| The carbon dioxide reforming methane makes full use of the two greenhouse gases CH4 and CO2,and produces a proper ratio of H2/CO for the the Fischer-Tropsch reaction.Nickel-based catalysts have become a hot spot research because of its high catalytic activity and low cost.However,these catalysts are easy to sinter and accumulate at high temperature.Therefore,it is a hot research to improve the dispersion of the activity Ni,reduce the particle size of Ni,improve the interaction between Ni and the carrier,and then inhibit the migration of Ni at high temperature.In this paper,high specific surface area mesoporous MCM-41 molecular sieve was used as the carrier which can make Ni highly dispersed.Then we use many ways to modify catalysts to further improve the dispersion of Ni,decrease the particle size,and then enhance the force between the carrier and the activity Ni which can improve the activity and stability of the catalysts.This paper mainly includes the following four contents:First,the Ni/MCM-41 molecular sieve catalysts was synthesized and the catalysts preparation conditions(such as Ni content,calcination temperature)and catalytic reaction conditions(such as reduction temperature,reduction time and space velocity)were optimized.The optimum preparation conditions of Ni/MCM-41-Imp catalyst were as following: the content of Ni was 10% and the calcination temperature was 550 ?.The optimum catalytic reaction conditions were as following: the reduction temperature was 700 ?.Respectively,the reduction time and the reaction space velocity were 1.5h and 36000 ml/(gcat.h).Under the optimum catalysts preparation conditions and the optimum catalytic reaction conditions,the conversion of CH4 and CO2 reached 54.9% and 63.1%,at the same time the yield of CO was 56.1% at 750 ?.In order to improve the catalytic activity of catalysts,some promoters were introduced.Addition of Ce,La,Co,Mn,Na and other promoters on the 10% Ni/MCM-41 catalyst were studied by impregnation method.It was found that the addition of Ce,La and Co had improved catalytic performance in different degrees.Compared to 10%Ni/MCM-41-Imp(in this paper,all the tempreture referred is 750?,except the special instructions),10%Ni/1%CeMCM-41-Imp demonstrated conversion enhancement of CH4 and CO2 by 7.2% and 7.2% respectively;In addition,the yield of CO also showed 3.1% increase.Compared to 10%Ni/MCM-41-Imp,10%Ni/3%LaMCM-41-Imp demonstrated conversion enhancement of CH4 and CO2 by 7.2% and 8.3% respectively;In addition,the yield of CO also showed 5.7% increase.Compared to 10%Ni/MCM-41-Imp,10%Ni/3%CoMCM-41-Imp demonstrated conversion enhancement of CH4 and CO2 by 6.2% and 4.9% respectively;In addition,the yield of CO also showed 3.3% increase.The catalysts were characterized by XRD,TPR and TPD.XRD results showed that the addition of Ce,La and Co had increased the dispersion of Ni and decreased the particle size.TPR characterization showed that the addition of Ce,La and Co had made the reduction peak of Ni move to high temperature,indicating that the addition of the prometors enhanced the interaction between Ni and the carrier.The characterization of TPD showed that the addition of Ce could increase the amount of CO2 adsorbed.In order to further improve the catalytic performance,the catalysts were prepared by sol-gel method and coprecipitation method investigating with Ce,La,Co.It was found that the addition of Ce,La and Co could also improve the activity of the catalysts in different degrees.Compared to 10%Ni/MCM-41-Sol,10%Ni3%Ce/MCM-41-Sol demonstrated conversion enhancement of CH4 and CO2 by 10.6% and 9.9% respectively;In addition,the yield of CO also showed 11.5% increase.Compared to 10%Ni/MCM-41-Sol,the 10%Ni5%La/MCM-41-Sol demonstrated conversion enhancement of CH4 and CO2 by 9.2% and 11.8% respectively;In addition,the yield of CO also showed 8.2% increase.Compared to 10%Ni/MCM-41-Sol,10%Ni3%Co/MCM-41-Sol demonstrated conversion enhancement of CH4 and CO2 by 7.3% and 8.4% respectively;In addition,the yield of CO also showed 11.5% increase.Compared to 10%Ni/MCM-41-CP,10%Ni3%Ce/MCM-41-CP demonstrated conversion enhancement of CH4 and CO2 by 10.9% and 9.1% respectively;In addition,the yield of CO also showed 12.1% increase.Compared to 10%Ni/MCM-41-CP,10%Ni3%La/MCM-41-CP demonstrated conversion enhancement of CH4 and CO2 by 3.2% and 8.4% respectively;In addition,the yield of CO also showed 11.5% increase.Compared to 10%Ni/MCM-41-Sol,10%Ni3%Ce/MCM-41-Sol demonstrated conversion enhancement of CH4 and CO2 by 8.3% and 4.9% respectively;In addition,the yield of CO also showed 9% increase.XRD results showed that the addition of Ce,La and Co could improve the dispersion of Ni and reduce its particle size.TPR characterization indicated that the addition of La was beneficial to improve the interaction between Ni and the carrier.In order to further improve the catalytic activity of the catalyst,the surface of the catalysts were modified by alcohol to enhance the number of hydroxyl groups on the catalyst surface,so that the Ni active component on the catalyst is highly dispersed and the catalytic activity of the catalysts is improved.10%Ni/MCM-41-Imp catalyst was prepared by co-impregnation with different alcohols,such as ethanol(EA),ethylene glycol(EG)and isopropanol(IA).The catalytic activity of the catalysts were improved to some extent,but there was no significant difference in the co-impregnation of the three alcohols in terms of the activity of the catalysts.Compared to 10%Ni/MCM-41-Imp,alcohol co-impregnation demonstrated conversion enhancement of CH4 and CO2 by 24% and 17% respectively;In addition,the yield of CO also showed 20% increase.The XRD characterization indicated that the modification of the alcohols improved the dispersion of Ni and reduced its particle size.Then,we used the surfactant to modify the catalyst.Compared to 10%Ni/MCM-41-P123(0),Ni/MCM-41-P123(1/50)demonstrated conversion enhancement of CH4 and CO2 by 18% and 8.4% respectively;In addition,the yield of CO also showed 14.5% increase.Compared to 10%Ni/MCM-41-TPAOH(0),Ni/MCM-41-TPAOH(1/50)demonstrated conversion enhancement of CH4 and CO2 by 18.7% and 12.4% respectively;In addition,the yield of CO also showed 14.1% increase.Compared to 10%Ni/MCM-41-CTAB(0),Ni/MCM-41-CTAB(1/50)demonstrated conversion enhancement of CH4 and CO2 by 18.6% and 15.1% respectively;In addition,the yield of CO also showed 17.3% increase.XRD results showed that the addition of surfactant could increase the dispersion of Ni and reduce its particle size.The BET characterization showed that the addition of surfactant could increase the specific surface area of the catalysts,which indicated that the dispersion of Ni on the carrier had been improved.The TPR indicated that the addition of surfactants could enhance the interaction between Ni and the carrier. |
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