The Zn and Fe modified /ZrO<sub>2</sub>-Al<sub>2</sub>O<sub>3</sub> catalyst (Zn-Fe-SZA) was prepared and mechanisms of deactivation and methods for regeneration of as-prepared cata...The Zn and Fe modified /ZrO<sub>2</sub>-Al<sub>2</sub>O<sub>3</sub> catalyst (Zn-Fe-SZA) was prepared and mechanisms of deactivation and methods for regeneration of as-prepared catalyst were explored with n-pentane isomerization as a probe reaction. The results indicated that the isopentane yield of the fresh Zn-Fe-SZA-F catalyst was about 57% at the beginning of the run, and declined gradually to 50% within 1500 min, then fell rapidly from 50% to 40% between 1500 and 2500 minutes. The deactivation of Zn-Fe-SZA catalyst may be caused by carbon formation on surface of the catalyst, sulfate group attenuation owing to reduction by hydrogen, removal of sulfur species and the loss of strong acid sites. It was found that the initial catalytic activity over Zn-Fe-SZA-T catalyst was 48%, which recovered by 84.3% as compared to that of fresh catalyst (57%). However, it showed a sharp decrease in isopentane yield from 48% to 29% within 1500 minutes, showing poor stability. This is associated to the loss of acidity caused by removal of sulfur species cannot be basically restored by thermal treatment. Resulfating the calcined catalyst could improve the acidity of catalyst significantly, especially strong acid sites, as compared with the calcined sample. The improved stability of the resulfated catalyst can be explained by: 1) eliminaton of carbon deposition to some extent by calcination process, 2) formation of improved acidic nature by re-sulfation, favoring isomerization on acidic sites, 3) restructuring of the acid and metal sites via the calcination-re-sulfation procedure.展开更多
Electrochemical behaviors of Zn-Fe alloy and Zn-Fe-TiO2 composite electrodeposition in alkaline zincatesolutions were studied respectively by the methods of linear potential sweep and cyclic voltammetry. From the re-s...Electrochemical behaviors of Zn-Fe alloy and Zn-Fe-TiO2 composite electrodeposition in alkaline zincatesolutions were studied respectively by the methods of linear potential sweep and cyclic voltammetry. From the re-sults it can be concluded that Zn shows under potential deposition, Zn-Fe alloy codeposition is anomalous codeposi-tion and Zn-Fe alloy cathode polarization is increased with the introduction of additive. From the view point of elec-trochemistry, the reasons that the content of Fe in the Zn-Fe coating changes with the composition of the electrolyteand the process conditions altering and the relationship between the content of Fe and the appearance of the coatingare interpreted. The cathode polarization of Zn-Fe alloy codeposition is enhanced obviously with addition of additive.In the course of composite electrodeposition, TiO2 has less promotion to electrodeposition of zinc ions than to iron i-ons, while the electrodeposition of iron ions improves the content of TiO2 in composite coating, which is inagreement with the results of process experiments.展开更多
文摘The Zn and Fe modified /ZrO<sub>2</sub>-Al<sub>2</sub>O<sub>3</sub> catalyst (Zn-Fe-SZA) was prepared and mechanisms of deactivation and methods for regeneration of as-prepared catalyst were explored with n-pentane isomerization as a probe reaction. The results indicated that the isopentane yield of the fresh Zn-Fe-SZA-F catalyst was about 57% at the beginning of the run, and declined gradually to 50% within 1500 min, then fell rapidly from 50% to 40% between 1500 and 2500 minutes. The deactivation of Zn-Fe-SZA catalyst may be caused by carbon formation on surface of the catalyst, sulfate group attenuation owing to reduction by hydrogen, removal of sulfur species and the loss of strong acid sites. It was found that the initial catalytic activity over Zn-Fe-SZA-T catalyst was 48%, which recovered by 84.3% as compared to that of fresh catalyst (57%). However, it showed a sharp decrease in isopentane yield from 48% to 29% within 1500 minutes, showing poor stability. This is associated to the loss of acidity caused by removal of sulfur species cannot be basically restored by thermal treatment. Resulfating the calcined catalyst could improve the acidity of catalyst significantly, especially strong acid sites, as compared with the calcined sample. The improved stability of the resulfated catalyst can be explained by: 1) eliminaton of carbon deposition to some extent by calcination process, 2) formation of improved acidic nature by re-sulfation, favoring isomerization on acidic sites, 3) restructuring of the acid and metal sites via the calcination-re-sulfation procedure.
基金The Research Project from Department of Science and Technology of Shandong Province(2012GGA01012)the Scientific Research Foundation for the Returned Overseas Chinese Scholars of State Education Ministry(2004-527)
文摘Electrochemical behaviors of Zn-Fe alloy and Zn-Fe-TiO2 composite electrodeposition in alkaline zincatesolutions were studied respectively by the methods of linear potential sweep and cyclic voltammetry. From the re-sults it can be concluded that Zn shows under potential deposition, Zn-Fe alloy codeposition is anomalous codeposi-tion and Zn-Fe alloy cathode polarization is increased with the introduction of additive. From the view point of elec-trochemistry, the reasons that the content of Fe in the Zn-Fe coating changes with the composition of the electrolyteand the process conditions altering and the relationship between the content of Fe and the appearance of the coatingare interpreted. The cathode polarization of Zn-Fe alloy codeposition is enhanced obviously with addition of additive.In the course of composite electrodeposition, TiO2 has less promotion to electrodeposition of zinc ions than to iron i-ons, while the electrodeposition of iron ions improves the content of TiO2 in composite coating, which is inagreement with the results of process experiments.
