Carla Costa

Activity–acidity relationship in zeolite ZSM-5. Application of Brönsted-type equations

In this paper the relation between activity and acidity in a variety of ZSM-5 zeolite catalysts, with different Si/Al ratios and different protonic content, is analysed and a quantitative correlation is obtained. The acid site strength distribution was estimated using temperature-programmed desorption (TPD) of ammonia by applying a digital deconvolution method to the curves. These data were then correlated with experimental catalytic activity data for the same catalysts towards n-heptane cracking reaction, by means of a Bronsted-type equation similar to the ones used for homogeneous acid catalysis and already used for other zeolites. It can be noticed that the same types of equation that are used for homogeneous acid catalysis also hold for heterogeneous acid catalysis and that the activation energy for ammonia desorption can be used as acid-strength scale for the purpose of correlation with catalytic activity.

Activity–acidity relationship in zeolite Y: Part 2. Determination of the acid strength distribution by temperature programmed desorption of ammonia

Abstract In this paper we will have a detailed look at a numerical procedure that allows the estimation of the acid site strength distribution using a single temperature programmed desorption (TPD) experiment. The possibility of estimating these parameters is of paramount importance in the determination of quantitative relationships between activity and acidity. The application of the procedure to a set of simulated thermograms gives a clear view of the applicability of this method. The procedure was tested both in single and multi energy distributions, as well as quasi-continuum distributions. Then the method has been applied on TPD thermograms obtained from catalysts based on two different forms of zeolite Y. In part 3 of this series, the acid site distributions obtained here will be used in an activity–acidity relationship, using a Bronsted type equation, similar to the one used in homogeneous acid catalysis.

Activity–acidity relationship in zeolite Y: Part 3. Application of Brönsted type equations

The relation between activity and acidity in a variety of Y zeolite catalysts for the transformation of small olefins: ethene, propene, 1-butene and iso-butene, is presented. The acid site distribution of these samples was estimated by temperature-programmed desorption of ammonia, by using a numerical deconvolution technique. This information was then correlated with catalytic activity measurements using Bronsted type equations. Despite the complexity of calculations it is clear that this gas phase solid acid catalysed reactions follow simple rules, similar to the one observed in homogeneous processes.

Activity–acidity relationship in zeolite Y: Part 1. Transformation of light olefins

Reactions of ethene, propene, 1-butene and iso-butene over two series of catalysts, HNaY (prepared from NaY zeolite) and HNaUSY (prepared from NH4USY zeolite), were studied. The catalytic activity for the transformation of these olefins follows the expected order according to the ease of formation of the respective carbocations: ethene<propene<1-butene<iso-butene, for all the samples that were studied. The catalytic results obtained over the HNaUSY series of catalysts are compatible with what was expected for light olefin transformation over acid catalysts. The catalytic activity of HNaY series of catalysts, however, does not follow a regular trend with the protonic content, showing a decrease when the protonic content is high.

Preparation of HNaY zeolite by ion exchange under microwave treatment. A preliminary study

Acidic samples of Y zeolite were prepared by ion exchange promoted using microwave irradiation. Interesting exchange levels were obtained with only a few minutes of irradiation. The catalytic properties of these samples were evaluated using the transformation of iso‐octane; the observed conversions lie in the same range as those for the samples prepared by the conventional ion‐exchange method of stirring the mixture of the sodium form with an ammonium salt solution for several hours; the deactivation with time‐on‐stream was significantly reduced for the catalysts prepared by the irradiation method in the cases of highest activity.

Acidity-activity relationship in zeolite Y. A preliminary study for n-heptane transformation

The transformation of n-heptane at 350°C has been studied on a variety of Y zeolite catalysts. The acidities of these samples were determined by temperature-programmed desorption of ammonia and, by using a numerical deconvolution technique, the acid strength distribution for the sites of each catalyst was obtained. Using these results we were able to correlate the catalytic activity with the acid strength distribution for all the catalysts using a Brønsted type equation, similar to the one that is used in homogeneous acid catalysis.

Homogeneous Ziegler–Natta Polymerisation: a Kinetic Approach1. Steady-State Kinetics

This series of papers describes a kinetic approach to the study of homogeneous Ziegler-Natta polymerisation of light olefins. Several kinetic rate laws, based on models proposed in the literature, are developed and discussed, and fitted to several sets of experimental results. In this first part, the questions that are raised in stationary state conditions are examined.

Homogeneous Ziegler-Natta polymerisation : a kinetic approach 2. Transient-state kinetics

An integrated view is presented of several possible mechanisms applicable to the interpretation of homogeneous Ziegler-Natta polymerisation. In this paper, the transient aspects related to the kinetics of Ziegler-Natta polymerisation are investigated. Extensive data are used to construct kinetic profiles (r M vs. t) from a theoretical approach. Special attention is given to the duration of the transient period as a function of the different kinetic parameters. The kinetic models developed are fitted to experimental data, either directly obtained by the authors or published in the literature. These general models have a broad range of application.

Low-carbon cement with waste oil-cracking catalyst incorporation

The present paper shows preliminary results of an ongoing project which one of the goals is to investigate the viability of using waste FCC catalyst (wFCC), originated from Portuguese oil refinery, to produce low carbon blended cements. For this purpose, four blended cements were produced by substituting cement CEM I 42.5R up to 20% (w/w) by waste FCC catalyst. Initial and final setting times, consistency of standard paste, soundness and compressive strengths after 2, 7 and 28 days were measured. It was observed that the wFCC blended cements developed similar strength, at 28 days, compared to the reference cement, CEM I 42.5R. Moreover, cements with waste FCC catalyst incorporation up to 15% w/w meet European Standard EN 197-1 specifications for CEM II/A type cement, in the 42.5R strength class.

A KINETIC APPROACH TO HOMOGENEOUS ZIEGLER TYPE POLYMERIZATION. STEADY STATE

In this paper we present a kinetic approach to the analysis of steady-state homogeneous Ziegler-Natta polymerization activity data. The influence of the number of monomeric species that are coordinated to the active site on the apparent rate law is discussed and the equations are fitted to the experimental results.