Low NOx options in catalytic combustion and emission control

Au-Modified Pd catalyst exhibits improved activity and stability for NO direct decomposition

The promotion of a Pd catalyst with Au leads to higher and stable activity for the direct decomposition of NO, due to improved oxygen desorption.

Spatially-resolved investigation of the water inhibition of methane oxidation over palladium

Pd/Al₂O₃ catalysts are known to be active for low temperature methane oxidation reactions, however it has been shown that gases normally associated with methane gas streams (H₂O, CO₂, H₂S) can have an inhibitory effect on the total oxidation reaction.

The Impact of CeO2 Loading on the Activity and Stability of PdO/γ-AlOOH/γ-Al2O3 Monolith Catalysts for CH4 Oxidation

This study reports on the activity and stability of PdO/γ-AlOOH/γ-Al2O3 monolith catalysts, promoted with varying amounts of CeO2, for CH4 oxidation. Although the beneficial effects of CeO2 have been reported for powdered catalysts, this study used a cordierite (2MgO.2Al2O3.5SiO2) mini-monolith (400 cells per square inch, 1 cm diameter × 2.5 cm length; ~52 cells), washcoated with a suspension of γ-Al2O3 combined with boehmite (γ-AlOOH), followed by sequential deposition of Ce and Pd (0.5 wt.%) by wetness impregnation. The monolith catalysts’ CH4 oxidation activity and stability were assessed in the presence of CO, CO2, H2O and SO2 at low temperature (≤550 °C), relevant to emission control from lean-burn natural gas vehicles (NGVs). The CeO2 loading (0 to 4 wt.%) did not significantly impact the adhesion and thermal stability of the washcoat, but CeO2 reduced the inhibition of CH4 oxidation by H2O and SO2. The catalyst activity, measured by temperature-programmed methane oxidation (TPO) in a dry feed gas with 0.07 vol.% CH4, showed that adding CeO2 to the γ-AlOOH/γ-Al2O3 washcoat suppressed the activity of the catalysts; whereas, CeO2 improved the catalyst activity when H2O (2 and 5 vol.%) was present in the feed gas. Moreover, adding CeO2 decreased catalyst deactivation that occurred in the presence of 10 vol.% H2O and 5 ppmv SO2 at 500 °C, measured over a 25 h time-on-stream (TOS) period. The highest catalyst activity and stability for CH4 oxidation in the presence of H2O was obtained by adding 2 wt.% CeO2 to the washcoat.

H2 adsorption and dissociation on PdO(101) films supported on rutile TiO2 (110) facet: elucidating the support effect by DFT calculations

To explore metal oxide-support interactions and their effect, H2 adsorption and dissociation on PdO(101)/TiO2(110) films with different film thicknesses, in comparison with that on pure PdO(101) surface without TiO2(110) support, were studied by density functional theory calculation. A monolayer PdO(101) film supported on TiO2 facet shows different properties to a pure PdO(101) surface. On the monolayer PdO(101)/TiO2(110) film, TiO2 support leads to stronger molecular adsorption of H2 on coordinatively unsaturated Pd top sites than that on a pure PdO surface. H2 dissociation with the formation of OH was preferred thermodynamically but slightly unfavorable kinetically on the monolayer PdO film due to the TiO2 support effect. Graphical abstract On the monolayer PdO(101)/TiO2(110) film, the TiO2 support effect leads to stronger H2 molecular adsorption on coordinatively unsaturated Pd top sites than on pure PdO surface. H2 dissociation with the formation of OH is preferred thermodynamically but slightly unfavorable kinetically on the film due to the TiO2 support effect.

Catalytic combustion of ventilation air methane (VAM) – long term catalyst stability in the presence of water vapour and mine dust

This paper presents long-term evaluation of catalyst stability and durability in the presence of water and coal mine dust.

The mechanism of N[sub 2]O formation via the (NO)[sub 2] dimer: A density functional theory study

Catalytic formation of N(2)O via a (NO)(2) intermediate was studied employing density functional theory with generalized gradient approximations. Dimer formation was not favored on Pt(111), in agreement with previous reports. On Pt(211) a variety of dimer structures were studied, including trans-(NO)(2) and cis-(NO)(2) configurations. A possible pathway involving (NO)(2) formation at the terrace near to a Pt step is identified as the possible mechanism for low-temperature N(2)O formation. The dimer is stabilized by bond formation between one O atom of the dimer and two Pt step atoms. The overall mechanism has a low barrier of approximately 0.32 eV. The mechanism is also put into the context of the overall NO + H(2) reaction. A consideration of the step-wise hydrogenation of O(ads) from the step is also presented. Removal of O(ads) from the step is significantly different from O(ads) hydrogenation on Pt(111). The energetically favored structure at the transition state for OH(ads) formation has an activation energy of 0.63 eV. Further hydrogenation of OH(ads) has an activation energy of 0.80 eV.