Insights into the effects of steam on propane dehydrogenation over a Pt/Al₂O₃ catalyst

Abstract

Catalytic propane dehydrogenation over an alumina supported Pt catalyst in the presence of steam is carried out and it is found that the catalyst activity is increased and the apparent activation energy lowered due to the presence of steam. Three possible mechanisms, i.e. co-adsorption, Langmuir-Hinshelwood and Eley-Rideal, of changes in energetics and pathways for propane dehydrogenation due to the presence of steam are explored by DFT calculation. The results show that co-adsorption of C 3 species with the surface oxygenated species would elevate dehydrogenation energy barriers due to repulsion interactions between them. Surface -OH is more active than surface -O in activating C-H bond in propane and propyl species through either Langmuir-Hinshelwood or Eley-Rideal mechanism and plays an important role in propane dehydrogenation with steam. The Langmuir-Hinshelwood mechanism is kinetically favorable, in which the activations of the first H in propane by surface -OH are the rate determining steps, but the activation energies are higher than that on clean Pt(111) surface. The observed enhanced catalyst's activity is ascribed to the lowered coking rates as well as the changes in surface coverage due to the co-adsorption of mechanism. For PDH under steam atmosphere, the role of surface -OH is essential, most likely through Langmuir-Hinshelwood mechanism, in which the first C-H bond activation is the rate determining step in the overall PDH reaction route. The promoting effect of steam can be ascribed to the removal of cokes deposited on active Pt surfaces and the changes of adsorption species coverage on Pt surface.

The role of H2S addition on Pt/Al2O3 catalyzed propane dehydrogenation: a mechanistic study

“…The elevated activation energies for Pt(111) and Pt(211)with co-adsorbed sulfur species may lead to the decreased activity. In our previous work, with oxygenated species co-adsorbed on Pt(111), the similar result in activation energies was found and the catalyst activity also decreased 63.…”

Thermally Stable and Regenerable Platinum–Tin Clusters for Propane Dehydrogenation Prepared by Atom Trapping on Ceria

“…When no water vapor was fed to the Pt–Sn/CeO 2 catalyst, the coke content increased from 0.5 to 2.8 wt % and the conversion dropped. The results confirm that the addition of water vapor can suppress the formation of coke during propane dehydrogenation at high temperature . The coke formed under the high temperature conditions was investigated by electron microscopy and Raman spectroscopy.…”

State-of-the-art catalysts for direct dehydrogenation of propane to propylene

“…Pt-based catalysts are the most widely used PDH catalysts that have been commercially employed in Oleflex (UOP) craft [21,23,[49][50][51]. Compared with CrOx-based catalysts, Pt-based catalysts display many advantages such as eco-friendliness and high stability.…”