以RuCl3为前驱体的无氯Ru/Al2O3氨合成催化剂的制备

用等体积浸渍法制备了一种以RuCl₃作为钌母体，分别以γ-Al₂O₃和δ,θ-Al₂O₃为载体的负载型无氯Ru/Al₂O₃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∶0.55∶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,θ-Al₂O₃为载体的催化剂，其氨合成活性高于以γ-Al₂O₃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10.0 MPa，空速10 000 h^-1的反应条件下，475 ℃转化率为81.2%，在500 ℃时转化率可以达到100%。而用H₂还原以RuCl₃作为钌母体的Ru/Al₂O₃催化剂时，因还原后催化剂上有Cl^-残留，其催化活性较低。

Preparation of the chlorine-free Ru/Al2O3 ammonia synthesis catalyst with RuCl3 as the precursor

A chlorine-free Ru/Al₂O₃ 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-Al₂O₃ or δ, θ-Al2O3 as the support, RuCl₃ as precursor for ruthenium, Sm(NO₃)₃ and Ba(NO3)2 as the promoter, and hydrazine hydrate as the reducing agent. The supports and resultant catalysts were characterized by N₂ physical adsorption, XRD, XRF and CO chemical adsorption. The results showed that activity of the catalyst was strongly dependent on crystalline phase of the Al₂O₃ support and reduction procedure. Compared with the catalysts reduced by H₂ and using RuCl₃ 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 H₂ and using chlorine-free Ru compound (e.g. Ru₃(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.