The Al2O3-supported PtAg catalysts were prepared and evaluated for the dehydrogenation of n-butane at 550°C in the presence of H2. The PtAg/Al2O3 catalyst prepared by an impregnation method using the Cl- removing...The Al2O3-supported PtAg catalysts were prepared and evaluated for the dehydrogenation of n-butane at 550°C in the presence of H2. The PtAg/Al2O3 catalyst prepared by an impregnation method using the Cl- removing Pt/Al2O3 and AgNO3 showed a higher activity and selectivity to butenes and 1,3-butadiene compared to the Pt/Al2O3 catalyst, but a large amount of coke (about 30 wt% versus the catalyst weight) was formed during the dehydrogenation. The free Ag metal on the prepared catalyst dramatically promoted the coke formation, because the dehydrogenation of 1-butene over the Ag/Al2O3 catalyst produced a large amount of coke. The Cl- addition to the Cl- free Pt/Al2O3 catalyst decreased the coke formation by the reaction of the free Ag particles and Cl to form AgCl which was inactive for the coke formation. The highest initial conversion (50.3%) was obtained with the selectivity to butenes and 1,3-butadiene (butenes = 80.2% and 1,3-butadiene = 5.9%) when the PtAg/Al2O3 catalyst modified with Cl- was used.展开更多
To improve the activity for glycerol oxidation reaction (GOR) of Pt, PtAg (mole ratio of Pt/Ag = 3 and 1) alloy nanoparticle-loaded carbon black (Pt/CB, PtAg(3:1)/CB, PtAg(1:1)/CB) catalysts were prepared by a wet met...To improve the activity for glycerol oxidation reaction (GOR) of Pt, PtAg (mole ratio of Pt/Ag = 3 and 1) alloy nanoparticle-loaded carbon black (Pt/CB, PtAg(3:1)/CB, PtAg(1:1)/CB) catalysts were prepared by a wet method. The resultant catalysts, moreover, were heat-treated in a N2 atmosphere at 200°C. The alloying of Pt with Ag for each PtAg/CB was confirmed by X-ray diffractometry and electron dispersive X-ray spectrometry. The heat-treatment did not change the crystal structure of the PtAg alloys and increased their particle size. X-ray photoelectron spectroscopy exhibited that stabilizers were completely removed from the PtAg alloy surface, and the Pt4f and Ag3d doublets due to metallic Pt and Ag, respectively, shifted to lower binding energies, supporting the alloying of Pt with Ag. Both PtAg/CB electrodes had two oxidation waves of glycerol irrespective of heat-treatment, which was different from the Pt/CB electrode. The onset potential of the first oxidation wave was -0.60 V, which was 0.20 V less positive than that for the Pt/CB electrode, indicating the alloying of Pt with Ag greatly improved the GOR activity of Pt. The heat-treated PtAg(3:1)/ CB electrode improved the GOR current density of the second oxidation peak. In the potentiostatic electrolysis at -0.1 and 0 V for both PtAg/CB electrodes, the ratio of oxidation current density at 60 min to that at 5 min (j<sub>60</sub>/j<sub>5</sub>), an indicator of the catalyst deterioration, at 0 V was higher than that at -0.1 V, because the adsorbed oxidation intermediates were greatly consumed at the larger overpotential. The heat-treatment of the PtAg(3:1)/CB electrode increased the j60</sub>/j5</sub> value at -0.1 V but decreased that at 0 V. This could be attributed to the formation of high-order oxidation intermediates which might have stronger poisoning effect.展开更多
Herein,a facile glycol reduction route is successful employed to synthesize bimetallic Pt Ag alloys with homogeneous distribution of sizes and elements.Experimental studies reveal that the ultrafine Pt Ag alloys with ...Herein,a facile glycol reduction route is successful employed to synthesize bimetallic Pt Ag alloys with homogeneous distribution of sizes and elements.Experimental studies reveal that the ultrafine Pt Ag alloys with well-defined sizes from around 3.3 nm to 5.8 nm are immobilized onto MnO_(2)microsphere,which remarkably enhances the catalytic performances for CO oxidation.Importantly,quasi in-situ X-ray photoelectron spectroscopy(XPS)result reveals that both Mn and Pt ions on the surface of catalysts would realize alternating reduction-oxidation by CO and O_(2)molecules,and the oxygen vacancy sites could be replenished and excited by gas-phase O_(2).展开更多
文摘The Al2O3-supported PtAg catalysts were prepared and evaluated for the dehydrogenation of n-butane at 550°C in the presence of H2. The PtAg/Al2O3 catalyst prepared by an impregnation method using the Cl- removing Pt/Al2O3 and AgNO3 showed a higher activity and selectivity to butenes and 1,3-butadiene compared to the Pt/Al2O3 catalyst, but a large amount of coke (about 30 wt% versus the catalyst weight) was formed during the dehydrogenation. The free Ag metal on the prepared catalyst dramatically promoted the coke formation, because the dehydrogenation of 1-butene over the Ag/Al2O3 catalyst produced a large amount of coke. The Cl- addition to the Cl- free Pt/Al2O3 catalyst decreased the coke formation by the reaction of the free Ag particles and Cl to form AgCl which was inactive for the coke formation. The highest initial conversion (50.3%) was obtained with the selectivity to butenes and 1,3-butadiene (butenes = 80.2% and 1,3-butadiene = 5.9%) when the PtAg/Al2O3 catalyst modified with Cl- was used.
文摘To improve the activity for glycerol oxidation reaction (GOR) of Pt, PtAg (mole ratio of Pt/Ag = 3 and 1) alloy nanoparticle-loaded carbon black (Pt/CB, PtAg(3:1)/CB, PtAg(1:1)/CB) catalysts were prepared by a wet method. The resultant catalysts, moreover, were heat-treated in a N2 atmosphere at 200°C. The alloying of Pt with Ag for each PtAg/CB was confirmed by X-ray diffractometry and electron dispersive X-ray spectrometry. The heat-treatment did not change the crystal structure of the PtAg alloys and increased their particle size. X-ray photoelectron spectroscopy exhibited that stabilizers were completely removed from the PtAg alloy surface, and the Pt4f and Ag3d doublets due to metallic Pt and Ag, respectively, shifted to lower binding energies, supporting the alloying of Pt with Ag. Both PtAg/CB electrodes had two oxidation waves of glycerol irrespective of heat-treatment, which was different from the Pt/CB electrode. The onset potential of the first oxidation wave was -0.60 V, which was 0.20 V less positive than that for the Pt/CB electrode, indicating the alloying of Pt with Ag greatly improved the GOR activity of Pt. The heat-treated PtAg(3:1)/ CB electrode improved the GOR current density of the second oxidation peak. In the potentiostatic electrolysis at -0.1 and 0 V for both PtAg/CB electrodes, the ratio of oxidation current density at 60 min to that at 5 min (j<sub>60</sub>/j<sub>5</sub>), an indicator of the catalyst deterioration, at 0 V was higher than that at -0.1 V, because the adsorbed oxidation intermediates were greatly consumed at the larger overpotential. The heat-treatment of the PtAg(3:1)/CB electrode increased the j60</sub>/j5</sub> value at -0.1 V but decreased that at 0 V. This could be attributed to the formation of high-order oxidation intermediates which might have stronger poisoning effect.
基金financially supported by the Research Funds of the Guilin University of Technology(No.GUTQDJJ202041)Guangxi Key Laboratory of Theory and Technology for Environmental Pollution Control(No.Guikeneng 2001K002)+2 种基金National Natural Science Foundation of China(Nos.51978189,51878292)National Key R&D Program of China(No.2017YFC0211503)China Postdoctoral Science Foundation(No.2020M683629XB)。
文摘Herein,a facile glycol reduction route is successful employed to synthesize bimetallic Pt Ag alloys with homogeneous distribution of sizes and elements.Experimental studies reveal that the ultrafine Pt Ag alloys with well-defined sizes from around 3.3 nm to 5.8 nm are immobilized onto MnO_(2)microsphere,which remarkably enhances the catalytic performances for CO oxidation.Importantly,quasi in-situ X-ray photoelectron spectroscopy(XPS)result reveals that both Mn and Pt ions on the surface of catalysts would realize alternating reduction-oxidation by CO and O_(2)molecules,and the oxygen vacancy sites could be replenished and excited by gas-phase O_(2).
