Optimizing Pt Particle Size and Lewis Acidity in Pt/θ-Al2O3 Catalysts for Enhanced Perhydro Benzyltoluene Dehydrogenation

Abstract

Liquid organic hydrogen carriers (LOHCs) are considered one of the ideal media for hydrogen storage and transportation. Achieving efficient cyclic utilization of LOHCs necessitates the development of highly active dehydrogenation catalysts. This work focuses on optimizing Pt/θ-Al2O3 catalysts for the dehydrogenation of Perhydro Benzyltoluene (H12-BT). Catalysts with Pt loadings ranging from 0.3 to 5.0 wt% were synthesized via impregnation, yielding Pt particle sizes between 2.1 and 7.1 nm. Surface acidity was systematically tuned by introducing nitric acid (HNO3) during impregnation, with HNO3/Pt molar ratios (n) varying from 0 to 24. Dehydrogenation testing revealed a distinct volcano-shaped dependence on Pt particle size. The peak activity, corresponding to 3.0 nm particles at 1 wt% loading, reached a dehydrogenation degree (DoDH) of 48.3% under optimal conditions (250 °C, 4h). HNO3 modification (n = 12) further enhanced performance under the same conditions, elevating the DoDH to 58.7%. Studies of the adsorption behavior revealed that the size effect competes with geometric and electronic influences: small Pt particles (<3nm) facilitated H12-BT adsorption but impeded product H2 desorption, whereas large particles (>5nm) exhibited insufficient active sites despite enhanced H2 desorption. Concurrently, optimized Lewis acid site distribution and strength dynamically balanced H12-BT adsorption capacity and product desorption behavior. This work elucidates the interplay between Pt particle size, acid site distribution, and adsorption-desorption behavior, providing a framework for designing efficient LOHCs dehydrogenation catalysts.