In this context, using nickel catalysts during the selective hydrogenation of alkyne is less studied and has been recently researched. As Pd has increased its cost, it is a challenge to synthesize cheaper catalysts. A major part of research efforts have been devoted to the partial hydrogenation of short-chain alkynes such as ethyne, with few works related to longer chain alkynes. Many catalysts, mono- or bimetallic as well as complexes of several transition metals, have also been proposed for these kinds of reactions. Another kind of material, not clearly included in any of these groups, is carbonaceous species, whose outstanding properties as a catalyst support are well recognized, among them are the possibility of modifying the specific surface area, the porosity and the surface chemistry moreover, carbon supports present the advantage of being inert in liquid reaction media. Besides, modified palladium or nanoparticles of Pd have also been investigated. Several materials have been used as supports, and they are usually classified as organic (macroreticular/macroporous polymers) or inorganic (silica, alumina, zeolites and clays). During decades, much research has been carried out modifying this type of catalyst in order to increase the activity and selectivity to alkenes of low molar weight. One of the most used catalytic systems for these kinds of reactions is the Lindlar catalyst (Pd/CaCO 3 modified with Pb(OAc) 2), developed in 1953. Many authors have found that supported palladium catalysts present the highest catalytic activity for the partial hydrogenation of alkynes to alkenes. Many natural products, such as biologically active compounds, are synthesized through this kind of reactions.Ĭlassical heterogeneous catalysts used to hydrogenate multiple carbon-carbon bonds contain noble metals such as Pd, Pt, Ru and Rh, which are highly active and selective. The hydrogenation of any alkyne conduces naturally to the alkene formation as the former trends to bind more strongly than the latter on the supported metal catalyst, thus blocking the possibility of the alkene readsorption or displacing it from the support surface. Specifically, the catalytic selective hydrogenation of alkynes using either homogeneous or heterogeneous catalysts has been widely studied in the past several years. Partial hydrogenation reactions using catalytic materials allow a reduction in operational costs and also enable high selectivity to alkenes. Alkenes have industrial and academic relevance on a large scale industries such as petrochemical, pharmaceutical and agrochemical use these compounds as raw materials. Among them, acetylenic hydrocarbons are very unstable so they must be transformed to olefins.
Petroleum cuts contain mixtures of unsaturated and aromatic compounds.
Nevertheless, the influence of geometrical effects and/or mixed active sites in the catalysts, as well as metal-metal and metal-support interactions, cannot be neglected. XPS technique allowed verifying that the presence of electron-deficient species on the catalyst surface with high metal loading affects the conversion and selectivity to the desired product. The Lindlar commercial catalyst, commonly used in these types of reactions, was used for comparative purposes. The objective of this work is to study 1-heptyne-selective hydrogenation using supported catalysts influenced by different factors: (a) pretreatment reduction temperature, (b) reaction temperature, (c) type of support, (d) metal loading, (e) precursor salt and (f) addition of a second metal to monometallic palladium catalyst. The catalysts were characterized by inductively coupled plasma, hydrogen chemisorption, temperature-programmed reduction and X-ray photoelectronic spectroscopy (XPS). Mono- and bimetallic catalysts (palladium, ruthenium and nickel) were synthetized by the incipient wetness technique using gamma alumina and an activated carbon as supports. Finding an economic, active and selective catalyst for the production of alkenes through partial hydrogenation of alkynes is thus an important challenge.
Partial hydrogenation of alkynes has industrial and academic relevance on a large scale industries such as petrochemical, pharmacological and agrochemical use these compounds as raw material.
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