Structure sensitivity of dodecahydro-N-ethylcarbazole dehydrogenation over Pd catalysts

The complete recovery of the H2 stored on dodecahydro-N-ethylcarbazole was achieved at 443 K and 101 kPa using Pd/SiO2 catalysts, prepared by incipient wetness impregnation with calcination in He rather than air. The dehydrogenation turn-over frequency (TOF) and selectivity to the completely dehydrogenated product, N-ethylcarbazole, were dependent upon Pd particle size, with a maximum in both occurring with a 4 wt.% Pd/SiO2 catalyst that had an average Pd particle size of 9 nm. Over this catalyst, the dehydrogenation reaction proceeded to complete conversion within 22 min and complete H2 recovery (5.8 wt.%) within 1.6 h at 443 K and 101 kPa. The structure sensitivity of the reaction and the observed product distribution are discussed in view of DFT calculations that showed that the adsorption of dodecahydro-N-ethylcarbazole on Pd required multiple catalytic sites and the heat of adsorption was dependent upon the surface structure.