Ce x Ti 1- x O 2 mixed oxides of different mole ratios ( x =0, 0.1, 0.2～0.9, 1.0) were prepared by co precipitation of TiCl 4 with Ce(NO 3) 3 and then loaded with different amounts of CuO. The effe...Ce x Ti 1- x O 2 mixed oxides of different mole ratios ( x =0, 0.1, 0.2～0.9, 1.0) were prepared by co precipitation of TiCl 4 with Ce(NO 3) 3 and then loaded with different amounts of CuO. The effects of CuO on NO+CO reaction were investigated, and the structure and reductive properties of various CuO/Ce x Ti 1- x O 2 were characterized by the methodologies of BET, TPR and XRD. The results show that different Ce/Ti mole ratios and calcination temperatures induce changes of structure and reductive properties of the Ce x Ti 1- x O 2 mixed oxides. When x =0.1～0.5, amorphous CeTi 2O 6 phase mainly forms at 650 ℃ compared to the formation of CeTi 2O 6 which crystallizes at 800 ℃. When x >0.6, some TiO 2 enters the CeO 2 lattice and a CeO 2 TiO 2 solid solution is formed. The activity of 6%CuO/Ce x Ti 1- x O 2 calcined at 650 ℃ is largely affected by the x values, which is the highest when x =0.3, 0.4 and 0.9. The NO conversion reaches 70% at a reaction temperature of 150 ℃. By comparison, the x values have little effect on the activity of 6%CuO/Ce x Ti 1- x O 2 calcined at 800 ℃ . There are strong interactions between CuO and CeTi 2O 6, i.e., formation of the CeTi 2O 6 phase shifts the CuO reduction peak temperature from 380 to 200 ℃, and CuO, in turn, shifts the CeTi 2O 6 reduction peak temperature from 600 to 300 ℃.展开更多
The catalysts with Rh loading on different cerium-zirconium mixed oxides were characterized by BET, H2-TPR and OSC. The effects of different cerium-zirconium mixed oxides on catalytic performance and thermal stability...The catalysts with Rh loading on different cerium-zirconium mixed oxides were characterized by BET, H2-TPR and OSC. The effects of different cerium-zirconium mixed oxides on catalytic performance and thermal stability of Rh loaded catalyst were studied. The results show that: (1) Rh can enhance cerium-zirconium mixed oxides OSC and catalytic reaction rates; (2) cerium-zirconium mixed oxides with high Ce contents and low Zr contents are more favorable to the stability of catalysts. Moreover, the contents of CeO2 have important effect on catalysts characteristics, and the addition of some rare earth components, such as La, Pr and Nd also have some influences.展开更多
CeO2-ZeO2 solid solutions are extensively used as oxygen storage promoters in the current automotive three-way catalysts. High thermal stability of the textural properties is one of the most important requirements for...CeO2-ZeO2 solid solutions are extensively used as oxygen storage promoters in the current automotive three-way catalysts. High thermal stability of the textural properties is one of the most important requirements for practical application since temperatures up to 1273 K are easily experienced by these materials under real working conditions. In the present paper, we investigated how hydrothermal treatments applied to cakes of doped and undoped ZrO2-rich CeO2-ZrO2 precursors might improve the thermal stability of the final CeO2-ZrO2 solid solution. A rationale was developed that allowed to correlate the morphology of the hydrothermaUy treated cake with the thermal stability at 1273 K of the final product, which did not depend on the composition of the mixed oxides.展开更多
Several Mo-V-Te-O mixed metal oxides catalysts with different dopant were prepared and used for catalytic oxidation propane to acrolein. It was revealed that the addition of P could greatly improve the performance of ...Several Mo-V-Te-O mixed metal oxides catalysts with different dopant were prepared and used for catalytic oxidation propane to acrolein. It was revealed that the addition of P could greatly improve the performance of the Mo-V-Te-O catalyst. The catalysts were examined by XRD and H2-TPR. The XRD characteristic of the Mo-V-Te-P-O showed that the addition of P could aggrandize the (V0.07Mo0.93)5O14 phase. H2-TPR illuminated that the MoV0.3Te0.23P0.15On catalyst took on the best redox ability.展开更多
The selective oxidation of propane to acrylic acid over an MoVTeNb mixed oxide catalyst, dried and calcined before reaction has been studied using high-throughput instrumentation, which is called nanoflow catalytic re...The selective oxidation of propane to acrylic acid over an MoVTeNb mixed oxide catalyst, dried and calcined before reaction has been studied using high-throughput instrumentation, which is called nanoflow catalytic reactor. The effects of catalyst dilution on the catalytic performance of the MoVTeNb mixed oxide catalyst in selective oxidation of propane to acrylic acid were also investigated. The effects of some reaction parameters, such as gas hourly space velocity （GHSV） and reaction temperature, for selective oxidation of propane to acrylic acid over diluted MoVTeNb catalyst have also been studied. The configuration of the nanoflow is shown to be suitable for screen catalytic performance, and its operating conditions were mimicked closely to conventional laboratory as well as to industrial conditions. The results obtained provided very good reproducibility and it showed that preparation methods as well as reaction parameters can play significant roles in catalytic performance of these catalysts.展开更多
A series of Mn-Cu mixed oxide catalysts were prepared by precipitation method. The catalysts were characterized by N2 adsorp- tion-desorption, H2-TPR and XPS. When the loading ratio of manganese oxides to copper oxide...A series of Mn-Cu mixed oxide catalysts were prepared by precipitation method. The catalysts were characterized by N2 adsorp- tion-desorption, H2-TPR and XPS. When the loading ratio of manganese oxides to copper oxides was 8：2 or 7：3, the catalysts possessed better catalytic activity, and benzene was converted completely at 558 K. Results of H2-TPR showed that the loading of a small amount of copper oxides decreased the reduction temperature of catalysts. Results of XPS showed that the loading of a small amount of copper oxides increased the proportion of manganese and defective oxygen on the surface of catalysts, and stabilized manganese at higher oxidation state. And the catalyst with the loading ratio 7：3 was a little worse than 8：2, since the interaction between manganese oxides and copper oxides is too strong, copper oxides migrate to the surface of catalysts and manganese oxides in excess are immerged.展开更多
A novel sol-gel process for preparing oxides and mixed oxides sols from precipitation and peptization process is reported in this article. Inorganic salts are used as raw materials in this study. It is found that the ...A novel sol-gel process for preparing oxides and mixed oxides sols from precipitation and peptization process is reported in this article. Inorganic salts are used as raw materials in this study. It is found that the amount of acid has great influence on the stability and particle diameter distribution of the precursor sols. Ultrasonic treatment is used to prepare alumina sol at room temperature. The result of27Al NMR shows that there exist Al13 7+ species in the sol. By controlling the sol particles with narrow particle diameter distribution, alumina, titania and silica-alumina (SA) materials with narrow mesoporous distribution are formed by regular packing of sol particles during gelation without using any templates. The results also show that the structure and particle diameter distribution of precursor sol determine the final materials’ texture.展开更多
A series of catalysts with (Ce-Zr-La-Pr)O contents range from 0 to 50% in coating and single-palladium loads on substrates were prepared to study effects of (Ce-Zr-La-Pr)O contents on catalytic activities and durabili...A series of catalysts with (Ce-Zr-La-Pr)O contents range from 0 to 50% in coating and single-palladium loads on substrates were prepared to study effects of (Ce-Zr-La-Pr)O contents on catalytic activities and durability by contrasting the characteristics of light-off, A/F and catalytic conversions of the fresh catalysts with that of the aged catalysts. The results show that (Ce-Zr-La-Pr)O can enhance the catalysts light-off characteristics, widen A/F windows and increase catalytic conversions at a certain extent through optimizing physical structural and chemical property of the mixed coating. However, (Ce-Zr-La-Pr)O contents influence greatly on the catalysts activities and durability, and the catalysts with contents ranging from 10% to 30% exhibited better integrative properties in all samples, and 10% was the optical content to make the catalyst performance highest in this thesis. It is indicated that an suitable content of (Ce-Zr-La-Pr)O plays an important role in assisting catalysis, enhancing durability and increasing oxygen storage capability.展开更多
Developing catalysts with not only hydrogenation activity but also cracking activity is very important for the advancement of suspended-bed hydrocracking technology.Within this respect,MoS_(2)/SiO_(2)-Al_(2)O_(3)bifun...Developing catalysts with not only hydrogenation activity but also cracking activity is very important for the advancement of suspended-bed hydrocracking technology.Within this respect,MoS_(2)/SiO_(2)-Al_(2)O_(3)bifunctional catalyst is a kind of typical catalysts with both hydrogenation and cracking activity.Herein,a series of Zr-doped SiO_(2)-Al_(2)O_(3)mixed oxides were synthesized by a sol-gel coupled with hydrothermal method.The synthesized mixed oxides were characterized for chemical structures and acidic properties.It is found that doping SiO_(2)-Al_(2)O_(3)with Zr atoms significantly increases the numbers of acidic sites.The Zr-doped SiO_(2)-Al_(2)O_(3)mixed oxides were then combined with dispersed MoS_(2),which was in-situ produced from oil-soluble Mo precursors,to fabricate a novel kind of bifunctional catalysts for suspended-bed hydrocracking of heavy oils.Owing to the significantly increased numbers of acidic sites in Zr-doped SiO_(2)-Al_(2)O_(3)mixed oxides,corresponding bifunctional catalysts demonstrate much enhanced activity for suspended-bed hydrocracking of heavy oils in relative to MoS_(2)/SiO_(2)-Al_(2)O_(3)bifunctional catalysts.展开更多
Important effects exist between precious metals and rare earths oxides in three-way catalyst, especially the coordinated effects. These effects were studied by using H2PtCl6, Pt(NH3)2(NO2)2 and Pt(OH)2(C2H5ONH2)2 as P...Important effects exist between precious metals and rare earths oxides in three-way catalyst, especially the coordinated effects. These effects were studied by using H2PtCl6, Pt(NH3)2(NO2)2 and Pt(OH)2(C2H5ONH2)2 as Pt precursors, and the mixed oxide of (Ce-Zr-La-Pr)O as base material to prepare a series of catalysts, and their performances of the catalysts were studied by TPR and CO pulse titration technologies. The results shown that Pt precursors and their solutions pH values influenced the oxygen storage capabilities, the active metal distribution degrees of the catalysts obviously, and every catalyst prepared by different precursors had an optimal pH values. It indicates that the active metals precursors and their solutions acidities have outstanding influences on the catalysts performances for the mutual effects existing between the active metals and the Rare Earth metal oxides, which results from the mate groups of the precursors and the solution acidity.展开更多
Magnesium and rare earth mixed oxides（Mg3 REOx（RE=La, Y. Ce）） were prepared and characterized by Xray diffraction（XRD）, N_2 adsorption-desorption, infrared spectra and microcalorimetry of CO_2. The results revea...Magnesium and rare earth mixed oxides（Mg3 REOx（RE=La, Y. Ce）） were prepared and characterized by Xray diffraction（XRD）, N_2 adsorption-desorption, infrared spectra and microcalorimetry of CO_2. The results reveal that the Mg_3 CeO_x catalyst is present in the form of Mg-Ce-O solid solution,while the Mg3 LaOx and Mg_3 YO_x catalysts are probably rare earth oxides dispersed on MgO surface. As a result, among the calcined Mg_3 REO_x catalysts, the Mg_3 CeO_x catalyst presents the highest rate constant for acetone aldolization, which is well correlated to its more homogeneous distribution of basic sites. In contrary, the Mg_3 YO_x catalyst exhibit the lowest catalytic activity for acetone aldolization. Upon hydration pre-treatment, the basic properties on the surface of the Mg_3 REO_x catalysts were changed markedly. The Mg_3 YO_x catalyst after hydration treatment shows the highest amount of basic sites on catalyst surface, and then exhibits the highest activity among the hydrated Mg_3 REO_x catalysts. These results make it possible to fine-tune basic sites for acetone aldolization.展开更多
The further improvement of methacrolein(MAL)selectivity from isobutene(IB)oxidation is crucial and challenging.In this study,based on the typical Mo-Bi-Fe-Co-K-O mixed metal oxide,the rare earth element Gd-doped,Ce-do...The further improvement of methacrolein(MAL)selectivity from isobutene(IB)oxidation is crucial and challenging.In this study,based on the typical Mo-Bi-Fe-Co-K-O mixed metal oxide,the rare earth element Gd-doped,Ce-doped and CeGd co-doped catalysts were prepared by co-precipitation strategy to increase the selectivity of MAL from 47.9%to 49.8%,64.2% and 68.6%,respectively.In order to elucidate in-depth the promoting effect of Ce and/or Gd,various characterizations were utilized including X-ray diffraction patterns(XRD),Raman,X-ray fluorescence spectrometry(XRF),X-ray photoelectron spectroscopy(XPS),O_(2)-temperature programmed desorption(O_(2)-TPD),H2-temperature programmed reduction(H2-TPR),CO_(2)-temperature programmed desorption(CO_(2)-TPD),IB-temperature programmed desorption(i-C4-TPD)and in-situ IB-Fourier transform infrared spectroscopy(IB-FTIR).Both Ce and Gd finely regulate the bulk and surface structure of the catalyst,thus altering the redox ability,oxygen mobility and storage ability and basicity.Compared with Ce,Gd addition slightly regulates the variation of Co^(2+)/Co^(3+)redox couples,greatly enhances the interaction among the components on the catalyst,thus only increases the content of surface oxygen species and has little effect on their mobility.While Cecontaining catalyst performs stronger oxygen storage and migration ability,thus leading to the overproduction of surface Odefectspecies,which are proposed to be the active sites for the production of MAL and COx.The CeGd co-doped catalyst possesses the proper content of surface Odefectspecies,thus exhibits much higher MAL selectivity.Moreover,the promoting mechanism of Ce and/or Gd over IB oxidation is proposed.Therefore,this work is helpful for understanding the influence of rare earth elements on the structure of mixed metal oxides and the olefin selective oxidation reaction.展开更多
文摘Ce x Ti 1- x O 2 mixed oxides of different mole ratios ( x =0, 0.1, 0.2～0.9, 1.0) were prepared by co precipitation of TiCl 4 with Ce(NO 3) 3 and then loaded with different amounts of CuO. The effects of CuO on NO+CO reaction were investigated, and the structure and reductive properties of various CuO/Ce x Ti 1- x O 2 were characterized by the methodologies of BET, TPR and XRD. The results show that different Ce/Ti mole ratios and calcination temperatures induce changes of structure and reductive properties of the Ce x Ti 1- x O 2 mixed oxides. When x =0.1～0.5, amorphous CeTi 2O 6 phase mainly forms at 650 ℃ compared to the formation of CeTi 2O 6 which crystallizes at 800 ℃. When x >0.6, some TiO 2 enters the CeO 2 lattice and a CeO 2 TiO 2 solid solution is formed. The activity of 6%CuO/Ce x Ti 1- x O 2 calcined at 650 ℃ is largely affected by the x values, which is the highest when x =0.3, 0.4 and 0.9. The NO conversion reaches 70% at a reaction temperature of 150 ℃. By comparison, the x values have little effect on the activity of 6%CuO/Ce x Ti 1- x O 2 calcined at 800 ℃ . There are strong interactions between CuO and CeTi 2O 6, i.e., formation of the CeTi 2O 6 phase shifts the CuO reduction peak temperature from 380 to 200 ℃, and CuO, in turn, shifts the CeTi 2O 6 reduction peak temperature from 600 to 300 ℃.
基金Project supported by Yunnan Province Science Technology Program (2002C001Z) the National High Technology Research and Development Program ( 863 ) of China ( 2002AA321060 ) Yunnan Province Science Technology Program (2004B0028Q)
文摘The catalysts with Rh loading on different cerium-zirconium mixed oxides were characterized by BET, H2-TPR and OSC. The effects of different cerium-zirconium mixed oxides on catalytic performance and thermal stability of Rh loaded catalyst were studied. The results show that: (1) Rh can enhance cerium-zirconium mixed oxides OSC and catalytic reaction rates; (2) cerium-zirconium mixed oxides with high Ce contents and low Zr contents are more favorable to the stability of catalysts. Moreover, the contents of CeO2 have important effect on catalysts characteristics, and the addition of some rare earth components, such as La, Pr and Nd also have some influences.
基金PRIN 2006, "Caratterizzazione spettroscopica e morfologica di Me-POSS eterogeneizzati", MEL Chemicals
文摘CeO2-ZeO2 solid solutions are extensively used as oxygen storage promoters in the current automotive three-way catalysts. High thermal stability of the textural properties is one of the most important requirements for practical application since temperatures up to 1273 K are easily experienced by these materials under real working conditions. In the present paper, we investigated how hydrothermal treatments applied to cakes of doped and undoped ZrO2-rich CeO2-ZrO2 precursors might improve the thermal stability of the final CeO2-ZrO2 solid solution. A rationale was developed that allowed to correlate the morphology of the hydrothermaUy treated cake with the thermal stability at 1273 K of the final product, which did not depend on the composition of the mixed oxides.
文摘Several Mo-V-Te-O mixed metal oxides catalysts with different dopant were prepared and used for catalytic oxidation propane to acrolein. It was revealed that the addition of P could greatly improve the performance of the Mo-V-Te-O catalyst. The catalysts were examined by XRD and H2-TPR. The XRD characteristic of the Mo-V-Te-P-O showed that the addition of P could aggrandize the (V0.07Mo0.93)5O14 phase. H2-TPR illuminated that the MoV0.3Te0.23P0.15On catalyst took on the best redox ability.
基金Ministry of Science Technology and Innovation (MOSTI),Malaysia,project number:IRPA RM8 SR33-02-03-3010.
文摘The selective oxidation of propane to acrylic acid over an MoVTeNb mixed oxide catalyst, dried and calcined before reaction has been studied using high-throughput instrumentation, which is called nanoflow catalytic reactor. The effects of catalyst dilution on the catalytic performance of the MoVTeNb mixed oxide catalyst in selective oxidation of propane to acrylic acid were also investigated. The effects of some reaction parameters, such as gas hourly space velocity （GHSV） and reaction temperature, for selective oxidation of propane to acrylic acid over diluted MoVTeNb catalyst have also been studied. The configuration of the nanoflow is shown to be suitable for screen catalytic performance, and its operating conditions were mimicked closely to conventional laboratory as well as to industrial conditions. The results obtained provided very good reproducibility and it showed that preparation methods as well as reaction parameters can play significant roles in catalytic performance of these catalysts.
基金Project supported by National Natural Science Foundation of China (20773090)the National High Technology Research and Development Program of China (863 Program, 2006AA06Z347)the Youth Fund of Sichuan University (2008119)
文摘A series of Mn-Cu mixed oxide catalysts were prepared by precipitation method. The catalysts were characterized by N2 adsorp- tion-desorption, H2-TPR and XPS. When the loading ratio of manganese oxides to copper oxides was 8：2 or 7：3, the catalysts possessed better catalytic activity, and benzene was converted completely at 558 K. Results of H2-TPR showed that the loading of a small amount of copper oxides decreased the reduction temperature of catalysts. Results of XPS showed that the loading of a small amount of copper oxides increased the proportion of manganese and defective oxygen on the surface of catalysts, and stabilized manganese at higher oxidation state. And the catalyst with the loading ratio 7：3 was a little worse than 8：2, since the interaction between manganese oxides and copper oxides is too strong, copper oxides migrate to the surface of catalysts and manganese oxides in excess are immerged.
基金Acknowledgements This work was supported by the Chinese Academy of Sciences, the Research Institute of Petroleum Processing SINOPEC and the National Natural Science Foundation of China (Grant Nos. 20073043 and 29873050).
文摘A novel sol-gel process for preparing oxides and mixed oxides sols from precipitation and peptization process is reported in this article. Inorganic salts are used as raw materials in this study. It is found that the amount of acid has great influence on the stability and particle diameter distribution of the precursor sols. Ultrasonic treatment is used to prepare alumina sol at room temperature. The result of27Al NMR shows that there exist Al13 7+ species in the sol. By controlling the sol particles with narrow particle diameter distribution, alumina, titania and silica-alumina (SA) materials with narrow mesoporous distribution are formed by regular packing of sol particles during gelation without using any templates. The results also show that the structure and particle diameter distribution of precursor sol determine the final materials’ texture.
文摘A series of catalysts with (Ce-Zr-La-Pr)O contents range from 0 to 50% in coating and single-palladium loads on substrates were prepared to study effects of (Ce-Zr-La-Pr)O contents on catalytic activities and durability by contrasting the characteristics of light-off, A/F and catalytic conversions of the fresh catalysts with that of the aged catalysts. The results show that (Ce-Zr-La-Pr)O can enhance the catalysts light-off characteristics, widen A/F windows and increase catalytic conversions at a certain extent through optimizing physical structural and chemical property of the mixed coating. However, (Ce-Zr-La-Pr)O contents influence greatly on the catalysts activities and durability, and the catalysts with contents ranging from 10% to 30% exhibited better integrative properties in all samples, and 10% was the optical content to make the catalyst performance highest in this thesis. It is indicated that an suitable content of (Ce-Zr-La-Pr)O plays an important role in assisting catalysis, enhancing durability and increasing oxygen storage capability.
基金the National Key Research&Development Program of China(2018YFA0209403)the National Natural Science Foundation of China(U1662108)the Science and Technology Project of Fujian Province(FG-2016002).
文摘Developing catalysts with not only hydrogenation activity but also cracking activity is very important for the advancement of suspended-bed hydrocracking technology.Within this respect,MoS_(2)/SiO_(2)-Al_(2)O_(3)bifunctional catalyst is a kind of typical catalysts with both hydrogenation and cracking activity.Herein,a series of Zr-doped SiO_(2)-Al_(2)O_(3)mixed oxides were synthesized by a sol-gel coupled with hydrothermal method.The synthesized mixed oxides were characterized for chemical structures and acidic properties.It is found that doping SiO_(2)-Al_(2)O_(3)with Zr atoms significantly increases the numbers of acidic sites.The Zr-doped SiO_(2)-Al_(2)O_(3)mixed oxides were then combined with dispersed MoS_(2),which was in-situ produced from oil-soluble Mo precursors,to fabricate a novel kind of bifunctional catalysts for suspended-bed hydrocracking of heavy oils.Owing to the significantly increased numbers of acidic sites in Zr-doped SiO_(2)-Al_(2)O_(3)mixed oxides,corresponding bifunctional catalysts demonstrate much enhanced activity for suspended-bed hydrocracking of heavy oils in relative to MoS_(2)/SiO_(2)-Al_(2)O_(3)bifunctional catalysts.
基金Project supported by the National High Technology Research and Development Programs (863 ) of China (2002 AA321060, 2004AA649040) Yunnan Province Science Technology Program (2004B0028Q)
文摘Important effects exist between precious metals and rare earths oxides in three-way catalyst, especially the coordinated effects. These effects were studied by using H2PtCl6, Pt(NH3)2(NO2)2 and Pt(OH)2(C2H5ONH2)2 as Pt precursors, and the mixed oxide of (Ce-Zr-La-Pr)O as base material to prepare a series of catalysts, and their performances of the catalysts were studied by TPR and CO pulse titration technologies. The results shown that Pt precursors and their solutions pH values influenced the oxygen storage capabilities, the active metal distribution degrees of the catalysts obviously, and every catalyst prepared by different precursors had an optimal pH values. It indicates that the active metals precursors and their solutions acidities have outstanding influences on the catalysts performances for the mutual effects existing between the active metals and the Rare Earth metal oxides, which results from the mate groups of the precursors and the solution acidity.
基金Project supported by National Basic Research Program of China(2010CB732300)111 Project(B08021)China Scholarship Council for the Joint-Training Scholarship Program with Institut de Recherches sur la Catalyse et l'Environnement de Lyon(IRCELYON)and Universite Claude Bernard Lyon 1(UCBL1)
文摘Magnesium and rare earth mixed oxides（Mg3 REOx（RE=La, Y. Ce）） were prepared and characterized by Xray diffraction（XRD）, N_2 adsorption-desorption, infrared spectra and microcalorimetry of CO_2. The results reveal that the Mg_3 CeO_x catalyst is present in the form of Mg-Ce-O solid solution,while the Mg3 LaOx and Mg_3 YO_x catalysts are probably rare earth oxides dispersed on MgO surface. As a result, among the calcined Mg_3 REO_x catalysts, the Mg_3 CeO_x catalyst presents the highest rate constant for acetone aldolization, which is well correlated to its more homogeneous distribution of basic sites. In contrary, the Mg_3 YO_x catalyst exhibit the lowest catalytic activity for acetone aldolization. Upon hydration pre-treatment, the basic properties on the surface of the Mg_3 REO_x catalysts were changed markedly. The Mg_3 YO_x catalyst after hydration treatment shows the highest amount of basic sites on catalyst surface, and then exhibits the highest activity among the hydrated Mg_3 REO_x catalysts. These results make it possible to fine-tune basic sites for acetone aldolization.
基金supported by Petro China Innovation Foundation(2019D-5007-0404)。
文摘The further improvement of methacrolein(MAL)selectivity from isobutene(IB)oxidation is crucial and challenging.In this study,based on the typical Mo-Bi-Fe-Co-K-O mixed metal oxide,the rare earth element Gd-doped,Ce-doped and CeGd co-doped catalysts were prepared by co-precipitation strategy to increase the selectivity of MAL from 47.9%to 49.8%,64.2% and 68.6%,respectively.In order to elucidate in-depth the promoting effect of Ce and/or Gd,various characterizations were utilized including X-ray diffraction patterns(XRD),Raman,X-ray fluorescence spectrometry(XRF),X-ray photoelectron spectroscopy(XPS),O_(2)-temperature programmed desorption(O_(2)-TPD),H2-temperature programmed reduction(H2-TPR),CO_(2)-temperature programmed desorption(CO_(2)-TPD),IB-temperature programmed desorption(i-C4-TPD)and in-situ IB-Fourier transform infrared spectroscopy(IB-FTIR).Both Ce and Gd finely regulate the bulk and surface structure of the catalyst,thus altering the redox ability,oxygen mobility and storage ability and basicity.Compared with Ce,Gd addition slightly regulates the variation of Co^(2+)/Co^(3+)redox couples,greatly enhances the interaction among the components on the catalyst,thus only increases the content of surface oxygen species and has little effect on their mobility.While Cecontaining catalyst performs stronger oxygen storage and migration ability,thus leading to the overproduction of surface Odefectspecies,which are proposed to be the active sites for the production of MAL and COx.The CeGd co-doped catalyst possesses the proper content of surface Odefectspecies,thus exhibits much higher MAL selectivity.Moreover,the promoting mechanism of Ce and/or Gd over IB oxidation is proposed.Therefore,this work is helpful for understanding the influence of rare earth elements on the structure of mixed metal oxides and the olefin selective oxidation reaction.
