Study On The Performance Of Multi-elements Doped Nano-magnesia And Its Supported Ru-based Catalysts For Ammonia Synthesis

This article was focused on the doping modification of nano-magnesia,and a series of multi-elements doped nano-magnesia(nano-MgO)and its supported Ru-based catalysts for ammonia synthesis were prepared by chemical precipitation-strong electrical adsorption(SEA)method with the aid of ultrasonic wave and by impregnation method,respectively.The effect of modified nano-MgO and its supported Ru-based catalysts with multi-elements on its matter phase,surface performance and texture,reduction and adsorption to hydrogen performance of catalysts were investigated by X-ray diffraction,FE-SEM,N2 physical-adsorption,H2-TPR,H2-TPD,etc.The activities of ruthenium catalysts for ammonia synthesis were measured at 10000 h-1,10 MPa and 375??450?.The main research contents and results were as follows:1.There existed both MgAl2O4 and BaAl2O4 matter phase in nano-magnesia support doped with Al2O3 and barium.Doping aluminum enhanced Ba amount and surface area of the support,but decreased surface bacity.When the molar ratio of A1 to Mg was 1/20 and the calcination temperature was 780?,the activity of Ru/Ba-Mg(Al)O4 catalyst was 69.17 mmol g-1·h-1 under the reaction condition of 425 ?,10 MPa and 10000 h"1.2.ZnO could form solid solution with MgO in Ru/Ba-Mg(1-x)ZnxO catalyst prepared by SEA method,the surface performance of catalyst was modified and barium content was increased.Compared to the activity of Ru/Zn-Ba-MgO and Zn-Ru/Ba-MgO catalysts prepared by impregnation method,it was improved a lot that the activity of Ru/Ba-Mg(1-x)ZnxO catalyst prepared by SEA method,and the activity of catalyst firstly increased and then decreased with the doping amount of zinc.When the molar ratio of Zn to Mg was 0.03:1,the activity of Ru/Ba-Mg(1-x)ZnxO catalyst was 73.25 mmol·g-1·h-1 at 425?,10 MPa and 10000 h-1.3.The effect of hydrogen inhibition of Ru-based catalyst could be effectively reduced by the addition of rare earth oxides.H2-TPD results showed that the strongly absorbed hydrogen species were disappeared absolutely above 600 ?.Furthermore,the doping of trivalent Sm2O3 and Eu2O3 rare earth oxides could increase barium content in the support and the content of the low-temperature barium carbonate(LT-BaCO3),which was the stable formation of barium carbonate phases.The activity of catalyst doped with both Sm2O3 and barium reached 70.73 mmol·g-1·h-1 under the reaction condition of 425?,10 MPa and 10000 h-1,increased by 4.12%compared to the catalyst without rare earth oxide.The activity of catalyst doped with both Eu2O3 and barium was 42.26 mmol·g-1·h-1 under the reaction condition of 375?,10 MPa and 10000 h-1,increased by 20.26%compared to the catalyst without rare earth oxide.The results showed Eu2O3 could improve the catalytic activity in low temperature.But CeO2 decreased the barium content in the support,and the catalytic activity of its.supported catalyst was decreased.4.Loading Ru3(CO)l2 with ball milling was an effective method to prepare Ru/Ba-MgO catalyst.The Ru particle size was quite small and the disperity of Ru paticle was nearly to 50%in the catalyst prepared by ball milling after impregnation.The results showed that the surface area of Ba-MgO support was improved by ball milling and the particle size of both MgO and BaC03 grain became smaller with the increase of ball milling time.At the same time,the content of Ba and Ru in the catalysts decreased.The appropriate ball milling time could improve the properties of nano-MgO and its supported Ru-based catalysts overall.When the catalyst was prepared by ball milling for 2 h,the activity of Ru/Ba-MgO catalyst reached 40.76 mmol·g-1·h-1 under the reaction condition of 375?,10 MPa and 10000 h-1.