Performance of alumina-supported noble metal catalysts for the combustion of trichloroethene at dry and wet conditions

The performance of four different alumina-supported noble metal catalysts (0.5% of Pd, Pt, Rh and Ru, respectively) for the deep oxidation of trichloroethene (1000–2500 ppmV, WHSV = 55 h⁻¹) in air was studied in this work. Experiments were carried out at both dry and wet (20,000 ppm of H₂O) conditions. Catalysts were compared in terms of activity, selectivity for the different reaction products (CO₂, HCl, Cl₂, C₂Cl₄, CCl₄ and CHCl₃), and stability at reaction conditions.

As general trend, the activity of the catalysts decreases in the order Ru  Pd > Rh > Pt. Concerning to the effect of the water addition, no important effect on the catalyst activity was observed, except in the case of Pt, for which an increase of the catalytic activity was observed. Reaction mechanism (and hence product distribution) is very similar for Rh, Pd and Pt, being in these cases C₂Cl₄ the only organochlorinated by-product detected. In the case of Ru, the reaction mechanism seems to be quite different, CCl₄ and CHCl₃ being the main organic by-products.

Simple power-law kinetic expressions (first order on trichloroethene concentration for Pd, Rh and Ru, and zeroth order for Pt) provide fairly good fits for catalytic performance of the studied catalysts.

Finally, deactivation studies show that both formation of active metal chlorides (especially in the case of Rh) and fouling (especially for Pd and Pt) are the main deactivation causes.     

Parameter selection in the design of displacement and motion functions by means of B-splines

Journal of Mechanical Science and Technology - This work analyses the incidence of the parameter selection of B-spline curves, used in the design of displacement and motion functions, on its degree...     

Mechanical Properties of Double-Layer and Graded Composite Coatings of YSZ Obtained by Atmospheric Plasma Spraying

Double-layer and graded composite coatings of yttria-stabilized zirconia were sprayed on metallic substrates by atmospheric plasma spray. The coating architecture was built up by combining two different feedstocks: one micro- and one nanostructured. Microstructural features and mechanical properties (hardness and elastic modulus) of the coatings were determined by FE-SEM microscopy and nanoindentation technique, respectively. Additional adherence and scratch tests were carried out in order to assess the failure mechanisms occurring between the layers comprising the composites. Microstructural inspection of the coatings confirms the two-zone microstructure. This bimodal microstructure which is exclusive of the layer obtained from the nanostructured feedstock negatively affects the mechanical properties of the whole composite. Nanoindentation tests suitably reproduce the evolution of mechanical properties through coatings thickness on the basis of the position and/or amount of nanostructured feedstock used in the depositing layer. Adhesion and scratch tests show the negative effect on the coating adhesion of layer obtained from the nanostructured feedstock when this layer is deposited on the bond coat. Thus, the poor integrity of this layer results in lower normal stresses required to delaminate the coating in the adhesion test as well as minor critical load registered by using the scratch test.     

Characterization of the intracellular and the plasma membrane Ca2+-ATPases in fractionated pig brain membranes using calcium pump inhibitors

The Ca2+-ATPase activity of isolated membranes and purified plasma membrane ATPase from pig brain was measured in the presence of specific inhibitors. The inhibition of the enzymatic activity by vanadate presents a lower affinity in microsomes than in the synaptic plasma membrane vesicles, showing K0.5 of 0.4 and 0.2 microM, respectively. The purified enzyme showed a higher sensitivity to vanadate with a K0.5 of 0.10 microM. Thapsigargin (Tg) and 2,5-di(tert-butyl)-1,4-benzohydroquinone (BHQ) were stronger inhibitors of the Ca2+-ATPase activity in microsomes than in the synaptic membrane vesicles. The activity of the purified enzyme was not affected by Tg and only partially by BHQ. Cyclopiazonic acid inhibited the enzymatic activity in all fractions, being more sensitive in microsomes. The microsome preparation incorporated 32P from [gamma-32P]ATP into two main proteins that appear at approx 110,000 and 140,000. According to the inhibition pattern, the lower phosphorylated band was identified as the sarco(endo)plasmic reticulum Ca2+-ATPase, being in a higher percentage than the upper band. Synaptic membrane vesicles also incorporated radioactive 32P into two protein bands. The 140,000 protein (upper band) shows the typical behavior of the purified plasma membrane Ca2+-ATPase, being more abundant in this preparation than the organellar Ca2+-pump (lower band). This study highlights the heterogeneous nature of the Ca2+-ATPase activity measured in brain membrane fractions.