Selective Hydrogenation of Acetylene over Pd-Mn/Al2O3 Catalysts

Dmitry Melnikov,Vladimir Vinokurov,Mikhail Kotelev,Evgenii Ivanov,Elena Saveleva,Valentina Lyubimenko,Aleksandr Glotov,Valentine Stytsenko

doi:10.3390/catal10060624

Abstract

Novel bimetallic Pd-Mn/Al2O3 catalysts are designed by the decomposition of cyclopentadienylmanganese tricarbonyl (cymantrene) on reduced Pd/Al2O3 in an H2 atmosphere. The peculiarities of cymantrene decomposition on palladium and, thus, the formation of bimetallic Pd-Mn catalysts are studied. The catalysts are characterized by N2 adsorption, H2 pulse chemisorption, temperature-programmed desorption of hydrogen (TPD-H2), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The modified catalysts show the changed hydrogen chemisorption properties and the absence of weakly bonded hydrogen. Using an organomanganese precursor provides an uniform Mn distribution on the catalyst surface. Tested in hydrogenation of acetylene, the catalysts show both higher activity and selectivity to ethylene (20% higher) compared to the non-modified Pd/Al2O3 catalyst. The influence of the addition of Mn and temperature treatment on catalyst performance is studied. The optimal Mn content and treatment temperature are found. It is established that modification with Mn changes the route of acetylene hydrogenation from a consecutive scheme for Pd/Al2O3 to parallel one for the Pd-Mn samples. The reaction rate shows zero overall order by reagents for all tested catalysts.

Highlights

Ethylene is one of the commonly used monomers in the petrochemical industry worldwide and is produced by the steam cracking of hydrocarbons
Decreasing strongly chemisorbed hydrogen is recommended for chemisorption data (Table 1)
Decreasing chemisorbed hydrogen is recommended for acetylene selective hydrogenation as reported strongly in [4,25,47]

Summary

Introduction

Ethylene is one of the commonly used monomers in the petrochemical industry worldwide and is produced by the steam cracking of hydrocarbons. Ethylene cuts typically comprise 0.5%–2% of acetylene, which is a poison for the polymerization catalysts and should be removed by selective hydrogenation to ethylene [1]. A number of active metals (Pd, Ni, Au) modified with a wide range of elements (Ag, Cu, Si, Ga, Sn, Pb, In, S, Fe) and supported on various carriers (Al2 O3 , SiO2 , TiO2 , ZnO). Monometallic Pd catalysts show a high activity but low selectivity to ethylene, so Pd is typically promoted with other metals. Pd-Ag/Al2 O3 catalysts are widely used and much research is devoted to Pd-Ag compositions supported on alumina or silica. It is supposed that the promotion is based on an increased electronic density of the Pd d-band resulting in a decrease in ethylene [3]

Methods

Results

Conclusion