Induction heating for catalytic dehydrogenation of liquid organic hydrogen carriers

Abstract

Hydrogen storage using liquid organic hydrogen carriers (LOHCs) is a promising solution due to their high hydrogen storage density, safe handling under ambient conditions and compatibility with existing crude oil infrastructure. However, large-scale implementation is limited by the high energy demands and uneven temperature profiles of the endothermic dehydrogenation reaction. Current heating approaches electrical heaters and hydrogen burners—suffer from heat losses, reducing the overall energy efficiency. Electromagnetic inductive heating offers a compelling alternative; it delivers rapid, volumetric heating by generating heat directly within inductively active materials and transferring it efficiently to the catalyst and surrounding fluid. This study explores inductive heating for LOHC dehydrogenation using perhydro￾benzyltoluene (H12-BT) as a model compound and Pt/-Al₂O₃ catalysts synthesised via wet impregnation (0.3–8 wt.% Pt). Catalyst loading was confirmed using Inductively coupled plasma–optical emission spectroscopy (ICP-OES), and characterisation was performed using Brunauer–Emmett–Teller (BET), Carbon monoxide (CO) pulse chemisorption, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), Transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and Hydrogen temperature programmed reduction (H₂-TPR). Four catalyst configurations were tested in an inductively heated reactor: (1) uncoated stainless steel (SS) pellets, (2) a mixture of SS and Pt/-Al₂O₃ pellets, (3) Pt/-Al₂O₃ coated SS pellets, and (4) a mixture of catalyst pellets and SS. The Pt/-Al₂O₃ coated SS pellets with 0.11 mol% Pt gave the highest performance: 0.35 gH₂/gPt/min productivity and 97.82% H12-BT conversion. Inductive and conventional electrical heating were compared using 5 wt.% Pt/Al₂O₃ coated SS pellets. Although electrical heating reached a higher maximum hydrogen flow rate (62.56 mL/min) and cumulative H₂ volume (2.03 L), inductive heating delivered a more stable profile (max flow rate: 27.78 mL/min, 1.65 L cumulative H₂), showing better thermal regulation. Among the catalyst loadings, 5 wt.% Pt gave optimal performance. Higher loadings (8 wt.%) led to decreased metal dispersion, larger particle sizes and pore blockage due to agglomeration. The influences of polymer binders, Polyvinyl alcohol (PVA) and Polyvinylpyrrolidone (PVP), and coating thickness on catalyst performance were also assessed. Binder molecular weight and concentration influenced coating uniformity, adhesion, and diffusion. PVP (MW 55,000) at 0.5 wt.% offered the best results (0.26 gH₂/gPt/min productivity, 65.39% conversion, 1.64 L H₂). Coating thickness effects were explored using eggshell Pt/-Al₂O₃ coatings on SS pellets. A thickness of 81 µm (5 wt.% Pt) maximised H₂ yield and minimised by-products, outperforming both the thinner (62 µm) and thicker (>100 µm) coatings. Gas chromatography–mass spectrometry (GC-MS) confirmed the dehydrogenation pathway via partially hydrogenated BT (H6-BT) to benzyltoluene (HBT). Using GC-MS with single quadrupole detection (GC-SQ￾MS) and advanced gas analysis, no by-products were detected at conversions >90%. Catalyst stability over four cycles showed signs of deactivation: productivity declined from 0.302 to 0.120 gH₂/gPt/min and Degree of dehydrogenation (DOD) from 27% to 3%. Despite this, by￾product formation declined, indicating reduced catalytic activity-limited side reactions. Kinetic analysis showed that the 82 µm coating gave the highest reaction rate constant and turnover frequency value (28.12 min⁻¹), suggesting an optimal balance between surface area and mass transfer. Thorough characterization confirmed the synthesis and dehydrogenation efficacy of Pt/γ-Al₂O₃. Results from ICP-OES revealed that Pt loadings exceeded the intended levels, ranging from +1.67% to +17%. This suggests a minor overloading that could enhance the active sites, while also posing a risk for particle agglomeration, potentially affecting catalyst performance. SEM-EDS showed a transition from well-dispersed nanoparticles (NP’s) at 0.3 wt.% Pt to aggregated clusters at 8 wt.%. BET analysis indicated a reduction in surface area from 186.8m²/g to 169.3 m²/g, while TEM demonstrated NP growth from 1.11nm to 4.53 nm pre￾reaction, increasing to 2.69nm and 6.91 nm post-reaction. XRD revealed sharper Pt peaks and enhanced crystallinity with increasing loadings, and CO pulse chemisorption indicated a decline in dispersion from 65.64% to 35.34%. Post-reaction HR-TEM indicated a contraction in d-spacing from 0.23 to 0.20 nm. TGA exhibited initial weight loss at ~200 °C (moisture removal) and primary decomposition between 300–450 °C, with PVP (MW 55,000) showing the most significant mass loss, while higher molecular weight binders exhibited slower degradation, suggesting enhanced thermal stability.