Chemical-looping oxidative dehydrogenation(CL-ODH)is a process designed for the conversion of alkanes into olefins through cyclic redox reactions,eliminating the need for gaseous O_(2).In this work,we investigated the...Chemical-looping oxidative dehydrogenation(CL-ODH)is a process designed for the conversion of alkanes into olefins through cyclic redox reactions,eliminating the need for gaseous O_(2).In this work,we investigated the use of Ca_(2)MnO_(4)-layered perovskites modified with NaNO_(3) dopants,serving as redox catalysts(also known as oxygen carriers),for the CL-ODH of ethane within a temperature range of 700-780℃.Our findings revealed that the incorporation of NaNO_(3) as a modifier significantly-nhanced the selectivity for-thylene generation from Ca_(2)MnO_(4).At 750℃and a gas hourly space velocity of 1300 h^(-1),we achieved an-thane conversion up to 68.17%,accompanied by a corresponding-thylene yield of 57.39%.X-ray photoelectron spectroscopy analysis unveiled that the doping NaNO_(3) onto Ca_(2)MnO_(4) not only played a role in reducing the oxidation state of Mn ions but also increased the lattice oxygen content of the redox catalyst.Furthermore,formation of NaNO_(3) shell on the surface of Ca_(2)MnO_(4) led to a reduction in the concentration of manganese sites and modulated the oxygen-releasing behavior in a step-wise manner.This modulation contributed significantly to the enhanced selectivity for ethylene of the NaNO_(3)-doped Ca_(2)MnO_(4) catalyst.These findings provide compelling evidence for the potential of Ca_(2)MnO_(4)-layered perovskites as promising redox catalysts in the context of CL-ODH reactions.展开更多
A series of monolithic MnO_(2)/iron mesh (IM) catalysts for oxidation of toluene were successfully prepared by using in situ hydrothermal growth.MnO_(2)can grow firmly on the IM substrates surface with a shedding rate...A series of monolithic MnO_(2)/iron mesh (IM) catalysts for oxidation of toluene were successfully prepared by using in situ hydrothermal growth.MnO_(2)can grow firmly on the IM substrates surface with a shedding rate of only 0.14%.Due to the highest O_(ads) and high-valent Mn^(4+) and Fe^(3+) elements,the temperature at 50% and 90% toluene conversion (T_(50%) and T_(90%)) was 252 and 265℃,respectively for the best performance catalyst (hydrothermal temperature of 80℃,hydrothermal time of 12 h,and precursor manganese ion concentration of 0.03 mol/L).The catalysts also presented good water resistance and cycle performance.In-situ DRIFTS results suggesting that toluene was first rapid transformed into the reaction intermediate species (benzoate species) and then converted to CO_(2)and H_(2)O.Therefore,this work provides a new direction for the research and application of IM-based monolithic catalysts.展开更多
The performance of catalysts used in after-treatment systems is the key factor for the removal of diesel soot,which is an important component of atmosphericfine particle emissions.Herein,three-dimensionally ordered ma...The performance of catalysts used in after-treatment systems is the key factor for the removal of diesel soot,which is an important component of atmosphericfine particle emissions.Herein,three-dimensionally ordered macroporous–mesoporous Ti_(x)Si+(1-x)O_(2)(3DOM-m Ti_(x)Si+(1-x)O_(2)) and its supported MnO_(x)catalysts doped with different alkali/alkaline-earth metals (AMnO_(x)/3 DOM-m Ti_(0.7)Si_(0.3)O_(2)(A:Li,Na,K,Ru,Cs,Mg,Ca,Sr,Ba)) were prepared by mesoporous template (P123)-assisted colloidal crystal template (CCT) and incipient wetness impregnation methods,respectively.Physicochemical characterizations of the catalysts were performed using scanning electron microscopy,X-ray diffraction,N_(2)adsorption–desorption,H_(2)temperature-programmed reduction,O_(2)temperature-programmed desorption,NO temperature-programmed oxidation,and Raman spectroscopy techniques;then,we evaluated their catalytic performances for the removal of diesel soot particles.The results show that the 3DOM-m Ti_(0.7)Si_(0.3)O_(2)supports exhibited a well-defined 3DOM-m nanostructure,and AMnO_(x)nanoparticles with 10–50 nm were evenly dispersed on the inner walls of the uniform macropores.In addition,the as-prepared catalysts exhibited good catalytic performance for soot combustion.Among the prepared catalysts,CsMnO_(x)/3DOM-m Ti_(0.7)Si_(0.3)O_(2)had the highest catalytic activity for soot combustion,with T10,T50,and T90(the temperatures corresponding to soot conversion rates of 10%,50%,and 90%) values of 285,355,and 393℃,respectively.The high catalytic activity of the CsMnO_(x)/3 DOM-m Ti_(0.7)Si_(0.3)O_(2)catalysts was attributed to their excellent low-temperature reducibility and homogeneous macroporous–mesoporous structure,as well as to the synergistic effects between Cs and Mn species and between CsMnO_(x)and the Ti_(0.7)Si_(0.3)O_(2)support.展开更多
Mn-based catalysts have exhibited promising performance in low-temperature selective catalytic reduction of NOx with NH_(3)(NH_(3)-SCR).However,challenges such as H_(2)O-or SO_(2)-induced poisoning to these catalysts ...Mn-based catalysts have exhibited promising performance in low-temperature selective catalytic reduction of NOx with NH_(3)(NH_(3)-SCR).However,challenges such as H_(2)O-or SO_(2)-induced poisoning to these catalysts still remain.Herein,we report an efficient strategy to prepare the dual single-atom Ce-Ti/MnO_(2)catalyst via ball-milling and calcination processes to address these issues.Ce-Ti/MnO_(2)showed better catalytic performance with a higher NO conversion and enhanced H_(2)O-and SO_(2)-resistance at a lowtemperature window(100−150°C)than the MnO_(2),single-atom Ce/MnO_(2),and Ti/MnO_(2)catalysts.The in situ infrared Fourier transform spectroscopy analysis confirmed there is no competitive adsorption between NOx and H_(2)O over the Ce-Ti/MnO_(2)catalyst.The calculation results showed that the synergistic interaction of the neighboring Ce-Ti dual atoms as sacrificial sites weakens the ability of the active Mn sites for binding SO_(2)and H_(2)O but enhances their binding to NH_(3).The insight obtained in this work deepens the understanding of catalysis for NH_(3)-SCR.The synthesis strategy developed in this work is easily scaled up to commercialization and applicable to preparing other MnO_(2)-based single-atom catalysts.展开更多
The selective catalytic reduction(SCR) of NO_(x) with NH_(3)(NH_(3)-SCR) technology has been widely applied for reducing NO_(x) emissions from stationary and mobile sources.In this work,the extruded monolith MnO_(x)-C...The selective catalytic reduction(SCR) of NO_(x) with NH_(3)(NH_(3)-SCR) technology has been widely applied for reducing NO_(x) emissions from stationary and mobile sources.In this work,the extruded monolith MnO_(x)-CeO_(2)-TiO_(2) catalyst was installed in a cement kiln for NH_(3)-SCR of NO_(x),where the flue gas temperature was 110-140℃.It is found that the monolith catalyst is severely deactivated after operating for about 200 h with almost no NO_(x) conversion at 160℃ under GHSV of 50000 h^(-1),while the fresh monolith catalyst remains 60% NO_(x) conversion.Scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS),X-ray photoelectron spectroscopy(XPS),temperature-programmed desorption of SO_(2)(SO_(2)-TPD) and thermogravimetric-differential thermal analysis(TG-DTG) experiments reveal that both MnO_(x) and CeO_(2) oxides in monolith are severely sulfated to manganese sulfate and cerium sulfate,and the external monolith walls are covered by massive ceria sulfate and little ammonium nitrate.In situ diffuse reflectance infrared Fourier trans form spectroscopy(DRIFTS) analysis demonstrates that the formation of nitrates at low temperatures is inhibited due to the occupation of active sites in MnO_(x)-CeO_(2)-TiO_(2) by sulfates,resulting in the decrease of low temperature activity.After washing with water,the activity of deactivated monolith catalyst can be partially recovered,together with significant loss of manganese and cerium from monolith.展开更多
In the present study,two nanosized MnO_(2)with β and δ phase structures and potassium loaded MnO_(2)catalysts with varied K loading amounts (denoted as K/MnO_(2)) were prepared.Temperature programmed oxidation and i...In the present study,two nanosized MnO_(2)with β and δ phase structures and potassium loaded MnO_(2)catalysts with varied K loading amounts (denoted as K/MnO_(2)) were prepared.Temperature programmed oxidation and isothermal reactions in loose contact modes were employed to examine the soot oxidation activity of the as-prepared catalysts.Characterization results show that as compared with β-MnO_(2),δ-MnO_(2)has larger surface area and higher content of hydroxyl groups.Upon K loading,abundant hydroxyl groups in δ-MnO_(2)effectively sequestrate K cation to form bound K species and free K species are available only at K loading above 3.0 wt.%.In contrast,the majority of K species present as free state in β-MnO_(2)even at a K loading of 1.0 wt.%due to its very low hydroxyl group content.The O_(2)temperature-programmed desorption (O_(2)-TPD) demonstrates that the catalysts with free K species exhibit strong ability in activating gaseous O_(2),whereas the catalysts only having bound K display minor O_(2)activation capability.As a result,despite of slightly lower activity of β-MnO_(2)than δ-MnO_(2),the K/β-MnO_(2)catalysts exhibit substantially higher activities than K/δ-MnO_(2)catalysts with identical K loadings.The finding in this study clearly demonstrates that for MnO_(2)based catalysts,the enhancement of catalytic activity for soot oxidation is highly K loading amount dependent and the dependency is strongly associated with the phase structure of MnO_(2).展开更多
Formaldehyde(HCHO) and carbon monoxide(CO) are both common air pollutants and hazardous to human body. It is imperative to develop the catalyst that is able to efficiently remove these pollutants. In this work, we act...Formaldehyde(HCHO) and carbon monoxide(CO) are both common air pollutants and hazardous to human body. It is imperative to develop the catalyst that is able to efficiently remove these pollutants. In this work, we activated Pt-MnO_(2)under different conditions for highly active oxidation of HCHO and CO, and the catalyst activated under CO displayed superior performance. A suite of complementary characterizations revealed that the catalyst activated with CO created the highly dispersed Pt nanoparticles to maintain a more positively charged state of Pt, which appropriately weakens the Mn-O bonding strength in the adjacent region of Pt for efficient supply of active oxygen during the reaction. Compared with other catalysts activated under different conditions, the CO-activated Pt-MnO_(2)displays much higher activity for oxidation of HCHO and CO. This research contributes to elucidating the mechanism for regulating the oxidation activity of Pt-based catalyst.展开更多
基金support of National Natural Science Foundation of China(22179027)gratefully acknowledged.This work was also supported by the Natural Science Foundation of Guangxi Province(2021GXNSFAA075063,2018GXNSFDA281005)+1 种基金the National Key Research and Development Program of China(2017YFE0105500)Science&Technology Research Project of Guangdong Province(2017A020216009).
文摘Chemical-looping oxidative dehydrogenation(CL-ODH)is a process designed for the conversion of alkanes into olefins through cyclic redox reactions,eliminating the need for gaseous O_(2).In this work,we investigated the use of Ca_(2)MnO_(4)-layered perovskites modified with NaNO_(3) dopants,serving as redox catalysts(also known as oxygen carriers),for the CL-ODH of ethane within a temperature range of 700-780℃.Our findings revealed that the incorporation of NaNO_(3) as a modifier significantly-nhanced the selectivity for-thylene generation from Ca_(2)MnO_(4).At 750℃and a gas hourly space velocity of 1300 h^(-1),we achieved an-thane conversion up to 68.17%,accompanied by a corresponding-thylene yield of 57.39%.X-ray photoelectron spectroscopy analysis unveiled that the doping NaNO_(3) onto Ca_(2)MnO_(4) not only played a role in reducing the oxidation state of Mn ions but also increased the lattice oxygen content of the redox catalyst.Furthermore,formation of NaNO_(3) shell on the surface of Ca_(2)MnO_(4) led to a reduction in the concentration of manganese sites and modulated the oxygen-releasing behavior in a step-wise manner.This modulation contributed significantly to the enhanced selectivity for ethylene of the NaNO_(3)-doped Ca_(2)MnO_(4) catalyst.These findings provide compelling evidence for the potential of Ca_(2)MnO_(4)-layered perovskites as promising redox catalysts in the context of CL-ODH reactions.
基金supported by the Fundamental Research Funds for the Central Universities (No. 2021ZY79)Beijing Municipal Education Commission through the Innovative Transdisciplinary Program "Ecological Restoration Engineering” (No. GJJXK210102)+2 种基金National Natural Science Foundation of China (Nos. 42075169, U1810209)National Key R&D Program of China (No. 2021YFE0110800)Chinese-Serbian collaboration project (No. 451-03-1205/2021-09)。
文摘A series of monolithic MnO_(2)/iron mesh (IM) catalysts for oxidation of toluene were successfully prepared by using in situ hydrothermal growth.MnO_(2)can grow firmly on the IM substrates surface with a shedding rate of only 0.14%.Due to the highest O_(ads) and high-valent Mn^(4+) and Fe^(3+) elements,the temperature at 50% and 90% toluene conversion (T_(50%) and T_(90%)) was 252 and 265℃,respectively for the best performance catalyst (hydrothermal temperature of 80℃,hydrothermal time of 12 h,and precursor manganese ion concentration of 0.03 mol/L).The catalysts also presented good water resistance and cycle performance.In-situ DRIFTS results suggesting that toluene was first rapid transformed into the reaction intermediate species (benzoate species) and then converted to CO_(2)and H_(2)O.Therefore,this work provides a new direction for the research and application of IM-based monolithic catalysts.
基金supported by Key Research and Development Program of Ministry of Science and Technology of the People’s Republic of China (MOST) (No. 2017YFE0131200) for collaboration between China and PolandNational Nature Science Foundation of China (NSFC) (Nos. 22072095, U1908204, 21761162016)+3 种基金General Projects of Liaoning Province Natural Fund (No. 2019-MS-284)National Engineering Laboratory for Mobile Source Emission Control Technology (No. NELMS2018A04)University level innovation team of Shenyang Normal University, Major Incubation Program of Shenyang Normal University (No. ZD201901)supported by the Research Grants Council (RGC) of Hong Kong through NSFC/RGC Joint Research Scheme (No. N_CUHK451/17)。
文摘The performance of catalysts used in after-treatment systems is the key factor for the removal of diesel soot,which is an important component of atmosphericfine particle emissions.Herein,three-dimensionally ordered macroporous–mesoporous Ti_(x)Si+(1-x)O_(2)(3DOM-m Ti_(x)Si+(1-x)O_(2)) and its supported MnO_(x)catalysts doped with different alkali/alkaline-earth metals (AMnO_(x)/3 DOM-m Ti_(0.7)Si_(0.3)O_(2)(A:Li,Na,K,Ru,Cs,Mg,Ca,Sr,Ba)) were prepared by mesoporous template (P123)-assisted colloidal crystal template (CCT) and incipient wetness impregnation methods,respectively.Physicochemical characterizations of the catalysts were performed using scanning electron microscopy,X-ray diffraction,N_(2)adsorption–desorption,H_(2)temperature-programmed reduction,O_(2)temperature-programmed desorption,NO temperature-programmed oxidation,and Raman spectroscopy techniques;then,we evaluated their catalytic performances for the removal of diesel soot particles.The results show that the 3DOM-m Ti_(0.7)Si_(0.3)O_(2)supports exhibited a well-defined 3DOM-m nanostructure,and AMnO_(x)nanoparticles with 10–50 nm were evenly dispersed on the inner walls of the uniform macropores.In addition,the as-prepared catalysts exhibited good catalytic performance for soot combustion.Among the prepared catalysts,CsMnO_(x)/3DOM-m Ti_(0.7)Si_(0.3)O_(2)had the highest catalytic activity for soot combustion,with T10,T50,and T90(the temperatures corresponding to soot conversion rates of 10%,50%,and 90%) values of 285,355,and 393℃,respectively.The high catalytic activity of the CsMnO_(x)/3 DOM-m Ti_(0.7)Si_(0.3)O_(2)catalysts was attributed to their excellent low-temperature reducibility and homogeneous macroporous–mesoporous structure,as well as to the synergistic effects between Cs and Mn species and between CsMnO_(x)and the Ti_(0.7)Si_(0.3)O_(2)support.
基金We gratefully acknowledge the financial supports from the National Natural Science Foundation of China(Nos.52070180,51938014,and 21802054)the Science Research Project of the Ministry of Education of the Heilongjiang Province of China(No.145109102)+2 种基金the Beijing Chenxi Environmental Engineering Co.,Ltd.Z.Z.thanks the financial support of Guangdong Key discipline fund for this collaborationY.J.thanks the financial supports from the Outstanding Youth cultivation program of Beijing Technology and Business University(No.19008021144)Research Foundation for Advanced Talents of Beijing Technology and Business University(No.19008020159).
文摘Mn-based catalysts have exhibited promising performance in low-temperature selective catalytic reduction of NOx with NH_(3)(NH_(3)-SCR).However,challenges such as H_(2)O-or SO_(2)-induced poisoning to these catalysts still remain.Herein,we report an efficient strategy to prepare the dual single-atom Ce-Ti/MnO_(2)catalyst via ball-milling and calcination processes to address these issues.Ce-Ti/MnO_(2)showed better catalytic performance with a higher NO conversion and enhanced H_(2)O-and SO_(2)-resistance at a lowtemperature window(100−150°C)than the MnO_(2),single-atom Ce/MnO_(2),and Ti/MnO_(2)catalysts.The in situ infrared Fourier transform spectroscopy analysis confirmed there is no competitive adsorption between NOx and H_(2)O over the Ce-Ti/MnO_(2)catalyst.The calculation results showed that the synergistic interaction of the neighboring Ce-Ti dual atoms as sacrificial sites weakens the ability of the active Mn sites for binding SO_(2)and H_(2)O but enhances their binding to NH_(3).The insight obtained in this work deepens the understanding of catalysis for NH_(3)-SCR.The synthesis strategy developed in this work is easily scaled up to commercialization and applicable to preparing other MnO_(2)-based single-atom catalysts.
基金supported by the National Natural Science Foundation of China (22188102,22072179)Cultivating Project of Strategic Priority Research Program of Chinese Academy of Sciences (XDPB190201)。
文摘The selective catalytic reduction(SCR) of NO_(x) with NH_(3)(NH_(3)-SCR) technology has been widely applied for reducing NO_(x) emissions from stationary and mobile sources.In this work,the extruded monolith MnO_(x)-CeO_(2)-TiO_(2) catalyst was installed in a cement kiln for NH_(3)-SCR of NO_(x),where the flue gas temperature was 110-140℃.It is found that the monolith catalyst is severely deactivated after operating for about 200 h with almost no NO_(x) conversion at 160℃ under GHSV of 50000 h^(-1),while the fresh monolith catalyst remains 60% NO_(x) conversion.Scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS),X-ray photoelectron spectroscopy(XPS),temperature-programmed desorption of SO_(2)(SO_(2)-TPD) and thermogravimetric-differential thermal analysis(TG-DTG) experiments reveal that both MnO_(x) and CeO_(2) oxides in monolith are severely sulfated to manganese sulfate and cerium sulfate,and the external monolith walls are covered by massive ceria sulfate and little ammonium nitrate.In situ diffuse reflectance infrared Fourier trans form spectroscopy(DRIFTS) analysis demonstrates that the formation of nitrates at low temperatures is inhibited due to the occupation of active sites in MnO_(x)-CeO_(2)-TiO_(2) by sulfates,resulting in the decrease of low temperature activity.After washing with water,the activity of deactivated monolith catalyst can be partially recovered,together with significant loss of manganese and cerium from monolith.
基金supported by the National Key Research and Development Program of China (No.2020YFC1807003)National Natural Science Foundation of China (Nos.21976086and 22002059)Open Fund of the State Key Lab of Pollution Control and Resource Reuse Research of China (No.PCRR-ZZ-202105)。
文摘In the present study,two nanosized MnO_(2)with β and δ phase structures and potassium loaded MnO_(2)catalysts with varied K loading amounts (denoted as K/MnO_(2)) were prepared.Temperature programmed oxidation and isothermal reactions in loose contact modes were employed to examine the soot oxidation activity of the as-prepared catalysts.Characterization results show that as compared with β-MnO_(2),δ-MnO_(2)has larger surface area and higher content of hydroxyl groups.Upon K loading,abundant hydroxyl groups in δ-MnO_(2)effectively sequestrate K cation to form bound K species and free K species are available only at K loading above 3.0 wt.%.In contrast,the majority of K species present as free state in β-MnO_(2)even at a K loading of 1.0 wt.%due to its very low hydroxyl group content.The O_(2)temperature-programmed desorption (O_(2)-TPD) demonstrates that the catalysts with free K species exhibit strong ability in activating gaseous O_(2),whereas the catalysts only having bound K display minor O_(2)activation capability.As a result,despite of slightly lower activity of β-MnO_(2)than δ-MnO_(2),the K/β-MnO_(2)catalysts exhibit substantially higher activities than K/δ-MnO_(2)catalysts with identical K loadings.The finding in this study clearly demonstrates that for MnO_(2)based catalysts,the enhancement of catalytic activity for soot oxidation is highly K loading amount dependent and the dependency is strongly associated with the phase structure of MnO_(2).
基金supported by the National Natural Science Foundation of China (Nos. 22025604, 21976196, 21972170 and 22072184)。
文摘Formaldehyde(HCHO) and carbon monoxide(CO) are both common air pollutants and hazardous to human body. It is imperative to develop the catalyst that is able to efficiently remove these pollutants. In this work, we activated Pt-MnO_(2)under different conditions for highly active oxidation of HCHO and CO, and the catalyst activated under CO displayed superior performance. A suite of complementary characterizations revealed that the catalyst activated with CO created the highly dispersed Pt nanoparticles to maintain a more positively charged state of Pt, which appropriately weakens the Mn-O bonding strength in the adjacent region of Pt for efficient supply of active oxygen during the reaction. Compared with other catalysts activated under different conditions, the CO-activated Pt-MnO_(2)displays much higher activity for oxidation of HCHO and CO. This research contributes to elucidating the mechanism for regulating the oxidation activity of Pt-based catalyst.
