以RuCl_3为前驱体的无氯Ru/Al_2O_3氨合成催化剂的制备

Preparation of the chlorine-free Ru/Al_2O_3 ammonia synthesis catalyst with RuCl_3 as the precursor

用等体积浸渍法制备了一种以RuCl3作为钌母体,分别以γAl2 O3和δ,θAl2 O3为载体的负载型无氯Ru/Al2 O3氨合成催化剂。该催化剂用水合肼还原,以Sm(NO) 3和Ba(NO3) 2 作助剂。催化剂各组分n(Ru)∶n(Ba)∶n(Sm) =1∶0 5 5∶1 6。用N2 物理吸附、XRD、XRF和CO化学吸附等方法对载体和催化剂进行表征。结果表明,以δ,θAl2 O3为载体的催化剂,其氨合成活性高于以γAl2 O3为载体的催化剂的活性;用水合肼还原并用热碱液和纯水洗涤的催化剂不残留Cl- ,Ru金属分散度高,其氨合成活性与用无氯钌前驱体制备并用H2 还原的催化剂的活性相当,在压力10 0MPa ,空速10 0 0 0h- 1的反应条件下,4 75℃转化率为81 2 % ,在5 0 0℃时转化率可以达到10 0 %。而用H2 还原以RuCl3作为钌母体的Ru/Al2 O3催化剂时,因还原后催化剂上有Cl- 残留。

A chlorine-free Ru/Al_2O_3 ammonia synthesis catalyst, with Ru loading of 4.0 wt% and n(Ru)∶n(Ba)∶n(Sm)=1∶0.55∶1.6, was prepared via impregnation method, using γ-Al_2O_3 or δ, θ-Al_2O_3 as the support, RuCl_3 as precursor for ruthenium, Sm(NO_3)_3 and Ba(NO_3)_2 as the promoter, and hydrazine hydrate as the reducing agent. The supports and resultant catalysts were characterized by N_2 physical adsorption, XRD, XRF and CO chemical adsorption. The results showed that activity of the catalyst was strongly dependent on crystalline phase of the Al_2O_3 support and reduction procedure. Compared with the catalysts reduced by H_2 and using RuCl_3 as the precursor of ruthenium, the title catalyst showed higher activity for ammonia synthesis owing to high dispersion of ruthenium and no residual Cl^- after reduction by the hydrazine hydrate and washing with alkaline solution. Activity of the title catalyst was comparable to that of the catalysts reduced by the H_2 and using chlorine-free Ru compound (e.g. Ru_3(CO)_(12)) as the precursor for ruthenium. Conversion of 81.2% at 475 ℃ and 100% at 500 ℃ was attained under 10.0 MPa, GHSV of 10 000 h^(-1).