It has been found that cold plasma is a facile and environmentally benign method for synthesizing supported metal catalysts, and great efforts have been devoted to enlarging its applications. However, little work has ...It has been found that cold plasma is a facile and environmentally benign method for synthesizing supported metal catalysts, and great efforts have been devoted to enlarging its applications. However, little work has been done to disclose the influence mechanism, which is significant for controllable synthesis. In this work, hydrogen cold plasma was adopted to synthesize a palladium catalyst supported on activated carbon （Pd/C-P） using HzPdC14 as a Pd precursor followed by calcination in hydrogen gas to remove the chlorine ions. The Pd/C-P catalyst was found to be made of larger Pd nanoparticles showing a decreased migration to the support outer surface than that prepared by the conventional thermal hydrogen reduction method （Pd/C-C）. Meanwhile, the pore diameter of the activated carbon support is small （,-~4 nm）. Therefore, Pd/C-P exhibits lower CO oxidation activity than Pd/C-C. It was proposed that the strong interaction between the activated carbon and PdC142-, and the enhanced metal-support interaction caused by hydrogen cold plasma reduction made it difficult for Pd nanoparticles to migrate to the support outer surface. The larger-sized Pd nanoparticles for Pd/C-P may be due to the Coulomb interaction resulting in the disturbance of the metal-support interaction. This work has important guiding significance for the controllable synthesis of supported metal catalysts by hydrogen cold plasma.展开更多
A series of CoPd/KIT-6 bimetallic catalysts with various Co:Pd molar ratios at different calcination temperatures were prepared and used for the direct synthesis of H_(2)O_(2) from H_(2) and O_(2).These catalysts were...A series of CoPd/KIT-6 bimetallic catalysts with various Co:Pd molar ratios at different calcination temperatures were prepared and used for the direct synthesis of H_(2)O_(2) from H_(2) and O_(2).These catalysts were characterized by nitrogen adsorption-desorption,low and wide-angle X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),transmission electron microscopy(TEM),scanning electron microscopy(SEM),elemental mapping and energy-dispersive X-ray(EDX)methods.It was found that the particle size,electronic interactions,morphology,and textural properties of these catalysts as well as their catalytic activity in the reaction of H_(2) with O_(2) were affected by Co addition and different calcination temperatures.Also,the results showed that while the H_(2)O_(2) selectivity depends on Pd^(2+) species,the H_(2) conversion is related to Pd0 active sites.Among these catalysts,CoPd/KIT-6 calcined at 350℃(CoPd/KIT-350 catalyst)showed the best catalytic activity with 50%of H_(2)O_(2) selectivity and 51%conversion of H_(2).展开更多
Enhancing the stability of supported noble metal catalysts emerges is a major challenge in both science and industry.Herein,a heterogeneous Pd catalyst(Pd/NCF)was prepared by supporting Pd ultrafine metal nanoparticle...Enhancing the stability of supported noble metal catalysts emerges is a major challenge in both science and industry.Herein,a heterogeneous Pd catalyst(Pd/NCF)was prepared by supporting Pd ultrafine metal nanoparticles(NPs)on nitrogen-doped carbon;synthesized by using F127 as a stabilizer,as well as chitosan as a carbon and nitrogen source.The Pd/NCF catalyst was efficient and recyclable for oxidative carbonylation of phenol to diphenyl carbonate,exhibiting higher stability than Pd/NC prepared without F127 addition.The hydrogen bond between chitosan(CTS)and F127 was enhanced by F127,which anchored the N in the free amino group,increasing the N content of the carbon material and ensuring that the support could provide sufficient N sites for the deposition of Pd NPs.This process helped to improve metal dispersion.The increased metal-support interaction,which limits the leaching and coarsening of Pd NPs,improves the stability of the Pd/NCF catalyst.Furthermore,density functional theory calculations indicated that pyridine N stabilized the Pd^(2+)species,significantly inhibiting the loss of Pd^(2+)in Pd/NCF during the reaction process.This work provides a promising avenue towards enhancing the stability of nitrogen-doped carbon-supported metal catalysts.展开更多
A series of Pd/MIL-53(Al) heterogeneous bifunctional catalysts with di erent Pd contents were prepared by an impregnation method. The prepared metal–organic frameworks MIL-53(Al) and catalysts were characterized by X...A series of Pd/MIL-53(Al) heterogeneous bifunctional catalysts with di erent Pd contents were prepared by an impregnation method. The prepared metal–organic frameworks MIL-53(Al) and catalysts were characterized by XRD, SEM, HRTEM,FT-IR and N2 adsorption/desorption techniques. The results showed that MIL-53(Al) was synthesized successfully, and the structure was unchanged during and after the preparation of the catalysts. The Pd nanoparticles(NPs) with an average particle size of 4.6 nm were uniformly dispersed on the MIL-53(Al). The catalyst exhibited good catalytic activity in the selective oxidation of liquid methanol to methyl formate. Under the conditions of 150 °C, 2 MPa O2 and solvent-free for5 h, the conversion of methanol could reach 60.3%, and the selectivity of methyl formate was up to 62.2%. In addition, the Pd/MIL-53(Al) bifunctional catalyst exhibited excellent stability and maintained high catalytic activity after five cycles.展开更多
Anatase TiO_(2)nanospindles containing 89%exposed{101}facets(TIO_(2)-101)and nanosheets with 77%exposed{001}facets(TiO_(2)-001)were hydrothermally synthesized and used as supports for Pd catalysts.The effects of the T...Anatase TiO_(2)nanospindles containing 89%exposed{101}facets(TIO_(2)-101)and nanosheets with 77%exposed{001}facets(TiO_(2)-001)were hydrothermally synthesized and used as supports for Pd catalysts.The effects of the TiO_(2)materials on the catalytic performance of Pd/TiO_(2)-101 and Pd/TiO_(2)-001 catalysts were investigated in the selective hydrogenation of acetylene to polymer-grade ethylene.The PdfTiO_(2)-101 catalyst exhibited enhanced performance in terms of acetylene conversion and ethylene yield.To understand these effects,the catalysts were characterized by H_(2)temperature-programmed desorption(H_(2)-TPD),H_(2)temperature-programmed reduction(H=-TPR),transmission electron microscopy(TEM),pulse CO chemisorption,X-ray photoelectron spectroscopy(XPS),and thermogravimetric analysis(TGA).The TEM and CO chemisorption results confirmed that Pd nanoparticles(NPs)on the TiO_(2)-101 support had a smaller average particle size(1.53 nm)and a higher dispersion(15.95%)than those on the TiO_(2)-001 support(average particle size of 4.36 nm and dispersion of 9.06%).The smaller particle size and higher dispersion of Pd on the Pd/TiO_(2)-101 catalyst provided more reaction active sites,which contributed to the improved catalytic activity of this supported catalyst.展开更多
Pd/oxide/cordierite monolithic catalysts(oxide = Al_2O_3, SiO_2 and SiO_2\\Al_2O_3) were prepared by the impregnation method. The results of ICP, XRD, SEM–EDX, XPS and N_2 adsorption–desorption measurements revealed...Pd/oxide/cordierite monolithic catalysts(oxide = Al_2O_3, SiO_2 and SiO_2\\Al_2O_3) were prepared by the impregnation method. The results of ICP, XRD, SEM–EDX, XPS and N_2 adsorption–desorption measurements revealed that the Pd penetration depth increased with increasing the thickness of oxide layer, and the catalysts with Al_2O_3 layers had the larger pore size than those with SiO_2 and SiO_2\\Al_2O_3 layers. Catalytic hydrogenation of 2-ethylanthraquinone(eA Q), a key step of the H_2O_2 production by the anthraquinone process, over the various monolithic catalysts(60 °C, atmosphere pressure) showed that the monolithic catalyst with the moderate thickness of Al_2O_3 layer(about 6 μm) exhibited the highest conversion of e AQ(99.1%) and hydrogenation efficiency(10.0 g·L^(-1)). This could be ascribed to the suitable Pd penetration depth and the larger pore size, which provides a balance between the distribution of Pd and accessibility of active sites by the reactants.展开更多
Palladium(Pd)‐based catalysts are essential to drive high‐performance Suzuki coupling reactions,which are powerful tools for the synthesis of functional organic compounds.Herein,we developed a solution‐rapid‐annea...Palladium(Pd)‐based catalysts are essential to drive high‐performance Suzuki coupling reactions,which are powerful tools for the synthesis of functional organic compounds.Herein,we developed a solution‐rapid‐annealing process to stabilize nitrogen‐mesoporous carbon supported Pd single‐atom/cluster(Pd/NMC)material,which provided a catalyst with superior performance for Suzuki coupling reactions.In comparison with commercial palladium/carbon(Pd/C)catalysts,the Pd/NMC catalyst exhibited significantly boosted activity(100%selectivity and 95%yield)and excellent stability(almost no decay in activity after 10 reuse cycles)for the Suzuki coupling reactions of chlorobenzenes,together with superior yield and excellent selectivity in the fields of the board scope of the reactants.Moreover,our newly developed rapid annealing process of precursor solutions is applied as a generalized method to stabilize metal clusters(e.g.Pd,Pt,Ru),opening new possibilities in the construction of efficient highly dispersed metal atom and sub‐nanometer cluster catalysts with high performance.展开更多
Alkali-promoted Pd/Al2O3 catalysts exhibit much higher activities in NO decomposition than Pd/Al2O3. FTIR study shows that on the alkali promoted catalyst.nitric oxide exists on the surface mainly in negatively charge...Alkali-promoted Pd/Al2O3 catalysts exhibit much higher activities in NO decomposition than Pd/Al2O3. FTIR study shows that on the alkali promoted catalyst.nitric oxide exists on the surface mainly in negatively charged form(NO-)at high temperatures.which is consistent with the activity improvement.展开更多
In the current study simultaneous reactions of hydrodesulfurization(HDS) of dibenzothiophene(DBT) and reforming of methanol in a micro-autoclave reactor were studied over bi-metallic(Co-Mo/Al2O3 and Ni-Mo/Al2O3) and t...In the current study simultaneous reactions of hydrodesulfurization(HDS) of dibenzothiophene(DBT) and reforming of methanol in a micro-autoclave reactor were studied over bi-metallic(Co-Mo/Al2O3 and Ni-Mo/Al2O3) and tri-metallic(Pd-Co-Mo/Al2O3 and Pd-Ni-Mo/Al2O3) catalyst systems which were prepared by incipient impregnation method.In situ hydrogen utilization and low Pd loadings were the major targets of this study.For comparison purpose,catalytic activity was separately determined for both the methanol reforming and HDS of DBT reactions as well.Ni based catalysts were confirmed with better activity than Co ones for both the reactions with Pd promoted ones ranking at the top i.e.Pd-Ni-Mo/Al2O3 > Ni-Mo/Al2O3 > Pd-Co-Mo/Al2O3 > Co-Mo/Al2O3 where Pd-Ni-Mo/Al2O3 showed 91% DBT conversion at 380 ℃ and 12 h reaction time.Some of the selected organic additives on catalytic activity were tested for their effect toward HDS reaction which was unique with close relation to their chemical nature.Reaction products were quantitatively and qualitatively analyzed via HPLC and GC-MS techniques respectively which helped in elucidating reaction mechanism.展开更多
Aerogel Pd/(Ce0.33Zr0.66O2)SiO2 catalysts (CeZry) were prepared with variable Ce and Zr loadings (molar ratio Ce/Zr = 1/2) by combining sol-gel and impregnation methods. First, N2-physisorption was used to investigate...Aerogel Pd/(Ce0.33Zr0.66O2)SiO2 catalysts (CeZry) were prepared with variable Ce and Zr loadings (molar ratio Ce/Zr = 1/2) by combining sol-gel and impregnation methods. First, N2-physisorption was used to investigate the texture evolution. Then, H2-chimisorption and TEM were performed to study the effect on particle dispersion. After, TPR was used to determine the catalyst reducibility. Furthermore, XPS characterization was done to identify the palladium oxidation state and to evaluate the Pd-support interaction. Finally, the prepared catalysts were tested in methane combustion to assess their catalytic activity. The obtained results showed that, when the Zr and Ce loadings are varied between 0% and 8% and between 0% and 6% respectively, the BET surface area was increased from 615 to 744 m2/g, the porosity diameter from 45.7 to 83.6 Å, the Pd particle diameter from 5.2 to 7.0 nm, the CeO2 and ZrO2 particle size from 0 to 68 nm, the reduction temperature shift reached 16°C, the Pd binding energy shift attained 0.6 eV, but an optimum amounts of Zr (4 wt.%) and Ce (3 wt.%) are needed to maximize the PdO reducibility and to enhance the catalytic activity. In effect, 100% conversion of methane was reached at around 415°C on the CeZr4 catalyst.展开更多
The main objective of this paper was to characterize the voltammetric profiles of the Pt/C,Pt/C-ATO,Pd/C and Pd/CATO electrocatalysts and study their catalytic activities for methane oxidation in an acidic electrolyte...The main objective of this paper was to characterize the voltammetric profiles of the Pt/C,Pt/C-ATO,Pd/C and Pd/CATO electrocatalysts and study their catalytic activities for methane oxidation in an acidic electrolyte at 25 ℃ and in a direct methane proton exchange membrane fuel cell at 80 ℃. The electrocatalysts prepared also were characterized by X-ray diffraction( XRD) and transmission electron microscopy( TEM). The diffractograms of the Pt/C and Pt/C-ATO electrocatalysts show four peaks associated with Pt face-centered cubic( fcc) structure,and the diffractograms of Pd/C and Pd/C-ATO show four peaks associated with Pd face-centered cubic( fcc) structure. For Pt/C-ATO and Pd/C-ATO,characteristic peaks of cassiterite( SnO_2) phase are observed,which are associated with Sb-doped SnO_2( ATO) used as supports for electrocatalysts. Cyclic voltammograms( CV) of all electrocatalysts after adsorption of methane show that there is a current increase during the anodic scan. However,this effect is more pronounced for Pt/C-ATO and Pd/C-ATO. This process is related to the oxidation of the adsorbed species through the bifunctional mechanism,where ATO provides oxygenated species for the oxidation of CO or HCO intermediates adsorbed in Pt or Pd sites. From in situ ATR-FTIR( Attenuated Total Reflectance-Fourier Transform Infrared) experiments for all electrocatalysts prepared the formation of HCO or CO intermediates are observed,which indicates the production of carbon dioxide. Polarization curves at 80 ℃in a direct methane fuel cell( DMEFC) show that Pd/C and Pt/C electroacatalysts have superior performance to Pd/C-ATO and Pt/C-ATO in methane oxidation.展开更多
基金supported by National Natural Science Foundation of China (Grant Nos. 11505019, 21673026)Dalian Youth Science and Technology Project (Grant No. 2015R089)
文摘It has been found that cold plasma is a facile and environmentally benign method for synthesizing supported metal catalysts, and great efforts have been devoted to enlarging its applications. However, little work has been done to disclose the influence mechanism, which is significant for controllable synthesis. In this work, hydrogen cold plasma was adopted to synthesize a palladium catalyst supported on activated carbon （Pd/C-P） using HzPdC14 as a Pd precursor followed by calcination in hydrogen gas to remove the chlorine ions. The Pd/C-P catalyst was found to be made of larger Pd nanoparticles showing a decreased migration to the support outer surface than that prepared by the conventional thermal hydrogen reduction method （Pd/C-C）. Meanwhile, the pore diameter of the activated carbon support is small （,-~4 nm）. Therefore, Pd/C-P exhibits lower CO oxidation activity than Pd/C-C. It was proposed that the strong interaction between the activated carbon and PdC142-, and the enhanced metal-support interaction caused by hydrogen cold plasma reduction made it difficult for Pd nanoparticles to migrate to the support outer surface. The larger-sized Pd nanoparticles for Pd/C-P may be due to the Coulomb interaction resulting in the disturbance of the metal-support interaction. This work has important guiding significance for the controllable synthesis of supported metal catalysts by hydrogen cold plasma.
基金the financial support(Research Council Grant)provided by Isfahan University of Technology(Iran).
文摘A series of CoPd/KIT-6 bimetallic catalysts with various Co:Pd molar ratios at different calcination temperatures were prepared and used for the direct synthesis of H_(2)O_(2) from H_(2) and O_(2).These catalysts were characterized by nitrogen adsorption-desorption,low and wide-angle X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),transmission electron microscopy(TEM),scanning electron microscopy(SEM),elemental mapping and energy-dispersive X-ray(EDX)methods.It was found that the particle size,electronic interactions,morphology,and textural properties of these catalysts as well as their catalytic activity in the reaction of H_(2) with O_(2) were affected by Co addition and different calcination temperatures.Also,the results showed that while the H_(2)O_(2) selectivity depends on Pd^(2+) species,the H_(2) conversion is related to Pd0 active sites.Among these catalysts,CoPd/KIT-6 calcined at 350℃(CoPd/KIT-350 catalyst)showed the best catalytic activity with 50%of H_(2)O_(2) selectivity and 51%conversion of H_(2).
基金support by the National Natural Science Foundation of China(U21A20306,U20A20152)Natural Science Foundation of Hebei Province(B2022202077).
文摘Enhancing the stability of supported noble metal catalysts emerges is a major challenge in both science and industry.Herein,a heterogeneous Pd catalyst(Pd/NCF)was prepared by supporting Pd ultrafine metal nanoparticles(NPs)on nitrogen-doped carbon;synthesized by using F127 as a stabilizer,as well as chitosan as a carbon and nitrogen source.The Pd/NCF catalyst was efficient and recyclable for oxidative carbonylation of phenol to diphenyl carbonate,exhibiting higher stability than Pd/NC prepared without F127 addition.The hydrogen bond between chitosan(CTS)and F127 was enhanced by F127,which anchored the N in the free amino group,increasing the N content of the carbon material and ensuring that the support could provide sufficient N sites for the deposition of Pd NPs.This process helped to improve metal dispersion.The increased metal-support interaction,which limits the leaching and coarsening of Pd NPs,improves the stability of the Pd/NCF catalyst.Furthermore,density functional theory calculations indicated that pyridine N stabilized the Pd^(2+)species,significantly inhibiting the loss of Pd^(2+)in Pd/NCF during the reaction process.This work provides a promising avenue towards enhancing the stability of nitrogen-doped carbon-supported metal catalysts.
基金Financial support received from the National Natural Science Foundation of China(Grant Nos.21573015,21872004)
文摘A series of Pd/MIL-53(Al) heterogeneous bifunctional catalysts with di erent Pd contents were prepared by an impregnation method. The prepared metal–organic frameworks MIL-53(Al) and catalysts were characterized by XRD, SEM, HRTEM,FT-IR and N2 adsorption/desorption techniques. The results showed that MIL-53(Al) was synthesized successfully, and the structure was unchanged during and after the preparation of the catalysts. The Pd nanoparticles(NPs) with an average particle size of 4.6 nm were uniformly dispersed on the MIL-53(Al). The catalyst exhibited good catalytic activity in the selective oxidation of liquid methanol to methyl formate. Under the conditions of 150 °C, 2 MPa O2 and solvent-free for5 h, the conversion of methanol could reach 60.3%, and the selectivity of methyl formate was up to 62.2%. In addition, the Pd/MIL-53(Al) bifunctional catalyst exhibited excellent stability and maintained high catalytic activity after five cycles.
文摘Anatase TiO_(2)nanospindles containing 89%exposed{101}facets(TIO_(2)-101)and nanosheets with 77%exposed{001}facets(TiO_(2)-001)were hydrothermally synthesized and used as supports for Pd catalysts.The effects of the TiO_(2)materials on the catalytic performance of Pd/TiO_(2)-101 and Pd/TiO_(2)-001 catalysts were investigated in the selective hydrogenation of acetylene to polymer-grade ethylene.The PdfTiO_(2)-101 catalyst exhibited enhanced performance in terms of acetylene conversion and ethylene yield.To understand these effects,the catalysts were characterized by H_(2)temperature-programmed desorption(H_(2)-TPD),H_(2)temperature-programmed reduction(H=-TPR),transmission electron microscopy(TEM),pulse CO chemisorption,X-ray photoelectron spectroscopy(XPS),and thermogravimetric analysis(TGA).The TEM and CO chemisorption results confirmed that Pd nanoparticles(NPs)on the TiO_(2)-101 support had a smaller average particle size(1.53 nm)and a higher dispersion(15.95%)than those on the TiO_(2)-001 support(average particle size of 4.36 nm and dispersion of 9.06%).The smaller particle size and higher dispersion of Pd on the Pd/TiO_(2)-101 catalyst provided more reaction active sites,which contributed to the improved catalytic activity of this supported catalyst.
基金Supported by the Sinopec Corp.Scientific Research Projects(414076)
文摘Pd/oxide/cordierite monolithic catalysts(oxide = Al_2O_3, SiO_2 and SiO_2\\Al_2O_3) were prepared by the impregnation method. The results of ICP, XRD, SEM–EDX, XPS and N_2 adsorption–desorption measurements revealed that the Pd penetration depth increased with increasing the thickness of oxide layer, and the catalysts with Al_2O_3 layers had the larger pore size than those with SiO_2 and SiO_2\\Al_2O_3 layers. Catalytic hydrogenation of 2-ethylanthraquinone(eA Q), a key step of the H_2O_2 production by the anthraquinone process, over the various monolithic catalysts(60 °C, atmosphere pressure) showed that the monolithic catalyst with the moderate thickness of Al_2O_3 layer(about 6 μm) exhibited the highest conversion of e AQ(99.1%) and hydrogenation efficiency(10.0 g·L^(-1)). This could be ascribed to the suitable Pd penetration depth and the larger pore size, which provides a balance between the distribution of Pd and accessibility of active sites by the reactants.
文摘Palladium(Pd)‐based catalysts are essential to drive high‐performance Suzuki coupling reactions,which are powerful tools for the synthesis of functional organic compounds.Herein,we developed a solution‐rapid‐annealing process to stabilize nitrogen‐mesoporous carbon supported Pd single‐atom/cluster(Pd/NMC)material,which provided a catalyst with superior performance for Suzuki coupling reactions.In comparison with commercial palladium/carbon(Pd/C)catalysts,the Pd/NMC catalyst exhibited significantly boosted activity(100%selectivity and 95%yield)and excellent stability(almost no decay in activity after 10 reuse cycles)for the Suzuki coupling reactions of chlorobenzenes,together with superior yield and excellent selectivity in the fields of the board scope of the reactants.Moreover,our newly developed rapid annealing process of precursor solutions is applied as a generalized method to stabilize metal clusters(e.g.Pd,Pt,Ru),opening new possibilities in the construction of efficient highly dispersed metal atom and sub‐nanometer cluster catalysts with high performance.
文摘Alkali-promoted Pd/Al2O3 catalysts exhibit much higher activities in NO decomposition than Pd/Al2O3. FTIR study shows that on the alkali promoted catalyst.nitric oxide exists on the surface mainly in negatively charged form(NO-)at high temperatures.which is consistent with the activity improvement.
基金Fundamental Research Foundation of Sinopec(X505015)
文摘In the current study simultaneous reactions of hydrodesulfurization(HDS) of dibenzothiophene(DBT) and reforming of methanol in a micro-autoclave reactor were studied over bi-metallic(Co-Mo/Al2O3 and Ni-Mo/Al2O3) and tri-metallic(Pd-Co-Mo/Al2O3 and Pd-Ni-Mo/Al2O3) catalyst systems which were prepared by incipient impregnation method.In situ hydrogen utilization and low Pd loadings were the major targets of this study.For comparison purpose,catalytic activity was separately determined for both the methanol reforming and HDS of DBT reactions as well.Ni based catalysts were confirmed with better activity than Co ones for both the reactions with Pd promoted ones ranking at the top i.e.Pd-Ni-Mo/Al2O3 > Ni-Mo/Al2O3 > Pd-Co-Mo/Al2O3 > Co-Mo/Al2O3 where Pd-Ni-Mo/Al2O3 showed 91% DBT conversion at 380 ℃ and 12 h reaction time.Some of the selected organic additives on catalytic activity were tested for their effect toward HDS reaction which was unique with close relation to their chemical nature.Reaction products were quantitatively and qualitatively analyzed via HPLC and GC-MS techniques respectively which helped in elucidating reaction mechanism.
文摘Aerogel Pd/(Ce0.33Zr0.66O2)SiO2 catalysts (CeZry) were prepared with variable Ce and Zr loadings (molar ratio Ce/Zr = 1/2) by combining sol-gel and impregnation methods. First, N2-physisorption was used to investigate the texture evolution. Then, H2-chimisorption and TEM were performed to study the effect on particle dispersion. After, TPR was used to determine the catalyst reducibility. Furthermore, XPS characterization was done to identify the palladium oxidation state and to evaluate the Pd-support interaction. Finally, the prepared catalysts were tested in methane combustion to assess their catalytic activity. The obtained results showed that, when the Zr and Ce loadings are varied between 0% and 8% and between 0% and 6% respectively, the BET surface area was increased from 615 to 744 m2/g, the porosity diameter from 45.7 to 83.6 Å, the Pd particle diameter from 5.2 to 7.0 nm, the CeO2 and ZrO2 particle size from 0 to 68 nm, the reduction temperature shift reached 16°C, the Pd binding energy shift attained 0.6 eV, but an optimum amounts of Zr (4 wt.%) and Ce (3 wt.%) are needed to maximize the PdO reducibility and to enhance the catalytic activity. In effect, 100% conversion of methane was reached at around 415°C on the CeZr4 catalyst.
基金The project was supported by the FAPESP(2014/09087-4,2014/50279-4).
文摘The main objective of this paper was to characterize the voltammetric profiles of the Pt/C,Pt/C-ATO,Pd/C and Pd/CATO electrocatalysts and study their catalytic activities for methane oxidation in an acidic electrolyte at 25 ℃ and in a direct methane proton exchange membrane fuel cell at 80 ℃. The electrocatalysts prepared also were characterized by X-ray diffraction( XRD) and transmission electron microscopy( TEM). The diffractograms of the Pt/C and Pt/C-ATO electrocatalysts show four peaks associated with Pt face-centered cubic( fcc) structure,and the diffractograms of Pd/C and Pd/C-ATO show four peaks associated with Pd face-centered cubic( fcc) structure. For Pt/C-ATO and Pd/C-ATO,characteristic peaks of cassiterite( SnO_2) phase are observed,which are associated with Sb-doped SnO_2( ATO) used as supports for electrocatalysts. Cyclic voltammograms( CV) of all electrocatalysts after adsorption of methane show that there is a current increase during the anodic scan. However,this effect is more pronounced for Pt/C-ATO and Pd/C-ATO. This process is related to the oxidation of the adsorbed species through the bifunctional mechanism,where ATO provides oxygenated species for the oxidation of CO or HCO intermediates adsorbed in Pt or Pd sites. From in situ ATR-FTIR( Attenuated Total Reflectance-Fourier Transform Infrared) experiments for all electrocatalysts prepared the formation of HCO or CO intermediates are observed,which indicates the production of carbon dioxide. Polarization curves at 80 ℃in a direct methane fuel cell( DMEFC) show that Pd/C and Pt/C electroacatalysts have superior performance to Pd/C-ATO and Pt/C-ATO in methane oxidation.
