Effect of the Size of Iron Nanoparticles on the Catalytic Activity and Selectivity of Fe/Cnt Nanocomposites in Hydrogenolysis of Ethylene

Abstract

It was established that increase in the size of the iron nanoparticles in Fe/CNT nanocomposites from 4 to 8 nm leads to increase of their activity and selectivity with respect to methane in the hydrogenolysis of ethylene. The activity and selectivity of the nanocomposites are significantly higher than those of macrocrystalline iron, and this may be due to differences in the thermal conductivity of the bulk iron and the carbon nanotubes.Hydrogenolysis reactions, which take place with cleavage of a C-C bond, lead to decrease in the chain length of aliphatic hydrocarbons and also to ring cleavage in cyclic hydrocarbons [1]. Such reactions are side processes and are undesirable in the reforming and isomerization of hydrocarbons [2,3]. Reactions that take place with cleavage of a C-C bond are structure-sensitive [3]. By studying the hydrogenolysis processes it is possible to discover new reasons for the effects of nanoparticle size, impurities, support, and the composition of bimetallic nanoparticles on their activity and also special features of the mechanisms of such processes [4]. As a rule, the effect of particle size on their activity in hydrogenolysis has been studied for the model hydrogenolysis of ethylene [3]. The hydrogenolysis of ethylene is of interest on account of the possibility of determining the effect of the size of the nanoparticles both on the activity of materials that contain such nanoparticles and on their selectivity in the process.Carbon nanotubes (CNTs) have relatively high chemical, thermal, and electrochemical stability, and this helps to extend the working life of catalysts that contain them. The accessibility of the surface and the possibility of controlling the porosity and the nature of the surface functional groups make carbon nanotubes more promising than activated carbon as catalyst material. Despite the lower specific surface area of carbon nanotubes compared with activated carbon, nanocomposites with deposited metal nanoparticles, including iron nanoparticles, on CNTs usually exhibit high activity in heterogeneous catalytic processes and particularly in hydrogenation and hydrogenolysis [5].Iron-containing catalysts are widely used in industry and particularly in the Fischer-Tropsch synthesis and in the synthesis of ammonia. At the present time catalysts with deposited nanoparticles of iron are being actively investigated in hydrogenation processes [6]. Study of the dependence of the effect of the size of the iron nanoparticles on the catalytic activity and selectivity of nanocomposites containing such nanoparticles are of both theoretical and practical interest in view of the fact that the establishment of such relationships may lead to the creation of novel catalytic systems with controllable activity and selectivity [7,8]. The literature does not contain any systematic investigations of hydrogenolysis reactions at iron-containing catalysts; this has led to interest in study of such systems and may lead to the discovery of new effects characteristic of iron but not of noble metals...

Green Synthesis of Size-Tunable Iron Oxides and Iron Nanoparticles in a Salt Matrix

“…Metal and alloy nanoparticle science and technology play very important role in various modern scientific fields. − Nanoparticles (NPs) of Fe, its alloys, and oxides receive great interest for use as magnetic materials, − battery anode materials, and catalysts, − as well as for biomedical − and water treatments. − Monodispersed Fe NPs have been synthesized by thermal decomposition of Fe­(CO) x , a toxic agent, in the presence of capping agents in organic solvents. ,− The particle size can be varied and well controlled with varying the stabilizing agents, the type of solvents, and other synthesis parameters. Iron carbonyl complexes have been also used in physical methods for synthesis of Fe NPs. , Toward a greener synthesis in an aqueous solvent, hydrothermal synthesis, reduction of Fe salts by NaBH 4 , , or more environmentally friendly leaf-extract compounds ,− as the reducing agents were used to produce Fe NPs.…”