TAP studies on 2% Ag/gamma-Al2O3 catalyst for selective reduction of oxygen in a H-2-rich ethylene feed

Catalysts currently employed for the polymerization of ethylene have previously been found to deactivate in the presence of oxygen. It is, therefore, important that oxygen is removed from the ethylene feedstock prior to the polymerization. The Ag/gamma-Al2O3 catalyst exhibits excellent activity and selectivity toward oxygen reduction with hydrogen in the presence of ethylene. TAP vacuum pulse experiments have been utilised to understand the catalytic behaviour of the Ag/gamma-Al2O3 catalyst. TAP multi-pulse experiments have determined the types of active sites that are found on the Ag/gamma-Al2O3 catalyst, and the intrinsic activity of these sites. The lifetime of the reactive adsorbed oxygen intermediate has also been determined through TAP consecutive pulse experiments. Multi-pulse and consecutive pulse data have been combined with ethylene adsorption/desorption rate constants to provide an overview of the Ag/gamma-Al2O3 catalyst system.

A fast transient kinetic study of the effect of H-2 on the selective catalytic reduction of NOx with octane using isotopically labelled (NO)-N-15

The H-2-assisted hydrocarbon selective catalytic reduction (HC-SCR) of NO, was investigated using fast transient kinetic analysis coupled with isotopically labelled (NO)-N-15. This allowed monitoring of the evolution of products and reactants during switches of H-2 in and out of the SCR reaction mix. The results obtained with a time resolution of less than 1 s showed that the effect on the reaction of the removal or addition of H-2 was essentially instantaneous. This is consistent with the view that H-2 has a direct chemical effect on the reaction mechanism rather than a secondary one through the formation of "active" Ag clusters. The effect of H-2 partial pressure was investigated at 245 degrees C, it was found that increasing partial pressure of H-2 resulted in increasing conversion of NO and octane. It was also found that the addition of H-2 at 245 degrees C had different effects on the product distribution depending on its partial pressure. The change of the nitrogen balance over time during switches in and out of hydrogen showed that significant quantities of N-containing species were stored when hydrogen was introduced to the system. The positive nitrogen balance on removal of H-2 from the gas phase showed that these stored species continued to react after removal of hydrogen to form N-2. (c) 2006 Elsevier Inc. All rights reserved.

Structural investigation of the promotional effect of hydrogen during the selective catalytic reduction of NOx with hydrocarbons over Ag/Al2O3 catalysts

In situ EXAFS has been used to examine the hydrogen effect on the selective catalytic reduction of NOx over silver/alumina catalysts. For all SCR conditions used, with or without co-reductant (H-2 or CO), the catalyst structure remained the same. Significant changes in the catalyst were only found under reducing conditions. The enhanced activity found in the presence of hydrogen is thought to be due to a chemical effect and not the result of a change in the structure of the active site.

The use of Short Time on Stream (STOS) transient kinetics to investigate the role of hydrogen in enhancing NOx reduction over silver catalysts

The role of hydrogen in promoting the reduction by ammonia of NOx on silver catalysts has been investigated using a Short Time on Stream (STOS) technique to allow differentiation between potentially reactive intermediates and relatively inactive spectator species. Under these conditions, we have used DRIFTS to identify surface nitrate species that are formed and removed on a timescale of seconds. This is in contrast to nitrate species observed under normal steady-state conditions which can continue to form over many tens of minutes. Since this timescale of seconds is very similar to the response rate at which the NH3/NOx to N-2 reaction is accelerated when H-2 is added, or decelerated when H-2 is removed, we conclude that this fast-forming and fast disappearing nitrate species is most probably adsorbed on or close to the active Ag sites. The removal of such a blocking nitrate species from the active sites can explain the effect of H-2 in greatly increasing the rate of the overall de-NOx reaction. 

Reduction of environmentally induced cracking of laser-welded shape memory NiTi wires via post-weld heat-treatment

In this study, the environmentally induced cracking behaviour of the NiTi weldment with and without post-weld heat-treatment (PWHT) in Hanks’ solution at 37.5 °C at OCP were studied by tensile and cyclic slow-strain-rate tests (SSRT), and compared with those tested in oil (an inert environment). Our previous results in the tensile and cyclic SSRT showed that the weldment without PWHT showed high susceptibility to the hydrogen cracking, as evidenced by the degradation of tensile and super-elastic properties when testing in Hanks' solution. The weldment after PWHT was much less susceptible to hydrogen attack in Hanks' solution as no obvious degradation in the tensile and super-elastic properties was observed, and only a very small amount of micro-cracks were found in the fracture surface. The susceptibility to hydrogen cracking of the NiTi weldment could be alleviated by applying PWHT at the optimized temperature of 350 °C after laser welding.

Data Reduction of Power System Disturbances using Wavelet Transforms for Network Operation and Control

Wavelet transforms provide basis functions for time-frequency analysis and have properties that are particularly useful for compression of analogue point on wave transient and disturbance power system signals. This paper evaluates the reduction properties of the wavelet transform using real power system data and discusses the application of the reduction method for information transfer in network communications.

Ambient Temperature Hydrocarbon Selective Catalytic Reduction of NOx Using Atmospheric Pressure Nonthermal Plasma Activation of a Ag/Al2O3 Catalyst

Atmospheric pressure nonthermal-plasma-activated catalysis for the removal of NOx using hydrocarbon selective catalytic reduction has been studied utilizing toluene and n-octane as the hydrocarbon reductant. When the plasma was combined with a Ag/Al2O3 catalyst, a strong enhancement in activity was observed when compared with conventional thermal activation with high conversions of both. NOx and hydrocarbons obtained at temperature at temperature ≤250 °C, where the silver catalyst is normally inactive. Importantly, even in the absence of an external heat source, significant activity was obtained. This low temperature activity provides the basis for applying nonthermal plasmas to activate emission control catalysts during cold start conditions, which remains an important issue for mobile and stationary applications.

Effect of methanol concentration on oxygen reduction reaction activity of Pt/C catalysts

The oxygen reduction reaction (ORR) activity of Pt/C catalysts was investigated in electrolytes of 0.5 mol/L H2SO4 containing varying concentrations of methanol in a half-cell. It was found that the ORR activity was improved notably in an electrolyte of 0.5 mol/L H2SO4 containing 0.1 mol/L CH3OH as compared with that in 0.5 mol/L H2SO4, 0.5 mol/L H2SO4 containing 0.5 mol/L CH3OH, or 0.5 mol/L H2SO4 containing 1.0 mol/L CH3OH electrolytes. The same tendency for improved ORR activity was also apparent after commercial Nafion (R) NRE-212 membrane was hot-pressed onto the catalyst layers. The linear sweep voltammetry results indicate that the ORR activities of the Pt/C catalyst were almost identical in the 0.5 mol/L H2SO4 + 0.1 mol/L CH3OH solution before and after coated with the Nafion (R) membrane. Electrochemical impedance spectroscopy results demonstrated that the resistance of the Nafion (R) membrane is smaller in the electrolyte of 0.5 mol/L H2SO4 + 0.1 mol/L CH3OH than in other electrolytes with oxygen gas feed. This exceptional property of the Nafion (R) membrane is worth investigating and can be applied in fuel cell stacks to improve the system performance. (c) 2013, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.