Abstract
The two structural modifications of Cu60Pd40 were synthesized as bulk powders and tested as unsupported model catalysts in the semi-hydrogenation of acetylene. The partly ordered low-temperature modification (CsCl type of structure) showed an outstanding ethylene selectivity of >90% over 20 h on stream while the disordered high-temperature modification (Cu type of structure) was 20% less selective, indicating an influence of the degree of order in the crystal structure on the catalytic properties. The results are supported by XRD and in situ XPS experiments. The latter suggest the existence of partly isolated Pd sites on the surface. In situ PGAA investigations proved the absence of metal hydride formation during reaction. Quantum chemical calculations of the electronic structure of both modifications using the CPA-FPLO framework revealed significant differences in their respective density of states, thus still leaving open the question of whether the degree of structural order or/and the electronic hybridization is the decisive factor for the observed difference in selectivity.
Highlights
The semi-hydrogenation of acetylene to ethylene is an important cleaning step in the industrial polymerization of ethylene and serves as a model reaction for the exploration and development of catalysts because of the small molecules involved [1,2]
Supported Cu–Pd catalysts or Cu–Pd nanoparticles have been tested in dimethyl ether reforming [18], the water gas shift reaction [19], electrochemical oxidation of methanol [20], nitrate hydrogenation [21,22], hydration of acrylonitrile [23,24], hexa-1,5-diene hydrogenation [25] and the reduction of nitrates [26]. In this contribution we report on the preparation of the disordered solid solution and the partly ordered intermetallic compound at the composition Cu60Pd40 as unsupported powders and their catalytic properties in the semi-hydrogenation of acetylene
In the partly ordered CsCl-type modification of Cu60Pd40, palladium atoms are sharing the central position in the unit cell, which is exclusively surrounded by eight copper atoms as first nearest neighbors, forming a cube
Summary
The semi-hydrogenation of acetylene to ethylene is an important cleaning step in the industrial polymerization of ethylene and serves as a model reaction for the exploration and development of catalysts because of the small molecules involved [1,2]. The two above-mentioned modifications were tested as unsupported catalysts in the decomposition of formic acid, showing significantly lower activation energy for the partly ordered intermetallic compound compared to the disordered solid solution [12]. Supported Cu–Pd catalysts or Cu–Pd nanoparticles have been tested in dimethyl ether reforming [18], the water gas shift reaction [19], electrochemical oxidation of methanol [20], nitrate hydrogenation [21,22], hydration of acrylonitrile [23,24], hexa-1,5-diene hydrogenation [25] and the reduction of nitrates [26] In this contribution we report on the preparation of the disordered solid solution and the partly ordered intermetallic compound at the composition Cu60Pd40 as unsupported powders and their catalytic properties in the semi-hydrogenation of acetylene. The influence of the density of states of the different modifications on the catalytic properties is discussed
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