Preparation And Catalytic Properties Of Nanoporous Ru(Fe,Co)alloys By Dealloying

Ru-based catalysts play an important role in catalyzing the hydrolysis of ammonia borane(AB).Most of the common Ru-based catalysts are supported particles,whose performance is affected by the carrier,and the particles are prone to agglomeration reducing the catalytic activity during the catalysis process.Nanoporous metal is a new type of functional material composed of three-dimensional bicontinuous nano pores and metal ligaments,which can exist independently without being supported by the carrier,and exhibits more excellent catalytic performance due to the combination of high specific surface area of nanoporous materials and the good electrical conductivity of metals.The development of Ru-based nanoporous alloys is expected to obtain new and efficient AB hydrolysis catalysts.The dealloying method is a common method for preparing the nanoporous metals because of its simple operation,short preparation process and relatively low cost.Amorphous alloys exhibiting uniform distribution of elements,a wide range of compositions,and significant differences in electrochemical activity between the elements,which are ideal precursors for preparing the nanoporous metals.There are few reports on the preparation of Ru-based nanoporous alloys by dealloying the amorphous alloys.It has been found that combining Fe/Co and Ru to a bimetallic alloy,which can not only save the cost by reducing the amount of Ru,but also improve the catalytic performance of the Ru alloys.In this paper,melt-spun Fe-Ru-B amorphous alloys are used as precursors,and nanoporous Ru Fe(np-Ru Fe)alloys are prepared by electrochemical dealloying in 0.1 mol/L H₂SO₄ solution.The influences of the precursor composition on the structure,morphology,composition,and catalytic performance for the AB hydrolysis of the np-Ru Fe alloys were systematically studied.Then,the effects of Co addition on the formation and catalytic performance of the np-Ru Fe were investigated.In addition,the formation mechanism of the nanoporous Ru(Fe,Co)(np-Ru(Fe,Co))alloys prepared by dealloying the(Fe,Co)-Ru-B amorphous alloys was discussed.The main research results are as follows:(1)The np-Ru Fe alloys composed of a single hcp-(Ru,Fe)phase can be obtained by dealloying Fe_xRu_75-xB₂₅(x=60-70)amorphous precursors.The np-Ru Fe alloys exhibit a uniform and interpenetrating ligament/channel structure.With the Fe content increasing from60 to 70 at.%in the precursors,the average pore size(d)increases from 5 to 10 nm,the average ligament thickness(l)decreases from 15 to 11 nm,the atomic ratio of Ru/Fe decreases from71.2/28.8 to 53.7/46.3.The catalytic performance for AB hydrolysis of the np-Ru Fe alloys increases with the increase of Fe content in the precursors.The initial turnover frequency(TOF)characterizing the catalytic activity of the np-Ru Fe alloys rises from 0.41 to 3.17 mol H₂ mol^-1Ru min^-1 with increasing x from 60 to 70.(2)The np-Ru Fe alloys with the hcp-(Ru,Fe)phase and uniform pore size distribution can be obtained by dealloying Fe₆₅Ru_35-xB_x(x=20-30)amorphous precursors.As the B content rises from 20 to 30 at.%in the precursors,the d increases from 5 to 7 nm,the l decreases from61 to 10 nm,and the atomic ratio of Ru/Fe decreases from 70.4/29.6 to 56.0/44.0.The catalytic performance for AB hydrolysis of the np-Ru Fe alloys increases with enriching of the B content in the precursors.The np-Ru Fe alloy prepared from a Fe₆₅Ru₅B₃₀alloy exhibits the outstanding catalytic activity,and the TOF is 5.05 mol H₂ mol^-1Ru min^-1.(3)The np-Ru(Fe,Co)alloys composed of a hcp-(Ru,Fe,Co)phase can be obtained by dealloying amorphous Fe_65-xCo_xRu₅B₃₀(x=5?40).The d and l of the np-Ru(Fe,Co)alloys are in the ranges of 6?9 nm and 17?20 nm,respectively.As the Co content increases in the precursors,the atomic ratio of Fe/Co gradually decreases,and that of Ru/(Fe+Co)ranges from55.5/44.5 to 49.7/50.3.The catalytic performance for AB hydrolysis of the np-Ru(Fe,Co)alloys increases with increasing the Co content,and reaches the best when x=40,and the TOF is 15.14mol H₂ mol^-1Ru min^-1.(4)In the course of dealloying,the active elements of B and partial(Fe,Co)are selectively dissolved from the amorphous alloys,which results in the decomposition of the amorphous phase.The retained(Fe,Co)and Ru atoms form a nanoporous structure composed of hcp-(Ru,Fe,Co)phase by short-distance surface diffusion and structure rearrangement.Therefore,the d gradually rises and the l keeps decreasing with enriching of the B and(Fe,Co)in the precursors.The l of the nanoporous alloys containing Co is larger than that of the np-Ru Fe,which might be due to the lower dissolution rate of the Co than Fe.