A BSTRA C T Pd-23 at% Ag and Pd-78 at% Y hydrogen-di$%sion membranes were (1) prepared by argon-arc melting of the constituent elements, (2) characterised, (3) examined for hydrogen permeation and (4) used as catalysts in ethylene hydrogenation reactions. Ethylene was self-hydrogenated on the membrane surfaces in the absence ofpermeate hydrogen. The hydrogenation with andfor without the permeate hydrogen was carried out in the temperature range 100-450°C at ethylene pressures of 1.0-1.5 bars and diferential pressures across the membrane in the range 1.0-68 bars. Mainly CI-C4 hydrocarbons and up to 60% conversion of ethylene to products were obtained.
Intermetallic alloys of the general formula Zr50NixCu50‐x (where 0 ⩽ × ⩽ 50) were prepared by argon arc melting and powdered by hydrogen decrepitation. These materials were used as catalysts for the H2/CO reaction in the temperature range 300–400°C, in the pressure range 1–9 barg and for H2/CO ratios in the range 1 to 5. Derived catalysts were prepared by air treatment of the hydrided alloys and were subjected to identical investigations to the latter.
The hydrided and derived catalysts behaved in a very similar manner in terms of selectivity, which increased with respect to higher hydrocarbon production with (i) increasing total pressure, (ii) decreasing values of H2/CO and (iii) increasing copper to the extent where CH4 contents was < 50% of the products. Increased temperature gave rise to increasing methane production. The activity of the alloy system exhibited a sharp activity maximum at the nickel‐rich end of the series and the copper‐rich alloys were almost ten times less active. The initial rate equation was observed to be of the form:
However, whereas n = 0, m varied between 0.5 and 1.2 for both series of catalysts.
The presence of copper promotes the formation of higher hydrocarbons, especially the formation of ethene. It is presumed that the presence of copper at the surface inhibits the polyerization of CHX species and favours the CO insertion.
Intermetallic alloys of the general type Zr50MxN50‐x, where 0 ≦x≧ 50, were prepared by argon arc melting of the constituent elements. M and N are combinations of cobalt, nickel, copper and ruthenium. The alloys were powdered by hydrogen decrepitation, which yielded hydrided species of the general composition Zr50MxN50‐′H150‐x′ in which form they were used as catalysts.
The reactions were carried out in a semi‐micro‐tubular flow reactor at 1 barg, 350°C and a H2/CO feed ratio of 3. It was observed that, while methane (CH4) was the dominant product, there was clear indication that intermetallic alloys containing Cu and Ru gave larger quantities of higher hydrocarbons and one alloy Zr50Ru25Co25 was 102‐103 times more active than any of the others, based on turnover number (TON) calculations; its activity was also observed to decline rapidly. The study of catalysts derived from intermetallic compounds provides a useful means of investigating alloy effects, due to the precise stoichiometry of the starting compounds which have long‐range order in respect of crystal structure. However, they can be rendered unstable by involvement with reactants, especially with oxygen.
Alloys of the general formula Zr50NixCO50‐x, where 0 ≦x≧ 50, have been prepared and used in the temperature range 300–400°C, in the pressure range 1–9 barg in a microtubular reactor for the reaction of hydrogen with carbon monoxide to give hydrocarbons.
The alloys or intermetallic materials were prepared by argon arc melting, powdered by hydrogen decrepitation and characterised by means of optical microscopy (metallography), scanning electron microscopy with surface analysis and magnetic susceptibility measurements.
The selectivity towards higher hydrocarbons increased with (i) increase in the total pressure and (ii) decrease in hydrogen content of the feed gases. The kinetics were found to be of the form:
where m = 1.0 ± 0.2 and n = 0. The apparent energy of activation (Ea) lay in the range of 80–130 kJ mole−1 and there appeared to be a compensation effect between Ea and the pre‐exponential factor A.
The turnover numbers for the reaction exhibited an activity maximum for alloys of composition around Zr50Ni40Co20 and Zr50Ni30Co20. Magnetic susceptibility measurements indicated that alloys changed their nature from moderately paramagnetic to strongly paramagnetic or even ferromagnetic after use and this is attributed to the conversion of zirconium to zirconium oxide during reaction with the attendant production of free 3d‐transition metals. Derived catalysts prepared by air treatment of the hydrogen‐decrepitated intermetallics behaved almost identically to the latter materials and gave similar magnetic susceptibility values to used hydrided materials.
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