0000000000294447
AUTHOR
Francesco Frusteri
DFT and kinetic evidences of the preferential CO oxidation pattern of manganese dioxide catalysts in hydrogen stream (PROX)
Abstract The oxidation functionality of Mn(IV) sites has been assessed by density functional theory (DFT) analysis of adsorption and activation energies of CO, H2 and O2 on a model Mn4O8 cluster. DFT calculations indicate that Mn(IV) atoms prompt an easy CO conversion to CO2 via a reaction path involving both catalyst and gas-phase oxygen species, while much greater energy barriers hinder H2 oxidation. Accordingly, a MnCeOx catalyst (Mnat/Ceat, 5) with large exposure of Mn(IV) sites shows a remarkable CO oxidation performance at T ≥ 293 K and no H2 oxidation activity below 393 K. Empiric kinetics disclose that the catalyst-oxygen abstraction step determines both CO and H2 oxidation rate, al…
Selective hydrogenation of acetylene in ethylene feedstocks on Pd catalysts
Abstract Pumice supported palladium catalysts were compared with Pd SiO 2 and Pd Al 2 O 3 in the hydrogenation of acetylene using typical industrial ethylene feedstocks: front-end and tail-end cuts. Pd/pumice catalysts exhibit good activity and excellent selectivity and stability in the title reaction. Their activity/selectivity pattern is controlled by the composition of the reaction mixture. The turnover frequency (TOF) increases, and the apparent activation energy (Ea) decreases, with the H 2 C 2 H 2 ratio, but they are not affected by the C 2 H 2 C 2 H 4 ratio. The selectivity to ethane (SE) does not change with acetylene conversion at low H 2 C 2 H 2 ratio (tail-end cut) and increases …