Selective Hydrogen Oxidation in the Presence of C₃ Hydrocarbons Using Perovskite Oxygen Reservoirs

Abstract

Perovskite-type oxides, ABO(3), can be successfully applied as solid "oxygen reservoirs" in redox reactions such as selective hydrogen combustion. This reaction is part of a novel process for propane oxidative dehydrogenation, wherein the lattice oxygen of the perovskite is used to combust hydrogen selectively from the dehydrogenation mixture at 550 degrees C. This gives three key advantages: it shifts the dehydrogenation equilibrium to the side of the desired products, heat is generated, thus aiding the endothermic dehydrogenation, and it simplifies product separation (H(2)O vs H(2)). Furthermore, the process is safer since it uses the catalysts' lattice oxygen instead of gaseous O(2). We screened fourteen perovskites for activity, selectivity and stability in selective hydrogen combustion. The catalytic properties depend strongly on the composition. Changing the B atom in a series of LaBO(3) perovskites shows that Mn and Co give a higher selectivity than Fe and Cr. Replacing some of the La atoms with Sr or Ca also affects the catalytic properties. Doping with Sr increases the selectivity of the LaFeO(3) perovskite, but yields a catalyst with low selectivity in the case of LaCrO(3). Conversely, doping LaCrO(3) with Ca increases the selectivity. The best results are achieved with Sr-doped LaMnO(3), with selectivities of up to 93 % and activities of around 150 mumol O m(-2). This catalyst, La(0.9)Sr(0.1)MnO(3), shows excellent stability, even after 125 redox cycles at 550 degrees C (70 h on stream). Notably, the activity per unit surface area of the perovskite catalysts is higher than that of doped cerias, the current benchmark of solid oxygen reservoirs.

Manganese‐containing redox catalysts for selective hydrogen combustion under a cyclic redox scheme

“…Early studies of the catalytic DH + SHC approach investigated the use of a Pt‐Sn‐ZSM‐5 dehydrogenation catalyst in the presence of bismuth, indium, and lead oxides or molybdates . Rothenberg et al further explored SHC by cerium oxides in CL‐ODH processes, identifying the importance of SHC to achieving improved olefin yields; in the absence of a DH co‐catalyst, these studies relied on simulated ethane DH or propane DH effluent streams containing H 2 and olefins . However, the attractiveness of these SHC materials is hindered by their high cost (cerium, bismuth, and indium oxides), toxicity (lead, molybdenum, and vanadium oxides), and lack of stability under continuous redox cycles.…”

Chemical looping beyond combustion – a perspective

“…273,[278][279][280][281][282] Mn-and La-containing perovskites also showed a high SHC selectivity and stability in the presence of C 3 hydrocarbons at 550 1C. 84 It is noted, however, that the SHC selectivity tends to decrease with increasing temperature due to the lower activation energy for hydrogen combustion compared to hydrocarbon oxidation. Therefore, these early SHC studies focusing mostly on operating temperatures o650 1C were exclusively geared towards dehydrogenation applications in combination with a DH catalyst such as supported PGM (e.g.…”

Reduction Kinetics of Perovskite Oxides for Selective Hydrogen Combustion in the Context of Olefin Production

“…[18,19] Pioneering contributions by Grasselli and coworkers identified a set of highly selective metal oxide-based catalysts capable of enhancing propylene yields from propane, including a supported Bi 2 O 3 catalyst which enabled a 140% increase in propylene generation at 540°C. [20][21][22] Subsequent research has focused on the incorporation of SHC catalysts into alkane dehydrogenation processes to improve the yields of ethylene, [23][24][25] propylene, [26][27][28][29][30] etc. Recent work within the chemical looping community showcased improved olefin yields from the conversion of ethane (via CL-ODH) and n-hexane feedstocks resulting from hydrogen combustion by highly selective redox catalysts.…”