Mao-Chu Gong

Methane activation by naked Ni0 atom: a theoretical study

Abstract The reactions between Ni (d 10 1 S) and CH 4 have been carried out at the B3LYP/6-311+G(2d, 2p) and B3LYP/6-311++G(3df,2p) theoretical levels. The reaction path in which the intermediates transfer from one to another via transition state is rationalized by their structures and natural bond orbital analysis. The reactions of Ni+CH 4 →NiCH 2 +H 2 , Ni+CH 4 →NiCH 3 +H and Ni+CH 4 →NiH +CH 3 are predicted to be endothermic, and the reaction Ni+CH 4 →NiH +CH 3 is the easiest to occur.

Partial oxidation and chemisorption of methane over Ni/Al2O3 catalysts

Partial oxidation of methane, adsorption of methane as well as co-adsorption of methane and O 2 on Ni/Al 2 O 3 catalyst have been studied by continuous flow micro-reactor and in situ FT-IR spectroscopy. The results show that with increasing temperature and space velocity, the CH 4 conversion and CO and H 2 selectivities increased and CO 2 selectivity decreased. With the decrease of CH 4 /O 2 ratio, the methane conversion and CO 2 selectivity increased while the CO and H 2 slectivities decreased. The onset of activity for methane partial oxidation occur at 230 °C. As reduced Ni/Al 2 O 3 was exposed to pure CH 4 , the two bands for adsorbed methane were observed at 3005 and 2998 cm −1 respectively. During TP (in CH 4 ) dynamic process, the intensities of the bands at 3005 and 2998 cm −1 increased with increase in temperature, indicating that the amount of adsorbed methane increase with increasing temperature which is indicative of chemisorption of methane. During TP (in CH 4 and O 2 ) dynamic process, two forms of chemisorbed methane are observed. The amount of chemisorbed methane increased with increasing temperature. At 250°C, the intensity of the band at 3015 cm −1 for free methane decreased remarkably and at the same time, CO, H 2 , CO 2 and H 2 O were detected in the gas phase, indicating that the partial oxidation of CH 4 occurs, which is in good agreement with the reaction start temperature observed above. These results indicate that the dissociation of chemisorbed methane dissociation in presence of chemisorbed, oxygen is a key step for methane partial oxidation.

Chemisorption of methane over Ni/Al2O3 catalysts

Abstract Adsorption of methane as well as co-adsorption of methane and O 2 on Ni/Al 2 O 3 catalyst have been studied by in situ FT-IR spectroscopy. The reaction start temperature measurements indicate that the methane partial oxidation occurs at 230°C. As the reduced Ni/Al 2 O 3 was exposed to pure CH 4 , two bands for adsorbed methane were observed at 3005 and 2998 cm −1 , respectively, which was confirmed by the appearance of two bands at 2242 and 2237 cm −1 when CD 4 was used. During temperature programmed (TP) dynamic process (in the presence of CH 4 ), the intensities of the bands at 3005 and 2998 cm −1 increased with increase in temperature, indicating that the amount of adsorbed methane increases with increasing temperature, which is indicative of chemisorption of methane. During TP dynamic process (in the co-presence of CH 4 and O 2 ), two forms of chemisorbed methane are observed. The amount of chemisorbed methane increased with increasing temperature. At 250°C, the intensity of the band at 3015 cm −1 for gaseous methane decreased remarkably and at the same time, CO, H 2 , CO 2 and H 2 O were detected in the gas phase, indicating that the partial oxidation of CH 4 occurs, which is in good agreement with the reaction start temperature observed above. These results suggest that the dissociation of chemisorbed methane in the participation of chemisorbed oxygen is a key step for methane partial oxidation.

C–H bond activation: Ni(d101S)+CH4→NiCH2+H2. A DFT study

Abstract The singlet state potential energy curve of the reaction Ni(d 10 1 S)+CH 4 →NiCH 2 +H 2 , the electronic 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 2988xa0cm −1 is typical of methane molecularly adsorbed on Ni. Frequencies of 2531 and 2438xa0cm −1 are indicative of the formation of a C–H⋯metal bond and a frequency of 355xa0cm −1 is typical of Ni–CH 4 stretching mode. 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 . For HNiCH 3 , frequencies of 2980 and 2853xa0cm −1 are representative of CH 3 coadsorbed with H on Ni, and a frequency of 565xa0cm −1 is indicative of the HNi–CH 3 stretching mode. 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. For (H 2 )NiCH 2 , frequencies of 3344 and 694xa0cm −1 are characteristic of H–H and (H 2 )Ni–CH 2 stretching modes, respectively. Subsequently, the final products NiCH 2 and H 2 evolve after the elimination of H 2 from the transition-metal center. For NiCH 2 , a frequency of 754xa0cm −1 is assigned to the Ni–CH 2 stretching mode. For all intermediates and transition states in the reaction path, the electron transfer is exclusively from nickel to carbon. In general, the overall reaction is mildly exothermic by 1.6xa0kJxa0mol −1 relative to Ni(d 10 1 S)+CH 4 reactants.