Efficient and stable Pt/CaO-TiO2-Al2O3 for the catalytic dehydrogenation of cycloalkanes as an endothermic hydrocarbon fuel

Abstract

The dehydrogenation of liquid hydrocarbon fuel is a potential endothermic reaction for the regenerative cooling of advanced aircraft. The high active and stable dehydrogenation catalyst plays a vital role in the catalytic heat exchange process. Herein, we show that a CaO-modified TiO2-Al2O3 supported Pt catalyst (Pt/CTA) is efficient and stable for the dehydrogenation of cycloalkanes (methylcyclohexane and decalin) under a supercritical condition. Adding an appropriate content of CaO (5 wt%) improves the catalyst durability. For the decalin dehydrogenation reaction (600 °C, 4 MPa, and WHSV = 208.8 h−1), the Pt/CTA maintains 27.9 wt% conversions at 600 min. For the methylcyclohexane dehydrogenation reaction (600 °C, 4 MPa, and WHSV = 188.4 h−1), the Pt/CTA maintains 42.6 wt% conversions at 600 min. The declines of cycloalkanes dehydrogenation conversion are < 7.0 % within 600 min, and no obvious sintering of Pt particles is observed. For a comparison, γ-Al2O3 supported Pt catalyst (Pt/A) exhibits poor catalytic activity and stability, and the conversion decreases to below 10 wt% at 180 min due to severe coke deposition and sintering of Pt particles over the catalysts. The characterization analyses demonstrate that the addition of CaO facilitates the formation of oxygen vacancy defects, thereby increasing the electron density of Pt particles (electronic effect) and promoting encapsulation of Pt particles (geometric effect). Furthermore, the addition of CaO reduces the acid amount and weakens the strength of acid sites over TiO2/Al2O3, inhibiting catalyst deactivation by mitigating coke formation. However, excessive CaO addition (10 wt%) rapidly decreases the surface area of the support, resulting in low dispersion and sintering of Pt particles, ultimately leading to poor catalytic activity and stability.