The soot combustion mechanism over potassium-supported oxides (MgO, CeO2 and ZrO2) was studied to... more The soot combustion mechanism over potassium-supported oxides (MgO, CeO2 and ZrO2) was studied to clarify the active sites and discover unified reaction intermediates in this typical gas-solid-solid catalytic reaction. The catalytically active sites were identified as free K(+) rather than K2CO3, which can activate gaseous oxygen. The active oxygen spills over to soot and forms a common intermediate, ketene, before it was further oxidized into the end product CO2. The existence of ketene species was confirmed by density functional theory (DFT) calculations. The oxygen spillover mechanism is proposed, which is explained as an electron transfer from soot to gaseous oxygen through the active K(+) sites. The latter mechanism is confirmed for the first time since it was put forward in 1950, not only by ultraviolet photoelectron spectroscopy (UPS) results but also by semi-empirical theoretical calculations.
The structures of the palladium-modified Mo–K/Al2O3 catalyst samples were characterized by the XR... more The structures of the palladium-modified Mo–K/Al2O3 catalyst samples were characterized by the XRD, LRS, and EXAFS techniques and correlated to the catalytic properties of the samples for alcohol synthesis from synthesis gas. It is found that in the oxidic palladium-modified samples a strong interaction of the palladium modifier with the supported K–Mo–O species occurs. This interaction leads to a decrease
The adsorption of neutral glycine onto amorphous silica was investigated both theoretically and e... more The adsorption of neutral glycine onto amorphous silica was investigated both theoretically and experimentally. DFT calculations were performed at the BLYP-631++G** level using a cluster approach. Several possible configurations involving the formation of H-bonds between glycine and one, two or three silanols, (SiOH) were considered. The most favorable bonding of glycine with one silanol (45 kJ/mol) occurs through the COOH moiety, forming a cycle in which the CO group is H-bond acceptor whereas the acidic OH group is H-bond donor. With two or three silanols, additional H-bonds are formed between the amine moiety and the silanols, leading to an increased adsorption energy (70 and 80 kJ/mol for two and three silanols respectively). Calculated ν CO , δ HNH and δ ΗCH are sensitive to the adsorption mode. A bathochromic shift of νCO as compared to νCO of free glycine (calculated in the 1755-1790 cm -1 range) is found for glycine in interaction with silanol(s). The more H-bonds of COOH with silanol groups, the higher the bathochromic shift. For δHNH, no shift is found for glycine adsorbed on one and two silanols (where the amine is either not bound or H bond donor), whereas a bathochromic shift is calculated with three silanols when the amine moiety is H-bond acceptor.
Several nanosized catalysts Co 3 O 4 -CeO 2 with varying compositions were synthesized by a surfa... more Several nanosized catalysts Co 3 O 4 -CeO 2 with varying compositions were synthesized by a surfactant-template method and further promoted by a small amount of Pd (0.5 wt%). These catalysts exhibit uniform mesoporous structure and high surface area (>100 m 2 g −1 ). The Co 3 O 4 crystallites in these catalysts are encapsulated by nanosized CeO 2 with only a small fraction of Co ions exposing on the surface and strongly interacting with CeO 2 . Such structure maximizes the interaction between Co 3 O 4 and CeO 2 in three dimensions, resulting in unique redox properties. The introduction of Pd prominently enhances both the reduction and oxidation performance of the catalysts, due to hydrogen or oxygen spillover. These catalysts prepared by surfactant-template method exhibit excellent oxidation performance, especially the ones promoted with Pd, which show markedly enhanced CO oxidation activity even at room temperature. Based upon the results of structural properties, redox behaviors and in situ DRIFTS study, two different reaction pathways over Co 3 O 4 -CeO 2 and Pd/Co 3 O 4 -CeO 2 are proposed. (M. Meng). to the cobalt oxide catalysts (Co 3 O 4 , Co 3 O 4 /Al 2 O 3 ) due to their unique activity for ambient CO oxidation . It is reported that the light-off temperature (T 50 ) for CO oxidation over Co-based catalysts is as low as −63 • C [4]. Cerium oxide, as oxygen storage material, is often added to TWCs, since it not only possesses high oxygen storage capacity (OSC), but also enhances and stabilizes the dispersion of transition metal oxides. Consequently, it is feasible to develop oxidation catalysts mainly consisting of cobalt and cerium oxides.
The NSR catalyst Pt/K/TiO2–ZrO2 was prepared by successive impregnation. In situ DRIFTS technique... more The NSR catalyst Pt/K/TiO2–ZrO2 was prepared by successive impregnation. In situ DRIFTS technique was employed to investigate the NOx storage mechanisms. The results show that no adsorbed NOx species were detected over TiO2–ZrO2, while nitrite and nitrate species could be identified simultaneously over K/TiO2–ZrO2. After Pt deposition, only nitrates species, such as free nitrate ions and monodentate or bidentate nitrates,
... Fig. 1. (a–c) Three most stable configurations of the zwitterion form of glycine stabilized b... more ... Fig. 1. (a–c) Three most stable configurations of the zwitterion form of glycine stabilized by two water molecules and differences in the energies ΔE isom (kJ/mol) of the conformers. ... Thus, positive values of (ΔE) isom indicate relative destabilizations. ...
The soot combustion mechanism over potassium-supported oxides (MgO, CeO2 and ZrO2) was studied to... more The soot combustion mechanism over potassium-supported oxides (MgO, CeO2 and ZrO2) was studied to clarify the active sites and discover unified reaction intermediates in this typical gas-solid-solid catalytic reaction. The catalytically active sites were identified as free K(+) rather than K2CO3, which can activate gaseous oxygen. The active oxygen spills over to soot and forms a common intermediate, ketene, before it was further oxidized into the end product CO2. The existence of ketene species was confirmed by density functional theory (DFT) calculations. The oxygen spillover mechanism is proposed, which is explained as an electron transfer from soot to gaseous oxygen through the active K(+) sites. The latter mechanism is confirmed for the first time since it was put forward in 1950, not only by ultraviolet photoelectron spectroscopy (UPS) results but also by semi-empirical theoretical calculations.
The structures of the palladium-modified Mo–K/Al2O3 catalyst samples were characterized by the XR... more The structures of the palladium-modified Mo–K/Al2O3 catalyst samples were characterized by the XRD, LRS, and EXAFS techniques and correlated to the catalytic properties of the samples for alcohol synthesis from synthesis gas. It is found that in the oxidic palladium-modified samples a strong interaction of the palladium modifier with the supported K–Mo–O species occurs. This interaction leads to a decrease
The adsorption of neutral glycine onto amorphous silica was investigated both theoretically and e... more The adsorption of neutral glycine onto amorphous silica was investigated both theoretically and experimentally. DFT calculations were performed at the BLYP-631++G** level using a cluster approach. Several possible configurations involving the formation of H-bonds between glycine and one, two or three silanols, (SiOH) were considered. The most favorable bonding of glycine with one silanol (45 kJ/mol) occurs through the COOH moiety, forming a cycle in which the CO group is H-bond acceptor whereas the acidic OH group is H-bond donor. With two or three silanols, additional H-bonds are formed between the amine moiety and the silanols, leading to an increased adsorption energy (70 and 80 kJ/mol for two and three silanols respectively). Calculated ν CO , δ HNH and δ ΗCH are sensitive to the adsorption mode. A bathochromic shift of νCO as compared to νCO of free glycine (calculated in the 1755-1790 cm -1 range) is found for glycine in interaction with silanol(s). The more H-bonds of COOH with silanol groups, the higher the bathochromic shift. For δHNH, no shift is found for glycine adsorbed on one and two silanols (where the amine is either not bound or H bond donor), whereas a bathochromic shift is calculated with three silanols when the amine moiety is H-bond acceptor.
Several nanosized catalysts Co 3 O 4 -CeO 2 with varying compositions were synthesized by a surfa... more Several nanosized catalysts Co 3 O 4 -CeO 2 with varying compositions were synthesized by a surfactant-template method and further promoted by a small amount of Pd (0.5 wt%). These catalysts exhibit uniform mesoporous structure and high surface area (>100 m 2 g −1 ). The Co 3 O 4 crystallites in these catalysts are encapsulated by nanosized CeO 2 with only a small fraction of Co ions exposing on the surface and strongly interacting with CeO 2 . Such structure maximizes the interaction between Co 3 O 4 and CeO 2 in three dimensions, resulting in unique redox properties. The introduction of Pd prominently enhances both the reduction and oxidation performance of the catalysts, due to hydrogen or oxygen spillover. These catalysts prepared by surfactant-template method exhibit excellent oxidation performance, especially the ones promoted with Pd, which show markedly enhanced CO oxidation activity even at room temperature. Based upon the results of structural properties, redox behaviors and in situ DRIFTS study, two different reaction pathways over Co 3 O 4 -CeO 2 and Pd/Co 3 O 4 -CeO 2 are proposed. (M. Meng). to the cobalt oxide catalysts (Co 3 O 4 , Co 3 O 4 /Al 2 O 3 ) due to their unique activity for ambient CO oxidation . It is reported that the light-off temperature (T 50 ) for CO oxidation over Co-based catalysts is as low as −63 • C [4]. Cerium oxide, as oxygen storage material, is often added to TWCs, since it not only possesses high oxygen storage capacity (OSC), but also enhances and stabilizes the dispersion of transition metal oxides. Consequently, it is feasible to develop oxidation catalysts mainly consisting of cobalt and cerium oxides.
The NSR catalyst Pt/K/TiO2–ZrO2 was prepared by successive impregnation. In situ DRIFTS technique... more The NSR catalyst Pt/K/TiO2–ZrO2 was prepared by successive impregnation. In situ DRIFTS technique was employed to investigate the NOx storage mechanisms. The results show that no adsorbed NOx species were detected over TiO2–ZrO2, while nitrite and nitrate species could be identified simultaneously over K/TiO2–ZrO2. After Pt deposition, only nitrates species, such as free nitrate ions and monodentate or bidentate nitrates,
... Fig. 1. (a–c) Three most stable configurations of the zwitterion form of glycine stabilized b... more ... Fig. 1. (a–c) Three most stable configurations of the zwitterion form of glycine stabilized by two water molecules and differences in the energies ΔE isom (kJ/mol) of the conformers. ... Thus, positive values of (ΔE) isom indicate relative destabilizations. ...
Uploads
Papers by Ming Meng