Periodic operation applied to kinetic studies of CO2-methanation

Periodic operation was applied to the CO2 methanation reaction at 383 K on 2% Ru/TiO2. A continuous feed recycle reactor combined with a diffuse reflectance infrared cell and a mass spectrometer allowed to follow simultaneously the gas phase CO2 and CH4 as well as the adsorbed species (CO)a and (formate)a. Experiments consisting of periodic variations of CO2 in the hydrogen feed showed response curves with maxima/minima shifted in time in the sequence CO2, (formate)a --> (CO)a --> CH4. Similar delays measured for the (CO)a formation and hydrogenation indicate that both of these processes are limiting the overall reaction rate. A kinetic model was proposed and verified under periodic conditions. The main experimental trends, which are pronounced time lags between CO2, (CO)a and CH4, could be described satisfactorily

Modeling the dynamics ofthe N2O reduction on Iron Oxide

The reduction of N2O to N2 on iron oxide under transient conditions was studied in the temperature range of 270–340°C. Six different models were used to simulate the experimental data. The conventional second-order reaction between gas phase N2O and surface oxygen vacancies failed to describe the dynamic experiments. Upon introducing linear or exponential distributions of the second-order surface reaction rate constant in function of the degree of reduction of the surface, satisfactory fittings to the experiment could not be achieved either. It was necessary to take into account subsurface oxygen diffusion to describe the low rates of reaction measured at low degrees of reduction of the catalyst. The combination of subsurface oxygen diffusion with a linear activity distribution for the surface reaction provided a good description of the transient N2O reduction. Finally, the surface reaction rate constant as well as the diffusion coefficient of oxygen in iron oxide could be fitted with the Arrhenius law

Catalyst development for the selective methylation of catechol

Gas-phase alkylation of catechol with methanol on g-alumina and modified g-alumina catalysts is studied exptl. By limiting the conversion of X < 0.3, the formation of polymethylated species can be avoided and only the three isomers guaiacol, 3-methylcatechol and 4-methylcatechol are obsd. Optimizing the catalyst compn. and the reaction conditions, a selectivity of 0.75 for the industrially most valuable product 3-methylcatechol can be obtained. [on SciFinder (R)

Role of complement and antibodies in controlling infection with pathogenic simian immunodeficiency virus (SIV) in macaques vaccinated with replication-deficient viral vectors

<p>Abstract</p> <p>Background</p> <p>We investigated the interplay between complement and antibodies upon priming with single-cycle replicating viral vectors (SCIV) encoding SIV antigens combined with Adeno5-SIV or SCIV pseudotyped with murine leukemia virus envelope boosting strategies. The vaccine was applied via spray-immunization to the tonsils of rhesus macaques and compared with systemic regimens.</p> <p>Results</p> <p>Independent of the application regimen or route, viral loads were significantly reduced after challenge with SIVmac239 (p < 0.03) compared to controls. Considerable amounts of neutralizing antibodies were induced in systemic immunized monkeys. Most of the sera harvested during peak viremia exhibited a trend with an inverse correlation between complement C3-deposition on viral particles and plasma viral load within the different vaccination groups. In contrast, the amount of the observed complement-mediated lysis did not correlate with the reduction of SIV titres.</p> <p>Conclusion</p> <p>The heterologous prime-boost strategy with replication-deficient viral vectors administered exclusively via the tonsils did not induce any neutralizing antibodies before challenge. However, after challenge, comparable SIV-specific humoral immune responses were observed in all vaccinated animals. Immunization with single cycle immunodeficiency viruses mounts humoral immune responses comparable to live-attenuated immunodeficiency virus vaccines.</p

Application of non-stationary and periodic processes in the study of heterogeneous catalytic kinetics

The use of transient methods to discriminate heterogeneous catalytic models was demonstrated for the catalytic epoxidn. of C2H4 on Ag and for the catalytic acetoxylation of C2H4 to vinyl acetate on a Pd catalyst. In sep. expts. the sorption kinetics on the carrier and the Pd catalyst were detd. and used to describe the dynamic behavior of the reactor. The proposed kinetic models described quant. both steady-state and the dynamic behavior of the reaction. [on SciFinder (R)