Hsieh, Tzung-En: Unraveling the Formation and Property Evolution of the Active Species in Supported Catalytically Active Liquid Metals by Photoelectron Spectroscopy. , Dissertation, Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2024
10.25593/open-fau-1437
Open Accesn Version
Abstract:
Efficient conversion of light alkanes into alkenes is highly demanded due to the wide application of alkene molecules in petrochemical industry and Liquid Organic Hydrogen Carrier (LOHC) for fuel cell industry.1-5 Within light alkane conversions, propane dehydrogenation reaction (PDH) is a critical reaction due to the wide application of propylene as a key precursor for chemical synthesis (Fig. 1.1). Typical cases requiring propene are polypropylene synthesis for plastic production and synthesizing propylene oxide as an important intermediate for further chemical syntheses, e.g., glycerol.6-7 The demand for propylene keeps increasing8-9 and is predicted to grow at an average annual rate of 2-3% at least until 2027 indicating the importance of efficient propene synthesis (Fig. 1.1b).8-10 The propane-to-propene conversion can be achieved with high propene selectivity via nonoxidative catalytic PDH.6, 11-12 Non-oxidative PDH has been reported as an endothermic reaction that is favorable to be triggered at high temperatures (≥ 550 oC) and near ambient pressure (1-2 bar) based on Le Chatelier’s principle: () ⇌ () + (), Δ= 124.3 ∙ During PDH, the byproducts such as ethene and methane are also observed to form which can be attributed to similar activation energies of C-H and C-C bonding cleavage.13 Side reactions other than C-H bonding cleavage not only reduce the selectivity of PDH, but also induce coke formation by cracking hydrocarbon molecules on catalyst surfaces passivating the catalyst, terminating the catalytic chain reactions.14-16 The typically used TiO2, Al2O3 or SiO2 supported transition metal catalysts, e.g. platinum and rhodium, show both, a high catalytic reactivity (≥ 20%) and a high selectivity (≥ 90%) for PDH.17-21 These supported metal catalysts are robust due to the suitable mechanical strength, high thermal conductivity and stability, which allow the catalysts to withstand harsh reaction conditions.6, 22 However, coke formation during the catalytic reaction decreases the reactivity of commercial PDH catalysts by 80 % during 3 hours of operation.15 In the petrochemical industry, an annealing procedure at 600 oC under an oxygen-rich environment is employed as a catalyst regeneration step to burn off the coke covering the catalyst surface.23 This regenerating procedure not only causes extra energy consumption but presumably also changes the catalyst structure.14, 24-25 Conventional supported Pt-based catalysts show an irreversible Pt sintering due to high temperature reaction and regeneration.6, 26 ...