Hydrogenation of the liquid organic hydrogen carrier compound dibenzyltoluene - reaction pathway determination by 1H NMR spectroscopy

The catalytic hydrogenation of the LOHC compound dibenzyltoluene (H0-DBT) was investigated by H-1 NMR spectroscopy in order to elucidate the reaction pathway of its charging process with hydrogen in the context of future hydrogen storage applications. Five different reaction pathways during H0-DBT hydrogenation were considered including middle-ring preference (middle-side-side, MSS), side-middle-side order of hydrogenation (SMS), side-ring preference (SSM), simultaneous hydrogenation of all three rings without intermediate formation and statistical hydrogenation without any ring preference. Detailed analysis of the H-1 NMR spectra of the H0-DBT hydrogenation over time revealed that the reaction proceeds with a very high preference for the SSM order at temperatures between 120 degrees C and 200 degrees C and 50 bar in the presence of a Ru/Al2O3-catalyst. HPLC analysis supported this interpretation by confirming an accumulation of H12-DBT species prior to full hydrogenation to H18-DBT with middle ring hydrogenation as the final step.