Cobalt-modified platinum catalyst sets new record for hydrogen release from liquid organic hydrogen carrier

Liquid organic hydrogen carriers (LOHCs) offer a safe and economically viable solution for hydrogen storage and long-distance transport. Among various LOHC materials, dibenzyltoluene (DBT) stands out due to its low melting point (−39 to −34 °C), high boiling point (390 °C), high hydrogen storage capacity (6.20 wt%), and non-flammable, environmentally friendly nature. However, the dehydrogenation of its hydrogenated form, perhydro-dibenzyltoluene (H₁₈-DBT), typically requires high temperatures around 300 °C due to stable C–H bonds. Developing efficient dehydrogenation catalysts remains a significant challenge.

In a study published in ENG. Chem. Eng., researchers at the University of Chinese Academy of Sciences and the Chinese Academy of Sciences report a precisely engineered CoOₓ-modified Pt/Al₂O₃ catalytic system that dramatically enhances H₁₈-DBT dehydrogenation.

The team systematically investigated CoOₓ loadings from 0 to 10 wt% on a 1 wt% Pt/Al₂O₃ catalyst. The results showed a volcano-shaped dependence on Co loading: 1 wt% Co > 3.3 wt% Co > 0.5 wt% Co > 0 wt% Co > 10 wt% Co. At the optimal Co loading of 1 wt%, the catalyst achieved a dehydrogenation degree of 93% after 3 hours at 300 °C and 0.1 MPa, with a hydrogen production rate of 20.98 × 10³ mol H₂·mol Pt⁻¹·h⁻¹ – outperforming all previously reported catalysts in the literature. The maximum instantaneous hydrogen flow rate rose from 213 to 379 mL·min⁻¹ as Co loading increased from 0.5 to 3.3 wt%, but declined to 65.3 mL·min⁻¹ at 10 wt% Co. Increasing Co loading to 10 wt% caused a dramatic decline in dehydrogenation degree from 93% to only 7.2%.

For hydrogenation (the reverse reaction), CoOₓ addition consistently suppressed activity. At 150 °C and 4.0 MPa, the degree of hydrogenation decreased from 86.9% (no Co) to 59.5% (0.5 wt% Co), 12.9% (1 wt% Co), 11.5% (3.3 wt% Co), and further to only 6.7% at 10 wt% Co.

Structural characterization revealed the origin of these performance differences. At low Co loadings (≤1 wt%), cobalt species exist as highly dispersed amorphous CoO clusters on the Al₂O₃ support, as confirmed by the absence of cobalt oxide diffraction peaks in XRD and the lack of significant Raman features. These amorphous CoO clusters reduce Pt particle size (from 2.56 nm to 1.09–1.32 nm) and increase Pt electron density. In situ DRIFTS showed red-shifts in CO adsorption peaks from 2085 to 2082 cm⁻¹ (well-coordinated Pt sites), 2060 to 2056 cm⁻¹ (undercoordinated Pt sites), and 2033 to 2030 cm⁻¹ (highly undercoordinated Pt sites). XPS revealed a decrease in Pt 4d₅/₂ binding energy from ∼316.0 eV to 315.4–315.8 eV, confirming electron transfer from CoO to Pt. DFT calculations further confirmed electron accumulation around Pt clusters. H₂ pulse adsorption measurements showed that CoOₓ introduction decreased H₂ adsorption capacity, which promotes hydrogen desorption.

At higher Co loadings (≥3.3 wt%), cobalt species transform into crystalline Co₃O₄, as evidenced by Raman peaks at 472, 514, and 676 cm⁻¹ and XRD diffraction peaks. Excessive Co promotes Pt particle agglomeration (HAADF-STEM showing Pt lattice fringes at 0.221 nm), and the higher Co valence state (Co³⁺/Co²⁺ ratio ∼2) reduces electron donation to Pt, leading to decreased catalytic activity.

This work provides a rational strategy for designing high-performance Pt-based catalysts for hydrogen storage and release using DBT as a liquid organic hydrogen carrier.