关键词: 乙苯化学链氧化脱氢, 钙钛矿型 SrMnO?, 碱金属负载, 氧载体, 苯乙烯

Abstract:

As a critical basic chemical raw material, styrene production via the traditional ethylbenzene direct dehydrogenation process is constrained by thermodynamic equilibrium and suffers from high energy consumption. Ethylbenzene chemical looping oxidative dehydrogenation (CL-ODH) has emerged as a highly promising alternative technology, while the development of high-performance oxygen carriers remains the core bottleneck for its industrialization. In this study, perovskite-type SrMnO₃ (SMO) was used as the matrix, and three alkali metals (K, Na, Li) were loaded onto SMO via the impregnation method. The objective was to reveal the regulatory mechanism of the differences in alkali metal ionic radii on the crystal structure, oxygen species characteristics, and CL-ODH catalytic performance of SMO. A combination of characterization techniques, including X-ray diffraction (XRD), H₂ temperature-programmed reduction (H₂-TPR), electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS), was employed, coupled with fixed-bed reactor activity evaluation, to systematically investigate the effect of alkali metal loading. The results indicated that K⁺ (ionic radius: 1.38 Å), due to its appropriate size matching with Sr²⁺ (1.18 Å), did not disrupt the main perovskite structure of SMO. Furthermore, K⁺ induced lattice distortion, which increased the surface Mn³⁺/Mn⁴⁺ molar ratio to 0.84 and enhanced the proportion of lattice oxygen (Oₗₐₜₜ) to surface-adsorbed oxygen (Oₐds) by 78%. Meanwhile, the initial reduction temperature was lowered, and the total oxygen release capacity was increased. Under the reaction condition of 600 °C, the K-loaded SMO (K-SMO) oxygen carrier exhibited the optimal performance: the ethylbenzene conversion reached 96.5%, the styrene selectivity was 88.2%, and the CO₂ selectivity was below 5%. Moreover, during 20 CL-ODH cycles, the conversion rate remained above 99%, with only a slight decrease in selectivity from 88.2% to 85.8%. In contrast, Na⁺ (1.02 Å) caused local structural stress, leading to a decline in catalytic performance (conversion: 89.3%; selectivity: 84.7%). For Li⁺ (0.76 Å), severe lattice mismatch resulted in the formation of the SrLiO₂ impurity phase, which caused a significant attenuation of catalytic activity (conversion: 75.1%; selectivity: 80.5%). This study confirms that K loading optimizes the oxygen vacancy concentration and lattice oxygen activity of SMO through ionic size engineering. It provides theoretical basis and experimental support for the design of efficient and stable perovskite-based oxygen carriers for CL-ODH, and simultaneously offers a feasible technical route for energy conservation and consumption reduction in styrene production.

Key words: ethylbenzene CL-ODH, perovskite-type SrMnO?, alkali metal loading, oxygen carrier, styrene