反应活化能为57.3 k J/mol.原位红外漫反射光谱（DRIFTS）实验结果表明：NH3能够强吸附到催化剂表面并达到饱和,进一步增加NH3的浓度并不能增加NO的转化速率;NO在有氧条件下能吸附到催化剂表面生成吸附态NO2和亚硝酸盐;在低于270℃的情况下SCR反应遵循Langmuir-Hinshelw ood（L-H）反应机理,在高于270℃的情况下则主要遵循Eley-Rideal（E-R）反应机理.展开更多
Cu-TDPAT(H_(6)TDPAT=2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine),a stable nanoporous metal-organic framework with rht topology,has sparked broad interest as an adsorbent for several chemical separation proces...Cu-TDPAT(H_(6)TDPAT=2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine),a stable nanoporous metal-organic framework with rht topology,has sparked broad interest as an adsorbent for several chemical separation processes.In this work,in situ synchrotron diffraction experiments followed by sequential LeBail refinements reveal that Cu-TDPAT shows unusually large anisotropic negative thermal expansion(NTE).The PASCal crystallography tool,used to analyze the magnitude of the NTE,reveals an average volumetric thermal expansion coefficientαv=-20.3 MK^(-1).This value is significantly higher than the one reported for Cu-BTC(also known as HKUST-1),which contains the same Cu-paddlewheel building unit,αv=-12 MK^(-1).In situ synchrotron single crystal X-ray diffraction and in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)were employed to shed light on the NTE mechanism.Using these two methods,we were able to elucidate the three main structural motions that are responsible for the NTE effect.The more pronounced NTE behavior of Cu-TDPAT is attributed to the lower symmetry combined with the more complex ligand structure when compared to Cu-BTC.The knowledge obtained in this work is important for understanding the behavior of the adsorbent under transient variable temperature conditions in fixed adsorption beds.展开更多
La_(1-x)CoO_(3-δ)catalysts with different non-stoichiometry of lanthanum ions were synthesized by using the sol-gel method,and their catalytic performance in toluene combustion was investigated.The results showed tha...La_(1-x)CoO_(3-δ)catalysts with different non-stoichiometry of lanthanum ions were synthesized by using the sol-gel method,and their catalytic performance in toluene combustion was investigated.The results showed that the catalytic activity and stability of A-site nonstoichiometric La_(1-x)CoO_(3-δ)were improved to a certain extent compared with pure LaCoO_(3)perovskite.Among them,the La_(0.9)CoO_(3-δ)catalyst gave the best catalytic performance for toluene oxidation.It achieved 90%toluene conversion at 205℃under the conditions of a WHSV(weight hourly space velocity)of 22,500 mL/(g·hr)and a 500 ppmV-toluene concentration.Various characterization techniques were used to investigate the relationship between the structure of these catalysts and their catalytic performance.It was found that the non-stoichiometric modification of the lanthanum ion at position A in LaCoO_(3)changed the surface element state of the catalyst and increased the oxygen vacancy content,thus,combined with improved reducibility,improving toluene degradation on the catalyst.展开更多
Series of Cu-USY zeolite catalyst with different Cu loading content were synthesized through simple impregnation method.The obtained catalysts were subjected to selective catalytic reduction of NOxwith NH_(3)(NH_(3)-S...Series of Cu-USY zeolite catalyst with different Cu loading content were synthesized through simple impregnation method.The obtained catalysts were subjected to selective catalytic reduction of NOxwith NH_(3)(NH_(3)-SCR) performance evaluation,structural/chemical characterizations such as X-ray diffraction (XRD),N2adsorption/desorption,H_(2)temperature-programmed reduction (H_(2)-TPR),NH_(3)temperature-programmed desorption (NH_(3)-TPD) as well as detailed in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments including CO adsorption,NH_(3)adsorption and NO+O_(2)in situ reactions.Results show that Cu-USY with proper Cu loading (in this work 5Cu-USY with5 wt.%Cu) could be promising candidates with highly efficient NH_(3)-SCR catalytic performance,relatively low byproduct formation and excellent hydrothermal stability,although its SO_(2)poisoning tolerability needs alleviation.Further characterizations reveal that such catalytic advantages can be attributed to both active cu species and surface acid centers evolution modulated by Cu loading.On one hand,Cu species in the super cages of zeolites increases with higher Cu content and being more conducive for NH_(3)-SCR reactivity.On the other hand,higher Cu loading leads to depletion of Br?nsted acid centers and simultaneous formation of abundant Lewis acid centers,which facilitates NH_(4)NO_(3)reduction via NH_(3)adsorbed on Lewis acid centers,thus improving SCR reactivity.However,Cu over-introduction leads to formation of surface highly dispersed CuOx,causing unfavorable NH_(3)oxidation and inferior N2selectivity.展开更多
Copper-cerium-zirconium catalysts loaded on Ti02 prepared by a wet impregnation method were investigated for NHz-selective catalytic reduction （SCR） of NOx. The reaction mechanism was proposed on the basis of result...Copper-cerium-zirconium catalysts loaded on Ti02 prepared by a wet impregnation method were investigated for NHz-selective catalytic reduction （SCR） of NOx. The reaction mechanism was proposed on the basis of results from in situ diffuse reflectance infrared transform spectroscopy （DRIFT）. When NH3 is introduced, ammonia bonded to Lewis acid sites is more stable over CuCe0.25Zr0.75/TiO2 at high temperature, while Brensted acid sites are more important than Lewis acid sites at low temperature. For the NH3＋NO＋O2 co-adsorption, NH3 species occupy most of activity sites on CuCe0.25Zr0.75/TiO2 catalyst, and mainly exist in the forms of NH4＋ （at low temperature） and NH3 coordinated （at high temperature）, playing a crucial role in the NHz-SCR process. Two different reaction routes, the L-H mechanism at low temperature （〈 200℃） and the E-R mechanism at high temperature （〉200℃）, are presented for the SCR reaction over C uCe0.25Zr0.75/TiO2 catalyst.展开更多
To understand how NO2 reacts with sea salt particles in the atmosphere of Mega-cities in coastal zones,the heterogeneous reaction of NO2 on the surface of wet sea salt was investigated with diffuse reflectance infrare...To understand how NO2 reacts with sea salt particles in the atmosphere of Mega-cities in coastal zones,the heterogeneous reaction of NO2 on the surface of wet sea salt was investigated with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and ion chromatography (IC).Kinetic measurements indicated that nitrate formation on sea salt was second order in NO 2 concentration and reactive uptake coefficients were (5.51 ± 0.19) × 10-7 and 1.26 × 10-6 respectively under 0% and 20% relative humidity (RH) at NO 2 molecular concentration of 1.96 × 1015 mol/cm3.The results showed that liquid water was formed at the site of MgCl2·6H2O,CaCl2·2H2O on the surface of sea salt and made the reaction more sustainable by releasing hydrated water and absorbing water from air even under a low RH (30%).Therefore,pure NaCl particles should not be used to represent sea salt in studies of the heterogeneous reaction with NO2.展开更多
A series of Pd/Co_3O_4 catalysts were prepared by Self-Propagating High-Temperature Synthesis(SHS)method in this study, and electric field was applied for catalytic combustion of lean methane over Pd/Co_3O_4 catalysts...A series of Pd/Co_3O_4 catalysts were prepared by Self-Propagating High-Temperature Synthesis(SHS)method in this study, and electric field was applied for catalytic combustion of lean methane over Pd/Co_3O_4 catalysts at low temperature. When electric field was applied, the catalytic combustion performance of Pd/Co_3O_4 catalysts was greatly improved, and the application of electric field could reduce the load of active element Pd to some extent while maintaining the same efficiency. Based on experimental tests and the analysis results of X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), H2-temperature-programmed reduction(H2-TPR) and in-situ diffuse reflectance infrared Fourier transform spectroscopy(in-situ DRIFTS), the mechanism of catalytic oxidation of CH_4 over Pd/Co_3O_4 catalysts in electric field was proposed. The catalytic combustion of CH_4 occurs only when the temperature is higher than 250?C normally, but when electric field was applied, the whole process of CH_4 oxidation was promoted significantly and the reaction temperature was reduced. Electric field could promote the reduction of the support Co_3O_4 to release the lattice oxygen, resulting in the increase of PdOxand the surface chemisorbed oxygen, which could provide more active sites for the low-temperature oxidation of CH_4. Furthermore, electric field could accelerate the dehydroxylation of CoOOH to further enhance the activity of the catalysts.展开更多
Well-defined surface structures and uniformity are key factors in exploring structure–activity relationships in heterogeneous catalysts.A modified atomic layer deposition method and three well-defined CeO_(2) nanosha...Well-defined surface structures and uniformity are key factors in exploring structure–activity relationships in heterogeneous catalysts.A modified atomic layer deposition method and three well-defined CeO_(2) nanoshapes,octahedra with(111)surfaces,cubes exposing(100)facets,and rods with(100)and(110)surface facet terminations,were utilized to synthesize ultra-low loading Pt/CeO_(2) catalysts and allow investigations on the influence of ceria surface facet on isolated Pt species under reducing conditions.A mild reduction temperature(150℃)reduces the initial platinum ions present on the surfaces of the ceria support but preserves the isolated Pt atoms on all ceria surface facets.In contrast,a reduction temperature of 350°C,reveals very different interactions between the initial single Pt atoms and the various ceria surface facets,leading to dissimilar and nonuniform Pt ensembles on the three ceria shapes.To isolate facet dependent Pt–CeO_(2) interactions and avoid variations between Pt species,the Pt1/CeO_(2) catalysts after reduction at 150°C were subjected to CO oxidation conditions.The isolated Pt atoms on the CeO_(2) octahedra and cubes are less active in the CO oxidation reaction,compared with Pt on CeO_(2) rods.In the case of Pt on the CeO_(2) octahedra this is due to strongly bound CO blocking active sites together with a stable CeO_(2)(111)surface limiting the oxygen supply from the support.On the CeO_(2) cubes,some Pt is not available for reaction and CO is bound strongly on the available Pt species.In addition,the Pt catalysts supported on the CeO_(2) cubes are not stable with time on stream.The isolated Pt atoms on the CeO_(2) rods are considerably more active under these conditions and this is due to a weaker Pt–CO bond strength and more facile reverse oxygen spillover from the defect-rich(110)surfaces of the rods due to the lower energy of oxygen vacancy formation on this CeO_(2) surface.The Pt supported on the CeO_(2) rods is also remarkably stable with time on stream.This work demonstrates the importance of using ultra-low loadings of active metal and well-defined oxide supports to isolate interactions between single metal atoms and oxide supports and determine the effects of the oxide support surface facet on the active metal at the atomic level.展开更多
CuCeZrO_x and KCuCeZrO_x catalysts were synthesized and coated on the blank diesel particulate filter(DPF)substrate and a particulate matter(PM)loading apparatus was used for soot loading.The catalytic performances of...CuCeZrO_x and KCuCeZrO_x catalysts were synthesized and coated on the blank diesel particulate filter(DPF)substrate and a particulate matter(PM)loading apparatus was used for soot loading.The catalytic performances of soot oxidation were evaluated by temperature programmed combustion(TPC)test and characterization tests were conducted to investigate the physicochemical properties of the catalysts.The reaction mechanism in the oxidation process was analyzed with diffuse reflectance infrared Fourier transform spectroscopy.The results demonstrated that CuCeZrO_x catalyst exhibited high activities of soot oxidation at low temperature and the best results have been attained with Cu_(0.9)Ce_(0.05)Zr_(0.05)O_x over which the maximum soot oxidation rate decreased to 410~?C.Characterization tests have shown that catalysts containing 90%Cu have uniformly distributed grains and small particle sizes,which provide excellent oxidation activity by providing more active sites and forming a good bond between the catalyst and the soot.The low-temperature oxidation activity of soot could be further optimized due to the excellent elevated NO’s conversion rate by partially substituting Cu with K.The maximum particle oxidation rate can be easily realized at such a low temperature as 347~?C.展开更多
文摘Solids and solutions of sodium phosphates with various chain lengths have been studied by using the techniques of diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and attenuated total reflection-Fourier transform infrared (ATR-ETIR) spectroscopy, respectively. A systematic study of the infrared spectra of the solid sodium phosphates has been conducted on the basis of the information available it? the literatures to establish the assignments of the infrared vibrations of the different groups in the phosphate molecules. The infrared spectra of the solutions of sodium phosphates have been analyzed according to the infrared study on the relevant solids, in conjunction with the study of the phosphate species distribution in solution on the basis of the acid-base reaction equilibria. The results obtained have revealed the correlations between the infrared absorption spectra and the structure of the different P-O groups in different kinds of phosphates and are useful in the analysis of phosphate solids and solutions widely used in the various operations of mineral processing.
文摘为了研究纳米γFe2O3催化剂选择性催化还原法（SCR）脱硝反应机理,采用微分反应器测量了纳米γFe2O3催化剂上SCR反应的动力学参数,并构建了SCR反应动力学模型.实验数据分析结果表明,NH3,NO和O2的反应级数分别为0,0.78~0.93和0.09~0.11,反应活化能为57.3 k J/mol.原位红外漫反射光谱（DRIFTS）实验结果表明：NH3能够强吸附到催化剂表面并达到饱和,进一步增加NH3的浓度并不能增加NO的转化速率;NO在有氧条件下能吸附到催化剂表面生成吸附态NO2和亚硝酸盐;在低于270℃的情况下SCR反应遵循Langmuir-Hinshelw ood（L-H）反应机理,在高于270℃的情况下则主要遵循Eley-Rideal（E-R）反应机理.
基金National Defense Basic Research Program of China(613142020201)Scientific and Technological Research and Development Foundation of Shenzhen City(JCYJ20140418193546111)
基金the Swiss National Science Foundation under Grant PYAPP2_160581.M.A.acknowledges the Swiss Commission for Technology and Innovation(CTI)(the SCCER EIP-Efflciency of Industrial Processes)for financial support.We also acknowledge the Swiss-Norwegian Beam Line BM01 at European Synchrotron Radiation Facility(ESRF)for the beamtime allocation and Dr.D m itry Chernyshov,Dr.Iurii Dovgaliuk,Dr.Olga Trukhina and Mr.Vikram Karve for the assistance on the beamline,BM01.M.A.also thanks Dr.Pascal Schouwink for assistance on X-ray diffraction experiments at EPFL Valais.
文摘Cu-TDPAT(H_(6)TDPAT=2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine),a stable nanoporous metal-organic framework with rht topology,has sparked broad interest as an adsorbent for several chemical separation processes.In this work,in situ synchrotron diffraction experiments followed by sequential LeBail refinements reveal that Cu-TDPAT shows unusually large anisotropic negative thermal expansion(NTE).The PASCal crystallography tool,used to analyze the magnitude of the NTE,reveals an average volumetric thermal expansion coefficientαv=-20.3 MK^(-1).This value is significantly higher than the one reported for Cu-BTC(also known as HKUST-1),which contains the same Cu-paddlewheel building unit,αv=-12 MK^(-1).In situ synchrotron single crystal X-ray diffraction and in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)were employed to shed light on the NTE mechanism.Using these two methods,we were able to elucidate the three main structural motions that are responsible for the NTE effect.The more pronounced NTE behavior of Cu-TDPAT is attributed to the lower symmetry combined with the more complex ligand structure when compared to Cu-BTC.The knowledge obtained in this work is important for understanding the behavior of the adsorbent under transient variable temperature conditions in fixed adsorption beds.
基金support from National Key Research and Development Program of China(No.2019YFC1903903)the National Natural Science Foundation of China(No.21876019)+1 种基金Fundamental Research Funds for the Central Universities(No.DUT20RC(4)003)Natural Science Foundation of Liaoning Province(No.2020-BS-056).
文摘La_(1-x)CoO_(3-δ)catalysts with different non-stoichiometry of lanthanum ions were synthesized by using the sol-gel method,and their catalytic performance in toluene combustion was investigated.The results showed that the catalytic activity and stability of A-site nonstoichiometric La_(1-x)CoO_(3-δ)were improved to a certain extent compared with pure LaCoO_(3)perovskite.Among them,the La_(0.9)CoO_(3-δ)catalyst gave the best catalytic performance for toluene oxidation.It achieved 90%toluene conversion at 205℃under the conditions of a WHSV(weight hourly space velocity)of 22,500 mL/(g·hr)and a 500 ppmV-toluene concentration.Various characterization techniques were used to investigate the relationship between the structure of these catalysts and their catalytic performance.It was found that the non-stoichiometric modification of the lanthanum ion at position A in LaCoO_(3)changed the surface element state of the catalyst and increased the oxygen vacancy content,thus,combined with improved reducibility,improving toluene degradation on the catalyst.
基金supported by the Key Program of Science Technology Department of Zhejiang Province (No.2018C03037)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (No.20KJB610005)+2 种基金the Natural Science Foundation of Jiangsu Province (Nos.BK20201037,BK20190705)Key Research and Development Program of Anhui Province (No.202104g01020006)the Scientific Research Fund of Nanjing Institute of Technology (Nos.YKJ2019111 and YKJ2019110)。
文摘Series of Cu-USY zeolite catalyst with different Cu loading content were synthesized through simple impregnation method.The obtained catalysts were subjected to selective catalytic reduction of NOxwith NH_(3)(NH_(3)-SCR) performance evaluation,structural/chemical characterizations such as X-ray diffraction (XRD),N2adsorption/desorption,H_(2)temperature-programmed reduction (H_(2)-TPR),NH_(3)temperature-programmed desorption (NH_(3)-TPD) as well as detailed in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments including CO adsorption,NH_(3)adsorption and NO+O_(2)in situ reactions.Results show that Cu-USY with proper Cu loading (in this work 5Cu-USY with5 wt.%Cu) could be promising candidates with highly efficient NH_(3)-SCR catalytic performance,relatively low byproduct formation and excellent hydrothermal stability,although its SO_(2)poisoning tolerability needs alleviation.Further characterizations reveal that such catalytic advantages can be attributed to both active cu species and surface acid centers evolution modulated by Cu loading.On one hand,Cu species in the super cages of zeolites increases with higher Cu content and being more conducive for NH_(3)-SCR reactivity.On the other hand,higher Cu loading leads to depletion of Br?nsted acid centers and simultaneous formation of abundant Lewis acid centers,which facilitates NH_(4)NO_(3)reduction via NH_(3)adsorbed on Lewis acid centers,thus improving SCR reactivity.However,Cu over-introduction leads to formation of surface highly dispersed CuOx,causing unfavorable NH_(3)oxidation and inferior N2selectivity.
文摘Copper-cerium-zirconium catalysts loaded on Ti02 prepared by a wet impregnation method were investigated for NHz-selective catalytic reduction （SCR） of NOx. The reaction mechanism was proposed on the basis of results from in situ diffuse reflectance infrared transform spectroscopy （DRIFT）. When NH3 is introduced, ammonia bonded to Lewis acid sites is more stable over CuCe0.25Zr0.75/TiO2 at high temperature, while Brensted acid sites are more important than Lewis acid sites at low temperature. For the NH3＋NO＋O2 co-adsorption, NH3 species occupy most of activity sites on CuCe0.25Zr0.75/TiO2 catalyst, and mainly exist in the forms of NH4＋ （at low temperature） and NH3 coordinated （at high temperature）, playing a crucial role in the NHz-SCR process. Two different reaction routes, the L-H mechanism at low temperature （〈 200℃） and the E-R mechanism at high temperature （〉200℃）, are presented for the SCR reaction over C uCe0.25Zr0.75/TiO2 catalyst.
基金supported by the National Natural Science Foundation of China(20637020,40490265 & 20077001)National Basic Research Program of China(2002CB410802)special fund of State Key Joint Laboratory of Environment Simulation and Pollution Control
文摘To understand how NO2 reacts with sea salt particles in the atmosphere of Mega-cities in coastal zones,the heterogeneous reaction of NO2 on the surface of wet sea salt was investigated with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and ion chromatography (IC).Kinetic measurements indicated that nitrate formation on sea salt was second order in NO 2 concentration and reactive uptake coefficients were (5.51 ± 0.19) × 10-7 and 1.26 × 10-6 respectively under 0% and 20% relative humidity (RH) at NO 2 molecular concentration of 1.96 × 1015 mol/cm3.The results showed that liquid water was formed at the site of MgCl2·6H2O,CaCl2·2H2O on the surface of sea salt and made the reaction more sustainable by releasing hydrated water and absorbing water from air even under a low RH (30%).Therefore,pure NaCl particles should not be used to represent sea salt in studies of the heterogeneous reaction with NO2.
基金the National Key R&D Program of China(No.2016YFC0208000)the National Natural Science Foundation of China(No.51676127)
文摘A series of Pd/Co_3O_4 catalysts were prepared by Self-Propagating High-Temperature Synthesis(SHS)method in this study, and electric field was applied for catalytic combustion of lean methane over Pd/Co_3O_4 catalysts at low temperature. When electric field was applied, the catalytic combustion performance of Pd/Co_3O_4 catalysts was greatly improved, and the application of electric field could reduce the load of active element Pd to some extent while maintaining the same efficiency. Based on experimental tests and the analysis results of X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), H2-temperature-programmed reduction(H2-TPR) and in-situ diffuse reflectance infrared Fourier transform spectroscopy(in-situ DRIFTS), the mechanism of catalytic oxidation of CH_4 over Pd/Co_3O_4 catalysts in electric field was proposed. The catalytic combustion of CH_4 occurs only when the temperature is higher than 250?C normally, but when electric field was applied, the whole process of CH_4 oxidation was promoted significantly and the reaction temperature was reduced. Electric field could promote the reduction of the support Co_3O_4 to release the lattice oxygen, resulting in the increase of PdOxand the surface chemisorbed oxygen, which could provide more active sites for the low-temperature oxidation of CH_4. Furthermore, electric field could accelerate the dehydroxylation of CoOOH to further enhance the activity of the catalysts.
基金supported by the National Science Foundation(NSF)(CHE-1507230 and CBET-1933723)the National High Magnetic Field Laboratory,which is supported by the NSF Cooperative Agreement(DMR-1644779)and the State of Florida.Startup funding from the University of Florida is also gratefully acknowledged.
文摘Well-defined surface structures and uniformity are key factors in exploring structure–activity relationships in heterogeneous catalysts.A modified atomic layer deposition method and three well-defined CeO_(2) nanoshapes,octahedra with(111)surfaces,cubes exposing(100)facets,and rods with(100)and(110)surface facet terminations,were utilized to synthesize ultra-low loading Pt/CeO_(2) catalysts and allow investigations on the influence of ceria surface facet on isolated Pt species under reducing conditions.A mild reduction temperature(150℃)reduces the initial platinum ions present on the surfaces of the ceria support but preserves the isolated Pt atoms on all ceria surface facets.In contrast,a reduction temperature of 350°C,reveals very different interactions between the initial single Pt atoms and the various ceria surface facets,leading to dissimilar and nonuniform Pt ensembles on the three ceria shapes.To isolate facet dependent Pt–CeO_(2) interactions and avoid variations between Pt species,the Pt1/CeO_(2) catalysts after reduction at 150°C were subjected to CO oxidation conditions.The isolated Pt atoms on the CeO_(2) octahedra and cubes are less active in the CO oxidation reaction,compared with Pt on CeO_(2) rods.In the case of Pt on the CeO_(2) octahedra this is due to strongly bound CO blocking active sites together with a stable CeO_(2)(111)surface limiting the oxygen supply from the support.On the CeO_(2) cubes,some Pt is not available for reaction and CO is bound strongly on the available Pt species.In addition,the Pt catalysts supported on the CeO_(2) cubes are not stable with time on stream.The isolated Pt atoms on the CeO_(2) rods are considerably more active under these conditions and this is due to a weaker Pt–CO bond strength and more facile reverse oxygen spillover from the defect-rich(110)surfaces of the rods due to the lower energy of oxygen vacancy formation on this CeO_(2) surface.The Pt supported on the CeO_(2) rods is also remarkably stable with time on stream.This work demonstrates the importance of using ultra-low loadings of active metal and well-defined oxide supports to isolate interactions between single metal atoms and oxide supports and determine the effects of the oxide support surface facet on the active metal at the atomic level.
基金the National Key R&D Program of China(Nos.2016YFC0205200 and 2016YFC0208000)the National Natural Science Foundation of China(No.51676127)
文摘CuCeZrO_x and KCuCeZrO_x catalysts were synthesized and coated on the blank diesel particulate filter(DPF)substrate and a particulate matter(PM)loading apparatus was used for soot loading.The catalytic performances of soot oxidation were evaluated by temperature programmed combustion(TPC)test and characterization tests were conducted to investigate the physicochemical properties of the catalysts.The reaction mechanism in the oxidation process was analyzed with diffuse reflectance infrared Fourier transform spectroscopy.The results demonstrated that CuCeZrO_x catalyst exhibited high activities of soot oxidation at low temperature and the best results have been attained with Cu_(0.9)Ce_(0.05)Zr_(0.05)O_x over which the maximum soot oxidation rate decreased to 410~?C.Characterization tests have shown that catalysts containing 90%Cu have uniformly distributed grains and small particle sizes,which provide excellent oxidation activity by providing more active sites and forming a good bond between the catalyst and the soot.The low-temperature oxidation activity of soot could be further optimized due to the excellent elevated NO’s conversion rate by partially substituting Cu with K.The maximum particle oxidation rate can be easily realized at such a low temperature as 347~?C.
