Propane dehydrogenation(PDH)on Ga/H-ZSM-5 catalysts is a promising reaction for propylene production,while the detail mechanism remains debatable.Ga_(2)O_(2)^(2+) stabilized by framework Al pairs have been identified ...Propane dehydrogenation(PDH)on Ga/H-ZSM-5 catalysts is a promising reaction for propylene production,while the detail mechanism remains debatable.Ga_(2)O_(2)^(2+) stabilized by framework Al pairs have been identified as the most active species in Ga/H-ZSM-5 for PDH in our recent work.Here we demonstrate a strong correlation between the PDH activity and a fraction of Ga_(2)O_(2)^(2+) species corresponding to the infrared GaH band of higher wavenumber(GaHHW)in reduced Ga/H-ZSM-5,instead of the overall Ga_(2)O_(2)^(2+) species,by employing five H-ZSM-5 supports sourced differently with comparable Si/Al ratio.This disparity in Ga_(2)O_(2)^(2+) species stems from their differing capacity in completing the catalytic cycle.Spectroscopic results suggest that PDH proceeds via a two-step mechanism:(1)C-H bond activation of propane on H-Ga_(2)O_(2)^(2+) species(rate determining step);(2)β-hydride elimination of adsorbed propyl group,which only occurs on active Ga_(2)O_(2)^(2+) species corresponding to GaHHW.展开更多
The singlet state potential energy curve of the reaction: Ni (d1 0 1S)+ CH 4 → NiCH 2 + H 2, and geometric structures and vibrational frequencies of all intermediates and transition states in the reaction path were s...The singlet state potential energy curve of the reaction: Ni (d1 0 1S)+ CH 4 → NiCH 2 + H 2, and geometric structures and vibrational frequencies of all intermediates and transition states in the reaction path were studied by B3LYP method. In the reaction, an atom molecule complex NiCH 4 acting as precursor in the breaking of C-H bond was predicted. For NiCH 4, a frequency of 2988 cm -1 is typical of methane molecularly adsorbed on Ni. A nickel hydrido methyl complex HNiCH 3 is formed upon the very low barrier insertion of Ni 0 into a C-H bond of CH 4. A dihydrogen complex of atom nickel carbene (H 2)NiCH 2 proceeds from the migration of α hydrogen from carbon to metal with considerably large barrier, indicating that this is the rate determining step in the whole reaction. In general, the overall reaction is mildly exothermic by 1.6 kJ·mol -1 relative to Ni(d1 0 1S) + CH 4 reactants.展开更多
文摘Propane dehydrogenation(PDH)on Ga/H-ZSM-5 catalysts is a promising reaction for propylene production,while the detail mechanism remains debatable.Ga_(2)O_(2)^(2+) stabilized by framework Al pairs have been identified as the most active species in Ga/H-ZSM-5 for PDH in our recent work.Here we demonstrate a strong correlation between the PDH activity and a fraction of Ga_(2)O_(2)^(2+) species corresponding to the infrared GaH band of higher wavenumber(GaHHW)in reduced Ga/H-ZSM-5,instead of the overall Ga_(2)O_(2)^(2+) species,by employing five H-ZSM-5 supports sourced differently with comparable Si/Al ratio.This disparity in Ga_(2)O_(2)^(2+) species stems from their differing capacity in completing the catalytic cycle.Spectroscopic results suggest that PDH proceeds via a two-step mechanism:(1)C-H bond activation of propane on H-Ga_(2)O_(2)^(2+) species(rate determining step);(2)β-hydride elimination of adsorbed propyl group,which only occurs on active Ga_(2)O_(2)^(2+) species corresponding to GaHHW.
文摘The singlet state potential energy curve of the reaction: Ni (d1 0 1S)+ CH 4 → NiCH 2 + H 2, and geometric structures and vibrational frequencies of all intermediates and transition states in the reaction path were studied by B3LYP method. In the reaction, an atom molecule complex NiCH 4 acting as precursor in the breaking of C-H bond was predicted. For NiCH 4, a frequency of 2988 cm -1 is typical of methane molecularly adsorbed on Ni. A nickel hydrido methyl complex HNiCH 3 is formed upon the very low barrier insertion of Ni 0 into a C-H bond of CH 4. A dihydrogen complex of atom nickel carbene (H 2)NiCH 2 proceeds from the migration of α hydrogen from carbon to metal with considerably large barrier, indicating that this is the rate determining step in the whole reaction. In general, the overall reaction is mildly exothermic by 1.6 kJ·mol -1 relative to Ni(d1 0 1S) + CH 4 reactants.
