Recent progress in high-temperature catalytic combustion

Pyrolysis of Mass-Selected (V2O5)NO− (N = 1−6) Clusters in a High-Temperature Linear Ion Trap Reactor

A high-temperature linear ion trap that can stably run up to 873 K was newly designed and installed into a homemade reflectron time-of-flight mass spectrometer coupled with a laser ablation cluster source and a quadrupole mass filter. The instrument was used to study the pyrolysis behavior of mass-selected (V2O5) NO− ( N = 1−6) cluster anions and the dissociation channels were clarified with atomistic precision. Similar to the dissociation behavior of the heated metal oxide cluster cations reported in literature, the desorption of either atomic oxygen atom or molecular O2 prevailed for the (V2O5) NO− clusters with N = 2−5 at 873 K. However, novel dissociation channels involving fragmentation of (V2O5) NO− to small-sized V xO y− anions concurrent with the release of neutral vanadium oxide species were identified for the clusters with N = 3−6. Significant variations of branching ratios for different dissociation channels were observed as a function of cluster size. The kinetic studies indicate that the dissociation rates of (V2O5) NO− monotonically increased with the increase of cluster size. The internal energies carried by the (V2O5) NO− clusters at 873 K as well as the energetics data for dissociation channels have been theoretically calculated to rationalize the experimental observations. The decomposition behavior of vanadium oxide clusters from this study can provide new insights into the pyrolysis mechanism of metal oxide nanoparticles that are widely used in high temperature catalysis.

Theoretical Study of the Catalytic Activity and Anti-SO2 Poisoning of a MoO3/V2O5 Selective Catalytic Reduction Catalyst

In this paper, density functional theory has been applied to study the mechanism of anti-SO₂ poisoning and selective catalytic reduction (SCR) reaction on a MoO₃/V₂O₅ surface. According to the calculation results, the SO₂ molecule can be converted into SO₃ on V₂O₅(010) and further transformed into NH₄HSO₄, which poisons V₂O₅. If V₂O₅ and MoO₃ are combined with each other, charge separation of V₂O₅ and MoO₃, which are negatively and positively charged, respectively, occurs at the interface. In ammonium bisulfate liquid droplets on the MoO₃/V₂O₅ surface, NH₄ ⁺ tends to adhere to the V₂O₅(010) surface and can be removed through the SCR reaction and HSO₄ ^- tends to adhere to the MoO₃(100) surface and can be resolved into SO₃ and H₂O, which can be released into the gas phase. Thus, MoO₃/V₂O₅ materials are resistant to SO₂ poisoning. In the MoO₃/V₂O₅ material, Brønsted acid sites are easily formed on the negatively charged V₂O₅(010) surface; this reduces the energy barrier of the NH₃ dissociation step in the NH₃-SCR process and further improves the catalytic activity.

Local structures and TWC activity of Pd supported on Ni-substituted aluminium oxide borates

The Pd catalyst supported on Ni-substituted aluminum oxide borate (Ni–10A2B) achieved the highest catalytic activity under three-way catalysis conditions, where NO adsorption onto the Ni site promoted the reaction with hydrogen spilt over from Pd under rich conditions.

Washcoating of cordierite honeycomb with vanadia–tungsta–titania mixed oxides for selective catalytic reduction of NO with NH3

The application of monolithic coated catalysts to NO_x abatement is a crucial issue for practical applications to enhance the mechanical strength, economize the cost, facilitate recycling etc., compared with the conventional monolithic extrusive catalysts.

Investigation of Parameters Influencing the Activation of a Pd/γ-Alumina Catalyst during Methane Combustion

The progressive activation of a Pd(2 wt %)/gamma-alumina catalyst under the reaction conditions of catalytic combustion of methane (CCM) was studied. The reasons of this activation were investigated by XPS, CO-chemisorption, and HR-TEM. The removal of carbon from the surface cannot explain the observed activation process. Sintering of the palladium particles was detected but this parameter alone does not fully explain the activation process of the catalyst. HR-TEM imaging evidences (i) that PdO is present both in the fresh and the active catalyst and (ii) that the PdO nanoparticles sinter and restructure (surface roughening) during the reaction. Development of preferential faces was not observed. It is suggested that this restructuring may be responsible for the activation process by facilitating the formation of an active oxygen layer on the PdO surface. CCM on Pd/gamma-Al(2)O(3) depends on the thermal history of the catalyst and is a structure-sensitive reaction.