Υδρογονωση Μονοξειδιου Του Ανθρακα Σε Ζεολιθικους Καταλυτες Νικελιου, Κοβαλτιου Και Ρουθηνιου

Abstract

Carbon monoxide hydrogénation has been investigated on Ni, Co, Ru and NiCo, RuCo bimetallics on zeolite Y, at atmospheric pressure and temperatures of 200-400°C. Catalysts were prepared by ion exchange to a total metal loading of 2% by weight; in the case of monometallic nickel catalysts, metal loadings of 2 to 5% were also examined.Controlled ion exchange ensured uniform metal distribution on the zeolite support. Atomic absorption spectroscopy and thermogravimetric analysis were used for the determination of catalyst composition and extent of exchange. Total surface area measurements and X-ray diffraction analysis were applied to samples in several stages of preparation, activation and activity testing. The prepared catalysts exhibited high surface area and crystallinity throughout their use.Catalysts were reduced in pure hydrogen by slow heating to 450°C. Metal surface area development depended on the nature of the active component, as evidenced by X-ray diffraction and hydrogen chemisorption at 35°C. Nickel agglomerated to form large crystallites on the external surface of the support, ruthenium remained finely dispersed within the zeolite cavities, while cobalt was stabilized by the zeolite and poorly reduced. Reduction of cobalt in bimetallic catalysts was enhanced by the presence of nickel or ruthenium, probably due to spillover of atomic hydrogen. X-ray analysis of bimetallics did not reveal the presence of any new metal phases.A number of techniques were employed to obtain catalyst dispersion; among these, volumetric chemisorption proved the most suitable one. Gas chemisorption on the active metals was relatively low, weak and to a large extent reversible, probably due to metal -support interactions. Ru and RuCo catalysts had the highest dispersion, followed by NiCo and Ni.A differential reactor was used for catalyst testing at a space velocity of 12500 h-i and H2/CO ratio of 3. At these conditions, reaction products on Ni, NiCo were Ci -C3 light hydrocarbons, while Ru and RuCo produced hydrocarbons in the Ci -CO range. Normal paraffins and α-olefins were the products of the hydrogénation reaction, while branched paraffins and ß-olefins were formed by secondary reactions of the primary synthesis products on zeolite acid sites. At 300°C carbon dioxide was formed, due to CO disproportionation and water-gas shift reaction. Carbon monoxide viii 2.5. ΔΙΜΕΤΑΛΛΙΚΟΙ ΚΑΤΑΛΥΤΕΣ 75 3. ΖΕΟΛΙΘΟΙ 85 3.1.