Paulo Araya

Study of the treatment of subbituminous coals by NaOH solutions

Abstract A subbituminous coal from La Union (Chile) has been treated with aqueous NaOH solutions. The quantity of coal solubilized and the elimination of ash was found to increase with increase in hydrolysis time, temperature and NaOH concentration and with decrease in particle size. Coal solubilization reached a maximum with respect to NaOH concentration in the range studied. The largest yield of solubilized products was 28 wt%, this occurred after 8 h of hydrolysis at 80 °C using an NaOH concentration of 10 g dm −3 and coal having a particle size between 125 and 177 μm. In the range of conditions studied, the greatest decrease in the ash yield of the undissolved coal was ≈ 29 wt%. Under the same conditions, the total sulphur content of the coal decreased by 30 wt%.

Adsorption mechanisms and surface heterogeneity in the oxidation reaction of CO

A Monte Carlo simulation study is made of the sensitivity of the CO oxidation reaction to changes in the characteristics of the catalyst’s surface on which the type of oxygen adsorption mechanism is dependent. Infinite rate models of the Ziff, Gulari, and Barshad (ZGB) type, and mechanisms having kinetics parameters of actual experiments from the literature are studied. It is shown that, if linear adsorption is assumed, the structural insensitivity becomes apparent in the phase diagram but not in the production of CO2. In the case of structural sensitivity it is seen that surface heterogeneity leads to a change in the character of the phase transition curve, and also allows information about the surface to be obtained from the shape of the transition curve.

MONTE CARLO SIMULATIONS AND KINETIC THEORY OF HOMOGENEOUS AND HETEROGENEOUS ADSORPTION WITH LATERAL INTERACTIONS

Using the kinetic form of the Monte Carlo (MC) simulation method, a comparison has been made between the results that predict the phenomenological equations for adsorption kinetics and MC experiments in systems with and without lateral interactions on homogeneous and heterogeneous surfaces with random topography and varying degrees of surface heterogeneity. A very good correspondence exists between the theoretical results and those obtained from the MC experiments.

Activity and infrared studies during carbon monoxide oxidation over bimetallic palladium-rhodium/silica catalysts

Abstract A study of the activity of bimetallic Pd-Rh catalysts supported on silica in the oxidation of carbon monoxide by oxygen is presented. The catalysts were prepared by three different methods (1) palladium and rhodium were coimpregnated on the support, (2) rhodium was impregnated first and, after calcining, the sample was impregnated with palladium, (3) the monometallic palladium and rhodium catalysts were physically mixed. The results showed that the activity of the catalysts prepared by coimpregnation was much lower than that of the other two catalysts. The low activity of the coimpregnated catalyst can be explained by the formation of alloys which affect the surface concentration of each metal and the dispersion of rhodium. The most active catalyst was the one prepared by physical mixture, which also shows the highest concentration of linearly adsorbed carbon monoxide detected by FT-IR.

Activity during reduction of NO by CO over bimetallic palladium-rhodium/silica catalysts

A study of the activity of bimetallic Pd-Rh catalysts supported on silica in the reduction of NO by CO is presented. The catalysts were prepared by three different methods: (1) Pd and Rh were coimpregnated on the support, (2) Rh was impregnated first and, after calcining, the sample was impregnated with Pd, (3) the monometallic Pd and Rh catalysts were physically mixed. The results showed that the activity of the catalysts prepared by coimpregnation was much lower than that of the other two catalysts.

Influence of the monoclinic and tetragonal zirconia phases on the water gas shift reaction. A theoretical study

We present a theoretical study of the water gas shift reaction taking place on zirconia surfaces modeled by monoclinic and tetragonal clusters. In order to understand the charge transfer between the active species, in this work we analyze the influence of the geometry of monoclinic and tetragonal zirconia using reactivity descriptors such as electronic che − mical potential (μ), charge transfer (

EFFECT OF LATERAL INTERACTIONS ON THE KINETICS OF THE OXIDATION OF CARBON MONOXIDE ON PALLADIUM

\left| {\varDelta N} \right|

The Dubinin–Radushkevich–Kaganer equation

) and molecular hardness (η). We have found that the most preferred surface is tetragonal zirconia (tZrO2) indicating also that low charge transfer systems will generate less stable intermediates, that will allow to facilitate desorption process.